Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS OF PRODUCING HEAT-TREATABLE ALUMINUM ALLOY SHEET
TECHNICAL FIELD
This invention relates to a process of producing
aluminum alloy sheet material having good formability and
yield strength improvement when subjected to the painting
and baking operations typically employed during the
fabricating automotive parts. More particularly, although
not exclusively, the invention relates to the production
to of aluminum alloy sheet material suitable for fabricating
automotive parts that are visible in the finished
vehicles, such as automotive skin panels and the like.
BACKGROUND ART
The automotive industry, in order to reduce the
weight of automobiles, has increasingly substituted
aluminum alloy panels for steel panels. Lighter weight
panels, of course, help to reduce automobile weight, which
reduces fuel consumption, but the introduction of aluminum
alloy panels creates its own set of needs. To be useful
in automobile applications, an aluminum alloy sheet
product must possess good forming characteristics in the
as-received (by the auto manufacturer) T4 temper
condition, so that it may be bent or shaped as desired
without cracking, tearing or wrinkling. At the same time,
the alloy panels, after painting and baking, must have
sufficient strength to resist dents and withstand other
impacts.
Several aluminum alloys of the AA (Aluminum
Association) 2000 and 6000 series are usually considered
for automotive panel applications. The AA6000 series
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alloys contain magnesium and silicon, both with and
without copper but, depending upon the Cu content, may be
classified as AA2000 series alloys. These alloys are
formable in the T4 temper condition and become stronger
after painting and baking (steps usually carried out on
formed automotive parts by vehicle manufacturers). Good
increases in strength after painting and baking are highly
desirable so that thinner and therefore lighter panels may
be employed.
To facilitate understanding, a brief explanation of
the terminology used to describe alloy tempers may be in
order at this stage. The temper referred to as T4 is well
known (see, for example, Aluminum Standards and Data
(1984), page 11, published by The Aluminum Association)
and refers to alloy produced in the conventional manner,
i.e. without intermediate batch annealing and pre-aging.
This is the temper in which automotive sheet products are
normally delivered to parts manufacturers for forming into
skin panels and the like. T8 temper designates an alloy
that has been solution heat-treated, cold worked and then
artificially aged. Artificial aging involves holding the
alloy at elevated temperatures) over a period of time.
T8X temper refers to a T4 temper material that has been
deformed in tension by 2% followed by a 30 minute
treatment at 177°C to represent the forming plus paint
baking treatment typically experienced by formed
automotive panels. An alloy that has only been solution
heat-treated and artificially aged to peak strength is
said to be in the T6 temper, whereas if the aging has
taken place naturally under room temperature conditions,
the alloy is said to be in the T4 temper, as indicated
above. Material that has undergone an intermediate batch
annealing, but no pre-aging, is said to have a T4A temper.
Material that has undergone pre-aging but not intermediate
batch annealing is said to have a T4P temper, and material
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that has undergone both intermediate annealing and pre-
aging is said to have a T4PA temper.
In prior US patent 5,616,189 issued on April 1, 1997
to Jin et al., assigned to the same assignee as the
present application, a process of producing aluminum sheet
of the 6000 series is described having T4 and T8X tempers
that are desirable for the production of automotive parts.
The process involves subjecting a sheet product, after
cold rolling, to a solutionizing treatment (heating to 500
to 570°C) followed by a quenching or cooling process
involving carefully controlled cooling steps to bring
about a degree of "pre-aging." This procedure results in
the formation of fine stable precipitate clusters that
promote a fine, well dispersed precipitate structure
during the paint/bake procedure to which automotive panels
are subjected, and consequently a relatively high T8X
temper.
Specifically, the quenching or cooling process
involves cooling the alloy from the solution heat
treatment temperature to an intermediate temperature
without interruption and, without further interruption,
cooling the aluminum alloy further to ambient temperature
at a significantly slower rate. The intermediate target
temperature may be approached in a single step or multiple ;.
steps.
Unfortunately, sheet products produced in this way
from direct chill (DC) cast ingots often suffer from a
phenomenon known as roping, ridging or "paint brush" line
formation (the term "roping" is used henceforth). It is
developed due to the component of strain transverse to the
rolling direction in the sheet product which is applied as
the sheet is formed into an automotive part. Roping is
the non-uniform pattern of surface relief, caused by
locally inhomogeneous deformation, which is heavily
AMENDED SHEET
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orientated in the rolling direction of the sheet article.
These bands of locally inhomogeneous deformation manifest
themselves as visible surface undulations, which detract
from the final surface finish of the automotive product.
Roping has been encountered by others in this art,
and it has been found that roping may be inhibited by
modifying the sheet production method so that
recrystallisation occurs at an intermediate stage of
processing. The inhibition of roping is addressed, for
example, in US Patent No. 5,480,498 issued on January 2,
1996 to Armand J. Beaudoin, et al., assigned to Reynolds
Metals Company, and also in US Patent No. 4,897,124 issued
on January 30, 1990 to Matsuo et al., assigned to Sky
Aluminum Co., Ltd. In these patents, roping is controlled
by introducing a batch annealing step (e.g. heating at a
temperature within the range of 316 to 538°C) at an
intermediate stage of the sheet product formation, e.g.
after hot rolling but before cold rolling, or after an
early stage of cold rolling.
However, it has been found that, if an intermediate
batch anneal of this kind is carried out on sheet made of
6000 or 2000 series aluminum alloy, there is a reduction
not only of the T4 temper strength, but also of the T8X
temper strength when the alloy is subjected to the
solutionizing treatment/controlled cooling steps of the
Jin et al. patent. Therefore, attempts to control or
prevent roping reduce or eliminate the benefits of the
favourable T4/T8X temper characteristics that are
otherwise achievable for these types of alloys.
There is consequently a need for an improved process '
of producing aluminum automotive alloy sheet products of
the 6000 or 2000 series that exhibit little or no roping "
while maintaining desirable T4/T8X characteristics.
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SUMMARY OF T~-IE INVENTION
An object of the present invention is to provide an
improved method of reducing or inhibiting roping
tendencies in aluminum alloy sheet products of the 6000 or
2000 series, while maintaining acceptable T4 and T8X
properties.
Another object of the invention is to provide an
improved process of reducing or inhibiting roping
tendencies in 6000 series or 2000 series aluminum alloy
sheet products.
According to one aspect of the invention, there is
provided a process for producing sheet articles made of
6000 or 2000 series aluminum alloy, in which a cast ingot
is formed by direct chill casting, the ingot is scalped to
form a scalped ingot, the scalped ingot is homcgenized at
a temperature between 480 and 580°C for less than 48 hours
to form an homogenized ingot, and the homogenized ingot is
rolled to form a sheet article of final gauge, character-
ized in that said homogenized ingot is rolled to final
gauge directly by hot rolling, or said homogenized ingot
is reduced in thickness by hot and optionally cold rolling
to form an article of intermediate gauge that requires a
reduction in thickness in the range of 15o to less than ;..
40o to reach final gauge, followed by cold rolling said
article of intermediate gauge to form said sheet article
of said final gauge, provided that, when both hot and cold
rolling are employed to produce said article of
intermediate gauge, a heat treatment step is carried out
on said article of intermediate gauge to anneal said
article, prior to said cold rolling to final gauge.
AiVI'Ei~.IDED SHEET
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S ~d
In this application, the term "cold rolling" may be
taken to mean rolling operations carried out at
temperatures from ambient to a maximum of about 150°C.
The term "hot rolling" may be taken to mean rolling
operations carried out at temperatures of above about
300°C, and preferably at about 520°C.
AMENDED SNEET
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The invention also relates to aluminum sheet products
produced by the process described above.
This process is based on the finding that it is the
cold rolling step that introduces a tendency to exhibit
roping into the finished sheet product. If the reduction
in thickness brought about in the cold rolling step is
excessive (40% or more), roping effects become
unacceptable.
In contrast, the hot rolling steps do not introduce a
roping tendency into the finished sheet articles.
Therefore, if the reduction to final gauge can be
accomplished by hot rolling alone, then the cold rolling
steps may be eliminated, together with any tendency to
produce roping effects.
In the case of the process that employs cold rolling
steps, the cold rolling preferably reduces the thickness
of the alloy sheet by an amount in the range of 18% to
less than 40% to said final gauge, more preferably 20 to
35%, and even more preferably 20 to 30%.
The process of the invention that employs cold
rolling also preferably employs a heat treating step (e. g.
heating the sheet to a temperature in the range of 280-
560°C for up to 18 hours) to bring about annealing at a
stage in the reduction of the thickness of the sheet
following the hot rolling step, e.g. before cold rolling
commences, or between cold rolling steps when more than
one is employed. When the heat treating step is carried
out between cold rolling steps, it is usually carried out
between the penultimate and the final cold rolling steps.
The 15% to less than 40% reduction in thickness is then
brought about by the final cold rolling step.
The processes of the invention (i.e. those both '
involving and avoiding cold rolling) also preferably
employ a solutionizing step (e.g. heating at a temperature '
of 480-580°C) carried out on the sheet article of final
gauge. This is preferably followed by a controlled pre-
aging step of the type described in the Jin et al. patent
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discussed above, e.g. by cooling the sheet article rapidly
from the solutionizing temperature to an intermediate
temperature, and then cooling from the intermediate
temperature to ambient at a slower rate (e. g. < 2°C/hour).
S The alloy on which the indicated processes are
carried is preferably AA6111 aluminum alloy, but the
processes are effective for other alloys of the 6000 or
2000 series, particularly if they contain Cu, e.g. alloy
AA6016.
Thus, a preferred form of the invention involves
direct chill casting the alloy to produce a cast ingot,
scalping the cast ingot to form a scalped ingot,
homogenizing the scalped ingot at a temperature between
480 and 580°C for less than 48 hours to form an
homogenized ingot, hot and cold rolling the homogenized
ingot to an intermediate gauge to form an intermediate
sheet article, heat treating the intermediate sheet
article at a temperature between 280 and 560°C for up to
18 hours to form a heat treated intermediate article, and
cold rolling the intermediate article between 15 and less
than 40% to a final gauge. The sheet article of final
gauge is then solutionized between 480 and 580°C,
preferably in a continuous heat treatment furnace, rapidly
cooled and then pre-aged according to the process
described earlier in the Jin et al. Finally, the pre-aged
material is optionally subjected to various finishing
operations including levelling to obtain a flat sheet
article.
The material produced in this manner shows an
improved bend formability, no or reduced roping (paint
brush) lines after being formed into panels and higher
strength during the paint cure than conventionally treated
alloys of the same kind (e. g. AA6111-T4 material).
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a flow chart showing the steps of a
preferred procedure according to the present invention;
Figure 2 is a flow chart similar to Figure 1 showing
another preferred procedure according to the invention;
and
Figure 3 is a schematic representation of preferred
equipment used for the procedures of Figures 1 and 2.
DETAILED DESCRIPTION OF THE INVENTION
As noted above, the inventors of the present
invention have unexpectedly discovered that 6000 series
alloy sheet materials, such as AA6111 and AA6016, and some
2000 series alloy sheet materials do not exhibit roping
after hot rolling alone. The hot-rolled materials tend to
show signs of roping after subsequent cold rolling of z30o
and become fully roped at about 40o reduction. Therefore,
the degree of cold work influences roping, although the
underlying mechanism for this is not yet fully understood.
In the following description, reference is made to
procedures carried out on alloy AA6111, but this will be
understood as representative of other alloys of the 6000
and 2000 series.
Conventional AA6111 alloy sheet is produced from a
commercial size ingot which is scalped, homogenized, hot-
and cold-rolled to __>60% before being solution heat treated
(solutionized) to impart the T4 temper. Such material
exhibits roping upon forming (the standard test is to
strain the sheet by 15% in the transverse orientation and
then to stone the surface lightly). According to the
present invention, a substantially roping-free sheet
material can be produced, provided the amount of cold
reduction after hot rolling (if cold rolling is required
at all) is <40%, preferably between 15o and less than 40%,
and more preferably 18% to less than 400, more preferably
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20% to 35%, and most preferably between 20% and 30%.
Below 15% cold reduction coarse grains may be formed
during solutionizing and they produce an "orange peel"
pattern after forming. Such an appearance is considered
unacceptable, especially in exterior automotive panel
applications.
Producing a quality hot rolled material (re-roll
sheet) that will undergo between 15 and 40% final cold
rolling in a commercial plant is very difficult. Other
than by producing very thin gauge re-roll, the only way to
obtain such a condition is to include an intermediate
gauge heat treatment after initial cold rolling. It
should be noted that the purpose of the intermediate heat
treatment is to reduce the stored energy of the hot and
cold rolled material without allowing extensive coarsening
of precipitate particles. Coarse particles are difficult
to fully dissolve during solutionizing and are undesirable
because they adversely affect the strength increase
achieved by the pre-aging process, carried out following
solutionizing of the final gauge material, as described in
the Jin et al. patent (US Patent 5,616,189). Moreover,
the undissolved particles are undesirable as they make it
difficult to achieve consistent mechanical properties.
The optional heat treatment involves heating the
sheet to a temperature between 280 and 560°C and heat
soaking for up to 18 hours. The minimum time required for
the heat treatment is dependent upon the temperature
employed. At the high end of the temperature range, the
minimum time required may be very short (essentially zero
time at the peak temperature), but a person skilled in the
art will readily appreciate the time required in any
' particular case. Preferably, the material is batch heat-
treated in coil form at a temperature less than or equal
' to 350°C for up to 18 hours. Alternatively, higher batch
annealing temperatures and shorter times may be used,
subjecting the material to a temperature of about 400°C
for approximately 1 hour. However, at temperatures
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between 350 and 400°C, the heat treatment times should be
minimized to avoid excessive particle coarsening for
reasons mentioned above.
After the heat treatment, cold rolling to final gauge
is commenced or completed and the final gauge material is
preferably subjected to a solutionizing step at a
temperature of 480-580°C, preferably in a continuous
anneal and solution heat treating line, and is the
subjected to pre-aging.
A preferred pre-aging process involves rapidly
cooling the sheet from the solutionizing temperature to a
temperature in the range of 65 to 75°C, followed by slower
cooling to ambient at a rate of < 2°C/hour.
However, a more complex pre-aging process involves
four uninterrupted cooling phases or sequences: first,
from the solution heat treatment temperature to a
temperature between about 350°C and about 220°C at a rate
faster than 10°C/sec, but no more than 2000°C/sec.; second,
the alloy sheet is cooled from about 350°C to about 220°C
to between about 270°C and about 140°C at a rate greater
than about 1°C but less than about 50°C/second; third,
further cooling to between about 120°C and about 50°C at a
rate greater than 5°C/min. but less than 20°C/sec; and
fourth, from between about 120°C and about 50°C to ambient
temperature at a rate less than about 10°C/hr.
The above pre-aging (or quenching) process may be
carried out with an additional step of coiling the sheet
before the final step of cooling the sheet to ambient
temperature at a rate less than 10°C/hour.
Alternatively, the quenching process may involve
forced cooling the sheet by means of water cooling, water
mist cooling or forced air cooling, and coiling the sheet
at a temperature of 50 to 100°C, then allowing the coil to
cool at a rate of less than about 10°C/hour. The sheet
most preferably exits the forced cooling at a temperature
of between 120 to 150°C and the sheet is preferably coiled
at a temperature of between 60°C and 85°C.
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The general stages of the procedure indicated above
are shown in Figure 1 of the accompanying drawings. This
shows the use of cold rolling steps and an intermediate
heat treatment. In contrast, Figure 2 of the accompanying
drawings shows a preferred procedure in those cases where
cold rolling steps are not involved and hot rolling
proceeds to final gauge. In both cases, quenching and
pre-aging steps are carried out on the material of final
gauge.
Figure 3 is representative of the apparatus employed
for the various steps of the preferred form of the process
of the invention. A DC cast ingot 10 is first subjected
to homogenization at 11 and then hot rolling in a rolling
mill 12 to form a hot-rolled material (re-roll) in coil
form 13. The arrows 14, 15 and 16 indicate alternative
routs. Arrow 14 relate to a re-roll material 13 hot
rolled to final gauge. This material is subjected to a
solutionizing step and pre-aging procedure in a continuous
annealing and solutionizing heat treatment line 17 to give
a final product in T4 temper suitable for delivery to an
automobile parts manufacturer.
Arrow 15 indicates a route taken by hot rolled
material 13 that is not in final gauge. The material is
first subjected to a cold rolling step at 18 to produce a
material that is still not in final gauge. This material
is then subjected to a heat treatment in a batch annealing
furnace 19 or in a continuous annealing line 20. The heat
treated product is then subjected to final cold rolling to
gauge in a rolling mill 21, undergoing the stated
reduction in thickness of 15% to less than 40%. The same
solutionizing and pre-aging steps may then be carried out
in line 17, as previously described.
Arrow 16 shows the option of carrying out cold
' rolling only after the heat treatment in furnace 19 or
line 20, as previously described (i.e., there is no
preliminary cold rolling in mill 18 in this case). The
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subsequent steps are then the same as for the material
following arrow 15.
In all cases, it will be seen that cold rolling is
either not employed at all, or it is used after the heat
treatment to reduce the thickness of the intermediate
product to final gauge by an amount in the range of 15% to
less than 40%. If this degree of thickness reduction
between the hot-rolled re-roll 13 and the final gauge
product is not sufficient, preliminary cold rolling may be
carried out prior to the heat treatment in rolling mill
18. The degree of thickness reduction produced by cold
rolling prior to the heat treatment step does not
influence the roping effect. It is cold rolling after
this the heat treatment that has to be carefully
controlled to avoid imparting roping characteristics to
the product.
The process of the invention is designed to produce
an optimized sheet material with a good combination of
bend formability, surface appearance after forming and
paint bake response. The material produced in this manner
is believed to be superior to the conventional product
commercially available at the present time.
The present invention and its advantages will be
understood from the following Comparative Examples and
Examples, which are not intended to limit the scope of the
present invention.
COMPARATIVE EXAMPLES 1-3
Three ingots of AA6111 composition of commercial size
were direct chill cast. The ingots were scalped,
homogenized at 560°C, hot rolled to 2.54 mm gauge. Two of
the hot rolled coils were annealed together by heating up
to 400°C in a batch furnace, held for 1 hour and then
cooled with a fan. All coils were cold rolled with 59 and
64% reduction to the final gauge of 1.03 and 0.93 mm,
respectively. The cold rolled coils were solutionized at
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560°C, coiled between 65 and 75°C and cooled to room
temperature at a rate s2°C/hour. The materials were then
. subjected to finishing operations which included cleaning,
levelling and cut-to-length operations. The cut-to-length
samples were used to characterize the materials.
Tensile properties in the transverse direction were
determined using standard ASTM specimens at a cross head
speed of 2.54 mm/minute to 0.025 strain followed by 12.7
mm/minute to failure. The bendability of the materials
was determined using the standard ASTM E290-B7 test
method. The microstructure of the material was optically
examined. A roping test was performed by straining 45 mm
wide panels by 15% in the transverse orientation and then
lightly stoning the surface to highlight the topography.
Table 1 summarizes the properties of conventional and
batch annealed materials as received from the plant.
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Table 1
Mechanical Properties of AA6111 Alloys in Different Tempers
ComparativeTempersTensile Min. RopingMean
Properties Bend
Example Radius Grain
No. Size
LxT,
Y5~'~UTS~2~
Pm
MPa MPa o a~ c4~ cs~ b>
/oEl n L 'f~
1 As- 140 276 26 0.27 0.400.50 Yes 35x15
No Batch received
Annealing
paint- 269 344 19 - -- -- -- --
Bake~'~
2 As- 116 240 25 0.28 0.400.30 No 23 x
19
Batch received
Annealing
Paint- 205 283 20 -- -- -- -- --
Bake
3 As- 131 259 25 0.27 0.490.39 No 27 x
18
Batch received
Annealing
Paint 23 312 21 -- -- -- -- --
S
Bake
Notes: 'Yield Strength
ZUltimate Tensile Strength
'Total Elongation
°Strain Hardening Index
SLongitudinal Direction
6Transverse Direction
'Simulated by 2% stretch plus'/~h @ 177°C
Conventional AA6111 properties, Example 1 in Table 1,
in the as-received and paint bake tempers are 140 MPa YS,
276 MPa UTS and 26%E1 and 269 MPa YS, 344 MPa and 19%E1,
respectively. The as-received material showed bend
formabilities (r/t) of 0.4 and 0.5 in the longitudinal and
transverse directions, respectively. The grain size of
the material was 35 x 15 ~Cm. The material showed
considerable roping after straining 15% in the transverse
orientation.
Example 2 and 3 in Table 1 represent properties of
two AA6111 coils that were batch annealed together in a
batch furnace. It can be seen that the properties of the
two coils differed significantly from each other, which
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clearly shows problems associated with the batch annealing
process when attempting to achieve consistent properties.
These differences were due to the differences in the
amount of precipitated coarse Mg2Si/Si. The alloy of
Example 2 showed more coarse particles than those in
Example 3. Generally, the paint bake responses of the
batch annealed material was lower than its non-batch
annealed counterpart (compare Example 1 with Examples 2
and 3 in Table 1). As mentioned above, this difference is
mostly related to the fact that the batch annealed
material does not respond to the pre-aging treatment.
The batch annealed material did not show roping and
this is consistent with the teaching of the US Patent Nos.
4,897,124 and 5,480,498 assigned to Sky Aluminum and
Reynolds Metal Company, respectively. However, the batch
annealed products could not provide paint bake strength to
a level normally seen in the non-batch annealed product.
In addition, the properties of the batch annealed material
are difficult to control in a commercial processing
environment. This illustrates a need to develop a better
fabrication process for automotive sheet applications.
EXAMPLES 1 AND 2
Two ingots of AA6111 composition of commercial size
were commercially direct chill cast. The ingots were
scalped and fully homogenized at 560°C. One of the ingots
was hot rolled to 2.54 mm gauge and the other was hot
rolled to 2.3 mm gauge. The hot rolled coils at 2.54 and
2.3 mm gauges were cold rolled to 1.5 and 1.3 mm gauges,
respectively. The cold rolled coils were then heat
treated at 550°C in a continuous annealing furnace and
rapidly cooled. The heat treated coils at 1.5 and 1.3 mm
gauge, respectively, were cold rolled by 33 and 20% to the
final 1.0 mm gauge. The cold rolled coils were
solutionized at 550°C, rapidly cooled and coiled at
between 65 and 75°C and then cooled to room temperature at
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a rate <_2°C/h. The material was then subjected to the
cut-to-length operation without any levelling. The
cut-to-length samples were used to characterize the
materials.
It can be seen that the YS of the materials of
Examples 1 and 2 in Table 2 are quite close in both
as-received and the paint bake tempers.
Table 2
Mechanical Properties of AA6111 Alloy Produced According to the Present
Invention
Example TempersTensile Min. Roping Mean
Properties Bend
No. Radius Grain
Size
YS UTS L x T,
MPa MPa %EI n L T hm
1 As- 121 257 25 0.290.300.30 No 43 x 28
20% Finalreceived
Rolling paint- 251 329 20 -- -- -- --
Bake
2 As- 125 264 24 0.290.30~ Reduced29 x 19
0.30
33% Finalreceived
Rolling Paint- 257 334 21 -- -- -- --
Bake
The YS of the as-received materials in Table 2 are
lower than that of Comparative Example 1 (Table 1). This
difference is primarily because the fact that the
materials were not subjected to levelling operations. The
bend formability of the materials in Examples 1 and 2 are
different from one another but represent an improvement
from that of the regular material - compare Comparative
Example 1 in Table 1 with Examples 1 and 2 in Table 2.
The paint bake response of the Examples 1 and 2 materials
is better than those obtained from the batch annealed
materials in Table 1.
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The 33% cold rolled material showed reduced roping
while 20% rolled material did not show any roping.
Generally, the surface appearance of the two materials
after subjecting to the roping test were better than the
conventional material. The grain size of the 20% cold
rolled material is higher than that of its 33% cold rolled
counterpart. The grain size ranges obtained from both
these Examples are within the normal product range.
EXAMPLE 3
One commercial sized ingot of AA6111 composition was
direct chill cast, scalped, homogenized at 560°C, hot and
cold rolled to an intermediate 1.25 mm gauge. The
material was then heat treated at 300°C for 4 hours in a
batch furnace and cold rolled to the final 1.00 mm gauge.
The cold rolled coils were solutionized at 550°C and
rapidly cooled on a continuous annealing line, coiled at
between 65 and 75°C and then cooled to room temperature at
a rate s2°C/h. The material was sampled to evaluate
different properties.
The tensile properties of the AA6111 material are
listed in Table 3.
Table 3
Mechanical Properties of AA6111 Alloy Produced According to the Present
Invention
ExampleTempersTensile Min. RopingMean Grain
Properties Bend
2 No. Radius Size L x
5 T,
YS UTS pm
MPa MPa %El n L T
3 As- 124 260 26 0.29 0.3 0.3 No 48 x 19
received
Paint- 254 329 20 -- -- _ __
Bake
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The properties are similar to those obtained from
Examples 1 and 2 in Table 2. The bend formability and
paint bake response are better than conventional material
(Comparative Example 1 in Table 1). The roping
characteristics of the material are also better than the
conventional material.
It is clear from the above Examples that the proposed
process provides a sheet product that is better in terms
of bend formability, roping and paint bake response than
product available in the marketplace today.
