Note: Descriptions are shown in the official language in which they were submitted.
CA 02602657 2007-09-20
Specification
ALUMINUM ALLOY SHEET FOR BOTTLE CANS SUPERIOR IN
HIGH-TEMPERATURE PROPERTIES
Technical Field
[0001] The present invention relates to an aluminum
alloy sheet for bottle cans (blank for bottle cans) which
even when reduced in thickness to 0.2 mm or less (about
120-130 m in a thickness-reduced central portion of a can
body) and heat-treated at a high temperature as a can body
material of a bottle can (beverage can), exhibits little
deterioration in strength, can ensure a high strength and
is difficult to be deformed, thus having high-temperature
properties. As the aluminum alloy sheet as referred. to
herein, reference will be made below to a rolled sheet
(cold rolled sheet) as an example which has been rolled
through hot rolling and cold rolling. It is applicable
widely to aluminum alloy sheets, including this type of
cold rolled sheets. The aluminum alloy will hereinafter be
referred to also as Al alloy.
Background Art
[0002] As aluminum beverage cans, 2-piece aluminum
cans fabricated by seaming a can body and a can lid (can
1
CA 02602657 2007-09-20
end) are popular. The can body is fabricated by subjecting
a cold rolled aluminum sheet to DI (deep drawing and
ironing), followed by trimming into a predetermined size,
subsequent degreasing and washing, further, painting,
printing, baking, and subsequent necking and flanging of
can body edge portions.
[0003] As the cold rolled sheet for can body, hard
sheets of, for example, JIS3004 alloy and 3104 alloy ,
which are Al-Mg-Mn alloys, have heretofore been widely used.
The JIS3004 alloy and-3104 alloy are superior in ironing
and exhibit a relatively good formability even when
subjected to cold molding at a high draft in order to
enhance the strength and are therefore considered suitable
as DI can body materials.
[0004] On the other hand, in the case of a bottle can,
an aluminum alloy sheet formed on both surfaces thereof
with thermoplastic resin coating layers and with lubricant
applied thereto is punched to obtain a blank, the blank is
then subjected to deep drawing into a cup shape, then this
cup-like molding is subjected to again deep drawing and
stretching or ironing (DI working) to form a bottomed
cylindrical can having a body portion of reduced diameter
and thickness. Then, the bottom side of the can is
subjected to deep drawing plural times to form a shoulder
2
CA 02602657 2007-09-20
portion and an unopened mouth portion, followed by washing
and trimming, subsequent printing and coating for the can
body portion, further, opening the mounting portion,
forming a curled portion and a screw portion
(threading/curling), subsequent neck-in working and
flanging, and sealing a separately-formed can lid by a
seamer to afford a bottle can (see Patent Literature 1).
[0005] Thus, in the case of a 2-piece can, after an
aluminum alloy sheet is subjected to substrate treatment
(e.g., chromate treatment), it is coated with resin
(application of resin or film laminate), then is punched
into a circular blank, followed by forming into a cup,
subjected deep drawing and ironing, further, printing,
coating, necking, and trimming.
[0006] In the case of a bottle can with a threaded
mouth portion, an aluminum alloy sheet is subjected to
substrate treatment (e.g., chromate treatment), followed by
resin coating (application of resin or film laminate),
subsequent punching into a circular blank, forming into a
cup, deep drawing and ironing, trimming, printing, coating,
threading/curling, and subsequent neck flanging.
[0007] Just after DI, the bottle can body is usually
in a substantially true circular form in its horizontal
section. However, at the time of printing/coating and heat
3
CA 02602657 2007-09-20
treatment for improving the adhesion of laminate film, the
can body is heated to a temperature of 200 C or higher.
[0008] At this time, the can body itself is in a state
in which it is reduced in thickness from the original 0.3
to 0.4 mm or so as a cold rolled sheet thickness to 0.2 mm
or less. Therefore, when the can body is heat-treated at
such a high temperature as exceeds 200 C, it is released
from its work strain and residual stress induced during DI
and softens thermally.
[0009] On this regard, in the case of a material which
softens easily, the degree of softening is marked, with the
result that the strength and hardness of the can are
deteriorated markedly, thus giving rise to the problem that
a sufficient can strength can longer be ensured.
[0010] Besides, since the degree of softening becomes
non-uniform in the circumferential direction of the can, a
cross section of the can body is not a true circle as
formed, but is deformed elliptically, thus giving rise to
the problem that the can body shape becomes non-uniform.
[0011] Recently, due to a demand for reduction of the
can weight, the aluminum can thickness is at the level of
0.2 mm or less and is becoming more and more small. At the
same time, the aforesaid phenomena caused by thermal
softening such as lowering in strength and hardness of the
4
CA 02602657 2007-09-20
can body and non-uniforming in shape of the can body are
becoming more and more marked.
[0012) Recently, moreover, from the standpoint of
improving the productivity of cans, the foregoing
printing/coating and heat treatment for improving the
adhesion of laminate film are becoming more and more high
in temperature and speed like, for example, 290 C x 20
seconds. Such a tendency also promote the lowering in
strength and hardness of the can body and non-uniforming of
the shape thereof caused by the aforesaid thermal softening.
[00131 If the thickness of the can body is increased
in an effort to prevent lowering in strength and
deformation of the can body caused by thermal softening, an
increase of the can weight results, while if the strength
of the aluminum material itself is increased without
increasing the sheet thickness, there occurs an
inconvenience such as breakage during the foregoing ironing
work. Thus, with only such selection of can material and
method as in the prior art, it is impossible to cope with
the problem in question.
[0014] Against the non-uniforming in shape of the can
body caused by the foregoing thermal softening there has so
far been proposed an aluminum alloy sheet for DI can
capable of preventing thermal deformation during painting
CA 02602657 2007-09-20
and heat treatment and affording a DI can high in true
circularity (Patent Literature 2) The composition of such
proposed aluminum alloy sheet for DI can is as follows: Mn
0.5-1.3 mass %, Mg 0.5-1.3 mass %, Cu 0.1-0.3 mass %, Fe
0.2-0.6 mass %, Si 0.1-0.5 mass %. When heat treatment is
performed at a baking temperature T( C) of 230 to 270 C for
20 minutes, it is intended to diminish a change ATS in
tensile strength before and after the heat treatment.
[0015] In addition, also as to controlling the
structure for improving the formability into a can, a large
number of proposals have heretofore been made. For example,
it has been proposed to control the amount of solute Mn and
crystal grain diameter of a hot rolled sheet within
respective predetermined ranges, thereby making the earing
rate of the hot rolled sheet stably to -3% to 6%, then
subject the sheet to cold rolling without going through
intermediate annealing, thereby making the earing rate of
the resulting cold rolled sheet stably to 0% to 2% (Patent
Literature 3).
Patent Literature 1: Japanese Unexamined Patent
Application Publication No. 2001-162344 (whole sentence)
Patent Literature 2: Japanese Unexamined Patent
Application Publication No. 2003-277865 (whole sentence)
Patent Literature 3: Japanese Unexamined Patent
6
CA 02602657 2007-09-20
Application Publication No. 2003-342657 (whole sentence)
Disclosure of the Invention
Problem to be Solved by the Invention
[0016] By only controlling the metallurgical factors
on the structure of aluminum alloy sheets for stabilizing
the earing rate such as controlling the amount of solute Mn
and crystal grain diameter, which has so far been conducted,
it is impossible to prevent thermal deformation during
coating and heat treatment.
[0017] Likewise, by only controlling the aluminum
alloy composition, including Mn, Mg, Cu, Fe and Si, a large
limit is encountered in suppressing the lowering in
strength and deformation of the can body caused by the
foregoing thermal softening.
[0018] More particularly, the method proposed in
Patent Literature 2 may be effective for its prescribed or
presumed heat treatment of 230-270 C x 20 minutes. However,
as noted above, against such a higher temperature and
shorter time heat treatment as 290 C x 20 seconds, since
the heat treatment temperature is higher and the can body
thickness is smaller, it is impossible to prevent lowering
in strength and deformation of the can body caused by
thermal softening.
7
CA 02602657 2007-09-20
[0019] The present invention has been accomplished in
view of such problems. On the 'premise that satisfactory
formability in DI, etc. is to be ensured, it is an object
of the present invention to provide an aluminum alloy sheet
for bottle can capable of preventing thermal deformation
during coating and heat treatment, securing can strength
after heat treatment, affording a bottle can high in true
circularity, and being superior in high-temperature
properties.
Means for Solving the Problems
[0020] For achieving the above-mentioned object, in a
first aspect of the present invention there is provided an
aluminum alloy sheet for bottle cans superior in high-
temperature properties, the aluminum alloy sheet comprising
the following composition: Mn 0.7-1.5% (mass %, also in
the following), Mg 0.8-1.7%, Fe 0.1-0.7%, Si 0.05-0.5%, Cu
0.1-0.6%, with the remainder being Al and inevitable
impurities, and comprising a crystal structure elongated in
a rolling direction and with an average aspect ratio of
crystal grains of 3 or more as determined through an
examination from above of a part located at the center in
the through-thickness direction, wherein the amount of
solute Cu is 0.05-0.3%, which means the amount of Cu in a
solution separated from a precipitate exceeding 0.2 p,m in
8
CA 02602657 2007-09-20
particle size by the extracted residue method using hot
phenol and the amount of solute Mg is 0.75-1.6%, which
means the amount of solute Mg separated from a precipitate
exceeding 0.2 m in particle size by the extracted residue
method using hot phenol.
[0021] As to a DI can body of a bottle can, as noted
above, a further reduction of thickness is desired mainly
for the purpose of reducing the manufacturing cost and
weight. For attaining the thickness reduction it is
necessary that the strength of the cold rolled aluminum
alloy sheet as the material be made high so as to not cause
a lowering of buckling strength. For achieving the
thickness reduction it is also strongly desired that the
earing rate in DI be low. If the earing rate in DI is made
low, it is possible to increase the yield in DI and further
possible to prevent the breakage of the can body caused by
edge cutting of the can body.
[0022] Heretofore, as noted above, in order to highly
stabilize the earing rate, there has publicly been known a
method wherein metallurgical factors of the structure of
the cold rolled aluminum alloy sheet as the DI bottle can
body material are controlled. Typical of such controls are
crystal grain size microsizing control, controlling the
number and size of a compound such as MgZSi, microscopic
9
CA 02602657 2007-09-20
segregation suppression for added elements, controlling the
amount of solute alloy elements such as Mn, and cube
orientation control.
[0023] However, a technique for controlling
metallurgical factors of the structure of the rolled
aluminum alloy sheet in order to prevent thermal
deformation in coating and heat treatment, which is to be
attained in the present invention, has not substantially
been proposed yet. This is because metallurgical factors
of the structure correlated with thermal deformation in
coating and heat treatment have not been made clear yet.
Moreover, by merely controlling various known metallurgical
factors of the structures for stabilizing the earing rate
as referred to above, it is impossible to prevent thermal
deformation in coating and heat treatment.
[0024] On the other hand, according to the present
invention it has been found out that among various
metallurgical factors of the structure, the form of crystal
grain and the amount of solute Cu and that of solute Mg in
the structure are correlated with the can strength after
heat treatment and thermal deformation in coating and heat
treatment.
[0025] Since such metallurgical factors of the
structure do not obstruct the stabilization of the earing
CA 02602657 2007-09-20
rate but rather act to stabilize the earing rate, it is
possible to secure can strength after heat treatment and
suppress thermal deformation in coating and heat treatment
and then secure formability in DI, etc. In other words, it
is possible to obtain an aluminum alloy sheet capable of
securing can strength after heat treatment and suppressing
thermal deformation in coating and heat treatment and then
securing formability in DI, etc.
[0026] By controlling each individual crystal grain of
the aluminum alloy sheet not into an equiaxed grain but
into an elongated structure in the rolling direction with
an average aspect ratio of 2 or more, it is possible to
suppress thermal deformation in coating and heat treatment
and secure can strength after heat treatment, thus possible
to cope with a high-speed heat treatment performed at a
higher temperature for a shorter time.
[0027] In the present invention, in addition to the
above crystal grain shape control, the amount of solute Cu
and that of solute Mg in the structure are controlled to
respective optimum ranges.
[0028] The amount of solute Cu and that of solute Mg
exert a great influence on anti-softening property in high-
temperature heat treatment. Therefore, by secur'ing both
such Cu and Mg quantities present in a solid solution form
11
CA 02602657 2007-09-20
it is possible to improve the anti-softening property in
high-temperature heat treatment and suppress elliptic
deformation. Besides, the amount of solute Mg exerts a
great influence on the strength property after high-
temperature heat treatment, so by securing the amount of
solute Mg it is possible to also secure strength after
high-temperature heat treatment.
[0029] Controlling the amount of other alloy elements,
e.g., Mn, present in a solid solution form in the prior art
described above makes contribution to improving the
formability in DI, etc. such as lowering the earing rate
of the cold rolled sheet. However, in point of suppressing
thermal deformation in coating and heat treatment and
securing can strength after heat treatment, which are to be
attained in the present invention, such solid solution
quantity control for other alloy elements is much less
effective than controlling both Cu and Mg solid solution
quantities. Thus, even if the amount of other alloy
elements as Mn present in a solid solution form are ensured,
thermal deformation during coating and heat treatment is
not suppressed and it is impossible to secure can strength
after heat treatment.
[0030] It is the first object of the present invention
to suppress thermal deformation in coating and heat
12
CA 02602657 2007-09-20
treatment and make it possible to secure can strength after
heat treatment in connection with a high-speed heat
treatment performed at a higher temperature for a shorter
time by controlling each individual crystal grain of the
aluminum alloy sheet not to an equiaxed grain but to an
elongated structure in the rolling direction with an
average aspect ratio of 3 or more. In the present
invention, in order to further ensure this effect, there is
made control so as to suppress anisotropy in the structure.
More specifically, among tensile strengths in 0 , 45 and
90 directions relative to the rolling direction, the
difference between the maximum and the minimum value is 25
MPa or less, and among n values obtained by tensile tests
in 0 , 45 and 90 directions relative to the rolling
direction, the difference between the maximum and the
minimum value is 0.3 or less.
Thus, in a second aspect of the present invention
there is provided an aluminum alloy sheet for bottle cans
superior in high-temperature properties, the aluminum alloy
sheet comprising the following composition: Mn 0.7-1.5%
(mass %, also in the following), Mg 0.8-1.7%, Fe 0.1-0.7%,
Si 0.05-0.5%, Cu 0.1-0.6%, with the remainder being Al and
inevitable impurities, and having a structure elongated in
a rolling direction and with an average aspect ratio of
13
CA 02602657 2007-09-20
crystal grains of 3 or more as determined through an
examination from above of a part located at the center in
the through-thickness direction, wherein among tensile
strengths in 0 , 45 and 90 directions relative to the
rolling direction, the difference between maximum and
minimum values is 25 MPa or less, and among n values
obtained by tensile tests in 00, 45 and 90 directions
relative to the rolling direction, the difference between
maximum and minimum values is 0.03 or less.
[00311 According to the second aspect of the present
invention, in a conventional aluminum alloy sheet
manufacturing process involving hot rolling and cold
rolling, when a hot rolled sheet is cold rolled to the
final sheet thickness by performing intermediate annealing
(intermediate annealing), the draft in cold rolling
inevitably becomes high, with consequent occurrence of
anisotropy in strength, and there occurs a difference of
about 30 MPa or more among tensile strengths in 0 , 450 and
90 directions relative to the rolling direction. As the
anisotropy in strength becomes higher, the internal stress
after cupping and ironing becomes non-uniform in the
circumferential direction, so that the degree of recovery
becomes non-uniform and elliptic deformation is apt to
occur during printing/painting and heat treatment performed
14
CA 02602657 2007-09-20
for improving the adhesion of laminate film. It is for
this reason that thermal deformation in coating and heat
treatment cannot be prevented when the conventional hot
rolling and cold rolling are performed.
[0032] Also in the case where a hot rolled sheet is
cold rolled directly to the final sheet thickness without
going through intermediate annealing, the draft in cold
rolling inevitably becomes high and there easily occurs
anisotropy in strength. Consequently, there occurs a
difference among tensile strengths in 0 , 45 and 90
directions relative to the rolling direction and hence
elliptic deformation is apt to occur. It is for this
reason that thermal deformation in coating and heat
treatment cannot be prevented in the conventional
intermediate annealing-free cold rolling.
[0033] On the other hand, in the present invention,
even when not the conventional cold rolling involving
interpass (halfway in cold rolling) intermediate annealing
but cold rolling is performed directly to the final sheet
thickness without intermediate annealing of a hot rolled
sheet, the foregoing thermal deformation in coating and
heat treatment is suppressed and can strength after heat
treatment can be secured.
[0034] Further, in the present invention, as noted
CA 02602657 2007-09-20
above, crystal grains of the cold rolled aluminum sheet are
controlled not to equiaxed grains but to an elongated
structure in the rolling direction with an average aspect
ratio of 3 or more, whereby thermal deformation in coating
and heat treatment is suppressed and can strength after
heat treatment can be secured in connection with a high-
speed heat treatment performed at a higher temperature for
a shorter time. In the present invention, for further
ensuring this effect, dispersed grains in the structure are
controlled. More specifically, an average grain size of
dispersed grains is controlled as fine as 5 m or less and
AT, which represents a solid-liquid coexistence temperature
range between liquid and solid phases of aluminum, is set
at 40 C or less.
[0035] The larger the solid-liquid coexistence
temperature range AT, the larger the solid-liquid
coexistence temperature range in a component system of both
dispersed grains of Al (Fe, Mn)-based intermetallic
compounds and the liquid phase of aluminum. That is, the
component system is apt to undergo a change of crystal
phase depending on casting conditions and the form thereof
is apt to scattered, and the structure obtained permits
easy formation of coarse compound grains.
[0036] Conversely, the smaller the solid-liquid
16
CA 02602657 2007-09-20
coexistence temperature range AT, the smaller the solid-
liquid coexistence temperature range in a component system
of both dispersed particles and the liquid phase of
aluminum. It can be said that in this structure the
variations in production of stable and metastable phases of
the intermetallic compound are small and compound grains
are fine particles.
Brief Description of the Drawings
[0037]
[Fig. 1] is a developed view of a cup formed by Di of
a blank.
[Fig. 2] is a schematic phase diagram showing AT
defined in the present invention.
[Fig. 3] is a calculation phase diagram for
determining AT by calculation.
Best Mode for Carrying Out the Invention
[0038] (Composition of Cold Rolled Al Alloy Sheet)
First, a preferred chemical components composition
(unit: mass %) of the cold rolled Al alloy sheet according
to the present invention will be described together with
the reason for limitation of each element.
[0039] The composition of the cold rolled aluminum
. 17
CA 02602657 2007-09-20
sheet for bottle can superior in high-temperature
properties according to the present invention is as
follows: Mn 0.7-1.5%, Mg 0.8-1.7%, Fe 0.1-0.7%, Si 0.05-
0.5%, Cu 0.1-0.6%, with the remainder being Al and
inevitable impurities.
[0040] In the present invention it is preferable to
design the components balance of main constituent elements
(Mn, Mg, Fe, Cu, Si) in such a manner that the required
amount of solute Mg and that of solute Cu can be ensured.
By making such a design, not only fine and stable crystals
are formed, but also it is possible to make control so as
to afford a structure of an optimum Cu or Mg solid solution
quantity.
[0041] Mn: 0.7-1.5%
Mn is an effective element contributing to
improvement of not only strength but also formability.
Particularly, since the can body material (cold rolled
sheet) used in the present invention is subjected to
ironing in DI, Mn is an extremely important element.
[0042] More particularly, Mn affords various Mn-based
intermetallic compounds, e.g., Al-Fe-Mn-Si-based
intermetallic compounds (a phase). The more appropriately
dispersed the a phase, the more can be improved the ironing
workability. In ironing an aluminum sheet, there usually
18
CA 02602657 2007-09-20
is employed an emulsion type lubricant. But if the amount
of the aforesaid a phase is small, even if an emulsion type
lubricant is used, the lubricity becomes deficient, with a
consequent fear of occurrence of an appearance defect such
as rubbed scratch or seizure called galling. Thus, Mn is
an indispensable element also for formation of a phase to
prevent a surface defect in ironing.
[0043] If the content of Mn is too low, the above
effect will not be exhibited. Therefore, the content of Mn
is 0.7% or more, preferably 0.8% or more, more preferably
0.85% or more, still more preferably 0.9% or more.
[0044] On the other hand, if the content of Mn is too
high, a giant metallic compound, MnA16, will be formed as a
primary crystal, with consequent deterioration of
formability. Therefore, the upper limit of the Mn content
is set at 1.5%, preferably 1.3%, more preferably 1.1%,
still more preferably 1.0%.
[0045] (Mn Solid Solution Quantity)
As noted above, by combining with cold rolling free
of intermediate annealing, the amount of solute Mn in the
cold rolled aluminum sheet contributes to improving the
formability in DI, etc. such as lowering of the earing ate
of the cold rolled sheet. Therefore, in order to improve
the formability in DI, etc., it is preferable to set the
19
CA 02602657 2007-09-20
amount of solute Mn at 0.12-0.38%, which means the amount
of Mn (total amount of both dissolved Mn quantity and the
amount of Mn contained in a precipitate of 0.2 m or less
in particle size) in a solution separated from a
precipitate exceeding 0.2 m in particle size by the
extracted residue method using hot phenol. If the amount
of solute Mn is less than 0.12%, there will be no effect of
improving the formability in DI, etc., while if the amount
of solute Mn exceeds 0.38%, the work hardening in cold
rolling will become excessive and rather the formability in
DI, etc. is very likely to be deteriorated.
[0046] Mg: 0.8-1.7%
Mg is effective in that it can improve its strength
by solid solution hardening. Further, by using it in
combination with Cu, as will be described later, it is
possible to prevent softening of the can body material
(cold rolled sheet) of the present invention at the time of
final annealing (also called finish annealing, e.g.,
annealing at a temperature of about 100 to 150 C for about
1 to 2 hours) and subsequent forming into a can and baking.
More particularly, in the presence of both Mg and Cu, it is
possible to ensure the required amount of solute Cu at the
c
stage of fabrication of a hot rolled sheet, and since Al-
Cu-Mg is precipitated at the time of baking, it is possible
CA 02602657 2007-09-20
to suppress softening during baking.
[0047] If the content of Mg is too low, it is
impossible to ensure the required amount of solute Mg and
the effect of improving the anti-softening property in
high-temperature heat treatment is not exhibited.
Therefore, the content of Mg is set at 0.8% or more,
preferably 0.9% or more, more preferably 1.0% or more.
[0048] On the other hand, if the content of Mg is too
much, work hardening is apt to occur and hence the
formability is deteriorated. Therefore, the upper limit of
the Mg content is set at 1.7%, preferably 1.6%, more
preferably 1.35%.
[0049] The content of Mg also exerts an influence on
the amount of Mn precipitated and the amount of solute Mn.
More particularly, the higher the Mg content, the more
suppressed the amount of Al-Fe-Mn-Si-based intermetallic
compounds (a phase) precipitated, so that the amount of
solute Mn is apt to become large. It is preferable to
determine the content of Mg in relation to the amount of
solute Mn.
[0050] (Sum of Mg Solid Solution Quantity and the amount of
Mg contained in Fine Precipitate of 0.2 jAm or less)
The sum of the amount of solute Mg and the amount of
Mg contained in a fine precipitate of 0.2 pm or less, like
21
CA 02602657 2007-09-20
the sum of the amount of solute Cu and the amount of Cu
contained in a fine precipitate of 0.2 m or less, exerts a
great influence on the anti-softening property in high-
temperature heat treatment. Heretofore there has been the
patent of Patent Literature 3 which defines both Mn and Cu
solid solution quantities for the purpose of eliminating
variations in the earing rate and stabilizing the same rate.
However, in order to suppress elliptic deformation after
can heating in intermediate annealing, the conventional
control if applied alone is insufficient. It is necessary
to also control the state of solid solution and
precipitation of Mg. As a result of detailed investigation
about the state of presence of Mg it turned out that not
only Mg was present as a solid solution and a fine
precipitate like that so far mentioned but also it was
dissolved in a coarse Al-Fe-Si- or Al-Mn-Fe-Si-based
precipitate and that if the amount thereof is large, the
amount of dissolved Mg and that of Mg contained in fine
precipitate become smaller and elliptic deformation is apt
to occur. The amount of solute Mg exerts a great influence
also on the strength property after high-temperature heat
treatment. In the present invention, therefore, both Cu
and Mg solid solution quantities required are ensured to
not only improve the anti-softening property in high-
22
CA 02602657 2007-09-20
temperature heat treatment but also ensure the required
strength after high-temperature heat treatment.
[0051] Accordingly, in the present invention, the Mg
solid solution quantity is set at 0.75-1.6% as the content
of Mg (the total quantity of both dissolved Mg quantity and
the amount of Mg contained in a precipitate of 0.2 pm in
particle size) in a solution separated from a precipitate
exceeding 0.2 m in particle size by the extracted residue
method using hot phenol.
[0052] Mg present in a coarse precipitate exceeding
0.2 pm in particle size rather deteriorates the anti-
softening property in high-temperature heat treatment and
the strength property after the same treatment. Thus,
ensuring the required amount of solute Mg also leads to
restricting the presence of a coarse precipitate exceeding
0.2 pm in particle size.
[0053] Not only Mg actually dissolved, but also Mg
contained in a precipitate of 0.2 pm or less in particle
size, like dissolved Mg, also improves the anti-softening
property in high-temperature heat treatment and ensures the
required strength after the same treatment. In the present
invention, therefore, the total amount of both dissolved Mg
quantity and the amount of Mg contained in a precipitate a
of 0.2 pm or less in particle size is defined to be the
23
CA 02602657 2007-09-20
dissolved Mg quantity. Accordingly, the dissolved Mg
quantity is defined as the amount of Mg contained in a
solution separated from a precipitate exceeding 0.2 pm in
particle size by the extracted residue method using hot
phenol.
[0054] If the dissolved Mg quantity is less than 0.75%,
the anti-softening property in high-temperature heat
treatment will become insufficient and deformation of the
can will not be suppressed; besides, the strength after
high-temperature heat treatment will be deteriorated.
[0055] On the other hand, even if the dissolved Mg
quantity exceeds 1.6%, the work hardening in cold rolling
will become excessive, rather resulting in deterioration of
formability in DI, etc.
[0056] Fe: 0.1-0.7%
Fe has a function of microsizing crystal grains and
produces the foregoing A1-Fe-Mn-Si-based intermetallic
compound (a phase), thus contributing to the improvement of
formability. Moreover, Fe is useful also in point of
promoting the crystallization and precipitation of Mn and
controlling the amount of solute Mn in aluminum base and
the state of dispersion of Mn-based intermetallic compounds
L
(e.g., the aforesaid a phase). On the other hand, if the
content of Fe is too high in the presence of Mn, a giant
24
CA 02602657 2007-09-20
intermetallic compound as a primary crystal is apt to be
produced, with consequent fear of formability being
impaired.
[0057] Thus, the content of Fe can be set in
accordance with the content of Mn and the mass ratio of Fe
to Mn (Fe/Mn) is, for example, in the range of 0.1 to 0.7,
preferably 0.2 to 0.6, more preferably 0.3 to 0.5.
[0058] In the case where the content of Mn falls under
the above range, a lower-limit content of Fe is 0.1% or
more, preferably 0.2% or more, more preferably 0.3% or more,
while an upper-limit content of Fe is 0.7% or less,
preferably 0.6% or less, more preferably 0.5% or less.
[0059] Si: 0.05-0.5%
Si produces Al-Fe-Mn-Si-based intermetallic compounds
(a phase) and controls the state of dispersion Mn-based
intermetallic compounds, thus being a useful element. The
more appropriate the distribution of a phase, the more can
be improved formability.
[0060] Accordingly, the content of Si is 0.05% or more,
preferably 0.1% or more, more preferably 0.2% or more. On
the other hand, if the Si content is too high, the material
will become too hard due to age hardening, resulting in
formability being deteriorated. Therefore, an upper-limit
Si content is set at 0.5%, preferably 0.45%, more
CA 02602657 2007-09-20
preferably 0.4%.
[0061] Cu: 0.1-0.6%
When performing baking in fabrication of the cold
rolled sheet into a can, Al-Cu-Mg precipitates, and when Cu
is used in combination with Mg, softening can be suppressed
by the action of both dissolved Mg and dissolved Cu.
Therefore, a lower-limit content of Cu is set at 0.1% or
more, preferably 0.150 or more, more preferably 0.2% or
more. On the other hand, if the Cu content is too high,
hardening proceeds to an excessive degree although age
hardening is attained easily, so that the formability is
deteriorated and so is corrosion resistance. Accordingly,
an upper-limit content of Cu is set at 0.6%, preferably
0.5%, more preferably 0.35%.
[0062] As other examples of strength improving element
exhibiting the same effect as Cu there are mentioned Cr and
Zn. Thus, Cr and/or Zn may be used selectively in addition
to Cu.
[0063] (Sum of Cu Solid Solution Quantity and the amount of
Cu contained in Fine Precipitate of 0.2 pm or less)
The sum of the amount of solute Cu and the amount of
Cu contained in a fine precipitate of 0.2 pm or less, like
the sum of the amount of solute Mg and the amount of Mg
contained in a precipitate of 0.2 m or less, exerts a
26
CA 02602657 2007-09-20
great influence on the anti-softening property in high-
temperature heat treatment.
[0064] In the present invention, the Cu content (total
quantity of both dissolved Cu quantity and the amount of Cu
contained in a precipitate of 0.2 m or less in particle
size) in a solution separated from a precipitate exceeding
0.2 m in particle size by the extracted residue method
using hot phenol is set at 0.05-0.3%.
[0065] Cu present in a coarse precipitate exceeding
0.2 pm in particle size rather deteriorates the anti-
softening property in high-temperature heat treatment and
the strength property after the same treatment. Therefore,
ensuring the required dissolved Cu quantity also leads to
restricting the formation of a coarse precipitate exceeding
0.2 m in particle size.
[0066] Not only Cu actually dissolved but also Cu
contained in a precipitates of 0.2 pm or less in particle
size, like dissolved Cu, also improves the anti-softening
property in high-temperature heat treatment and ensures the
required strength after the same treatment. In the present
invention, therefore, the total amount of both dissolved Cu
quantity and the amount of Cu contained in a precipitate of
0.2 pm or less in particle size is defined to be the
27
CA 02602657 2007-09-20
dissolved Cu quantity. Accordingly, the dissolved Cu
quantity is defined as the amount of Cu contained in a
solution separated from a precipitate exceeding 0.2 m in
particle size by the extracted residue method using hot
phenol.
[0067] If the dissolved Cu quantity is less than 0.05%,
the anti-softening property in high-temperature heat
treatment will become insufficient and deformation of the
can will not be suppressed; besides, the strength after
high-temperature heat treatment will be deteriorated.
[0068] On the other hand, even if the dissolved Cu
quantity exceeds 0.3%, the work hardening in cold rolling
will become excessive, rather resulting in deterioration of
formability in DI, etc. and deterioration of corrosion
resistance.
[0069] Cr: 0.001-0.3%
For exhibiting the strength improving effect, the
content of Cr is set at 0.001% or more, preferably 0.002%
or more. On the other hand, if the Cr content is too.high,
a giant product will be formed by crystallization, with
consequent deterioration of formability. Therefore, an
upper limit of the Cr content is set at 0.3%, preferably
0.25%.
[0070] Zn: 0.05-1.0%
28
CA 02602657 2007-09-20
In the presence of Zn, there occurs age precipitation
of Al-Mg-Zn particles, whereby the strength can be improved.
For exhibition of this effect, the content of Zn is set at
0.05% or more, preferably 0.06% or more. On the other hand,
a too high content of Zn will result in deterioration of
corrosion resistance. Therefore, an upper limit of the Zn
content is set at 0.5%, preferably 0.45%.
[0071] Ti: 0.005-0.2%
Ti is a crystal grain microsizing element. When this
effect is to be exhibited, Ti is used selectively. In this
case, the content of Ti is set at 0.005% or more,
preferably 0.01% or more, more preferably 0.015% or more.
If the Ti content is too high, giant Al-Ti-based
intermetallic compounds will be formed by crystallization
and impair the formability. Therefore, an upper limit of
the Ti content is set at 0.2%, preferably 0.1%, more
preferably 0.05%.
[0072] Ti may be used alone or in combination with a
very small amount of B. A combined use thereof with B will
further improve the crystal grain microsizing effect.
Therefore, the content of B in a selective use thereof is
set at 0.0001% or more, preferably 0.0005% or more, more
preferably 0.0008% or more. On the other hand, a too high
content of B will result in formation of coarse Ti-B
29
CA 02602657 2007-09-20
particles and deterioration of formability. An upper limit
of the B content is set at 0.05%, preferably 0.01%, more
preferably 0.005%.
[0073] The balance other than the elements described
above consists of inevitable impurities. In order not to
impair the sheet properties described above, it is
preferable that the content of such impurities be as low
as possible. But their contents up to approximately the
upper-limit values of elements in 3000 series aluminum
alloys defined in JIS insofar as they do not impair the
above properties.
[0074] (Structure of Cold Rolled Al Alloy Sheet)
The following description is now provided about the
structure of cold rolled Al alloy sheet of the present
invention.
[0075] (Average Aspect Ratio of Crystal Grain)
As noted above, by making each individual crystal
grain of the cold rolled aluminum alloy sheet into not the
ordinary equiaxed grain but an elongated crystal grain in
the rolling direction with an average aspect ratio of 3 or
more, thermal deformation in coating and heat treatment is
suppressed and the required can strength after heat
treatment can be ensured in connection with high-speed heat
treatment at a higher temperature for a shorter time.
CA 02602657 2007-09-20
[0076] That is, by making each individual crystal
grain of the cold rolled aluminum alloy sheet into an
elongated grain in the rolling direction, it is possible to
impart ironing processability to the sheet and ensure the
formability in DI, etc. and further possible to ensure the
required can strength after heat treatment under the above
components' composition and the state and texture of solid
solution and precipitation to be described later. As a
result, thermal deformation in coating and heat treatment
is also suppressed.
[0077] If the average aspect ratio of crystal grains
is less than 3, there is no great difference from the
ordinary equiaxed grains and the foregoing effect is not
attained to a satisfactory extent, so that it is impossible
to suppress thermal deformation in painting and heat
treatment and ensure the required can strength after heat
treatment. In this point, the larger the extension in the
rolling direction of crystal grains, the better. More
preferably, an average aspect ratio of crystal grains is
3.1 or more.
[0078] Without intermediate annealing, the aspect
ratio of each individual crystal grain depends on the
crystal structure of the hot rolled sheet, as well as the
draft in cold rolling and the cold rolling temperature. In
31
CA 02602657 2007-09-20
this point, an upper limit of the average aspect ratio of
crystal grains is determined from a capacity limit of the
manufacturing process for making the crystal grains into
the elongated grains, including hot rolling and cold
rolling. Its level is 6 or so.
[0079] (Method for Measuring Average Aspect Ratio)
An average aspect ratio of crystal grains is measured
through an observation (polarization observation) from
above of a part located at the center in the through-
thickness direction. A rolled upper surface of the central
part in the thickness direction of the sheet after thermal
refining (before forming the bottle can) is examined by
polarization observation after mechanical polishing,
electrolytic polishing and anodic oxidation using barker's
liquid.
[0080] When the crystal structure is examined by
polarization observation from the upper surface side of the
central part in the thickness direction of the sheet, there
occurs black-white difference due to the difference in
crystal orientation. In this observation, with respect to
crystal grains in a visual field permitting clear
observation of the contour, both maximum length in the
rolling direction and maximum length in the sheet width
direction of each individual crystal grain are measured.
32
CA 02602657 2007-09-20
In this case, (maximum length in the rolling direction)/
(maximum length in the sheet width direction) of each
individual crystal grain is calculated as an aspect ratio.
Through observation using an optical microscope of 100
magnifications, the number of crystal grains to be
subjected to measurement is determined to be 100 grins and
a mean value of aspect ratios of those crystal grains is
determined as an average aspect ratio of crystal grains.
[0081] (Suppressing Anisotropy)
In the present invention, even when the hot rolled
sheet is subjected to cold rolling directly up to the final
sheet thickness without going through intermediate
annealing in order to attain the thus-defined average
aspect ratio of crystal grains and improve the formability
of the sheet into a can and the strength thereof, the
foregoing thermal deformation in coating and heat treatment
is suppressed and the required can strength after heat
treatment is ensured.
[0082] To this end, in the present invention, not only
the above crystal grain control is made, but also a control
is made so as to suppress anisotropy in the structure. For
this anisotropy control, two anisotropy indices, which are
ten~ile strength and n value, are used selectively.
[0083] In connection with the tensile strength as one
33
CA 02602657 2007-09-20
,, .
anisotropy index, when the tensile strength becomes more
and more anisotropic, as noted above, an internal stress
after cupping and ironing becomes non-uniform in the
circumferential direction and the degree of recovery
becomes non-uniform in printing/coating and during heat
treatment performed for improving the adhesion of laminate
film, with the result that elliptic deformation is apt to
occur.
[0084] For diminishing the anisotropy of the tensile
strength, the difference between maximum and minimum values
among tensile strengths in 0 , 45 and 90 directions
relative to the rolling direction is made as small as
possible. More specifically, this difference is reduced to
25 MPa or less, preferably 20 MPa or less.
[0085] In addition to the above tensile strength,
anisotropy in the rolling direction of a work hardening
index, i.e., n value, is also important. If the anisotropy
of n value is large, even if the anisotropy of the tensile
strength referred to above is small (even if it is within
the prescribed range), an internal stress induced by
cupping and ironing becomes non-uniform in the
circumferential direction, and the degree of recovery
becomes non-uniform in printing/coating and when heat
treatment is performed for improving the adhesion of
34
CA 02602657 2007-09-20
laminate film, resulting in elliptic deformation being apt
to occur.
[0086] Therefore, in order to diminish the anisotropy
of n value, the difference between maximum and minimum
values among n values in 0 , 45 and 90 directions relative
to the rolling direction of the aluminum alloy sheet is
made as small as possible. More specifically, this
difference is set at 0.03 or less, preferably 0.028 or less,
more preferably 0.025 or less, still more preferably 0.02
or less, and still more preferably 0.015 or less.
[0087] If the aluminum alloy sheet has one or both of
the anisotropic indices, there will occur the foregoing
thermal deformation in coating and heat treatment even if
the foregoing crystal grain control is made, although the
can formability may not be influenced. More particularly,
if the difference between maximum and minimum values among
the foregoing tensile strengths exceeds 25 MPa and/or if
the difference between maximum and minimum values among the
foregoing n values exceeds 0.03, there will occur the
foregoing thermal deformation in coating and heat treatment.
[0088] (Anisotropy Suppressing Method)
Even when the hot rolled sheet is subjected to cold
rolling without intermediate annealing, hot rolling
conditions are controlled in order to satisfy both
CA 02602657 2007-09-20
anisotropic indices. More specifically, hot finish rolling
is performed by a tandem rolling mill equipped with three
to six rolling stands and the coil winding tension in those
final stands is made relatively high to increase the
forward slip of the rolled sheet.
[0089] In this connection, an average coil winding
tension in the final stands is made as high as possible in
excess of at least 20 MPa. If an average coil winding
tension is 20 MPa or less, crystal grains such as cube
orientation are apt to be formed, and when cold rolling is
performed without intermediate annealing, the sheet
anisotropy becomes conspicuous. An ordinary average coil
winding tension is in the range of 5 to 10 MPa.
[0090] A description will now be given also about
controlling dispersed particles in the cold rolled aluminum
alloy structure. In the present invention, as noted above,
in order to ensure the exhibition of the effect of the
foregoing elongated crystal grains, an average particle
size of dispersed particles in this structure is controlled.
More specifically, in the observation of particles of 0.5
m or more, an average particle size of dispersed particles
is microsized to 5 m or less and AT which represents the
liquid-solid phase coexistence temperature range of
aluminum is set at 40 C or lower.
36
CA 02602657 2007-09-20
[0091] (Average Particle Size of Dispersed Particles)
Dispersed particles in the cold rolled aluminum alloy
structure are various intermetallic compound particles,
including the foregoing Al-Fe-Mn-Si-based intermetallic
compounds (a phase) . In this case, the finer the average
particle size of the dispersed particles, the better.
[0092] If the proportion of coarse dispersed particles
(precipitated compounds) exceeding 5 Eun in average particle
size increases, they are apt to become the nucleus of
recovery and recrystallization, so that softening at a high
temperature becomes conspicuous and there easily occur
elliptic deformation and a lowering of strength in high-
temperature heat treatment. As a result, the aforesaid
effect of the elongated crystal grains is offset.
[0093] In the present invention, therefore, an average
particle size of dispersed particles in the observation of
0.5 m or larger particles is set at 5 m or less,
preferably 4.5 Eun or less.
[0094] It is assumed that the dispersed particles to
be analyzed have a size (barycentric diameter) of 0.5 or
more. This is because the presence of particles of 0.5 m
or larger exerts a great influence on the anti-softening
property as noted above, while particles smaller than 0.5
37
CA 02602657 2007-09-20
m are little influential. Moreover, dispersed particles
smaller than 0.5 m are difficult to be observed and
measurement variations in this measurement become large.
Therefore, such small particles are excluded from the
measurement range defined in the present invention.
[0095) (Measurement of Average Particle Size)
An average particle size of dispersed particles in
the observation of particles of 0.5 m or more is
determined using a scanning electron microscope (SEM) for
the sheet structure. More specifically, a test piece of an
upper rolled surface of a central sheet portion is mirror-
polished and the structure of the polished surface is
observed in ten visual fields each about 200 p.m by about
150 Rn in size through an SEM (e.g., Model S4500 FE-SEM:
Field Emission Scanning Electron Microscopy, a product of
Hitachi, Ltd.) having 500 or 1000 magnifications.
[0096] In this case, for observing the dispersed
particle phase (intermetallic compound phase) clearly, the
observation is made by observing a reflected electron image.
A black image indicates Al and different contrasts make the
dispersed particle phase clear. The dispersed particles
are traced and an average size (mean value of barycentric
diameters) of the dispersed particles is determined using
Image-ProPlus (a product of MEDIACYBERNETICS Co.) as
38
CA 02602657 2007-09-20
software for image analysis. The number of measured
dispersed particles is 200 or more as a total in the above
ten-visual field structure observation and calculation was
made using a mean value.
[0097] (Solid-Liquid Coexistence Temperature Range AT)
Fig. 2 is a schematic phase diagram of Al-Mg-Mn-based
alloy, showing schematically a relation among a liquidus
line of aluminum, a solidus line of aluminum, and the
crystallization temperature of AlMn- and Al(Fe,Mn)-based
compounds as main crystals. In Fig. 2, the temperature
range (temperature difference) between the Al liquidus and
solidus lines corresponds to the solid-liquid coexistence
temperature range AT as referred to herein.
[0098] There is a tendency that the wider (longer) the
AT of a component system, variations in production between
stable and metastable phases of the intermetallic compound
become larger, depending on solidifying and cooling
conditions in casting. In this state of structure,
elements other than the constituent elements of the
intermetallic compounds are forcibly dissolved in those
crystals. Therefore, at the stage of the bottle can body,
softening at a high temperature becomes conspicuous and
elliptic deformation and a lowering of strength are apt to
occur in high-temperature heat treatment. Accordingly, as
39
CA 02602657 2007-09-20
is the case with coarsening in average particle size of
dispersed particles, the effect of the foregoing elongated
crystal grain is offset.
[0099] Moreover, the wider (larger) the AT of a
component system, the more easily is formed a coarse
compound particle distribution because intermetallic
compounds grow rapidly in liquid phase. As a result, it
becomes impossible to microsize the average particle size
of dispersed particles defined above. Consequently, as
explained above in connection with the dispersed particles,
coarse particles become the nucleus of recovery and
recrystallization and softening of the bottle can body in
heat treatment become more conspicuous, so that elliptic
deformation is apt to occur. Further, the presence itself
of a coarse compound is apt to be a cause of defect of the
can surface.
[0100] Strictly speaking, in connection with AT, there
is a method for defining the range of crystallization
temperature of Al-Mn-based intermetallic compounds and that
of the solid phase temperature of Al, as noted above.
However, in the Al alloy system according to the present
invention, the melting point of the Al alloy system and the
crystallization temperature of Al-Mn-based compounds
exhibit a change of only about 4 to 7 and thus cannot be
CA 02602657 2007-09-20
an exact index. For this reason, there was used the range
(temperature difference) between the Al liquid phase
temperature and the Al solid phase temperature, which can
be an exact index, with a sufficient difference (margin)
found in AT in point of measurement evaluation.
[0101] The narrower (smaller) the AT (solid-liquid
coexistence temperature range), the smaller the solid-
liquid coexistence temperature range between dispersed
particles and aluminum liquid phase in the component system
concerned, and the smaller the variations in the production
of stable phase and metastable phase in intermetallic
compounds and the finer the compound particles.
Consequently, at the stage of the bottle can body, the
anti-softening property at high temperatures is enhanced
and it is possible to suppress elliptic deformation and a
lowering of strength in high-temperature heat treatment.
[0102] As will be seen in Examples to be described
later, as AT becomes larger, the average particle size of
dispersed particles increases as well. Particularly, when
the value of AT exceeds 40 C, the average particle size of
dispersed particles shows a coarsening tendency. Thus, the
smaller the value of AT in the range of not higher than
C
40 C, the better. More preferably, the value of AT is 38 C
41
CA 02602657 2007-09-20
or less, still more preferably 36 C or less, and still more
preferably 34 C or less.
[0103] (Calculation of Solid-Liquid Coexistence Temperature
Range AT)
The value of AT is calculated by measuring the
melting point and solid phase temperature of a cold rolled
aluminum sheet (test piece) concerned by differential
thermal analysis and thereby calculating the temperature
range AT in which the liquid phase of aluminum is existent.
In the range related to the aluminum alloy system according
to the present invention, the melting point lies in the
range of approximately 645 to 660 C and a change detected
at a temperature of approximately 600 to 630 C is the
solid phase temperature.
[0104] Tests were conducted using, for example, TG/DTA
(TGD7000) manufactured by ULVAC-RIKO, Inc. and under the
following conditions:
Heat pattern: RT - 700 C - RT: 10 C/min
Atmosphere: Ar (100 ml/min)
Sample weight: about 500 mg
Reference: Alumina powder
Sample container: Alumina (Macro type 8 x 10 mm)
[0105] As a method other than differential thermal
42
CA 02602657 2007-09-20
analysis, AT may be determined from a calculation phase
diagram, but the method using differential thermal analysis
is more accurate. However, AT determined by a
thermodynamic equilibrium phase diagram calculation is
useful in case of making alloy design beforehand so that
the value of AT becomes 40 C or less. Fig. 3 illustrates
AT in a calculation phase diagram of C alloy according to
an Example of the present invention which is described in
Table 7 to be shown later.
[0106] (Control of AT)
The control of AT is basically made by designing the
balance of the main constituent elements (Mn, Mg, Fe, Cu,
Si) in the present invention in such a manner that the
solid-liquid coexistence temperature range AT of aluminum
becomes 40 C or less. According to a general trend of the
alloy elements (components), as to Mn and Fe, the value of
AT becomes larger as the content thereof increases or
decreases from a median in the defined content range. As
to Mg, Cu and Si, the value of AT tends to become larger as
their contents increases. Within the contents' ranges
defined in the present invention, generally, the lower the
contents of these alloy elements, the smaller the value of
AT.
43
CA 02602657 2007-09-20
[0107] However, in order for the cold rolled aluminum
alloy sheet for bottle cans to satisfy the required
strength and formability, it is difficult to simply
decrease the respective contents of the main constituent
elements.
[0108] Further, the crystallization temperature of Al
(Fe, Mn)-based intermetallic compound varies depending on
multi-element components, including the foregoing other
selective added elements and impurity elements. Therefore,
the value of AT also varies largely depending on such other
selective added elements and impurity elements.
[0109] Particularly, the proportion of can material
scraps in molten material used as can material has been
increasing every year in comparison with base metal and the
proportion of inevitable impurity elements present other
than basic component elements is increasing. Examples of
such inevitable impurity elements are Zr, Bi, Sn, Ga, V, Co,
Ni, Ca, Mo, Be, Pb, and W. The total (total amount) of
contents of these elements has heretofore been 0.01% or
less, but with the recent increase of the scrap proportion,
it is now 0.015% or more, or 0.02% or more, as the case may
be it is 0.05% or 0.1% or more, as inevitable impurities.
[0110] Consequently, even assuming that the amounts of
the main constituent elements and the amounts of the
44
CA 02602657 2007-09-20
selective added elements remains the same, if the total
amount of the impurity elements exceeds 0.01%, the value of
AT is influenced thereby and varies greatly. The degree of
such influence differs depending on the kind of alloying
elements; besides, in a multi-component system, the solid-
liquid coexistence temperature range varies also depending
on interaction of the constituent components. Therefore,
in the case where the amount of such inevitable impurity
elements becomes large, with a mere control of the content
range and the balance of basic components (e.g., Mg/Mn
ratio), it is very difficult to make a components design
for making the solid-liquid coexistence temperature range
into an optimal range, because of complicatedness of the
component system.
[0111] For this reason, when controlling the value of
AT, first there is made design of components balance with
respect to the main constituent elements (Mn, Mg, Fe, Cu,
Si) and selective added elements in the present invention
and there is made alloy design so as to satisfy the
strength and formability required of the cold rolled
aluminum alloy sheet for bottle cans.
[0112] Then, for calculating the liquid phase
temperature and solid phase temperature, there is made such
a thermodynamic equilibrium phase diagram calculation as
CA 02602657 2007-09-20
shown in Fig. 2 and the alloy design is modified so that
the solid-liquid coexistence temperature range AT of
aluminum becomes 40 C or less. Thereafter, it is necessary
to make a trial manufacture and check beforehand whether
the solid-liquid coexistence temperature range AT of
aluminum becomes 40 C or less under mass-productive
manufacturing conditions to be described later.
[0113] (Manufacturing Method)
The cold rolled aluminum sheet of the present
invention can be manufactured without greatly changing the
conventional soaking, hot rolling and cold rolling
processes. However, in order to attain the structure
defined in the present invention and ensure the basic
material properties (earing rate and strength), as well as
formability and ironing processability, without impairing
them, it is necessary to limit each of the above individual
processes to an optimal condition range and combine those
processes.
[0114] (Soaking Condition)
The soaking temperature is set at 550-650 C. If the
soaking temperature is too low, it will take too much time
for soaking, resulting in productivity being deteriorated,
while if the soaking temperature is too high, there occurs
swelling on ingot surface. Therefore, the soaking
46
CA 02602657 2007-09-20
temperature is set to a temperature falling under the above
range. A preferred soaking temperature range is in the
range of 580 C (especially 590 C) to 615 C (especially
610 C) .
[0115] The shorter the soaking time (homogenizing
time), the better insofar as the ingot can be homogenized.
For example, the soaking time is preferably 12 hours or
less, more preferably 6 hours or less. However, if the
soaking temperature is set at 550 C or higher, the soaking
time is required to be 6 hours or more. Likewise, if the
soaking temperature is set at 580 C or higher, the soaking
time is required to be 5 hours or more, and if the soaking
temperature is set at 590 C or higher, the soaking time is
required to be 4 hours or more.
[0116] The soaking treatment may be done dividedly in
plural stages. In the soaking treatment, control of the
heating speed, of the soaking temperature (homogenizing
temperature) and of the cooling speed may be done in any
stage. Such control may be done in all the stages, but is
preferably done at least in the first stage.
[0117] In the case where the temperature of the first
soaking treatment is set to a temperature falling under the
above range, the temperatures of the second and subsequent
soaking treatments are in many cases set lower than the
47
CA 02602657 2007-09-20
temperature of the first soaking treatment. For example,
the temperatures of the second and subsequent soaking
treatments are set lower by about 100 to 100 C, preferably
about 50 to 100 C, as compared with the temperature of the
first soaking treatment.
[0118] (Hot Rolling Start Condition)
After end of the soaking process, the ingot may be
once cooled, then re-heated and thereafter subjected to
rough hot rolling, or without cooling to excess, it may be
subjected directly to rough hot rolling. In case of
subjecting the ingot directly to rough hot rolling without
excessive cooling, the sum of the amount of solute Cu and
the amount of Cu contained in a fine precipitate of 0.2 Wm
or less can be easily set at a value in the range of 0.05%
to 0.3%, which means the amount of Cu in a solution
separated from a precipitate exceeding 0.2 pm in particle
size by the extracted residue method using hot phenol, and
the sum of the amount of solute Mg and the amount of Mg
contained in a fine precipitate of 0.2 m or less can be
easily set at a value in the range of 0.75% to 1.6%, which
means the amount of solute Mg separated from a precipitate
exceeding 0.2 pm in particle size by the extracted residue
method using hot phenol. Moreover, it is possible to
48
CA 02602657 2007-09-20
utilize self-heat generation of the ingot after the soaking
process, whereby not only the production time and heat
energy can be saved, but also it is possible to diminish
the number density of alloy elements' precipitates and
hence possible to diminish the earing rate.
[0119] In case of once cooling the ingot and re-
heating it, it is preferable to perform rapid heating at a
rate of 30 C/hr or higher. By this rapid heating it is
possible to suppress dissolving of Mg and Cu to the coarse
compounds so far produced or precipitation at the interface
of coarse precipitates, whereby the sum of the amount of
solute Cu and the amount of Cu contained in a fine
precipitate of 0.2 Wn or less in particle size can be
easily set at a value in the range of 0.05% to 0.3%, which
means the amount of Cu in a solution separated from a
precipitate exceeding 0.2 Eun in particle size by the
extracted residue method using hot phenol, and the sum of
the amount of solute Mg and the amount of Mg contained in a
fine precipitate of 0.2 m or less in particle size can be
easily set at a value in the range of 0.75% to 1.6%, which
means the amount of solute Mg separated from a precipitate
exceeding 0.2 m in particle size by the extracted residue method using hot
phenol. Moreover, it is possible to
prevent an excessive increase in the number density of
49
CA 02602657 2007-09-20
alloying elements' precipitates.
[0120] (Rough Hot Rolling Condition)
When performing hot rolling dividedly into rough
rolling and finish rolling and in a continuous manner, if
the end temperature in rough hot rolling is too low, the
rolling temperature will become low in the next finish hot
rolling and an edge crack becomes easier to occur.
Moreover, if the end temperature in rough hot rolling
becomes too low, the self heat required for
recrystallization after finish rolling is apt to become
deficient, so that the crystal grain diameter becomes too
small. Therefore, it is preferable that the end
temperature in rough hot rolling be set at 420 C or higher,
more preferably a temperature in the range of 430 C
(especially 440 C) to 470 C (especially 460 C) .
[0121] In order to ensure the end temperature in rough
hot rolling of 420 to 480 C it is preferable that the
start temperature in rough hot rolling be set at, for
example, about 490 to 550 C, more preferably about 495 to
540 C, still more preferably about 500 to 530 C. As long
as the said start temperature is kept at a temperature of
550 C or lower, it is also possible to prevent surface
oxidation of the hot rolled sheet. Further, it is possible
CA 02602657 2007-09-20
to prevent coarsening of recrystallized grains and hence
possible to further enhance the formability.
[0122] It is preferable that the aluminum alloy sheet
having gone through the rough hot rolling process be
subjected to finish hot rolling rapidly, for example
continuously, whereby it is possible to prevent recovery of
the strain accumulated in rough hot rolling and hence
possible to enhance the strength of the cold rolled sheet
to be obtained subsequently. It is preferable that the
aluminum alloy sheet after the end of rough hot rolling be
subjected to finish hot rolling for example within 5
minutes,. preferably within 3 minutes.
[0123] (Finish Hot Rolling Condition)
It is preferable that the end temperature in finish
hot rolling be set at 310 to 350 C. The finish hot rolling
process is a process for finishing the cold rolled alloy
sheet to predetermined dimensions, and since the structure
after the end of rolling becomes a recrystallized structure
due to self-heat generation, the end temperature in finish
hot rolling exerts an influence on the recrystallized
structure. By setting the end temperature in finish hot
rolling at 310 C or higher, in combination with the cold
rolling condition which follows, the final sheet structure
can be made into an elongated structure in the rolling
51
CA 02602657 2007-09-20
direction with an aspect ratio of 3 or more and it is
possible to ensure both Cu and Mg solid solution quantities
defined in the present invention. If the end temperature
in finish hot rolling is lower than 310 C, it is difficult
to attain the above structure in the present invention even
if the draft in cooling rolling in the subsequent cold
rolling process is set large.
[0124] On the other hand, if the end temperature in
finish hot rolling exceeds 350 C, it will be impossible to
make the final sheet structure into an elongated structure
in the rolling direction and the desired amount of solute
Mg cannot be ensured. Accordingly, a lower limit of the
end temperature in finish hot rolling is set at 310 C or
higher, preferably 320 C or higher, while an upper limit
thereof is set at 350 C or lower, preferably 340 C or lower.
[01251 (Type of Finish Hot Rolling Mill)
As a finish hot rolling mill there is used a tandem
hot rolling mill equipped with three or more stands. By
setting the number of stands at three or more it is
possible to diminish the draft per stand and accumulate
strain while ensuring surface properties of the hot rolled
sheet, so that it is possible to further enhance the
strength of the cold rolled sheet and that of its DI-formed
product.
52
CA 02602657 2007-09-20
[0126] (Total Draft in Finish Hot Rolling)
It is preferable that the total draft in finish hot
rolling be set at 80% or more. By setting the total draft
at 80% or more, in combination with cold rolling to be
described later, the final sheet structure can be easily
made into an elongated structure in the rolling direction
with an average aspect ratio of 3 or more. It is also
possible to enhance the strength of the cold rolled sheet
and its DI-formed product.
[0127] (Thickness of Hot Rolled Sheet)
It is preferable that the thickness of the alloy
sheet after hot (finish) rolling be about 1.8 to 3 mm. By
setting the sheet thickness at 1.8 mm or more it is
possible to prevent worsening (e.g., seizure or roughening)
of surface properties of the hot rolled sheet and the sheet
thickness profile. On the other hand, by setting the sheet
thickness at 3 mm or less it is possible to prevent the
draft from becoming too high when fabricating the cold
rolled sheet (the sheet thickness is usually about 0.28 to
0.3S mm) and hence possible to suppress the earing rate
after DI.
[0128] In the hot rolled sheet obtained in the above
manner, the amount of solute Cu and that of solute Mg are
in a controlled state to the respective optimum ranges, so
53
CA 02602657 2007-09-20
that the average earing rate is controlled to its
predetermined range. Therefore, it is possible to effect
cold rolling without intermediate annealing and make the
average earing rate of the cold rolled sheet as small as 0%
to 3.5%. Moreover, by combination with cold rolling to be
described later, the final sheet structure can be made into
an elongated structure in the rolling direction with an
average aspect ratio of crystal grains of 3 or more and the
sum of the amount of solute Cu and the amount of Cu
contained in a fine precipitate of 0.2 m or less in
particle size can be easily set at 0.05-0.3%, which means
the amount of Cu in a solution separated from a precipitate
exceeding 0.2 m in particle size by the extracted residue
method using hot phenol, likewise, the sum of the amount of
solute Mg and the amount of Mg in a fine precipitate of 0.2
m or less in particle size can be easily set at 0.75-1.6%,
which means the amount of solute Mg separated from a
precipitate exceeding 0.2 m in particle size by the
extracted residue method using hot phenol.
[0129] (Cold Rolling)
In the cold rolling process, rolling is performed
directly through plural number of passes without
intermediate annealing and it is preferable that the total
draft be 77-90%. By making the total draft 77% or more
54
CA 02602657 2007-09-20
without intermediate annealing, the final sheet structure
can be made into an elongated structure in the rolling
direction with an average aspect ratio of crystal grains of
3 or more and the sum of the amount of solute Cu and the
amount of Cu contained in a fine precipitate of 0.2 m or
less in particle size can be easily set at 0.05-0.3%, which
means the amount of Cu in a solution separated from a
precipitate exceeding 0.2 m in particle size by the
extracted residue method using hot phenol, likewise, the
sum of the amount of solute Mg and the amount of Mg present
in a fine precipitate of 0.2 m or less can be set at 0.75-
1.6%, which means the amount of solute Mg separated from a
precipitate exceeding 0.2 p.m in particle size by the
extracted residue method using hot phenol. Besides, it is
possible to secure compressive strength of the can. In the
case where intermediate annealing is performed or where the
total draft is low, the crystal grains are apt to become
equiaxed grains and the final sheet structure is difficult
to become an elongated structure in the rolling direction
with an average aspect ratio of crystal grains of 3 or more.
[0130] On the other hand, if the draft exceeds 90%,
although the average aspect ratio of crystal grains can be
made large, the plus earing in DI becomes too large and the
strength becomes too high, so a cupping crack or a can
CA 02602657 2007-09-20
bottom crack is very likely to occur during DI.
[0131] The sheet thickness after cold rolling is set
at about 0.28-0.35 mm in view of formability thereof into a
bottle can.
[0132] In the cold rolling process it is preferable to
use a tandem rolling mill with two or more stages of
rolling stands arranged in series. By using such a tandem
rolling mill, in comparison with a single rolling mill
having one stage of rolling stand and wherein cold rolling
to a predetermined sheet thickness is performed by repeated
pass (sheet pass), a smaller number of pass suffices even
at the same total draft in cold rolling and it is possible
to increase the draft in one pass.
[01331 Thus, the final sheet structure can be made
more easily into an elongated structure in the rolling
direction with an average aspect ratio of crystal grains of
3 or more.
[0134] Moreover, in comparison with the conventional
cold rolling process using a single rolling mill wherein
finish annealing is performed after the cold rolling, it is
possible to let recovery occur continuously at a lower
temperature and produce subgrains. However, the rolling
mill to be used is not limited to the tandem rolling mill
insofar as the rolling mill adopted can cause recovery in
56
CA 02602657 2007-09-20
cold rolling and produce subgrains sufficiently.
[0135] In cold rolling using a tandem rolling mill,
the amount of heat generated in one pass is large because
the draft in one pass is high. In the case where the
amount of heat generated becomes too large, the amount of
precipitates of Cu and Mg produced, especially the amount
of precipitates at the boundary of coarse precipitates,
increases due to strain introduction and heat generation in
cold rolling. Consequently, there is the possibility that
it will be impossible to ensure the required amount of
solute Cu and that of solute Mg and the required amount of
a fine precipitate.
[0136] Accordingly, in cold rolling using a tandem
rolling mill, when the temperature of the aluminum alloy
sheet rises to the greatest extent just after cold rolling
in the cold rolling process, it is preferable to cool the
aluminum alloy sheet forcibly so as to prevent the aluminum
alloy sheet temperature after cold rolling from rising to a
level exceeding 200 C.
[0137] As means for cooling the aluminum alloy sheet
forcibly in cold rolling it is preferable to adopt cooling
means such that water-free rolling oil used commonly is
changed into an emulsion type such as water-soluble oil or
lubricant and an aqueous solution of the emulsion is used
57
CA 02602657 2007-09-20
to strengthen the cooling performance without deteriorating
the lubricating performance.
[0138] After cold rolling, finish annealing (final
annealing) may be done at a temperature lower than the
recrystallization temperature, if necessary. Finish
annealing results in recovery of the structure and
improvement of both DI formability and can bottom
formability. It is preferable that the finish annealing
temperature be, for example, about 100-150 C, more
preferably 115-150 C. By setting the temperature at 100 C
or higher, it is possible to effect a satisfactory recovery
of the structure. On the other hand, by setting the
temperature at 150 C or lower, it is possible to prevent
excessive precipitation of dissolved elements and further
enhance the DI formability and flange formability.
[0139] It is preferable that the finish annealing time
be 4 ours or less (especially about 1 to 3 hours). By
avoiding too long annealing it is possible to prevent
excessive precipitation of dissolved elements and further
enhance the DI formability.
[0140] However, in cold rolling using the foregoing
tandem rolling mill, finish annealing is basically not
required because it is possible to let recovery occur at a
lower temperature and continuously and product subgrains.
58
CA 02602657 2007-09-20
[0141] The present invention will be described below
more concretely by way of Examples, but the present
invention is not limited by the following Examples and
changes may be made appropriately within the scope
conforming to the above and following gists of the present
invention, which changes are all included in the technical
scope of the present invention.
Example 1
[0142] Using aluminum metal alone as a melting raw
material and using molten metal of Al alloy components in A
to N shown in Table 1 below, ingots each 600 mm thick by
2100 mm wide were produced by the DC casting method. In
Table 1, the element content indicated by "-" represents
that it is below the detection limit.
[0143] As shown in Table 1, in both working examples
and comparative examples, the ingots contained inevitable
impurity elements Zr, Bi, Sn, Ga, V, Co, Ni, Ca, Mo, Be, Pb
and W in total contents of 0.01% or less as the total
amount of other elements.
[0144] The ingots were each subjected to a soaking
treatment in accordance with the conditions shown in Table
2. The soaking treatment was conducted twice. That is,
after the first soaking treatment, each ingot was cooled to
room temperature at a cooling speed shown in Table 2,
59
CA 02602657 2007-09-20
followed by re-heating to effect the second soaking
treatment. The heating speed as a first soaking condition
indicates a heating speed in the temperature range from
300 C to the highest temperature which temperature range
substantially exerts an influence on properties. The
cooling speed as a first soaking condition indicates a
cooling speed in the temperature range from the highest
temperature to 300 C which temperature range substantially
exerts an influence on properties. After this soaking
treatment, rough hot rolling was performed using a
reversing rough hot rolling mill having one stand, followed
by finish hot rolling using a tandem hot rolling mill
having four stands. The finish hot rolling was started
within three minutes after the end of rough hot rolling.
In this way there were obtained hot rolled aluminum alloy
sheets 2 to 2.5 mm in thickness as a common condition after
finish hot rolling.
[0145] The hot rolled sheets were then subjected to
cold rolling by only one pass with use of a tandem rolling
mill having two stages of rolling stands without
intermediate annealing to afford sheets (cold rolled
sheets) for bottle can body 0.3 mm in final thickness as a
common condition. In the cold rolling by the tandem
rolling mill, the aluminum sheets were cooled forcibly
CA 02602657 2007-09-20
using an aqueous emulsion so as to prevent the aluminum
sheet temperature just after cold rolling from rising to a
temperature exceeding 250 C. Finish annealing (final
annealing) after this cold rolling was not conducted.
[0146] In only comparative example 10, two passes were
performed in a single rolling mill having one stage of
rolling stand and intermediate annealing of 150 C x 1 hour
was performed between the first and the second pass for
comparison purpose although the total draft in cold rolling
was the same.
[0147] A test piece was sampled from each sheet (coil)
for bottle can body after cold rolling and the structure
thereof was checked. More particularly, an average aspect
ratio of crystal grains and the amount of solute Cu and
that of solute Mg were checked by the methods described
above, the results of which are shown in Table 3.
[0148] For determining high temperature properties of
the test piece, hardness and 0.2% proof stress of the test
piece surface at room temperature, as well as hardness and
0.2% proof stress of the test piece surface in 290 C x 20
sec. heat treatment of the test piece, were measured and a
change in hardness (hardness reduction) AHv (Hv) of the
test piece before and after the heat treatment was
determined. Further, an elliptic deformation quantity upon
61
CA 02602657 2007-09-20
bake-hardening of the can body after forming was measured.
These results are also shown in Table 3.
[0149] (Measurement of 0.2% Proof Stress)
Tensile test for measuring 0.2% proof stress was
conducted in accordance with JIS Z 2201 and, as the test
piece shape, there was used the shape of JIS No. 5 test
piece. The test piece was obtained in such a manner that
its longitudinal direction was coincident with the rolling
direction. Crosshead speed was 5 mm/min and a constant
speed was adopted until breakage of the test piece.
[0150] (Hardness Measurement)
Each cold rolled sheet sample was measured for
hardness at four positions under the application of 100 g
load by means of a micro Vickers hardness tester and a mean
value of the measured values was used as the hardness value.
[0151] (Evaluation of Elliptic Deformation)
For evaluation of elliptic deformation, as will be
described later, a bottle can body obtained by DI of the
above sheet for a bottle can body was washed and then baked
under the condition that the bodily temperature of the can
should reach 300 C in 30 seconds, then the degree of
elliptic deformation was checked. For checking the degree
0
of elliptic deformation, the diameter of the mouth portion
of the bottle can body was checked successively in the
62
CA 02602657 2007-09-20
circumferential direction, then an amount obtained by
subtracting the minimum diameter from the maximum diameter
was determined as an elliptic deformation quantity (mm),
and evaluation was made using a mean value from N = 10 cans.
In the case where the elliptic deformation quantity is 4 mm
or less, it was evaluated that the elliptic deformability
came up to a passing point. If the elliptic deformation
quantity exceeds 4 mm, there will occur defects such as
falling-down and jam during conveyance and necking as post-
steps in the can manufacturing process, thus making
continuous and efficient manufacture of cans difficult.
[0152] Further, as formability which the sheet for
bottle can body should satisfy basically, both earing rate
and DI formability (the number of times of cracking in
forming) were measured and evaluated, the results of which
are also shown in Table 3.
[0153] (Earing Rate)
For checking the earing rate, a blank was sampled
from the sheet for a bottle can body and lubricating oil
(Nalco 147, a product of D.A. Stuart Co.) was applied
thereto, then the blank was subjected to 40% deep drawing
test and formed into a cup for investigation, using an
Erichsen tester. The test was performed under the
following conditions: blank dia. 66.7 mm, punch dia. 40 mm,
63
CA 02602657 2007-09-20
R of the die-side shoulder portion 2.0 mm, punch shoulder R
3.0 mm, blank holder pressure 400 kgf.
[0154] Mountain-valley shapes formed in eight
directions (0 , 45 , 90 , 135 , 180 , 225 , 270 and 315
directions, assuming that the rolling direction is 0 ) in
the peripheral edge portion of the opening of the cup thus
obtained were measured and an average earing rate was
calculated.
[0155] An average earing rate calculating method will
now be described with reference to Fig. 1. Fig. 1 is a
developed view of the cup formed by DI of the sheet for a
bottle can body. In this developed view, earing heights (T1,
T2, T3, T4, designated minus earings) created in 0 , 90 ,
180 and 270 directions, assuming that the rolling
direction is 0 , are measured and likewise earing heights
(Yl, Y2, Y3, Y4, designated plus earings) created in 45 ,
135 , 225 and 315 directions are measured. The heights Yi
to Y4 and Ti to T4 are from the bottom of the cup. From
the measured values, an average earing rate is calculated
in accordance with the following equation:
Average Earing Rate [{(Yl+Y2+Y3+Y4)-
(T1+T2+T3+T4)}/{1/2x(Yl+Y2+Y3+Y4+T1+T2+T3+T4)}]x100
[0156] In the cold rolled sheet according to the
64
CA 02602657 2007-09-20
present invention, when the average earing rate is set at
near 0, the development of the four plug earings (Yl to Y4)
and the two minus earings (T2 and T4 in Fig. 1) in 90 and
270 directions are suppressed, but the development of the
two minus earings (T1 and T3 in Fig. 1) in 0 and 180
directions are difficult to be suppressed. Even if the
absolute value of the average earing rate is merely made
small, for example when the average earing rate is set at -
2% to 2% (2% or less in absolute value), the minus earings
(Ti and T3 in Fig. 1) are not suppressed to a satisfactory
extent even if the average earing rate is not less than -2%
and less than 0%, so that the blank holder pressure in deep
drawing is concentrated on the two minus earings (Ti and T3
in Fig. 1), causing edge rise and edge crack, which are
inconvenient to the manufacture. On the other hand, when
the average earing rate is set at 0-2% (plus side), it is
possible to prevent breakage of the can body caused by edge
crack because the remaining two minus earings (Tl and T3 in
Fig. 1) can also be suppressed to a satisfactory extent.
In the present invention, the range of +0% to +3.5% is
defined to be an allowable range.
[0157] (DI Formability)
A blank 156 mm in diameter was punched from the above
sheet for bottle can body (sheet thickness 0.3 mm). Using
CA 02602657 2007-09-20
the blank, a cup having a diameter of 92 mm was formed and
then subjected to re-deep drawing, ironing and trimming,
whereby DI can bodies for bottle can (inside diameter 66 mm,
height 170 mm, side wall thickness 103 m, side wall tip
thickness 165 m, final third ironing rate 40%) were
fabricated at a can manufacturing speed of 300 cans/min.
The number of body-cracked cans per 50,000 formed cans was
determined and DI formability was evaluated. The
evaluation was made in accordance with the following
criterion. 0: no cracked can (extremely good), 0: one
cracked can or less (good), 0: two to four cracked cans
(generally good), X: more than five cracked cans (bad)
[0158] As is apparent from Table 3, working examples 1
to 6 have compositions according to the present invention,
average aspect ratios of crystal grains therein are 3 or
more, Cu solid solution quantities as determined in the
foregoing manner are in the range of 0.05% to 0.3%, and Mg
solid solution quantities are in the range of 0.75% to 1.6%.
[0159] Thus, in working examples 1 to 6, as is seen
from Table 3, after heat treatment at 290 C for 20 seconds
(after bake-hardening), the hardness change AHv is 30 Hv or
less, 0.2% proof stress is 210 MPa or more, there is little
lowering of hardness and strength, and high-temperature
66
CA 02602657 2007-09-20
properties are excellent.
[0160] Working examples 1 to 6 are superior also in
earing rate and DI formability. Thus, it is seen that the
improvement of high-temperature properties in the present
invention does not impair the formability which the sheet
for bottle can body should satisfy basically.
[0161] On the other hand, in comparative examples 7 to
10, conditions for soaking and hot rolling do not fall
under the foregoing preferred conditions, although the
compositions adopted therein fall under those defined in
the present invention, so that any of the average aspect
ratio of crystal grains, the amount of solute Cu and that
of solute Mg deviates from the range defined in the present
invention. As a result, in comparison with the foregoing
working examples, a lowering of hardness and that of
strength are marked and high-temperature properties are
inferior.
[0162] In comparative example 7, the second soaking
temperature is too low, and the end temperature in finish
hot rolling is too low. In comparative example 8, the end
temperature in finish hot rolling is too low. In
comparative example 9, the end temperature in finish hot
rolling is too low. In comparative example 10, the rolling
mill used is a single cold rolling mill and intermediate
67
CA 02602657 2007-09-20
annealing was performed halfway of cold rolling.
[0163] Comparative examples 11 to 20 follow preferred
manufacturing conditions. However, alloy compositions used
therein deviate from those defined in the present invention.
As a result, in comparison with the foregoing Examples of
the present invention, a lowering of hardness and that of
strength are marked and high-temperature properties are
inferior. Formability is also low.
[0164] From the above results, critical meanings of
the conditions defined in the first invention can be
understood.
68
CA 02602657 2007-09-20
049
1A v) P+ 1~ 1~ 1() tt) O tf) ~f) 1f) ~f) K)
C O O O O r O O O O O O O O 0 O
p O O O O O O O O O O O O O O
E~ O O C= O O O O O O O O p O O
- ~.
120
m ' a ~. O ~ M cM M M M M M M
!h N N r r C) O N NV) t+) N N
O O O O O O O O O O O O O
O O O C C O O C C O O O O
m
N . r O . . . . ~ . ~ . . ~ .
c o . o o . . . . . . . . . . .
o 0
E
n
d U) ~y N r~t) ~t Hf !7 N t7 N)
~ N N Oo O O O~~ M CD 0 O N N
N r e- O r r r r O O C r r r r C
m $
oa 04 tonoooo
o o aNN a
r r r~- ~ ~ r- r r v-
O C
~ ~ N N t? t+f 1, M ~ ~
c O O O O O O O C O ci O O O C
Z
n
V H) O r~- r K) O O H) O V
E 0
~f ~ ~ t+f M W v> O O aD
v C O O C O O O C O O O O C O
~
m
G
U
tp -~f ~ --
C) N N N ~
O
G O O
Q v
Qa1 U 0 W LL. (7 I-~ Y J m
E IV
U) W o
J 0
f > 7
Q
N p~ ~ ".0 R
~ C. c n. W d
,-i E om E fl ~ :00:
W UW
69
CA 02602657 2007-09-20
m Y y M M M M M M M M M M M M M M M M M M M M
c=t m~ O O O O O O O O O OIO O O0 O O O O O O
ll(O ~- C...
co o0 0o co 0o w co 0o co vn co ao ac ao 0o m ao ao ao 00
00 oD eO a0 co co co 00 a0 CO a0 EO QO 00 CO a0 00 CO OO OD
C/
C
o E E E E E E E E Ev E E E E E E E E E E
co m m m m 0 N m N 0 Om N N m m m m d m m
c v v V V V V a V ~ v v v vV 'D v v V
c c c c c c c c c c c c c c c c c c c c
F- o~~ hW FW 1W F~ H FW F~ F~ F~ ~ 1~ F~ FW !~ -W F 1~ F~ H 1~
V,p ~ ~n ~A ~A tn u) w tA Y) ~A O tn M~A O v) N
N N N cv cV N N N N N N N N N N N N N N N
fnFL- C ~
vi
G. 0) N r M 0) O N O r N m et r 0) NL() <+) t!) O n
E M st N MV N O(O C> M <+) M M r r N 0 N M N
c p U M M C9 M~+) p) M M N M M M M M t~) M M M M M
W !-
2
y Y ~ ~ ~ ~ 'ah '~t st at ~ O v ~ ~' V v 'at ~ V ~ v ~
c ~ o p~ ~ 0) 0) 0) O> 0) Of 0) O) Of 0) 0) 0) O> 0) 0) O 0) 0) 0)
O)
LL - -3.=_~~
a O OW (D O v) O O O OLfl n OLO O) Lf) NLA M O
E~ ~ M N~ M m r 0) 00 N mao m m nV m N
cW U V qt ~ ~ ~ v lw M qe q? ~ It It '~ ~ V V
2
c c v) 0 O O u'f O ---
a, Ol 0 0 U ~ ~ ~ ~ '~7 '~nd tOA ~ ~ ~
~ N
I~S~'.
n ~ o~ w m v ao co 0o 0o 0o 0o co 0o co co 0o ao
6.9 -
H
O!
0 c O O O O O O O O O O O O O O O O O O O O
M Y d r r r N M tq M O O O O O O O O O O O O
~ 0 E Ln v) v) N W) V) ~- tn W) LO U) w LA %n H) tf) ull H) NU)
N M
A
0 0 o mul) o 0 0 0 0 0 0 0CD O o 0 o 0 0
o Q 00- M ~ ~ ~t vt M '~f ~ V ~ ~ V V V V ~F ~ V ~ ~
O
50 o m m=r v CD Oc co 0o ao w oo ao ao eo so 0o ao eo
E
=HS
co
o 0 o O o o O o 0 0 0 0 0 0 o O o 0 0 0
~C a r r r r Qf r r r r r- r r r r r r r r r ~-
A E~ m m eD m Hf m m~D 10 oD ~D m~O ~O m m m~C m iD
co)0-
O
C
O C M U
.~..
M M) ap l+f W N O O O O O O O O O O O O O O
~ a U N N N r r V V ~ V ~ ~ 'O Y V V V
r = ~ :.
O ~
aT a a a an m U a U a o w w - z
co
o N M ~nm n co rn o
N IV) ~m n ao o) N
N E r r r r r rir+r r r
J m I ~
m
la-
a~ ~m ~aNi
2 c n M a
E sF ~~
W 3t'~ Uu'S
CA 02602657 2007-09-20
O O OO OO OO O x Q d O x x x x x x x x x x
Q
>
LL W
~ c o0
a V C
c a
Il ~~~ t '.. r O O O O T CO ~~! r h m ~ Of f~ 1~ ~A m o0 ~A
yy~~ E E o n c
Z Z o 0 o0~ 8
O
0
O O O O O N O O O T ~~~ Ol O p 1~ ~ O
w rw ~ N r N r- N N ~f r N N v C r p e+) N r N O Crj
a W~~ t t i t + t t . t t t t ~ ~ + + . +
. ~
0 O O OLA aO r r CD tA r r W! o m Y9 N~A O r O
N tr> 'w qe u'i u'i d ~[i 'C t1i d ~ ~ri K> K>
w E.E.
ao o v) Qi N m o ao o M o~n v~ N~ N o~
eo ~ r- i= m ~ r w r. ao T ao oD cn ao o ~ ao
Hd
0- N N N N N N N N N N N N N N N N N
g w w Nl O N N~ 40 r T e0 h tr> to Hf M) m 0
1~ N
$~ a o T o o Q) T p r r N Q Q o a~~ t~) M t9 M N N e+f N) M M 0 N ~ N tp~) N
e+) N 1 f
~i, y!~ w~ ) b N~ ~ff Of N O O~ N~ tm+f N
o
t p g~ ~ N r r M M C+f
N o~9 t09
~ ti w.~ r O iO Uf h M M l+f m r~ r m l+~ ~ r N T
e0 GD 1- A so O 1I- 1- f~ 1- 1+ 1.- 1- P 1- I~ f- 1,
O ~p ~p
p ~ ~~ N O O~ p~ W ~
~_ . c~
o~ N O O 1~ O~ff T N T h ~ff A r N N~~~ N N
~ w~ M N M
ca N N r O O N r~ O N N
C 0~~ O O O O O a a a O O O O a O O O 0 O
M O h N O CO r- 10 r OD OD ~O 1~ O~ Go O p h O
r 1~ A 1~ O 1~ O 1~ eD A O O
O r p p O O O T T
O~ p Q~O O r r T r O p O O O O O
~mt~C7~O'
.f1 N W O f- t+~ af) aD h
~p 11) M r af) ~p M H)
~~~ r T O r O S O r O O O O T T O N N N N
O C O O C C O O O C O O O O C C C C
v
a~~j h O O N 1f1 Hf O r e7 Uf h e0 t~ 4D O~O CO 1- v r
ap0 ~- ~f) N) ~f) H! v ~t v v N 1D V Yf v U) t~) t+) M ~-
a
0
o' Q Q Q fO m Q () Q ~ W 1L 0 2-~ Jm Z
aa ~'
I-
CV) o
W r N e7 d Uf m t,- tp W O r N M d N 1~ a m o
J ~ T r r T r r r r r f~i
m y
>
~ E r
E $E
e
0
71
CA 02602657 2007-09-20
Example 2
[0168] Using aluminum metal alone as a melting raw
material and using molten metal of alloy components in A to
N shown in Table 4 below, ingots each 600 mm thick by 2100
mm wide were produced by the DC casting method. In Table 4,
the element content indicated by "-" represents that it is
below the detection limit.
[0169] As shown in Table 4, in both working examples
and comparative example, the ingots contained inevitable
impurity elements Zr, Bi, Sn, Ga, V, Co, Ni, Ca, Mo, Be, Pb
and W in total contents of 0.03% or more as the total
amount of other elements.
[0170] The ingots were each subjected to a soaking
treatment in accordance with the conditions shown in Table
5. The soaking treatment was conducted twice. That is,
after the first soaking treatment, the ingot was cooled to
room temperature at a cooling speed shown in Table 5,
followed by re-heating to effect the second soaking
treatment. The heating speed as a first soaking condition
indicates a heating speed in the temperature range from
300 C to the highest temperature which temperature range
substantially exerts an influence on properties. The
cooling speed as a first soaking condition indicates a
cooling speed in the temperature range from the highest
72
CA 02602657 2007-09-20
temperature to 300 C which temperature range substantially
exerts an influence on properties. After this soaking
treatment, rough hot rolling was performed using a
reversing rough hot rolling mill having one stand, followed
by finish hot rolling using a tandem hot rolling mill
having four stands. The finish hot rolling was started
within three minutes after the end of rough hot rolling,
and for controlling the foregoing anisotropic index, an
average winding tension was controlled as in Table S. In
this way there were obtained hot rolied aluminum alloy
sheets 2 to 2.5 mm in thickness as a common condition after
finish hot rolling.
[0171] The hot rolled sheets were then subjected to
cold rolling by only one pass with use of a tandem rolling
mill having two stages of rolling stands without
intermediate annealing to afford sheets (cold rolled
sheets) for bottle can body 0.3 mm in final thickness as a
common condition. In the cold rolling by the tandem
rolling mill, the temperature of each aluminum sheet just
after cold rolling was controlled to 130-200 C. Finish
annealing (final annealing) after this cold rolling was not
conducted.
[0172] In only comparative example 110, two passes
were performed in a single rolling mill having one stage of
73
CA 02602657 2007-09-20
rolling stand and intermediate annealing of 150 C x 1 hour
was performed between the first and the second pass for
comparison purpose although the total draft in cold rolling
was the same.
[0173] A test piece was sampled from each sheet (coil)
for a bottle can body after cold rolling and the structure
thereof was checked. More particularly, an average aspect
ratio of crystal grains and tensile properties were checked.
These results are shown in Table 6.
[0174] For determining high temperature properties of
the test piece, hardness and 0.2% proof stress of the test
piece surface at room temperature, as well as hardness and
0.2% proof stress of the test piece surface in 290 C x 20
sec. heat treatment of the test piece, were measured and a
change in hardness (hardness reduction) AHv Hv) of the test
piece surface before and after this heat treatment was
determined. Tensile test was conducted under the following
conditions and in 0 direction relative to the rolling
direction. Further, an elliptic deformation quantity upon
bake-hardening of the can body after forming was measured.
These results are also shown in Table 6.
[0175] (Anisotropy Measurement by Tensile Test)
Tensile test of each test piece was conducted in
accordance with JIS Z 2201 and, as the test piece shape,
74
CA 02602657 2007-09-20
there was used the shape of JIS No. 5 test piece.
Crosshead speed was 5 mm/min and a constant speed was
adopted until breakage of the test piece. In this case,
there were provided test pieces whose longitudinal
directions were 0 , 45 and 90 directions respectively
relative to the rolling direction and tensile strength and
n value of each of the test pieces were determined. There
were determined a difference (MPa) between maximum and
minimum values of tensile strength and a difference between
maximum and minimum values of the n values (strain
quantities in the range of between 2% and 4%). Mean values
in the above directions of both tensile strength and n
values were also determined.
[0176] (Hardness Measurement)
Each cold rolled sheet sample was measured for
hardness at four positions under the application of 100 g
load and a mean value of the measured values was used as
the hardness value.
[0177] (Evaluation of Elliptic Deformation)
For evaluation of elliptic deformation, as will be
described later, a bottle can body obtained by DI of the
above sheet for a bottle can body was washed and then baked
under the condition that the bodily temperature of the can
should reach 300 C in 30 seconds, then the degree of
CA 02602657 2007-09-20
elliptic deformation was checked. For checking the degree
of elliptic deformation, the diameter of the mouth portion
of the bottle can body was checked successively in the
circumferential direction, then an amount obtained by
subtracting the minimum value from the maximum value was
determined as an elliptic deformation quantity (mm), and
evaluation was made using a mean value from N = 10 cans.
In the case where the elliptic deformation quantity is 4 mm
or less, it was evaluated that the elliptic deformability
came up to a passing point. If the elliptic deformation
quantity exceeds 4 mm, there will occur defects such as
falling-down and jam during conveyance and necking as post-
steps in the can manufacturing process, thus making
continuous and efficient manufacture of cans difficult.
[0178] Further, as formability which the sheet for
bottle can body should satisfy basically, both earing rate
and DI formability (the number of times of cracking in
forming) were measured and evaluated, the results of which
are also shown in Table 6.
[0179] (Earing Rate)
For checking the earing rate, in the same way as in
Example 1, a blank was sampled from the sheet for bottle
can body and lubricating oil (Nalco 147, a product of D.A.
Stuart Co.) was applied thereto, then the blank was
76
CA 02602657 2007-09-20
subjected to 40% deep drawing test and formed into a cup
for investigation, using an Erichsen tester. The test was
performed under the same conditions as in Example 1 and an
average earing rate was calculated.
[0180] (DI Formability)
In the same manner as in Example 1 the number of
body-cracked cans per 50,000 formed cans was determined and
DI formability was evaluated. The evaluation was made in
accordance with the following criterion, @: no cracked
can (extremely good), 0: one cracked can or less (good),
two to four cracked cans (generally good), X: more than
five cracked cans (bad).
[0181] As is apparent from Table 6, working examples
101 to 106 have compositions according to the present
invention, average aspect ratios of crystal grains therein
are 3 ore more, the difference between maximum and minimum
values in tensile strength in 0 , 45 and 90 directions
relative to the rolling direction is 25 MPa or less, and
the difference between maximum and minimum values among n
values obtained by tensile tests in 0 , 45 and 90
directions relative to the rolling direction is 0.03 or
less. Thus, the structures obtained in these working
examples are less anisotropic.
77
CA 02602657 2007-09-20
[0182] In working examples 101 to 106, as is seen from
Table 6, after heat treatment at 290 C for 20 seconds
(after bake-hardening), the hardness change OHV is 30 Hv or
less, 0.2% proof stress is 215 MPa or more, there is little
lowering of hardness and strength, and high-temperature
properties are excellent.
[0183] Working examples 101 to 106 are superior also
in earing rate and DI formability. Thus, it is seen that
the improvement of high-temperature properties in the
present invention does not impair the formability.which the
sheet for a bottle can body should satisfy basically.
[0184] From the above results, critical meanings of
the conditions defined in the second invention can be
understood.
78
CA 02602657 2007-09-20
r-.=
o
~ m M M~t ~!9 ~ er M M M M M M M M
O~ O O O O O O O O O O O O O O
~ 0 0 0 O O 0 O O 0 O O O O O
_
~o
...
F~ O
m O O O O O 0 O O O O O O O
~ ~~t et M M M M M CM M CM
M N N~- ~ M M N N M M N N
~ O O O O O O O O O O O O O
O O O O C C O C O O C O G
W
~
O
M M
W O O
.n
~
a
N v o.- r o o ~p v> .n v v~ .-
~ N N W O O O e0 h A O o r N
O O O
m
O C
O A Mop 4D O O O A O N W ~
O " O O O O a
a o
E. b ~ M ~ M N ~ O M dm
N N 'd N M l+) O't "It M V)
o V O O C C C C C O 0 C O O C C V
C
0
Z
0
N m Mv ~in h M 1- M N Ntfl U
o ~ et ~f N N -f * ~ w O O
U.
O O O O O O G C O O G O O O ~
V
U c
~ ~ 1- n M ~ N M N ~~t M Uf ~
N N NV) V N V) O(O M N
a C O O O O C O O O O O C O C
C
~ U 0 W tL C9 =--~ Y-j m Z ~ co W J m
J
0
~ X >
0
m
;v ao E
co
co ~ CL w o c ~ w - -
79
CA 02602657 2007-09-20
ci M m ch th cn V~ cli co ci co cn co c~ co V~~
t m E o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
LL.tAH C~.
vi
a c_ n co m v~ o o cl) rn u> rn r~ rn ~ 10 ~ cn o) co
O E~ '0 v L[) v v v) K) v 1n co v c7 o v) Y) v v) .r v) v tnF-? wU~~
ao co ao co co m ao m co v) co ao ao aO co m m ao m m
C m aG 10 co {D co m 1D m m cD m aD m m co m mCG co
C
V ~...o= - -~~~~~~~~~
U F- o x M n M F- 9 n -- ~ -- ~ r- ~ -- -- f- n -- ~ ~-- f- --
$ u g E N Ln h W~ W~ W~ W) U) t0 10 Ln O w w W) Lo v~ u~ v~ 1()
m~ E N fV N N N N N N N N fV fV N N(V N fV (V N N
p pC ~
Cm CO
~ p d
w N 0 0 1p t() 0 O N 0 O 0 0 O a 0 0 O 0 O
tV N!~') N N N ~ N ~ N N N N N N N N N N N
O
C
a d r- ~ 0 N O - O O ~Op N) ~ 17 U) r- ((~~
O W O l ~ f M ~ 9 M ~ 1'7 M l ' M 9 ('~7 ('N7 7 M C ~ V ) C9 lN N
x
LL ;3 ~ ~ ~ ~ ~ ~ ~ ~ a cl a a a l I l I a
~~ Op O~~ ~ 0 ~ u) ~ O a0 O OaO 0 m N~=) 0 O
C O V V ~ V ~ .07 LO m kO U) C-4
'
ZS W ~ 7
1- :..
x
Ol
p C n f~ N 0 1f~ ~A pf !O ~.- h O 0 OV ~O aD W N ~ 1!>
O ~ O O O O) 0 OO O) a a p~ a ap p~ ap O p
a ~ V 1ff IA IA ~ 1f~ ~ N ~ 7 ~f ~ = V ~ 't ~ ~t = ~
Q
C
E,~ n ~0 v n~ m v m m ao ao m m ac m ao to co co
P~
_________
0 0 o g g o o O o o 0 0 0 0
~- - m a .-
~ o O o 0 0 g 0 o
o o 0
M m m m a~ h h m m~n v~ v~ v> u~ v> v~ m
N ~~ p~~~ p O ~t O O O O O O O O O O O
~t t v ~f < v ~f v v ~f ~t v
mv m =CD aD ~ a o 0 0 0 O 0 O 0 0 0 o O O 00 0 0 0 0 0
ao
0 e~j m O O m 10 m m m m m m m m m m m m m m m
p fn1-:.
C
32
U) O) Hf q, ~y m O O O O O O O O O O O O O O
pO ~ V N N N N N ~ O d' lw sf v V~ ~~v v v v Vv
~ xvgL.
O O
aaa mmUaUa
~ W~c9--Ym z
W) o
W N 19 O n aO W O - N 17 v tp m co W O
O O O O O O O - - .- - - N
lfl O p O W O
OD a
E E E
0
CA 02602657 2007-09-20
OO OO OO OO OO x d d p x x x x x x x x x x
~w
o
C p O O
E C t) "
LL O or- O 0 O 0 0 0 0 m O') N ~ CO Hf Ol m aD m m f- 1, U)
E~ = o ~ o>
E c
z oo XOg c~ ' a
0 C o O O N O ~ p O~ N N m F- 4p aD CD ~ aD
a'C ===-= (N r' N ~ N (V V ~ 1+) (V V 0 ~ l+) .=~ '
W ~'~ t i t t t i t ~ t t t t ~ ~ 4 t ~i + i +
'o
OD
Cl s W
o O ~- N CO O! Y) O C~) o P 01 1,~ 7 1, 0 M 0 a~
p/0 E ~ e- ~ ~ ~ fV V ~ ~t ~ b ~ ef Q if el ~ 10 ~ r=
wo E E o
0 0 t0 m~ Nv N. m 0 aD r- M LA tfl O N t~ N m W ~
N. m t~ P m -~ f~ m aD O 1~ Ol -~ a0 m 1~ h 1~
oa71SR
~ o g a c~ ~ c~ ~} 4 0 c o c +~ oy~ o o M~y o
O a N N N N N fV N N N N
"~ A - CD 0 Co tf) t[) 1() Mf 1~) M 0 1~ ~y ~ ='
0 N p~ a ~ ~ 0 aD O) O O 0 Ol 0 - I~ N aD o a aD a P O C .
a o N N M N N N N M N M M N M N M N N N N M y n
d a
0 ao m M ~ ~y M a~ M o u~ ao -W o
t w~~ p 2 ~ N M N N~v N~t N M N Nn N N :N
a=c~c1:=d o
= c a
N r- OD ~ O tA N N O O M O M ~ N O ~ O O N '$
O M
oe a a Q O M O M ~ D a a
a t/~ ~C O
= O)
Q ~ =C
=-
U) N r. ~f) N tf) O 0 N N M ~~fy) W O O M h ~ c
M a w O ~ O O O ~ O O O O O C O O O O N O O O
c o 0 0 0 0 0 0 0 0 o 0 0 o c o o
c o ~ N = m eD O Ip N O ~D o Op N O O O =O Op
O O O O O O O O O O O O O O O O O O O E
O o O O C o O C o C o 0 0 0 0 0 o C o =~
no
C~ h 1~ O h O ~ O ~ 10 a0 O f~ ~- N N N M ~ ~ p E .~
~~ ~' r'= N ~' ~ ~ M N M N M N M M M M M M M A 7 E
o E
od~oTSi:
q ~ o 0 o m W N o kn aD O 0 1A 1A N o 1A ~ o ~ E
= a M N M M N N r- LV N N N M N r- N N N M
~ =~
e O +1
M M M M M M M M M M M M M M M ~
m N M m U) U) N W O m t- O
O d~ ~ 1A N) Vf N ~ ~f ~ ~ N b ~ ~(f ~ LU ~ v m m v
Q A p ~ V
p~ Q Q Q m m U Q U Q O W LL _ --~ Y J~ z~ 0
Qam o 0
cp
W ~ N M ~t O m 1- m Of O N M ~ ~ m 1~ CO Q O 0
,J E o 0 0 0 0 0 0 0 0 N~
U o 0 0
a a
p ~ b b
[~ m oo m
~ E ~ E E E
C:~ 0
3 u'S c
uS ;~
w
81
CA 02602657 2007-09-20
Example 3
[0188] Using aluminum metal alone as a melting raw
material and using molten metal of alloy components in A to
N shown in Table 7 below, ingots each 600 mm thick by 2100
mm wide were produced by the DC casting method. In Table 7,
the element content indicated by "-" represents that it is
below the detection limit.
[0189] As shown in Table 7, in both working examples
and comparative examples, the ingots contained inevitable
impurity elements Zr, Bi, Sn, Ga, V, Co, Ni, Ca, Mo, Be, Pb
and W in total contents of 0.03% or less as the total
amount of other elements.
[0190] Therefore, first an alloying design satisfying
strength and formability required of the cold rolled
aluminum alloy sheet for a bottle can was made by designing
balance of main constituent elements (Mn, Mg, Fe, Cu, Si)
and selective added elements. Thereafter, a thermodynamic
equilibrium phase diagram calculation in each example was
made to effect control of AT, thereby calculating the
solid-liquid coexistence temperature range AT of aluminum
to make an alloying design or modification. There were
obtained such actual aluminum alloy components'
compositions in A to N as shown in Table 7.
[0191] Ingots of the said compositions were subjected
82
CA 02602657 2007-09-20
to a soaking treatment in accordance with the conditions
shown in Table 8. The soaking treatment was conducted
twice. More specifically, after the first soaking
treatment, each ingot was cooled to room temperature at a
cooling speed shown in Table 8, followed by re-heating to
effect the second soaking treatment.
[0192] The heating speed as a first soaking condition
indicates a heating speed in the temperature range from
300 C to the highest temperature which temperature range
substantially exerts an influence on properties. The
cooling speed as a first soaking condition indicates a
cooling speed in the temperature range from the highest
temperature to 300 C which temperature range substantially
exerts an influence on properties. After this soaking
treatment, rough hot rolling was performed using a
reversing rough hot rolling mill having one stand, followed
by finish hot rolling using a tandem hot rolling mill
having four stands. The finish hot rolling was started
within three minutes after the end of rough hot rolling.
In this way there were obtained hot rolled aluminum alloy
sheets 2.5 mm in thickness as a common condition after
finish hot rolling.
[0193] The hot rolled sheets were then subjected to
cold rolling by only one pass with use of a tandem rolling
83
CA 02602657 2007-09-20
mill having two stages of rolling stands without
intermediate annealing to afford sheets (cold rolled
sheets) for bottle can body 0.3 mm in final thickness as a
common condition. In the cold rolling by the tandem
rolling mill, the aluminum sheets were cooled forcibly
using an aqueous emulsion so as to prevent the aluminum
sheet temperature just after cold rolling from rising to a
temperature exceeding 250 C. Finish annealing (final
annealing) after this cold rolling was not conducted.
[0194] In only comparative example 210, two passes
were performed in a single rolling mill having one stage of
rolling stand and intermediate annealing of 150 C x 1 hour
was performed between the first and the second pass for
comparison purpose although the total draft in cold rolling
was the same.
[0195] A test piece was sampled from each sheet (coil)
for a bottle can body after cold rolling and the structure
thereof was checked. More particularly, an average aspect
ratio of crystal grains, an average size (central part in
the through-thickness direction) of intermetallic compounds
of 0.5 m or more,.and the solid-liquid coexistence
temperature range AT, were checked by differential thermal
analysis, the results of which are shown in Table 9.
[0196] For determining high temperature properties of
84
CA 02602657 2007-09-20
the test piece, hardness and 0.2% proof stress of the test
piece surface at room temperature, as well as hardness and
0.2% proof stress of the test piece surface in 290 C x 20
sec. heat treatment of the test piece, were measured and a
change in hardness (hardness reduction) AHv (Hv) of the
test piece before and after the heat treatment was
determined. Further, an elliptic deformation quantity upon
bake-hardening of the can body after forming was measured.
These results are also shown in Table 9.
[0197] (Measurement of 0.2% Proof Stress)
Tensile test for measuring 0.2% proof stress was
conducted in the same way as in Example 1 and in accordance
with JIS Z 2201 and, as the test piece shape, there was
used the shape of JIS No. 5 test piece. The test piece was
obtained in such a manner that its longitudinal direction
was coincident with the rolling direction. Crosshead speed
was 5 mm/min and a constant speed was adopted until
breakage of the test piece.
[0198] (Hardness Measurement)
Each cold rolled sheet sample was measured for
hardness at four positions under the application of 100 g
load by means of a micro Vickers hardness tester and a mean
value of the measured values was used as the hardness value.
[0199] (Evaluation of Elliptic Deformation)
CA 02602657 2007-09-20
As will be described later, evaluation of elliptic
deformation was made in the same way as in Example 1.
[0200] Further, as formability which the sheet for
bottle can body should satisfy basically, both earing rate
and DI formability (the number of times of cracking in
forming) were measured and evaluated, the results of which
are also shown in Table 9.
[0201] (Earing Rate)
For checking the earing rate, as in Example 1, a
blank was sampled from the sheet for bottle can body and
lubricating oil (Nalco 147, a product of D.A. Stuart Co.)
was applied thereto, then the blank was subjected to 40%
deep drawing test and formed into a cup for investigation,
using an Erichsen tester. The test was performed under the
following conditions: blank dia. 66.7 mm, punch dia. 40 mm,
R of the die-side shoulder portion 2.0 mm, punch shoulder R
3.0 mm, blank holder pressure 400 kgf.
[0202] Mountain-valley shapes formed in eight
directions ( 0 , 45 , 90 , 135 , 180 , 225 , 270 and 315
directions, assuming that the rolling direction is 0 ) in
the peripheral edge portion of the opening of the cup thus
obtained were measured and an average earing rate was
calculated.
[0203] How to calculate the earing rate is as
86
CA 02602657 2007-09-20
. ' ' described in Example 1.
[0204] (DI Formability)
In the same way as in Example 1 the number of body-
cracked cans per 50,000 formed cans was determined and DI
formability was evaluated. The evaluation was made in
accordance with the following criterion. @: no cracked
can (extremely good), 0: one cracked can or less (good),
two to four cracked cans (generally good), X: more than
five cracked cans (bad).
[0205] As is apparent from Table 9, working examples
201 to 206 have compositions according to the present
invention and have structures such that an average particle
size of 0.5 m or larger dispersed particles with an aspect
ratio of crystal grains of 3 or more is 5 m or less, and
solid-liquid coexistence temperature range AT of aluminum
is 40 or lower.
[0206] Thus, in working examples 201 to 206, as is
seen from Table 9, after heat treatment at 290 C for 20
seconds (after bake-hardening), the hardness change AHv is
30 Hv or less, 0.2% proof stress is 270 MPa or more, there
is little lowering of hardness and strength, and high-
temperature properties are excellent.
[0207] Working examples 201 to 206 are superior also
87
CA 02602657 2007-09-20
in earing rate and DI formability. Thus, it is seen that
the improvement of high-temperature properties in the
present invention does not impair the formability which the
sheet for bottle can body should satisfy basically.
[0208] On the other hand, in comparative examples 207
to 210, conditions for soaking and hot rolling do not fall
under the foregoing preferred conditions, although the
compositions adopted therein fall under those defined in
the present invention, so that any of the average aspect
ratio of crystal grains, the average particle size of
dispersed grains 0.5 Eun or more in particle size, and AT,
deviates from the range defined in the present invention.
As a result, in comparison with the foregoing working
examples, a lowering of hardness and that of strength are
marked and high-temperature properties are inferior.
[0209] In comparative example 207, the second soaking
temperature is too low and so is the end temperature in
finish hot rolling. In comparative example 208, the end
temperature in finish hot rolling is too low. In
comparative example 209, the end temperature in finish hot
rolling is too low. In comparative example 210,
intermediate annealing was performed halfway of cold
rolling.
[0210] Comparative examples 211 to 220 follow
88
CA 02602657 2007-09-20
preferred manufacturing conditions. However, alloy
compositions used therein deviate from those defined in the
present invention. As a result, any of the average aspect
ratio of crystal grains, the average particle size of 0.5
m or larger dispersed particles, and AT, deviates from the
range defined in the present invention. Consequently, in
comparison with the working examples, a lowering of
hardness and that of strength are marked and high-
temperature properties are inferior. Formability is also
low.
[0211] From the above results, critical meanings of
the conditions defined in the present invention can be
understood.
89
CA 02602657 2007-09-20
o~
~ C
M c7 M M M l'M M l'M
OE O O O O O O O O O O O O
~ O O O O O O O O O O O O C O
- ~
+~-= Z
F~ O
M'O O M 0
M N N M M N N M M N N
P . O O O O O O 0 O O O O 0 O
O O C C O O Q O O C O G O
C O
N . =- o o . . . . . . . . . . .
M M
E U . o o . . . . . . . . . ~ .
a o 0
a
c
04
cm 0~~-
a co
O O A!h n m ~ ~ ~ p O O~D N A ~
O p ~ p a
W G
N N N ~~- N M M 1~ CI'00) M m
C V O O G O C O C O C O O O CO O
o
a
E Z
V
a~ V~ N N., ~tf v ~ e0 V
LL o o o c o 0 o a o 0 0 0 0 0 >
E ea
m a
CE
o N N N M~ N Nf r p Pf N
C O G C O O C G G 6 ~ C C C m
Q -~
C
p Q m U 0 W ti 0 =-'~ Z m
E
~ N ( s
LU
J o
~ m c
o
U) ~ U)
Cc
G. C a a cc
E6 ~ ~ E n e~p
w Uw ~
CA 02602657 2007-09-20
Y ul ~ lh l7 M C7 t7 07 f7 M M C7 lh M C7 t7 e) f7 C7 Ci C7 l7
ctt E o 0 0 0 0 0 0 0 0 a 0 0 0 0 0 0 0 0 0 a
iiU)1- c~
~ ao ao co ao ao v~ m ao ao to ao ao ao ao ao ao ao ao ao ao
mao ao m ao m m ao m m OD ao w m ao m ao m oo ao ao
rn
C
c E F~ F~ E F~ F~ E~F F~ E E E F~ E E E E Et t
~ _ o o m m m m m m m o m
v v v v v v v v v v v v v o v v v v v
~ 0 c c c c c c c c c c c c c c c c c c c c
V 1~ o~ 1 - Fa !W 1~ F~ 1~ FW H iW F H H FW 1~ H IW H H H H
.. ~ _ u) u~ ln l(~ tA Y) ln tn 1A 1t~ 1n ln l u~ ln tn 1n K~ V) U) m U a E N
N tv N N fv N CV N N N N C%i fv N N N N N N
)!t- c E
0 N 0 ~ O O O f0 P9 t() ~- v ~ N N Of N
C d st ~ N CO st N O O C) <'~) V' l'O m N ~ CV 0 N N N
C7
~O C E U l'9 fh l+) f+) m C~) ('9
N<+) <+) C9 (~) O') (+) l~) C~) f+) (+) O)
~ WFo
0
t Y O N N N N N N N N aD N N N N N N N N N N N
N O) Of 0) O) 0) Ol O) O) c0 O) O D) Of 0 O) O) Gf O) 0 O)
~ ~
a o 0 0 0 0 0 ~ o 0 0 o m r.- r~ o o r~ o 0
v E fc LO n m to O r~ c+) v> <o v m to fo r= C r~
w'- - ~ v~v v vvvv~vv vvv ~ vv~
, _
~
OI C d 4) O 0 O O O O O O CD O aD f0 I~ Ow m - O O0
= V- E O - 0 - 10 10 O) Ol O) O w 1~ 0 O!.- 0 CO O) Ol
00 ~ 0 U in v) v) v) U) v) v v v v v) v v v v.r ~ff v v v
nc~ ~n~ s~
cm
m ~ ~ m v ao OD ao ao ao co cO m ao ao ao ao
_E
tm
c
Y
0 C O O O O O O O O O O O O O O O O O p O O
U Y d ~ ~W Lo 1+f O O O O O O O O O O O
v a F V v) v~ v~ h v kn Lo ko w In W) W) w v~ uli, w
N f/)0
H:.
n '
C p~ O H) N O O Yll O O O O O O O O O O O O O O o
p U ~t I+f ~t h ~ Nf ~ ~ ~ O ~t ~f ~ V' tt ~ ~ ~ ~f
U
o f0 OD V m CO m 0) ED m m OD aO OD 00 a0 aD 10 m OD
E
IH
00 _
o O o 0 00 0 0 0 0 o 0 00 0 0 0 0 o 0
~ E v m m m 10 ~f m m m f0 fo f0 m m m m m b p
w I
O)
0 O M) N O w O O O O O O O O O O O O O O
V) n N N N N N - IT Iq v st lw v lt v v
y = ~ v
O
aE aaammUaUaow~z
T
fA
N M '=t tO t0 1~ aD Ol O N m v uli 0 t- Cp 0 O
CO O O O O O O O O
W E N N~NIN N~N N N N N N N N N N N N N N N
CO
m
~
(~ m 0 0 m
~ E
E 3 E a
cv m om Eio
w w ciw
91
CA 02602657 2007-09-20
o
w 1 O O0 OO O OO x d d O x x x x x x x x x x
Ã.2
o >
~ lL W
E o
ps V O
~ C O
0
LL. 1A r= ~ O O ~ O i~ fr) < O f~ O m m K) (O N 1~ IA
~ Er E c
y Z o 0 00Ec=i
>,
o g
N 1p O O/ h M 0 m m O m {'q
a W Wo ~ + + i + + t + t i i i t ~ + ~ ~ } Q }
OD O m U) r- ~t) O c'~') O O O O O t+) 1() N N N O
C7 - fV (V 'C N w 1n OD 1n LA 1A 1A -W 1f'1 tA In {A
wo~E
0 m o m - ~ o w n a p m o P- w o oo co w $
(L m m 1~ 1~ P m OJ m m m m m O) m
C O c
dIrF
a o (v N ~) o O o o in o N M~ o 0 o N u~
d l'7 N ly '- ~- ~ N ,- O ~ O '- -
N N N N N N NN N N N N N N N N N
a
g~,~ ~ o 0 0 0 ~ oW) 0 0 0 U) o 0 0 0 o w w w w
C o = O - o O a Oo O.- N m Nf O N C7 o !'9 N O m r-
o ~ l7 91f 1'7 V9 N N l'7 M l'O !'7 N t9 t7 {V)
o < a
d
eo m Go to m ie eli o ~ v~ m o m co v~ o v v~ v~ .-
w $ C~ N N ~ N N ~ t~) 1+) l+) !+) < N~f N P) N) N Of N P)
Q S =e~ .o~.
S ---
I
P fV b ~ O O~
1~ 1- 1,
~ f~
1~ !~
~W ~ Om O~0
r- - .-
a wmi ! N ~ N 'Oi 7' : (N~) ~ ~m +) ~ .
e U) e w )
=
= a c m~ m m o v i= 0 m v r~ ao o mw n a> mm
~ = o'~
~.= a~ ~
Q'i%J~a ?
~ =
p~ O) m Y) ~ ~ QI N N 1~ l'9 U) Y) 0 m 1~ O m U) O
. h 7
a Q ~ ~
O
o F Q Q Q m m U Q U Q 0 W LL S -~ Y J~ Z
aacoS.
-6 N~'f ~ -p p 1~ m O/ O.- N t_7 ~ h tp 1~ m CD O
O O O O O O
J ~ N N N N N N N N N N N N N N N N N N N IV
m ~
~ a>
~' O O~O p O
C d = d
c
V E ae~s E~
0 ul
92
CA 02602657 2007-09-20
Industrial Applicability
[0215] According to the present invention, as set
forth above, it is possible to provide a cold rolled
aluminum alloy sheet for a bottle can which, on the premise
that formability in DI, etc. is to be secured, even in a
high-speed heat treatment performed at a higher
temperature for a shorter time, can be prevented from being
thermally deformed in coating and heat treatment, can
ensure required can strength after heat treatment, and can
afford a bottle can high in true circularity, and which has
excellent high-temperature properties. Thus, the cold
rolled aluminum alloy sheet of the present invention is
suitable for such applications as require strict properties
while retaining formability intact.
93
