Note: Descriptions are shown in the official language in which they were submitted.
A
~ACKGROUND OF THE INVENTION
The present invention teaches a process for preparing strip
stock from aluminum and aluminurn alloys, preferably Al-Mg-Mn
alloys, by means o~ strip casting machinesg wherein the strip
exhibits low earing properties and is suitable for use in the
manufacture o~ deep drawn and ironed hollow articles such as
cans or the like.
In recent years Al-Mg-Mn alloys, in the form of cold rolled
strip, have been success~ully processed into beverage cans by
deep drawing and ironing. A number of processes are known for
the production of aluminum strip for use in these beverage cans.
Typically, aluminum is cast by known methods such as horizontal
and vertical direct chill casting, or strip casting for fur~her
treatment. One such known process is disclosed in U.S. Patent
3,787,248 to Setzer et al. and assigned to the Assignee of the
present invention. The process comprises casting an Al-Mg-Mn
alloy, homogenizing this alloy at a temperature of between 455C
to 620C for 2 to 24 hours, hot rolling from a starting
temperature Or 3115C to 510C with a total reduction in thickness
of at least 20%, subsequent rolling, starting from a temperature
Or 205C to 430C with reduction Or at least 20%, subsequent
rolling, starting ~rom a temperature Or less than 205C with
reduction o~ at least 20%, heating the alloy between 95C and
230C ror at least 5 seconds but no longer than a time determined
by the equation T(10 t log t) - 12,500, T standing for degrees
Kelvin and t for maxirnum time in minutes.
While the process disclosed in the aforenoted patent has
been used successfully ror making rnetal strip to be used in
the manufacture of cans, it has been found that strip produced
by said process is not completely satisfactory in that the
-- 2 --
material experiences a high degree of earing.
A further known process for ~he production of strip is
disclosed in Light' ~et'aI'Age, Volume 33, 1975g December,
;' Pages 28-33. In the aforenoted ar~icle the strip was prepared
'` by a strip casting process and was thereafter treated so as to
be useful in the manufacture of cans. One basic problem which
arises in the production of strip via strip casting machines as
disclGsed in the above-noted article is that the dendritic arm
spacing or cell size at the surface of the strip is too large.
As a result of this large dendritic arm spacing, the strip
exhibits extensive surface porosity which leads to cracks in
the ~inal rolled strip. In addition, when the dendritic arm
spacing is too large, there is a danger of surface segregation
which can lead to poor quality in the final rolled strip which
in turn causes difficulties during the drawing and ironing
operation.
~ ccordingly, it is a principal object of the present
invention to provide a process for preparing alwninum alloy strip
stock by means of a continuous strip casting machine which
exhibits properties favorable for further processing by
cold rolling~
It is a further object of the present invention to provide
an improved process for cold rolling continuous strip cast
stock to thereby :Lmprove the earing properties thereof.
It is still a further object of the present invention
to provide the process as aforesaid which enables t'he aluminum
alloy strip to be used in the production of cans and the llke.
~ urther objects and advantages will appear hereinbelow.
s~
UMMAR~ OF THE INVENTION
In accordance with the present invention, the
foregoing objects and advantages may be readily obtained.
In accordance with one embodiment of the invention,
there is provided a multi-stepped process for fabricating
high strength, improved formability, low earing aluminum
strip stock from an aluminum melt comprising: A) continuously
casting said aluminum melt in strip form; B) holding said
casting strip at casting speed after the start of solidifica-
tion at a ternperature be-tween 400C and the liquidus te~pera-
ture of the alloy for about 2 to 15 minutes prior to hot
rolling so as to obtain a preferred dendritic arm spacing;
C) continuously hot rolling the cast strip at casting speed
at a temperature range betwee~ 300C and the non-equilibrium
solidus temperature of the alloy to a total reduction of at
least 7~/0; and D) hot coiling said hot rolled strip wherein
said coiled strip is allowed to cool in air to room temperature
prior to further worklng.
In accordance with another embodiment of the
invention, there is provided a multi-stepped process for
fabricating high strength, improved formability, low earing
aluminum strip stock from an aluminum melt comprising:
A) continuously casting said aluminum melt in strip form so
as to obtai.n a preferred dendritic arrn spacing B) continuous-
ly hot rolling the cast stri.p at casting speed at a tempera-
ture range between 300C and the non-equilibrium solidus
ternperature of the alloy to a total reduction of at least
70/0, C) hot coiling said hot rolled strip wherein said coiled
str.ip is allowed to cool in air to room ternperature prior to
further working; D) cold rolling said cooled hot rolled strip
il~ a first series of passes to a strip of intermediate gauge;
-- 4 --
E) flash annealing said cold rolled strip for not more than
90 seconds at a temperature of from about 350C to about
500C, and F) cold rolling said annealed strip in a second
series oE passes to final gauge.
In accordance with yet another embodiment of the
invention, there is provided a process for fabricating high
strength, improved formability, low earing aluminum strip
stock from hot ro:Lled aluminum strip comprising: A) cold
rolling said hot rolled strip in a first series of passes to
an intermediate gauge, B) flash annealing said cold rolled
strip for not more than 90 seconds at a temperature of from
about 350C to 500C, and C) cold rolling said flash annealed
strip in a second series of passes to final gaugeO
In accordance with yet another embodiment of the
invention the cast strip may be held at casting speed after
the start of solidification at a temperature between 500C and
the ]iquidus temperature of the alloy for frorn about 10 to
50 seconds prior to hot rolling.
In accordance with a broad embodiment of the invention,
there is provided a multi-stepped process for fabricating high
strength, improved formability, low earing aluminum strip stock
from an aluminum melt. According to this broad embodiment the
aluminum melt is cast continuously in strip form. Then the cast
strip is continuously hot rolled at casting speed, at a tempera-
ture range between 300C and the non-equilibrium solidus temp-
erature of the alloy to a total reduction of at least 70%.
Finally, the hot rolled strip is hot coiled and then the coiled
strip is allowed to cool in air at room temperature prior to
further working.
In accordance with yet another embodiment of the
present invention, there is provided a high strength aluminum
- 4a -
: base alloy particularly Al-Mg-Mn alloys having improved earing
properties which comprises: A) continuously casting said alloy
melt in strip forrn on a strip casting machine so as to obtain
a dendritic arm spacing in the region of the surface of the
as-cast strip from about 2 to 25 ~m, preferably from about 5
to 15 ~m and the dendritic arm spacing in the center of the
strip is from about 20 to 120 ~m, preferably from about 50 to
80 ~rn' B) continuously hot rolling the cast strip at casting
speed at a temperature range between 300~C and the non- -
equilibrium solidus temperature of the alloy to a total
reduction of at least 70~/O~ whereby the temperature of the
strip at the start of hot rolling is between said non-
equilibrium solidus temperature and a temperature of about
150C below said non-equilibrium solidus temperature
wherein the temperature of the strip at the end of the
hot rolling is at least 280C; C) hot coili.ng said strip
whereby said coiled strip is allowed to cool to room
temperature in air, D) cold rolling said cooled strip in a
first series of passes with a total reduction of at least
50%, preferably at least 65%, E) Elash annealing said
cold rolled strip for not more than 90 seconds at a
temperature of from about 350C to 500C, and
- 4b -
F. cold rolling said strip in a second series of passes
with a total reduction not to exceed 75%, preferably not
to exceed 70%.
In the preferred embodiment, the cast strip of the present
invention is cast on a strip casting machine having a plurality
of continuously moving chilling blocks, as is kno~n in the art,
such that the cast strip arter the start o~ solidification is
held at a temperature between 400C and the liquidus temperature
of the alloy for 2 to 15 minutes, preferably above 500C for
preferably 10 to 50 seconds. By controlling the solidification
rate the desired dendritic arm spacing-as well as optimum
distribution of insoluble heterogeneities is achieved. In
addition, by controlling the cooling rate, homogenization
treatments required in conventional processes can be eliminated
due to the uniformity of composition of the as-cast strip.
The present invention resides in an improved process
~or casting aluminurn and aluminum alloys, and in particular
Al-Mg-Mn alloys wherein the total concentration of magnesium
and manganese is from 2.0 to 3.3%, the ratio of magnesium
20 to rnanganese is from 1.4:1 to 4.4:1 and the total concentration
of other alloying elements and impurities is 1.5% maximum.
The process of the present invention lowers the cost of
rnanu~facturing aluminum strip by eliminating ingot casting,
su~sequent hornogenization treatment, and the additional cost
of hot rolling the large ingots.
_RIEF DESCR:~PTlON OF THR DRAWING
Figure 1 is a schematic illustration Or the strip casting
machine used in the process of the present invention.
-- 5 --
r~
DE~AILED DESCRIPTION
. ~
As indicated hereinabove; the present invention
comprises a process for producing hot rolled aluminum sheet by
a strip casting machine which is characterized by a preferred
dendritic arm spacing and insoluble heterogeneity distribution
which structures are essentially desirable when the strip is
to be further processed by subsequent cold rolling operations.
rrhe present invention further comprises an improved cold
rolling process for further processing the hot rolled strip
which improves the earing properties thereof thus making the
strip stock especially suitable for use in the proauction of
deep drawn and ironea articles such as cans'or the like.
Figure 1 is a schematic illustration of the strip
caster employed in the process of the present invention. ~he
details of the strip caster employed in the present invention
can be found in U.S. Patents 3,709,281, 3,744,545, 3,759,313
3,77~670 and 3~835,917. With reference to Figure 1, two sets
of chilling blocks are employed and rotate in opposite senses
to form a casting cavity into which the aluminum alloy is
brought through a thermally insulated nozzle system, not shown.
rrhe liquid metal upon contact with the chilling blocks is
cooled and solidified. The strip of metal travels during this
cooling and solidifying phase along with the chilling blocks
ulltil the strip exits the casting cavity where the chilling
blocks lift off the cast strip and start the return path to a
cooler where the chi]ling blocks are cooled before returning
to the casting cavity.
It has been found that by controlling the cooling
rate and thereby the rate of solidification of the cast
strip as it passes through the casting cavity the desired
dendritic and heterogeneity
C~U ~ A
structure can be obtained. On cooling the aluminum alloy from
the liquid state there are two important ternperature ranges.
The first temperature range being that temperature between the
liquidus and the solidus of the aluminum alloy. The second
temperature range being between the solidus and a temperature
100C below the solidus. The time taken to cool through the
li~uidus to solidus temperature range controls the average
secondary dendrite arm spacing. While the time taken to cool
în the range of the solidus temperature to a point 100C below
the solidus ternperature eliminates to-a large extent nonunifor-
mities in the as-cast strip by controlling the rounding of the
heterogeneities in the as-cast structure, the equalization or
distribution of the heterogeneities and the transformation of
non-equilibrium phases to equilibrium phases.
The rate of cooling as the cast strip passes through the
casting cavity of the strip casting machine illustrated in Figure
1 is controlled by controlling various process and product
parameters. These parameters include material cast, strip gauge~
chill block material, length of casting cavity, casting speed
and efflciency of the chill block cooling system.
It is a surprising advantage of the process of the present
invention that this process imparts significant improved physical
characteristics to the aluminum material processed characterized
by improved stren~th arld earing properties. These characteristics
will be discussed in greater detail hereinbelow.
As an example Or the foregoing, conventional materials
currently used in the production of strip include Aluminum
Alloy 3004. Alloy 3004 having the following composition has
been found to be particularly suitable ~or use in the process
of the present invention: magnesium from o.8 to 1.3%, magnanese
- 7 -
2~
from 1.0 to 1. 5% a iron up to 0.7%, silicon up to O.3%, copper
up to 0.25%, zinc up to 0.25%, balance essentially aluminum.
The processing o~ the present invention achieves superior
properties in 3004 than that obtained by conventional processes.
A particular ad~antage of the material processed in accordance
with the present invention is its superior strength and improved
earing properties over the same material processed in a
conventional manner.
Other alloys which are particularly suitable for use in
the process of the present inYention are characterized by having
a total concentration of magnesium and manganese from 2 0 to 3.3%
while maintaining the ratio of magnesium to manganese rrom 1.4:1
to 4.4:1 and maintaining the total concentration of other
alloying elements to 1.5% maximum. It has been found that when
these alloys are processed in accordance with the present
invention, they exhibit superior earing properties as well as
deep drawing properties at least as good as conventional A1-Mg-Mn
alloys in spite Or the high concentration o~ solid solution
strengthening elements, magnesium and manganese. It is prererred
that the total magnesium and manganese concentration be between
2.3 and 3.0% thus resulting in the combined solid solution
strengthening influence Or magnesium and manganese to approximate
that Or the magnesium addition in the 5000 series aluminum alloy.
In addltlon, it is prererred that the ratio Or magnesium to
manganese is kept in the range of 1.8:1 to 3.0:1. Prererred
add-ltlonal alloy~ng elements include copper up to 0.3%, silicon
from 0.1 to 0.5%, iron from 0.1 to 0.65%, titanium and/or vanadium
up to 0.15%, with the totai additional alloying elernents and
irnpurities not to exceed 1.5%.
-- 8 --
The surprising advantage Or the present invention is that
it enables strip stock to be -nade ~rom alloys containi.ng a high
concentration of solid solution strengthening elements while
maintaining excellent deep drawing properties as well as improving
the earing properties thereof~ It is a particular advantage
that material processed in accordance with the present invention
exhibit superior earing, strength and deep drawing properties
over the same material processed in a conventional ]nanner.
In accordance with the process of the present invention~
the aluminum alloys utilized herein are continuously cast into
strip rorm on a strip casting machine having continuously moving
chilling blocks such that the dendritic arm spacing in the region
of the as-cas~ strip is between 2 and 25 ~m, pre.ferably between
and 15 ym~ and the den~ritic arm spacing in the center region of
the strlp ~s between 20 to 120 ~m, preferably between 50 and 80 ~m.
In.accordance with the process of the present invention, in order
to achieve the aforenoted preferred dendritic structure as well
as uniformity in the composition of the cast strip in the alloys
utilized herein, it has been found ~avorable in the process of
the present :Invention to keep the cast strip arter the start o~
solidi~ication to the start of hot rolling at a temperature o~
between ll00C and the liquidus temperature of the cast alloy
~or 2 to 15 m:lnute~s, preferably above 500C for pre~erably
10 to 50 seconds. By controlling the cooling rate at the
start Or solidi~ication of`the cast strip, the desired
dendrltic arm spacing~is readily obtained~ It has also been
fourld that as a result Or the relativelg slow cooling rate
achieved by the process of the present invention there ls an
optimum distribut:lon of insoluble heterogeneities within the
_ g _
cast strip~ a feature which is favorable in connection with
subsequent cold rolling. As a result of the relatively long time
the solidified strip spends at high temperatures-the heat
contained ~n the as-cast strip promotes diffus~on controlled
processes in khe structure which results in eliminating non~
uniformities by spheroidication and rounding Or the heterogeneities,
equalization of the micro-segregation, ~.e., coring and
transformation of non-equilibrium phases to equilibrium phases.
Thus, by the strip casting process of the present invention the
normal homogenization treatment required in conventional processes
can be eliminated.
The process o~ the present invention comprises a series of
hot rolling steps which fall into critical temperature limits.
In accordance with the process of the present invention the cast
strip is hot rolled continuously at the casting speed, with
additional heating being applied thereto ir desired, in a
temperature range between 300C and the non-equilibrium solidus
temperature o~ the alloy with a total reduction of thickness of at
least 70%, whereby the temperature o~ the strip at the start of
hot rolling is between the non-equilibrium solidus temperature
and a temperature 150C below the non-equilibrium solidus
temperature and the temperature Or the strip at the end o~ hot
rolling is at least 280C. It has been found in order to minimize
undesirable properties, particularly excessive earing which would
result from direct processing of the cast strip into fin~shed
products such as cans or the like, special attention must be
given to insure that the hot working takes place at a sufficiently
hlgh temperature, prererably above 440C and ideally about 490C.
Only hot worklng in accordance with the process of the present
invention at the required temperature and with the requlred
-- 10 .--
t~
amount of formlng will guarantee adequate working of the strip
materlal so as to enable the elimination Or a homogenization
strip without impairing the quality Or the end product. As
previously noted, only an amount of hot forming of at least 70%
can guarantee the same favorable products in the end product,
i.e., strip stock as can be achieved with conventional methods.
One of the essential steps in the process according to
the present invention .i5 the hot coiling of the cast strip
after it has been hot worked, and the cooling down of the hot
rolled coil in air to room temperature. As previously noted
above, the temperature of the strip at the end of hot rolling
should be at least 2~0C and preferably at least 300C. It has been
found that when the hot strip is coiled and allowed to cool in
air to room temperature, the heat stored ~n the coils allows
precipitation of the intermetallic phases whlch slowly precipitate
out and at the same time brings about a softening of the strip
which is favorable for subsequent cold rolling. In addition,
a certain degree of recrystallization-occurs.in this stage of
the process which, due to a reduction in the amount of rolling
texture, has a favorable effect in reducing the earing at ~5
to the rolling direction when the strip is further processed
into cans or the like.
The coiled strip as cast according to the process of the
present invention as described above is at a gauge selected
to give the finished gauge after appropriate rolling. ~The
cold rolling operation may be carried out in any known manner.
In accordance with the process Or the present inventiong
it has been found particularly advantageous to introduce an
intermediate flash anneal at 350C to 500C during cold
rolling whereby in the cold rolling to final thickness after
the intermediate anneal a reduction of at rnost 75%, preferably
at most 70% is carried out. The-process comprises the following
A. cold rolling in a first series of passes with a total
reduction of at least 50%,- preferably at least 65%;
B. subjecting the cold rolled strip to a brief flash
anneal at a temperature between 350C to 500~C for not more
than 90 seconds;~and
C. cold rolling in a second series of passes with a
total reduction of at most 75%, preferably at most 70%.
It has been round that due to the brief flash anneal, in
particular with strip produced by strip casting as described
above, the amount Or earing at 45~ to the rolling direction
in the finished strip is substantially reduced. A decrease
in the amount o~ earing during subsequent drawing and ironing
operations is particularly advantageous in that the ironing
step can proceed symmetrically and is not influenced by
asy~netry due to excessive earing.
It has been round that the intermediate flash anneal
in accordance with the process of the present invention is
superior when compared with the normal conventional anneal
lnvolving slow heating up, slow cooling down, and long holding
times. It has been ~ound that the brief flash anneal, A) reduces
the rolling texture in the cold rolled strlp to a greater
extent than is accomplished with conventlonal annealing and,
B) at the s~ne time results in a smaller loss Or strength
than that which occurs ~rom the conventional processing. As
a result o~ feature A described above, the second series Or
cold rolling passes which brings the strip to final gauge
is carrled out with less pronounced rolling texture and can,
- 12 -
2~
as a result o~ feature B, be carried out with less hard working
thus resulting in an overall less pronounced rolling texture.
As is well known~ a smaller amount of rolling texture results
in a smaller amount of earing at 45 to the rolling direction.
In accordance with the process of the present- inven~ion the
time and temperature of i~termediate flash anneal are inter-
dependent. It can be determined in accordance with the
equation lnt = AT ~ C where, ~ is the time and seconds, T is
the temperature degrees Kelvin and A and C are constants. The
interdependency between the time and temperature is such that
the higher the temperature of the flash anneal the shorter
the amount of time required. In the preferred embodiment o~
the present invention, the duration of the intermediate ~lash
anneal is pre~erably at most 90 seconds including heating up~
holding at temperature and cooling down. It is preferred
thak when carrying out the intermediate anneal in the process
of the present invention heat up be not more than 30 seconds
and preferably 4 to 15 seconds~ holding the strip at temperature
for prererably between 3 to 33 seconds and cooling the strip
to room temperature within 25 seconds.
The process o~ the present invention will be more readily
understandable from a consideration of the ~ollowing illustrative
examples.
EXAMPLE I
As previously noted~ on cooling ~rom the liquid state
there are two -lmportant temperature ranges, the temperature
between ~the liquidus and solidus, ~TL/S, and the temperature
range between the solidus and a temperature 100C below the
solidus ATS/s lOO~c. The time taken to cool through the range
ATL/S controls average dendritic arm spacing while the time
- 13 -
~ ~ r ~
spent in the region ATSjs 100C controls the rounding of the
heterogeneities in the as-cast structure, equalization Or the
microstructure and the transformation of non-equilibrium phases
to equilibrium phases.
Aluminum Alloy 3004 was provided and was cast in accordance
with both the strip casting process according to the present
invention and conventional direct chill casking. In accordance
with the present invention the strip was cast on a casting
machine similar to that shown in Figure 1 wherein the casting
speed was 3 meters per minute. The temperature Or the strip
at the start of solidification was 650C, the temperature falling
to 500C after 35 seconds and reaching a temperature of 400C
after 6 minutes. The cell size Or the strip as cast is illustrated
in Table I, the times spent in each Or the temperature ranges
listed in Table I was roughly estimated from the measurement of
the cell size. Another melt Or Alloy 3004 was cast by the
conventional direct chill casting method. The surface o~ the
direct chilled cast lngots was scalped so as to remove non-
unirormities in the compositlon from the outer surface of the
ingot. As previous notedg Table I set forth below was the
dendritic arm spacing obtained on the surface and in the center
Or the as~cast alloy for both the process Or the present invention
and the conventional direct chill cast process. The QTL/S and
~TS/s 100C values have been calculated from the measurement
Or the dendritic arm spacing.
TABLE I
Cel~ Slze ~TL/s ~Ts/s-loooc
- Sample (~m) (sec) (sec)
Surface of strip cast in
accordance with the present 15 5 120
invention
Center of strip cast in
accordance with the present 50 20 120
invention
Direct chill cast, surface30 15 5
Direct chill cast~ center 70 80 15
As can be seen from Table I, the strip cast in accordance
with the process of-the present invention spends a longer
time in temperature range where diffusion controlled transforma-
tions are possible than is the case with conventional direct
chill casting. For this reason~ the transformations involved
pro~ressed much more in the structure of the strip casting than
in the structure produced by conventional direct chill casting.
In addition, the strip cast in accordance wlth the process of
the present invention has undergone a larger amount Or
homogenization than the direct chill cast. In particular, at
the surface of the as-cast strip, the diffusion controlled
transformations effectlng the equalization Or concentration
differeIlces is especially advanced since these transformations
proceed faster the finer the dendritic arm spacing. This
distlnguishes the final dendritic arm spacing of the strip Or
the present invention from the coarser structure obtained from
direct chill casting.
EXAMPLE II
Two Al-Mg-Mn alloys were provided having the compositions
set forth in Table II below.
- 15 -
t~
TABLE II
Mg Mn 'Cu 'S~ Fe ''Al
A ,`0.90%0.96% 0.90% 0.18% o.58% Balance
B 1.86% o.66% 0.04% 0.23% 0~39% Balance
, Two samples of both Alloys A and E were cast as 20 mm
thick strip in a strip casting machine, hot rolled in two
passes in line with the caster and then coiled hot in accordance
with the process of the present invention. The first pass was
made at a starting temperature of 550C to a finished temperature
of 440C with reduction o~ thickness o~ the strip from 20 mm
to 6 mm. The second pass was made at a starting temperature
of 360C to a finished temperature of 320C with a reduction
in thickness from 6 mm to 3 mm. Table III below lists the 0~2%
offset yield strength and the ultimate tensile strength for the
hot rolled strip for both Alloys A and B.
TABLE 'III
Ultimate
0.2% Tenslle
';Yi'e'l'd 'Strength ''Stren~
A130 MPa 210 MPa
B140 MPa 220 MPa
Strip A was then cold rolled with reduction from 3 mm to
1.05 mm and Strip B was cold rolled with reduction from 3 mm
to 0.65 mm. Both str:lps were given an intermediate anneal at
425C before being cold rolled to a final gauge of 0~31l mm.
One sample Or each Alloy A and B were subjected to conventional
intermecl:late anneal where heat up time was approximately 10
hours and the strip was held for one hour at 425C with a
coollng down of 3 hours. The second samples o~ each alloy
were f'lash annealed in accordance with the process of the
present invention. The alloy strips were held for 10 seconds
- 16 -
at 425C with a heat up time of 15 seconds and a cooling down
time of 15 seconds. Both annealing treatments as set forth
above produce complete recrystallizat~on of the strip. Table
IV below lists the 0.2% yield strength and earing values
obtained for each of the samples after annealing and prior
to cold rolling to final thickness Or 0.34 mm.
TABLE_IV
~0.2% Yield Strength_
Before cold After cold
Intermediate rolling torolling to
Anneal 0.34 mm 0.34 mm Earin~
A a)71 MPa 261 MPa 3.0%
b)87 MPa 274 MPa 2.4g
B a)88 MPa 266 MPa 1.8%
b)104 MPa 278 MPa 1.2~
It is clearly seen from Table IV that the brief flash
anneal ln accordance with the process of the present invention
produces lower earing values in spite of higher strength than
does the conventional anneal.
EXAMPLE III
The cold rolling passes were chosen such that after the
flash anneal treatment of the present invention the same final
strength was obtained as arter the conventional intermediate
anneal so as to show that the reduction in the earing by
the process of the present lnvention is even more striking.
To illustrate this point Strip A was cold rolled from 3 mm to
o.8 mm and Strlp B from 3 mm to 0.52 mm. Both strips were
then sub;ected to the flash anneal treatment described above
ln accordance with the present invention. Strips A and B
were then cold rolled to a final thickness of 0.34 mm. The
results that are set forth in Table V show ~hat when the cold
- 17 -
3~
rolling passes are chosen so as to obtain the same yield
strength as was obtained by conventlonal processing as set
forth in Example II, Table I of the improvement in earing
values of the material processed in accordance with the present
invention, is even more striking.
TABLE V
0.2% Yield Strength
(After cold rolling to 0.3 mm) E.aring
A 261 MPa 1.9%
B 266 MPa 0.9%
_AMPLE IV
Three samples of the same alloy designated Alloy B in
Table II of Example II were processed in accordance with Example
II to produce a 3 mm thick hot rolled strip. The strip was
then cold rolled with reduction from 3 mm to 0.65 mm. Each
sample was then annealed using three different treatments
after which each sample was cold rolled to an 85% reduction to
final thlckness. One sample was treated at 350C for 20
seconds, the second was treated at 425C for 20 seconds and
the third was treated at 425C for one hour. Table VI below
llsts the 0.2% yield strength and tensile strength of the
material for the three different anneal treatments.
TABLE VI
Ultimate
0.2% Tensile
Intermed _te Anneal Yield Strength Strength
350C/20 s 336 MPa 341 MPa
425C/20 s 331 MPa 339 MPa
425C/1 h 334 MPa 340 MPa
- 18 -
~ ~ ~
1~ IIA b~ ~ 3 ~ :It
Finally, ln order to simulate stove lacquering, i.e.,
when stock for can bodies are coated with a polymeric layer
to prevent direct contact between the alloy container and the
material contained therein, each sample of the material was
given a treatment at a-temperature of l90~C for 8 minutes
which is typical for curing the polymeric coating. This heat
treatment tends to produce a partial softening in the alloy.
The strength losses after this treatment are given in Table
VII hereinbelow with details of the corresponding intermediate
anneal.
~ABLE VII
IntermediateLoss of 0.2% -L~ss of Ultimate
Anneal Yield StrengthTensile Strength
350C/20 s 18 MPa 0 MPa
425C/20 s 40 MPa 15 MPa
425C/1 h 55 MPa 40 MPa
As can be seen from Table VII the brief heat treatments in
accordance with the process of the present invention produce
a much smaller loss of strength than the conventional inter-
mediate anneals which are at 45C.
This invention may be embodied in other forms or carried
out ln other ways without departing from the spirit or essentlal
characteristics thereof. The present embodiment is therefore
to be cons:ldered as in all respects illustrative and not
restrictive, the scope of the invention being indicated by the
appended claims, and all changes which come within the meaning
and range Or equivalency are intended to be embraced therein.
ThiS i5 a division of application Serial No. 333,160, filed
on August 3, 1979.
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