U.S. patent application number 10/360386 was filed with the patent office on 2003-09-18 for continuous casting process for producing aluminum alloys having low earing.
This patent application is currently assigned to Golden Aluminum Company. Invention is credited to Blakely, Theodore E., Ivy, Jackie S., Lawrence, Harry L., Pridmore, Charles, Selepack, Mark S..
Application Number | 20030173003 10/360386 |
Document ID | / |
Family ID | 28044052 |
Filed Date | 2003-09-18 |
United States Patent
Application |
20030173003 |
Kind Code |
A1 |
Selepack, Mark S. ; et
al. |
September 18, 2003 |
Continuous casting process for producing aluminum alloys having low
earing
Abstract
The present invention provides an improved process for
continuously casting aluminum alloys and improved aluminum alloy
compositions. The process includes the steps of continuously
annealing the cold rolled strip in an intermediate anneal using an
induction heater and/or continuously annealing the hot rolled strip
in an induction heater. The alloy composition has mechanical
properties that can be varied selectively by varying the time and
temperature of a stabilizing anneal.
Inventors: |
Selepack, Mark S.; (Jackson,
TN) ; Blakely, Theodore E.; (Henderson, NV) ;
Pridmore, Charles; (Bowling Green, KY) ; Lawrence,
Harry L.; (San Antonio, TX) ; Ivy, Jackie S.;
(Jonesboro, AR) |
Correspondence
Address: |
SHERIDAN ROSS PC
1560 BROADWAY
SUITE 1200
DENVER
CO
80202
|
Assignee: |
Golden Aluminum Company
|
Family ID: |
28044052 |
Appl. No.: |
10/360386 |
Filed: |
February 6, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10360386 |
Feb 6, 2003 |
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09445477 |
Jul 13, 2000 |
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09445477 |
Jul 13, 2000 |
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PCT/US98/11235 |
May 29, 1998 |
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60052326 |
Jul 11, 1997 |
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Current U.S.
Class: |
148/551 |
Current CPC
Class: |
C22C 21/00 20130101;
C22C 21/06 20130101; C22F 1/04 20130101; C22F 1/047 20130101 |
Class at
Publication: |
148/551 |
International
Class: |
C22F 001/04 |
Claims
What is claimed is:
1. A method for fabricating aluminum alloy sheet, comprising: (a)
continuously casting an aluminum alloy melt to form a cast strip;
(b) continuously imparting electromagnetic energy to the cast strip
to form a heated cast strip having a temperature greater than a
recrystallization temperature of the cast strip; and (c) further
processing the heated cast strip to form aluminum alloy sheet.
2. The method of claim 1, wherein the continuously casting step is
performed by a continuous caster.
3. The method of claim 1, wherein the continuously imparting step
is performed by continuously passing the cast strip through a
solenoidal heater.
4. The method of claim 1, wherein the cast strip has a cast output
temperature ranging from about 426 to about 538.degree. C. and the
output temperature of the heated cast strip ranges from about 432
to about 565.degree. C.
5. The method of claim 1, wherein the cast strip has a gauge of no
more than about 24 mm.
6. The method of claim 1, wherein the continuously imparting step
is performed before hot rolling of the cast strip.
7. The method of claim 1, wherein the continuously imparting step
is performed between hot rolling stands.
8. The method of claim 1, wherein step (c) comprises the step of:
hot rolling one of the cast strip and heated cast strip to form a
hot rolled strip, wherein the hot rolled strip is free of annealing
directly after the hot rolling step.
9. The method of claim 1, wherein step (c) comprises the step of:
recrystallizing the heated cast strip.
10. The method of claim 9, wherein the recrystallization step is
performed in the absence of heating after the continuously
imparting step.
11. The method of claim 1, wherein step (c) comprises the step of:
hot rolling the heated cast strip to form a hot rolled strip,
wherein the hot rolling step reduces the gauge of the cast strip by
about 88 to about 94 percent.
12. The method of claim 11, wherein the hot rolled strip has a
gauge ranging from about 1.45 to about 3.17 mm.
13. The method of claim 1, wherein the cast strip has a gauge
ranging from about 12 to about 19 mm.
14. The method of claim 1, wherein the aluminum alloy melt
comprises: (a) from about 3.5 to about 4.9% by weight magnesium;
(b) from about 0.05 to about 0.5% by weight manganese; (c) from
about 0.05 to about 0.15% by weight copper; (d) from about 0.05 to
about 0.35% by weight iron; and (e) from about 0.05 to about 0.20%
by weight silicon, the balance being aluminum and incidental
additional materials and impurities.
15. The method of claim 14, wherein step (c) comprises: hot rolling
the heated cast strip to form a hot rolled strip; cold rolling the
hot rolled strip to form a cold rolled sheet having a gauge of no
more than about 0.021 inches; and annealing the cold rolled sheet
at an annealing temperature to form the aluminum alloy sheet.
16. The method of claim 15, wherein, in the cold rolling step, the
gauge of the hot rolled strip is reduced by at least about 70% to
form the aluminum alloy sheet.
17. The method of claim 15, wherein the annealing temperature
ranges from about 149 to about 200.degree. C.
18. The method of claim 15, wherein the annealing step comprises
magnetically inducing a magnetic flux in the cold rolled sheet.
19. The method of claim 15, wherein the aluminum alloy sheet has an
as-rolled yield strength of at least about 41 ksi.
20. The method of claim 15, wherein the aluminum alloy sheet has an
as-rolled tensile strength of at least about 49 ksi.
21. The method of claim 11, wherein the aluminum alloy sheet has an
elongation at break of at least about 3 percent.
22. The method of claim 1, wherein the cast strip is outputted from
a continuous caster at a cast output temperature and further
comprising between steps (a) and (b): maintaining the cast strip at
or near a cast output temperature.
23. The method of claim 1, wherein the aluminum alloy melt
comprises: (a) from about 0.9 to about 1.5% by weight magnesium;
(b) from about 0.85 to about 1.2% by weight manganese; (c) from
about 0.05 to about 0.5% by weight copper; (d) from about 0.05 to
about 0.6% by weight iron; and (e) from about 0.05 to about 0.5% by
weight silicon, the balance being aluminum and incidental
additional materials and impurities.
24. The method of claim 23, wherein step (c) comprises: hot rolling
the heated cast strip to form a hot rolled strip; cold rolling the
hot rolled strip to form a partially cold rolled sheet, wherein in
the cold rolling step the gauge of the hot rolled strip is reduced
by at least about 50%; annealing the partially cold rolled strip at
an intermediate annealing temperature to form an intermediate
annealed cold rolled sheet; and further cold rolling the
intermediate annealed cold rolled sheet to form the aluminum alloy
sheet, wherein the gauge of the intermediate annealed cold rolled
sheet is reduced by less than about 55%.
25. The method of claim 24, further comprising: further annealing
the aluminum alloy sheet to form a further annealed aluminum alloy
sheet, wherein in the further annealing step at least one of the
yield and ultimate tensile strengths of the aluminum alloy sheet is
increased.
26. The method of claim 1, wherein the aluminum alloy melt
comprises: (a) from about 3.8 to about 5.2% by weight magnesium;
(b) from about 0.05 to about 0.2% by weight manganese; (c) from
about 0.05 to about 0.15% by weight copper; (d) from about 0.2 to
about 0.35% by weight iron; and (e) from about 0.05 to about 0.2%
by weight silicon, the balance being aluminum and incidental
sadditional materials and impurities.
27. A method for fabricating aluminum alloy sheet, comprising: (a)
continuously casting an aluminum alloy melt to form a cast strip,
wherein the cast strip, when outputted from the continuous caster,
has a cast output temperature; (b) continuously imparting
electromagnetic energy to the cast strip to form a heated cast
strip having a temperature greater than the cast output
temperature; and (c) further processing the heated cast strip to
form aluminum alloy sheet.
28. The method of claim 27, wherein, in the continuously imparting
step, the temperature of the heated cast strip is greater than a
recrystallization temperature of the cast strip.
29. The method of claim 27, wherein the continuously imparting step
is performed by continuously passing the cast strip through a
solenoidal heater.
30. The method of claim 27, wherein the output temperature of the
cast strip ranges from about 426 to about 538.degree. C. and the
output temperature of the heated cast strip ranges from about 432
to about 565.degree. C.
31. The method of claim 27, wherein the cast strip has a gauge
ranging from about 14 mm to about 19 mm.
32. The method of claim 27, wherein the continuously imparting step
is performed before hot rolling of the cast strip.
33. The method of claim 27, wherein the continuously imparting step
is performed between hot rolling stands.
34. The method of claim 27, wherein step (c) comprises the step of:
hot rolling one of the cast strip and heated cast strip to form a
hot rolled strip, wherein the hot rolled strip is free of annealing
directly after the hot rolling step.
35. The method of claim 28, wherein step (c) comprises the step of:
recrystallizing the heated cast strip.
36. The method of claim 35, wherein the recrystallization step is
performed in the absence of heating after the continuously
imparting step.
37. The method of claim 27, wherein step (c) comprises the step of:
hot rolling the heated cast strip to form a hot rolled strip,
wherein the hot rolling step reduces the gauge of the cast strip by
about 88 to about 94 percent.
38. The method of claim 37, wherein the hot rolled strip has a
gauge ranging from about 1.45 to about 3.17 mm.
39. The method of claim 27, wherein the cast strip has a gauge
ranging from about 12 to about 19 mm.
40. The method of claim 27, wherein the aluminum alloy melt
comprises: (a) from about 3.5 to about 4.9% by weight magnesium;
(b) from about 0.05 to about 0.5% by weight manganese; (c) from
about 0.05 to about 0.15% by weight copper; (d) from about 0.05 to
about 0.35% by weight iron; and (e) from about 0.05 to about 0.20%
by weight silicon, the balance being aluminum and incidental
additional materials and impurities.
41. The method of claim 40, wherein step (c) comprises: hot rolling
the heated cast strip to form a hot rolled strip; cold rolling the
hot rolled strip to form a cold rolled sheet having a gauge of no
more than about 0.021 inches; and annealing the cold rolled sheet
at an annealing temperature to form the aluminum alloy sheet.
42. The method of claim 41, wherein, in the cold rolling step, the
gauge of the hot rolled strip is reduced by at least about 70% to
form the aluminum alloy sheet.
43. The method of claim 41, wherein the annealing temperature
ranges from about 149 to about 200.degree. C.
44. The method of claim 41, wherein the annealing step comprises
magnetically inducing a magnetic flux in the cold rolled sheet
using a transflux induction heater.
45. The method of claim 41, wherein the aluminum alloy sheet has an
as-rolled yield strength of at least about 41 ksi.
46. The method of claim 41, wherein the aluminum alloy sheet has an
as-rolled tensile strength of at least about 49 ksi.
47. The method of claim 40, wherein the aluminum alloy sheet has an
elongation at break of at least about 3 percent.
48. The method of claim 27, wherein the cast strip is outputted
from a continuous caster at a cast output temperature and further
comprising between steps (a) and (b): (d) maintaining the cast
strip at or near a cast output temperature.
49. The method of claim 27, wherein the aluminum alloy melt
comprises: (a) from about 0.9 to about 1.5% by weight magnesium;
(b) from about 0.85 to about 1.2% by weight manganese; (c) from
about 0.05 to about 0.5% by weight copper; (d) from about 0.05 to
about 0.6% by weight iron; and (e) from about 0.05 to about 0.5% by
weight silicon, the balance being aluminum and incidental
additional materials and impurities.
50. The method of claim 49, wherein step (c) comprises: hot rolling
the heated cast strip to form a hot rolled strip; cold rolling the
hot rolled strip to form a partially cold rolled sheet, wherein in
the cold rolling step the gauge of the hot rolled strip is reduced
by at least about 50%; annealing the partially cold rolled strip at
an intermediate annealing temperature to form an intermediate
annealed cold rolled sheet; and further cold rolling the
intermediate annealed cold rolled sheet to form the aluminum alloy
sheet, wherein the gauge of the intermediate annealed cold rolled
sheet is reduced by less than about 55%.
51. The method of claim 50, further comprising: further annealing
the aluminum alloy sheet to form a further annealed aluminum alloy
sheet, wherein in the further annealing step at least one of the
yield and ultimate tensile strengths of the aluminum alloy sheet is
increased.
52. The method of claim 27, wherein the aluminum alloy melt
comprises: (a) from about 3.8 to about 5.2% by weight magnesium;
(b) from about 0.05 to about 0.2% by weight manganese; (c) from
about 0.05 to about 0.15% by weight copper; (d) from about 0.2 to
about 0.35% by weight iron; and (e) from about 0.05 to about 0.2%
by weight silicon, the balance being aluminum and incidental
additional materials and impurities.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 09/445,477, filed Dec. 6, 1999, entitled
"CONTINUOUS CASTING PROCESS FOR PRODUCING ALUMINUM ALLOYS HAVING
LOW EARING," which claims priority from a) PCT Patent Application,
Serial No. PCT/US98/11235; b) U.S. Provisional Application Serial
No. 60/052,326, filed Jul. 11, 1997; and c) U.S. patent application
Ser. No. 08/864,883, filed Jun. 4, 1997; Ser. No. 08/869,817, filed
Jun. 4, 1997; and Ser. No. 08/869,245, filed Jun. 4, 1997.
FIELD OF THE INVENTION
[0002] The present invention relates generally to aluminum alloy
sheet and methods for making aluminum alloy sheet and specifically
to aluminum alloy sheet and methods for making aluminum alloy sheet
for use in forming drawn and ironed container bodies.
BACKGROUND OF THE INVENTION
[0003] Aluminum beverage containers are generally made in two
pieces, one piece forming the container sidewalls and bottom
(referred to herein as a "container body") and a second piece
forming a container top. Container bodies are formed by methods
well known in the art. Generally, the container body is fabricated
by forming a cup from a circular blank aluminum sheet (i.e., body
stock) and then extending and thinning the sidewalls by passing the
cup through a series of dies having progressively smaller bore
sizes. This process is referred to as "drawing and ironing" the
container body. The ends of the container are formed from end stock
and attached to the container body. The tab on the upper container
end that is used to provide an opening to dispense the contents of
the container is formed from tab stock.
[0004] Aluminum alloy sheet is most commonly produced by an ingot
casting process. In the process, the aluminum alloy material is
initially cast into an ingot, for example, having a thickness
ranging from about 20 to about 30 inches. The ingot is then
homogenized by heating to an elevated temperature, which is
typically 1075.degree. F. to 1150.degree. F., for an extended
period of time, such as from about 6 to about 24 hours.
"Homogenization" refers to a process whereby ingots are raised to
temperatures near the solidus temperature and held at that
temperature for varying lengths of time. The process reduces
microsegregation by promoting diffusion of solute atoms within the
grains of alumina and improves workability. Homogenization does not
alter the crystal structure of the ingot. The homogenized ingot is
then hot rolled in a series of passes to reduce the thickness of
the ingot. The hot rolled sheet is then cold rolled to the desired
final gauge.
[0005] Although ingot casting is a common technique for producing
aluminum alloy sheet, a highly advantageous method for producing
aluminum alloy sheet is by continuously casting molten metal. In a
continuous casting process, molten metal is continuously cast
directly into a relatively long, thin slab and the cast slab is
then hot rolled and cold rolled to produce a finished product.
[0006] Some alloys are not readily cast using a continuous casting
process into an aluminum sheet having mechanical properties
suitable for forming operations, especially for making drawn and
ironed container bodies. By way of example, some alloys have low
yield and tensile strengths, a low degree of formability and/or a
high earing which lead to a number of problems.
[0007] It would be desirable to have a continuous aluminum casting
process in which the aluminum alloy sheet can be readily fabricated
into desired objects. It would be advantageous to have a continuous
casting process in which the aluminum alloy sheet has a high degree
of formability, low earing and high strength.
SUMMARY OF THE INVENTION
[0008] These and other needs are addressed by the process and alloy
compositions of the present invention. In a first embodiment, the
method can include the steps of:
[0009] (a) continuously casting an aluminum alloy melt to form a
cast strip;
[0010] (b) hot rolling the cast strip to form a hot rolled
strip;
[0011] (c) cold rolling the hot rolled strip to form an
intermediate cold rolled strip;
[0012] (d) continuously annealing the intermediate cold rolled
strip at a temperature ranging from about 371 to about 565.degree.
C. to form an intermediate annealed strip; and
[0013] (e) cold rolling the intermediate cold rolled strip to form
aluminum alloy sheet.
[0014] The use of a continuous anneal can provide significant
savings in operating and alloy costs and improvements in production
capacity. As will be appreciated, batch anneals require a
significantly increased amount of labor to perform, and batch
anneal ovens have a limited capacity.
[0015] The continuous annealing step (d) is preferably conducted in
an induction heater with a transflux induction furnace being most
preferred. The annealing step (d) surprisingly yields an
intermediate annealed strip having mechanical properties (i.e.,
yield tensile strength and ultimate tensile strength) that can be
selectively controlled by varying the temperature and duration of a
later stabilizing or back annealing step (collectively referred to
as a "stabilizing anneal"). For the induction furnace, the
residence time of any portion of the cold rolled strip in the
continuously annealing step (d) ranges from about 2 to about 30
seconds.
[0016] It has been discovered that induction heaters can provide
aluminum alloy sheet having not only a finer grain size but also a
substantially uniform distribution of the finer grain size
throughout the coil formed by the intermediate annealed strip. The
relatively fine grain size can provide not only more uniform
mechanical properties throughout the coil but also mechanical
properties that are controllable by varying the temperature and
duration of a later stabilizing or back annealing step.
[0017] The induction furnace can be superior to radiant furnaces in
annealing aluminum alloys because the induction furnace more
uniformly heats the strip. Radiant furnaces place the strip in a
heated atmosphere and rely on thermal transfer to anneal the entire
cross-section of the strip, which can lead to more exposure of the
exterior portions of the strip/coil to heat and less exposure of
the middle of the strip/coil to heat. In contrast, induction
furnaces use electromagnetic energy to heat the strip substantially
uniformly throughout the strip's cross-section. Accordingly,
induction heaters can provide for greater gains in mechanical
properties through annealing than radiant heaters and, therefore,
permit the use of lower amounts of expensive alloying elements to
realize selected mechanical properties.
[0018] Aluminum alloy sheet produced by this process is especially
useful as body stock in canmaking applications. To provide the
desired low earing for container manufacture, cold rolling step (c)
can be used to produce a relatively large reduction in the gauge of
the strip while cold rolling step (e) is used to produce a
relatively low reduction in the gauge of the intermediate cold
rolled strip (i.e., a low amount of work hardening). The low amount
of work hardening can produce a concomitant relatively low increase
in yield and ultimate tensile strengths. The yield and ultimate
tensile strengths can then be increased to desired levels in a
later stabilizing annealing step by selecting the appropriate
annealing or back temperature and time, without a significant
increase in earing.
[0019] Other embodiments of the method employ the induction furnace
in annealing steps performed after hot rolling, such as in a
stabilizing anneal. The unique performance advantages of the
induction furnace can provide highly desirable mechanical
properties in the aluminum alloy sheet which can be controlled in
later annealing steps as noted above.
[0020] In a particularly preferred process for producing aluminum
sheet useful as body stock, a number of additional steps. The
complete process includes the following steps:
[0021] (a) continuously casting an aluminum alloy melt to form a
cast strip having a cast output temperature;
[0022] (b) heating the cast strip, either before hot rolling or
after partial hot rolling, to a heated temperature that is from
about 6 to about 52.degree. C. more than the cast output
temperature to cause later recrystallization of the cast strip
after step (c) below;
[0023] (c) hot rolling the cast strip to form a hot rolled
strip;
[0024] (d) cold rolling the hot rolled strip to form an
intermediate cold rolled strip;
[0025] (e) intermediate annealing of the intermediate cold rolled
strip in an induction furnace at a temperature ranging from about
371 to about 565.degree. C. to form an intermediate annealed strip;
and
[0026] (f) cold rolling the intermediate cold rolled strip to form
aluminum alloy sheet.
[0027] After step (f), the aluminum alloy sheet can be subjected to
a stabilizing anneal, as desired, to provide desired mechanical
properties. "Recrystallization" refers to a change in grain
structure without a phase change as a result of heating of the
strip above the strip's recrystallization temperature.
[0028] An alloy useful in this process for producing body stock has
the following composition:
[0029] (i) from about 0.9 to about 1.5% by weight magnesium,
[0030] (ii) from about 0.8 to about 1.2% by weight manganese,
[0031] (iii) from about 0.05 to about 0.5% by weight copper,
[0032] (iv) from about 0.05 to about 0.5% by weight iron, and
[0033] (v) from about 0.05 to about 0.5% by weight silicon.
[0034] Body stock produced using this alloy and process can have
particularly attractive properties. By way of example, the aluminum
alloy sheet can have an as-rolled yield strength of at least about
38 ksi, an as-rolled tensile strength of at least about 42.5 ksi,
an earing of. less than about 1.8%, and/or an elongation of at
least about 3%. As will be appreciated, "earing" is typically
measured by the 45 degree earing or 45 degree rolling texture.
Forty-five degrees refers to the position of the aluminum alloy
sheet which is 45 degrees relative to the rolling direction. The
value for the 45 degree earing is determined by measuring the
height of the ears which stick up in a cup, minus the height of
valleys between the ears. The difference is divided by the height
of the valleys and multiplied by 100 to convert to a percentage.
Surprisingly, strip that is intermediate annealed using an
induction heater generally has as-rolled yield and tensile
strengths that are about 3 to about 5 ksi more than that of a strip
that is intermediate annealed using a batch heater.
[0035] Container bodies produced from the body stock can also have
superior properties. Container bodies produced from aluminum alloy
sheet can have a buckle strength of at least about 90 psi and a
column strength of at least about 180 psi.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1 is a diagram of the equiaxed grain structure of
aluminum alloy stock produced according to the present
invention;
[0037] FIG. 2 is a diagram of the striated grain structure of
aluminum alloy stock produced according to a conventional
process;
[0038] FIGS. 3-6 are block diagrams illustrating various
embodiments of processes according to the present invention;
[0039] FIG. 7 is a block diagram illustrating yet another
embodiment of a process according to the present invention;
[0040] FIG. 8 is a block diagram depicting a further embodiment of
a process according to the present invention;
[0041] FIG. 9 is a block diagram depicting a further embodiment of
a process according to the present invention;
[0042] FIG. 10 is a block diagram depicting a further embodiment of
a process according to the present invention; and
[0043] FIGS. 11 and 12 depict test results for various samples.
DETAILED DESCRIPTION
[0044] Introduction
[0045] The various continuous casting processes of the present
invention have a number of novel process steps for producing
aluminum alloy sheet having high strength, low earing, highly
desirable forming properties, and/or an equiaxed/finer grain
structure. As used herein, "continuous casting" refers to a casting
process that produces a continuous strip as opposed to a process
producing a rod or ingot. By way of example, the continuous casting
processes can include heating the cast strip in front of the last
hot mill stand (i.e., between the caster and first hot mill stand
or between hot mill stands). The heater can reduce the load on the
hot mill stands, thereby permitting greater reductions of the cast
strip in the hot mill, provide a hot milled strip having an
equiaxed grain structure, and/or facilitate self-annealing (i.e.,
recrystallization) of the unheated strip when the unheated strip is
cooled, thereby obviating, in many cases, the need for a hot mill
anneal. The increased hot mill reductions can eliminate one or more
cold mill passes. The processes can further include continuous
intermediate annealing of the cold rolled strip in an induction
heater. The continuous anneal can provide more uniform mechanical
properties for the aluminum alloy sheet, a finer grain size,
controllable mechanical properties using a stabilizing anneal, and
significant savings in operating and alloy costs and improvements
in production capacity. It is a surprising and unexpected discovery
that an induction heater in the continuous intermediate anneal can
produce aluminum alloy sheet, that is useful for body stock, having
yield and ultimate tensile strengths and percent elongation at
break that are closely related to the temperature and duration of
the stabilizing anneal. Commonly, the yield and ultimate tensile
strengths of body stock decrease with increasing anneal time and
temperature. These superior properties of the aluminum sheet of the
present invention result from the relatively fine grain size and
alloying of the sheet. The intermediate anneal is particularly
useful for body stock. Finally, the continuous casting processes
can include stabilization or back annealing of the cold rolled
strip in an induction heater. The induction heater can provide
aluminum alloy sheet having highly desirable properties,
particularly useful for the production of body stock used for
containers.
[0046] An important aspect of the present invention is that the
aluminum alloy sheet that is produced in accordance with the
various embodiments of the present invention can maintain
sufficient strength and formability properties while having a
relatively thin gauge. This is especially important when the
aluminum alloy sheet is utilized in tab, end, and body stock for
making drawn and ironed containers. The trend in the can making
industry is to use thinner aluminum alloy sheet for the production
of drawn and ironed containers, thereby producing a container
containing less aluminum and having a reduced cost. However, to use
thinner gauge aluminum sheet, the aluminum alloy sheet must still
have the required physical characteristics. Surprisingly,
continuous casting processes have been discovered which produce an
aluminum alloy sheet that meets the industry's standards for tab,
end, and/or body stock, particularly when utilized with the alloys
of the present invention.
[0047] Heating the Cast Strip Between the Caster and First Hot Mill
or Between Hot Mill Stands
[0048] In the first novel process step discussed above, the cast
and/or partially hot rolled strip (hereinafter collectively
referred to as "unheated strip") is heated to an elevated
temperature to provide an aluminum alloy sheet having a more
equiaxed grain structure relative to other aluminum alloy sheet and
to permit greater thickness reductions in hot milling. While not
wishing to be bound by any theory, it is believed that the heater
causes the strip to self-anneal, or recrystallize, after hot
milling is completed, to form the equiaxed grain structure.
[0049] Referring to FIGS. 1 and 2, the substantial differences in
grain structure between the aluminum alloy sheet of the present
invention and a comparative aluminum alloy sheet are illustrated.
As shown in FIG. 2, the grains 10 of continuously cast comparative
aluminum alloy sheet are shaped as a series of striations (i.e.,
long lenticular grains) oriented longitudinally throughout the
aluminum alloy sheet. As will be appreciated, the striations cause
the aluminum alloy sheet to have a high strength in the direction
"X" parallel to the orientation of the striation and low strength
in the direction "Y" that is normal to the direction of the
striation (i.e., low shear strength). As a result, during
fabrication, the comparative aluminum alloy sheet experiences edge
cracking and excessive fines generation. Referring to FIG. 1, the
aluminum alloy sheet of the present invention has a substantially
equiaxed grain structure providing a relatively high strength
substantially uniformly in all directions. An equiaxed grain
structure provides a high degree of formability of the sheet, with
a low degree of edge cracking, fines generation and earing.
[0050] The heating step is preferably conducted on a continuous as
opposed to a batch basis and can be conducted in any suitable
heating device. Preferred furnaces are solenoidal heaters,
induction heaters, such as transflux induction furnaces, infrared
heaters, and gas-fired heaters with solenoidal heaters being most
preferred. Gas-fired heaters are less preferred for elevating the
temperature of the unheated strip to the desired levels due to the
limited ability of gas-fired heaters to reach the desired annealing
temperatures at a reasonable cost and time allotted.
[0051] Preferably, the unheated strip is heated to a temperature
(i.e., the output temperature of the heated strip as it exits the
heater) that is in excess of the temperature of the unheated strip
(i.e., the input temperature of the unheated strip as it enters the
heater) and the recrystallization temperature of the strip but less
than the melting point of the cast strip. Preferably, the heated
temperature exceeds the heater input temperature of the unheated
strip by at least about 20.degree. F. (i.e., about 6.degree. C.)
and most preferably by at least about 50.degree. F. (i.e., about
10.degree. C.) but by no more than about 125.degree. F. (i.e.,
about 52.degree. C.) and most preferably by no more than about
80.degree. F. (i.e., about 27.degree. C.).
[0052] The temperature in the heating step depends upon whether the
cast strip or partially hot rolled strip is heated. For heating of
the cast strip, the minimum heated temperature preferably is about
820.degree. F. (i.e., about 432.degree. C.) and most preferably
about 850.degree. F. (i.e., about 454.degree. C.) and the maximum
heated temperature is about 1,080.degree. F. (i.e., about
565.degree. C.) and most preferably about 1,000.degree. F. (i.e.,
about 538.degree. C.). For heating of the partially hot rolled
strip, the heated temperature preferably ranges from about
750.degree. F. (i.e., about 399.degree. C.) to about 850.degree. F.
(i.e., about 454.degree. C.). If the heated temperature is too
great, the aluminum alloy sheet produced from the cast strip can
experience edge cracking during hot rolling. The residence time of
any portion of the unheated strip in the continuous heater is
preferably at least about 8 seconds and no more than about 3
minutes, more preferably no more than about 2 minutes and most
preferably no more than about 30 seconds. Other than cooling
experienced in hot rolling, the heated strip is preferably not
subjected to rapid cooling, such as by quenching, before hot
milling.
[0053] It has been discovered that the thickness of the unheated
strip is important to the degree of post hot mill self-annealing
(i.e., recrystallization) realized due to the heating of the strip
before hot milling. If the strip is too thick, portions of the
strip can fail to be completely heated. Preferably, the gauge of
the unheated strip is no more than about 24 mm, more preferably
ranges from about 12 to about 24 mm, and most preferably ranges
from about 16 to about 19 mm.
[0054] Continuous Intermediate Annealing of the Cold Rolled Strip
in an Induction Heater
[0055] In the second novel process step, a partially cold rolled
strip is subjected to a continuous high temperature anneal to yield
an aluminum sheet having a high degree of formability,
substantially uniform physical properties, and strength properties
that are controllable (i.e., the strength properties can increase
with increasing temperature and time of stabilization or back
annealing). The continuous anneal is preferably performed in an
induction heater, such as a transflux induction furnace.
[0056] While not wishing to be bound by any theory, it is believed
that these properties result from the ability of the induction
heater to uniformly heat the partially cold rolled strip throughout
its volume to produce a substantially uniform, fine-grain size
throughout the length and width of the intermediate annealed strip.
This is so because the induction heater magnetically induces
magnetic fluxes substantially uniformly throughout the thickness of
the strip. In contrast, conventional radiant heaters, particularly
batch heaters, non-uniformly heat the partially cold rolled strip,
whether in coiled or uncoiled form, throughout its volume. In such
heaters, heat is conducted from the outer surfaces of the
strip/coil towards the middle of the strip/coil with the outer
surfaces experiencing greater exposure to thermal energy than the
middle of the strip/coil. The nonuniform exposure to heat can cause
a variation in grain size, especially in annealed coils, along the
length of the strip. The middle of the strip/coil commonly has a
smaller grain size and the exterior of the strip/coil a larger
grain size.
[0057] The minimum annealing temperature is preferably about
700.degree. F. (i.e., about 371.degree. C.), more preferably about
800.degree. F. (i.e., about 426.degree. C.), and most preferably
about 850.degree. F. (i.e., about 454.degree. C.), and the maximum
annealing temperature is preferably about 1050.degree. F. (i.e.,
about 565.degree. C.), more preferably about 1025.degree. F. (i.e.,
about 547.degree. C.), and most preferably about 1000.degree. F.
(i.e., about 537.degree. C.). The minimum residence time of any
portion of the annealed strip in the heater preferably is about 2
seconds, and the maximum residence time is preferably about 2.5
minutes, more preferably about 30 seconds, and most preferably
about 20 seconds, depending on the line speed of the strip through
the heater.
[0058] Stabilization or Back Annealing of the Cold Rolled Strip in
an Induction Heater
[0059] In yet another novel process step, a cold rolled strip is
subjected to a stabilization or back anneal (hereinafter
collectively referred to as "stabilizing anneal") in a continuous
heater to form aluminum alloy sheet having highly desirable
properties. As in the continuous intermediate anneal above, the
stabilization or back anneal can produce aluminum sheet having
predetermined physical properties and provide increased capacity.
The physical properties are highly controllable by varying the
temperature and duration of the anneal (i.e., the line speed of the
strip through the heater).
[0060] The continuous heater is preferably an induction heater,
with a transflux induction furnace being most preferred.
[0061] The annealing temperature preferably ranges from about 300
to about 550.degree. F. (i.e., about 148 to about 287.degree. C.).
The minimum residence time of any portion of the cold rolled strip
in the induction heater is preferably about 2 seconds and the
maximum residence time of any portion of the cold rolled strip is
preferably about 2.5 minutes, more preferably about 30 seconds, and
most preferably about 20 seconds, depending upon the line speed of
the strip through the heater.
[0062] Processes Incorporating the Novel Process Steps
[0063] A first embodiment of a continuous casting process
incorporating the step of heating the unheated strip is depicted in
FIG. 3. This process is particularly useful for forming tab, body,
and end stock for container manufacture.
[0064] Referring to FIG. 3, a melt of the aluminum alloy
composition is formed and continuously cast 20 to form a cast strip
24. The continuous casting process can employ a variety of
continuous casters, such as a belt caster or a roll caster.
Preferably, the continuous casting process includes the use of a
block caster for casting the aluminum alloy melt into a sheet. The
block caster is preferably of the type disclosed in U.S. Pat. Nos.
3,709,281; 3,744,545; 3,747,666; 3,759,313 and 3,774,670, all of
which are incorporated herein by reference in their entireties.
Continuous casting is generally described in copending U.S. patent
application Ser. Nos. 08/713,080 and 08/401,418, which are also
incorporated herein by reference in their entireties.
[0065] The alloy composition according to the present invention can
be formed in part from scrap metal material, such as plant scrap,
container scrap and consumer scrap. Preferably, the alloy
composition is formed with at least about 75% and more preferably
at least about 95% total scrap for body stock and from about 5 to
about 50% total scrap for tab and end stock.
[0066] To form the melt, the metal is charged into a furnace and
heated to a temperature of about 1385.degree. F. (i.e., 752.degree.
C.) (i.e., above the melting point of the feed material) until the
metal is thoroughly melted. The alloy is treated to remove
materials such as dissolved hydrogen and non-metallic inclusions
which would impair casting of the alloy and the quality of the
finished sheet. The alloy can also be filtered to further remove
non-metallic inclusions from the melt. The melt is then cast
through a nozzle and discharged into the casting cavity. The nozzle
can include a long, narrow tip to constrain the molten metal as it
exits the nozzle. The nozzle tip has a preferred thickness ranging
from about 10 to about 25 millimeters, more preferably from about
14 to about 24 millimeters, and most preferably from about 14 to
about 19 millimeters and a width ranging from about 254 millimeters
to about 2160 millimeters.
[0067] The melt exits the tip and is received in the casting cavity
which is formed by opposing pairs of rotating chill blocks. The
metal cools and solidifies as it travels through the casting cavity
due to heat transfer to the chill blocks. At the end of the casting
cavity, the chill blocks, which are on a continuous web, separate
from the cast strip 24. The blocks travel to a cooler where the
treated chill blocks are cooled before being reused.
[0068] The cast temperature of the cast strip 24 exiting the block
caster preferably exceeds the recrystallization temperature of the
cast strip. The cast output temperature (i.e., the output
temperature as the cast strip exits the caster) preferably ranges
from about 800 to about 1050.degree. F. (i.e., about 426 to about
565.degree. C.) and more preferably from about 900 to about
1050.degree. F. (i.e., about 482 to about 565.degree. C.).
[0069] Upon exiting the caster, the cast strip is subjected to a
heating (or annealing) step 28 as noted above to form a heated
strip 32 having an equiaxed grain structure.
[0070] Upon exiting the heating step 28, the heated strip 32 is
then subjected to hot rolling 36 in a hot mill to form a hot rolled
strip 40. A hot mill includes one or more pairs of oppositely
rotating rollers (i.e., one or more hot mill stands) having a gap
separating the rollers that reduces the thickness of the strip as
it passes through the gap between the rollers. The heated strip 32
preferably enters the hot mill with a minimum input temperature of
about 800.degree. F. (i.e., about 426.degree. C.) and more
preferably about 900.degree. F. (i.e., about 482.degree. C.) and a
maximum input temperature of about 1000.degree. F. (i.e., about
538.degree. C.) and more preferably about 1000.degree. F. (i.e.,
about 538.degree. C.). The hot mill preferably reduces the
thickness of the strip by at least about 80%, more preferably by at
least about 84%, and most preferably by at least about 88% but by
no more than about 94%. The gauge of the hot mill strip preferably
ranges from about 0.065 to about 0.105 inches. The hot rolled strip
preferably exits the hot mill with a minimum output temperature of
about 550.degree. F. (i.e., about 260.degree. C.) and more
preferably about 600.degree. F. (i.e., about 315.degree. C.) and a
maximum output temperature of about 800.degree. F. (i.e., about
426.degree. C.) and more preferably about 800.degree. F. (i.e.,
about 426.degree. C). In accordance with the present invention, it
has been found that a relatively high reduction in gauge can take
place with each pass of the hot rollers which can later eliminate
one or more cold rolling passes.
[0071] For some alloys, the hot rolled strip 40 is commonly not
annealed or solution heat treated directly after exiting the hot
mill. The elimination of the additional annealing step and/or
solution heat treating step (i.e., self-annealing) can lead to
significant increases in capacity relative to processes using a
batch anneal hot milling.
[0072] The hot rolled strip 40 is allowed to cool in a convenient
manner to a temperature ranging from ambient temperature to about
120.degree. F. (i.e., about 49.degree. C.). Typically, the cooling
time ranges from about 48 to about 72 hours. Depending upon the
alloy, the strip 40 can be subjected to rapid cooling, such as by
quenching, to cool the strip 40 for cold milling.
[0073] After the hot rolled sheet has cooled, it is subjected to
further treating steps 44 to form the aluminum alloy sheet 48. The
further treating steps 44 depend, of course, upon the alloy and
intended use for the aluminum sheet 48.
[0074] In one embodiment, FIG. 4 depicts the further treating steps
44 for tab stock useful in container fabrication. Referring to FIG.
4, the cooled hot rolled strip 40 is subjected to cold rolling 52
to form a cold rolled strip 68 having the final gauge. The cold
rolling can be performed in a number of cold mill passes through
one or more pairs of rotating cold rollers. During cold rolling 52,
the thickness of the strip is preferably reduced by at least about
35%/stand and more preferably from about 35 to about 60%/stand and,
more preferably, by from about 45 to about 55%/stand for a total
reduction in the cold rolling step 52 preferably of at least about
70% and more preferably ranging from about 85 to about 95%.
Preferably, the reduction to final gauge is performed in 2 to 3
passes through rotating cold rollers.
[0075] The final gauge is selected based on the final desired
properties of the aluminum alloy sheet 48. Preferably, the minimum
final gauge of the aluminum alloy sheet is about 0.20 mm, more
preferably about 0.22 mm, and most preferably, about 0.24 mm while
the maximum final gauge is about 0.61 mm, more preferably about
0.56 mm, and most preferably about 0.46 mm.
[0076] The cold rolled strip 68 is subjected to a stabilizing
anneal 72 to form the aluminum alloy sheet 48. Although any heater
can be employed in the stabilizing anneal, it is most preferred
that a continuous heater, such as an induction heater, be used. The
temperature and duration of a stabilizing anneal 72 utilizing an
induction heater are discussed above. The temperature of a batch
stabilizing 72 anneal preferably ranges from about 300 to about
500.degree. F. (i.e., about 149 to about 260.degree. C.). The
duration of a batch stabilizing anneal 72 preferably ranges from
about 10 to about 20 hours.
[0077] In one process configuration, the stabilizing anneal can be
located in the tab cleaning line. As will be appreciated, the tab
cleaning line includes the steps of (i) contacting the aluminum
alloy sheet with a caustic cleaning solution, such as a caustic
cleaning solution, to remove oil and other residue from the sheet;
(ii) contacting the sheet with a rinsing solution, such as water,
to remove the caustic cleaner from the sheet; and (iii) applying a
lubricant, such as oil, to the rinsed sheet. The lubed sheet is
later passed through a leveler and splitter to form tab stock. The
stabilizing anneal 72 can be located directly before step (i)
provided that the caustic cleaning solution has a lower
concentration of caustic cleaner than conventional processes to
avoid overetching of the sheet. Overetching can result from the
increased temperature of the sheet due to the stabilizing anneal.
Alternatively, the stabilizing anneal 72 can be located after step
(i), such as between steps (i) and (ii) or steps (ii) and (iii), or
after step (iii). This process configuration is highly beneficial
because the ability to use more dilute caustic cleaning solutions
due to more efficient cleaning caused by the higher sheet
temperature from the stabilization annealing can result in
significant cost savings.
[0078] Aluminum alloy sheet produced by this process is
particularly useful as tab stock. An aluminum alloy composition
that is particularly useful for tab stock includes:
[0079] (i) Manganese, preferably in an amount of at least about
0.05 wt % and more preferably at least about 0.10 0.20 wt % and no
more than about 0.5 wt % and more preferably no more than about
0.20 wt %.
[0080] (ii) Magnesium, preferably in an amount ranging from about
3.5 to about 4.9 wt %.
[0081] (iii) Copper, preferably in an amount of at least about 0.05
wt % and no more than about 0.15 wt % and most preferably no more
than about 0.10 wt %.
[0082] (iv) Iron, preferably in an amount of at least about 0.05 wt
% and more preferably at least about 0.10 wt % and no more than
about 0.35 wt % and more preferably no more than about 0.20 wt
%.
[0083] (v) Silicon, preferably in an amount of at least about 0.05
wt % and no more than about 0.20 wt % and more preferably no more
than about 0.10 wt %.
[0084] The aluminum alloy sheet 48 has properties that are
particularly useful for tab stock. Preferably, the as-rolled yield
strength is at least about 41 ksi and more preferably at least
about 46 ksi and no more than about 49 ksi and more preferably no
more than about 51 ksi. Preferably, the aluminum alloy sheet 48 has
an elongation of at least about 3% and more preferably at least
about 6% and no more than about 8%. The as-rolled tensile strength
of the aluminum alloy sheet 48 preferably is at least about 49 ksi,
more preferably at least about 55 ksi and most preferably at least
about 57 ksi and no more than about 61 ksi, and most preferably no
more than about 59 ksi. The sheet 48 preferably has a tab strength
of at least about 2 kg, more preferably at least about 5 pounds,
(i.e., about 2.3 kg), and most preferably at least about 6 pounds
(i.e., about 2.7 kg), and preferably no more than about 3.6 kg and
most preferably no more than about 8 pounds (i.e., about 3.6
kg).
[0085] In another embodiment shown in FIG. 5, a stabilizing anneal
to produce end stock and/or tab stock (that is later coated) is
optional. As will be appreciated, heating of the end or tab stock
in the coating line can perform.s the same function as the
stabilizing or back anneal.
[0086] Referring to FIG. 5, the cooled hot rolled strip 40 is
subjected to cold rolling 80 to yield aluminum alloy sheet 84.
During cold rolling 80, the thickness of the strip is preferably
reduced by at least about 70% and more preferably by from about 80
to about 95%. The minimum final gauge of the aluminum alloy sheet
84 is preferably about 0.007 inches, more preferably about 0.095
inches, and most preferably about 0.085 inches, and the maximum
final gauge is preferably about 0.012 inches, more preferably about
0.0115 inches, and most preferably about 0.0110 inches.
[0087] If a stabilizing anneal is used, the anneal can be performed
in a batch or continuous heater (with an induction heater being
more preferred) at a temperature preferably ranging from about 250
to about 400 F (i.e., from about 120 to about 205 C) and more
preferably from about 300 to about 375 F (i.e., from about 145 to
about 190 C) (for a batch heater) and from about 300 to about 500 F
(i.e., from about 145 to about 260 C) and more preferably from
about 400 to about 450 F (i.e., from about 200 to about 235 C) (for
an induction heater).
[0088] An aluminum alloy composition that is particularly useful in
this process for tab stock includes:
[0089] (i) Manganese, preferably in an amount of at least about
0.05 wt % and no more than about 0.23 wt % and more preferably no
more than about 0.15 wt %.
[0090] (ii) Magnesium, preferably in an amount of at least about
3.8 wt % and no more than about 4.9 wt %, and most preferably no
more than about 4.7 wt %.
[0091] (iii) Copper, preferably in amount of at least about 0.05 wt
% and no more than about 0.15 wt % and more preferably no more than
about 0.10 wt %.
[0092] (iv) Iron, preferably in an amount of at least about 0.20 wt
% and no more than about 0.35 wt % and more preferably no more than
about 0.30 wt %.
[0093] (v) Silicon, preferably in an amount of at least about 0.05
wt % and no more than about 0.20 wt % and more preferably no more
than about 0.10 wt %.
[0094] A most preferred aluminum alloy composition for tab stock
includes the following constituents:
[0095] (i) Manganese in an amount of at least about 0.05 wt % and
no more than about 0.15 wt %.
[0096] (ii) Magnesium in an amount of at least about 4.0 wt % and
no more than about 4.7 wt %.
[0097] (iii) Copper in an amount of at least about 0.05 wt % and no
more than about 0.10 wt %.
[0098] (iv) Iron in an amount of at least about 0.20 wt % and no
more than about 0.30 wt %.
[0099] (v) Silicon in an amount of at least about 0.05 wt % and no
more than about 0.10 wt %.
[0100] An aluminum alloy composition that is particularly useful in
this process for the production of end stock includes:
[0101] (i) Manganese, preferably in an amount of at least about
0.05 wt % and no more than about 0.20 wt % and more preferably no
more than about 0.15 wt %.
[0102] (ii) Magnesium, preferably in an amount of at least about
3.8 wt % and more preferably at least about 4.0 wt %, and no more
than about 5.2 wt %, and more preferably no more than about 4.7 wt
%.
[0103] (iii) Copper, preferably in amount of at least about 0.05 wt
% and no more than about 0.15 wt % and more preferably no more than
about 0.10 wt %.
[0104] (iv) Iron, preferably in an amount of at least about 0.20 wt
% and no more than about 0.35 wt % and more preferably no more than
about 0.30 wt %.
[0105] (v) Silicon, preferably in an amount of at least about 0.05
wt % and no more than about 0.20 wt % and more preferably no more
than about 0.15 wt %.
[0106] A most preferred aluminum alloy composition for end stock
includes the following constituents:
[0107] (i) Manganese in an amount of at least about 0.05 wt % and
no more than about 0.15 wt %.
[0108] (ii) Magnesium in an amount of at least 3.8 wt % and no more
than about 5.0 wt %.
[0109] (iii) Copper in an amount of at least about 0.05 wt % and no
more than about 0.10 wt %.
[0110] (iv) Iron in an amount of at least about 0.20 wt % and no
more than about 0.30 wt %.
[0111] (v) Silicon in an amount of at least about 0.05 wt % and no
more than about 0.15 wt %.
[0112] The aluminum alloy sheet 84 has properties that are
particularly useful for end stock. The aluminum alloy sheet 84
preferably has an after-coated yield strength of at least about 41
ksi, more preferably at least about 47 ksi, and most preferably at
least about 47.5 ksi. The aluminum alloy sheet 84 preferably has an
after-coated ultimate tensile strength of at least about 49 ksi and
more preferably at least about 51 ksi and most preferably at least
about 53 ksi and of no more than about 55 ksi and most preferably
no more than about 60 ksi. The aluminum alloy sheet 84 preferably
has an elongation of at least about 3% and most preferably at least
about 6% and of no more than about 8%.
[0113] In yet another embodiment shown in FIG. 6, the further
treating steps 44 include both an intermediate anneal 100 and a
stabilizing anneal 104 to produce body stock. The time and
temperature of the stabilizing or back anneal determine the
properties of the body stock.
[0114] Referring again to FIG. 6, the cooled hot rolled strip 40 is
subjected to cold rolling 108 to form a partially cold rolled strip
112. During cold rolling 108, the thickness of the strip is
preferably reduced by at least about 40% and more preferably by at
least about 45% and most preferably by at least about 50% and no
more than about 70% and most preferably no more than about 65%. The
minimum gauge of the partially cold rolled strip 112 is preferably
at least about 0.012 inches and more preferably at least about
0.015 inches, and the maximum gauge is preferably no more than
about 0.035 and more preferably no more than about 0.030 inches.
The reductions are performed in 1 pass through rotating cold
rollers.
[0115] The partially cold rolled strip 112 is subjected to an
intermediate annealing step 100 to form an intermediate annealed
strip 116 having reduced residual cold work and less earing. In the
intermediate annealing step 100, a continuous or batch heater can
be employed, with a continuous heater such as an induction heater
being most preferred.
[0116] The temperature of the intermediate anneal depends upon the
type of furnace employed. The temperature and duration of the
anneal using a continuous heater are discussed above. For a batch
heater, the strip 112 is preferably intermediate annealed at a
minimum temperature of at least about 650.degree. F. (i.e., about
343.degree. C.), and preferably at a maximum temperature of no more
than about 900.degree. F. (i.e., about 482.degree. C.) for a soak
time ranging from about 2 to about 3 hrs.
[0117] The intermediate annealed strip 116 is subjected to further
cold rolling 120 to form the cold rolled strip 124. The amount of
reduction in the cold rolling step 120 depends on the final gauge
of the cold rolled strip 124 and the gauge of the partially cold
rolled strip 112. Preferably, the final gauge of the aluminum alloy
sheet 128 is at least about 0.009 inches, more preferably at least
about 0.010 inches and no more than about 0.013 inches and more
preferably no more than about 0.125 inches. In a preferred
embodiment, the cold mill reduction in the cold rolling step 120 is
from about 40 to about 65%. The cold rolling step is preferably
performed in 1 pass.
[0118] The cold rolled strip 124 is subjected to a stabilizing
anneal 104 to form the aluminum alloy sheet 128. Although any
heater can be employed in the stabilizing anneal, it is most
preferred that a continuous (e.g., induction) heater be used if a
continuous (e.g., induction) heater were employed in the
intermediate annealing step 100. The temperature and duration of a
stabilizing anneal 104 utilizing an induction heater is discussed
in detail above. For a batch heater, the annealing temperature
ranges from about 300 to about 450.degree. F. for a soak time
ranging from about 2 to about 3 hrs.
[0119] Aluminum alloy sheet 128 is particularly useful as body
stock. An aluminum alloy composition that is particularly useful in
this process for body stock includes:
[0120] (i) Manganese, preferably in an amount of at least about
0.85 wt % and more preferably at least about 0.9 wt % and of no
more than about 1.2 wt % and more preferably no more than about 1.1
wt %.
[0121] (ii) Magnesium, preferably in an amount of at least about
0.9 wt % and more preferably at least about 1.0 wt % and of no more
than about 1.5 wt %.
[0122] (iii) Copper, preferably in amount of at least about 0.05 wt
% and more preferably at least about 0.20 wt % and no more than
about 0.50 wt %.
[0123] (iv) Iron, preferably in an amount of at least about 0.05 wt
% and more preferably of at least about 0.35 wt % and of no more
than about 0.60 wt %.
[0124] (v) Silicon, preferably in an amount of at least about 0.05
wt % and more preferably of at least about 0.3 wt % and of no more
than about 0.5 wt % and more preferably no more than about 0.4 wt
%.
[0125] A most preferred aluminum alloy composition for body stock
includes the following constituents:
[0126] (i) Manganese in an amount of at least about 0.85 wt % and
no more than about 1.1 wt %.
[0127] (ii) Magnesium in an amount of at least about 0.10 wt % and
no more than about 1.5 wt %.
[0128] (iii) Copper in an amount of at least about 0.35 wt % and no
more than about 0.50 wt %.
[0129] (iv) Iron in an amount of at least about 0.35 wt % and no
more than about 0.60 wt %.
[0130] (v) Silicon in an amount of at least about 0.2 wt % and no
more than about 0.4 wt %.
[0131] The various alloying elements are believed to account partly
for the superior properties of the aluminum alloy sheet of the
present invention. Without wishing to be bound by any theory,
magnesium and manganese are believed to increase the ultimate and
yield tensile strengths; copper is believed to retard after-bake
drops in mechanical properties for body stock; iron is believed not
only to provide increased ultimate and yield tensile strengths but
also to provide a smaller grain size; and silicon is believed to
provide a larger alpha phase transformation particle size which
helps inhibit galling/scoring in the body maker operation.
[0132] The aluminum alloy sheet has properties that are
particularly useful for body stock. When the aluminum alloy sheet
is to be used as body stock, the alloy sheet preferably has an as
rolled tensile strength of at least about 40 ksi, more preferably
at least about 42 ksi, and most preferably at least about 42.5 ksi
and of no more than about 47 ksi, more preferably no more than
about 46 ksi, and most preferably no more than about 45 ksi. The
as-rolled yield strength preferably is at least about 37 ksi, more
preferably at least about 38 ksi, and most preferably at least
about 39 ksi and no more than about 43 ksi, more preferably no more
than about 42 ksi, and most preferably no more than about 41 ksi.
The aluminum alloy sheet 128 preferably has an elongation of at
least about 3% and most preferably at least about 4% and of no more
than about 10% and most preferably no more than about 8%.
[0133] To produce acceptable drawn and ironed container bodies,
aluminum alloy sheet 128 used as body stock should have a low
earing percentage. The earing should be such that the bodies can be
conveyed on the conveying equipment and the earing should not be so
great as to prevent acceptable handling and trimming of the
container bodies. Preferably, the aluminum alloy sheet 128,
according to the present invention, has a tested earing of no more
than about 2.0% and more preferably no more than about 1.9% and
most preferably no more than about 1.8%.
[0134] Container bodies fabricated from the aluminum alloy sheet
128 of the embodiment of the present invention have relatively high
strengths. The container bodies have a minimum dome reversal
strength (or minimum buckle strength) of about 90 psi and more
preferably at least about 93 psi and a maximum dome reversal
strength (or maximum buckle strength) of no more than about 98 psi
at current commercial thicknesses. The column strength of the
container bodies is preferably at least about 180 psi and most
preferably at least about 210 psi and no more than about 280 psi
and most preferably no more than about 260 psi.
[0135] The relatively low earing and high strength properties are
readily realized due to the ability of the properties of the cold
rolled strip to be varied with anneal time and temperature. The
direct relationship between the strip's strength properties on the
one hand and the time and temperature of the stabilize anneal on
the other permits the physical properties of the aluminum alloy
sheet to be selectively controlled. Because earing is directly
related to the amount of cold rolling reduction performed, the cold
rolling step 120 can use a relatively low amount of cold rolling
reduction to realize an acceptable earing. Preferably, at least
about 30% of the total gauge reduction attributable to cold rolling
is performed in the cold rolling step 108. Because the reduced
amount of cold rolling means less work hardening and therefore
lower strength properties, the stabilization anneal is used to
improve the strength properties to the desired levels.
[0136] FIG. 7 depicts an alternative configuration for body stock
to that shown in FIGS. 3 and 6. As shown in FIG. 7, the heating
step 132 is performed during (but not after) hot rolling. As will
be appreciated, this configuration can be combined with any of the
embodiments for the further treating steps 44 shown in FIGS.
4-6.
[0137] Referring to FIG. 7, the heating step 132 is performed
between one or more pairs of hot rolling stands. This will
typically be between the first and second hot rolling stands to
elevate the temperature of the strip, during hot milling, to a
level above the heater input temperature of the strip. Thus, the
cast strip 24 is hot rolled 36a to form a partially hot rolled
strip 136, heated 132 to form a heated strip 140, and hot rolled
36b to form a hot rolled strip 144. The preferred temperature in
the heating step ranges from about 750 to about 850.degree. F.
(i.e., about 399 to about 454.degree. C.). In this configuration,
the cast strip 24 is preferably not annealed or otherwise heated
prior to the first hot rolling stand.
[0138] The above-noted processes employed for end and body stock
can be employed with some modification to produce sheet for other
applications. By way of example, the sheet can be used to fabricate
foil products such as cooler fins. The preferred alloy composition.
for such sheet is as follows:
[0139] (i) Manganese in an amount of no more than about 0.05 wt
%.
[0140] (ii) Magnesium in an amount ranging from about 0.05 to about
0.10 wt %.
[0141] (iii) Copper in an amount ranging from about 0.05 to about
0.10 wt %.
[0142] (iv) Iron in an amount ranging from about 0.4 to about 1.0
wt %.
[0143] (v) Silicon in an amount ranging from about 0.3 to about 1.1
wt %.
[0144] FIG. 8 depicts yet another embodiment of a process according
to the subject invention. In this embodiment, the process includes
an optional heating step 28 before or during hot rolling, an
optional hot mill annealing step 148, and an intermediate annealing
step 152. Best results are realized for a batch intermediate anneal
if both a batch hot mill anneal and continuous heating, before the
last hot rolling stand, are employed, and for an intermediate
anneal using an induction heater if no hot mill anneal and only
continuous heating before the last hot rolling stand is employed.
This process produces aluminum sheet 156 having superior physical
properties that is particularly useful for body stock.
[0145] Referring to FIG. 8, a melt of the aluminum alloy
composition is formed and continuously cast 20 to provide a cast
strip 24. The nozzle tip size preferably ranges from about 10 to
about 25 mm and more preferably from about 10 to about 18.0 mm,
with a maximum tip size of 17.5 mm being most preferred, and the
cast strip 24 is hot rolled 160 to form a hot rolled strip 164. The
cast strip 24 can optionally be subjected to a heating step 28 as
noted above to provide a more equiaxed grain structure in the
strip. In the hot rolling step 160, the cast strip 24 is preferably
reduced in thickness by an amount of at least about 80%, more
preferably at least about 84%, and most preferably at least about
88% but no more than about 94%, more preferably no more than about
94%, and most preferably no more than about 94% to a gauge
preferably ranging from about 0.065 to about 0.105 inches.
[0146] The hot rolled strip 164 is hot mill annealed 148 in a batch
or continuous heater. The continuous heater can be a gas-fired,
infrared, or an induction heater.
[0147] The temperature and duration of the anneal depend upon the
type of furnace employed. The strip is preferably intermediate
annealed at a minimum temperature of at least about 650.degree. F.
(i.e., about 343.degree. C.), and preferably at a maximum
temperature of no more than about 900.degree. F. (i.e., about
482.degree. C.). For continuous heaters, the annealing time for any
portion of the strip is preferably a maximum of about 2.5 minutes,
more preferably about 30 seconds, and most preferably about 20
seconds and a minimum of about 2 seconds. For batch heaters, the
annealing time is preferably a minimum of about 2 hours and is
preferably a maximum of about 3 hours.
[0148] Referring again to FIG. 8, the hot mill anneal strip 170 is
allowed to cool and then subjected to cold rolling 174 to form a
partially cold rolled strip 178. During cold rolling 174, the
thickness of the strip 170 is reduced by at least about 40% and
more preferably at least about 50% but no more than about 70% and
more preferably no more than about 65%. Preferably, the reduction
to intermediate gauge is performed in 1 to 2 passes. The minimum
gauge of the partially cold rolled strip 178 is preferably about
0.012 inches and more preferably about 0.0115 inches, and the
maximum gauge is preferably about 0.035 inches and more preferably
about 0.030 inches.
[0149] The partially cold rolled strip 178 is intermediate annealed
152 to form an annealed strip 182. The intermediate annealing step
152 can be performed in a continuous or batch heater. The preferred
continuous heater is an induction heater, with a transflux
induction heater being most preferred. The duration and temperature
of the anneal 152 using an induction heater preferably are set
forth above. For a batch heater, the strip 178 is preferably
intermediate annealed 152 at a minimum temperature of at least
about 650.degree. F. (i.e., about 343.degree. C.), and preferably
at a maximum temperature of no more than about 900.degree. F.
(i.e., about 482.degree. C.). The annealing time for a batch heater
preferably ranges from about 2 to about 3 hours.
[0150] The annealed strip 182 is preferably not rapidly cooled,
such as by quenching, after the annealing step or solution heat
treated.
[0151] The annealed strip 182 is allowed to cool and subjected to
cold rolling 186 to form aluminum alloy sheet 156. Preferably, the
partially cold rolled strip 178 is reduced in thickness by an
amount of at least about 40% and more preferably at least about 50%
but no more than about 70% and more preferably no more than about
65% to a gauge ranging from about 0.009 to about 0.013 inches in
one pass.
[0152] An aluminum alloy composition that is particularly useful
for body stock in this embodiment includes:
[0153] (i) Manganese, preferably in an amount of at least about
0.85 wt % and more preferably at least about 0.9 wt % but no more
than about 1.2 wt % and more preferably no more than about 1.1 wt
%.
[0154] (ii) Magnesium, preferably in an amount of at least about
0.9 wt % and more preferably at least about 1.0 wt % but no more
than about 1.5 wt %.
[0155] (iii) Copper, preferably in amount of at least about 0.20 wt
% but no more than about 0.50 wt %.
[0156] (iv) Iron, preferably in an amount of at least about 0.35 wt
% but no more than about 0.50 wt % and more preferably no more than
about 0.60 wt %.
[0157] (v) Silicon, preferably in an amount of at least about 0.3
wt % but no more than about 0.5 wt % and more preferably no more
than about 0.4 wt %.
[0158] A particularly useful aluminum alloy composition for body
stock using this process includes the following constituents:
[0159] (i) Manganese in an amount of at least about 0.85 but no
more than about 1.1 wt %.
[0160] (ii) Magnesium in an amount of at least about 0.10 but no
more than about 1.5 wt %.
[0161] (iii) Copper in an amount of at least about 0.35 but no more
than about 0.50 wt %.
[0162] (iv) Iron in an amount of at least about 0.35 but no more
than about 0.60 wt %.
[0163] (v) Silicon in an amount of at least about 0.2 but no more
than about 0.4 wt %.
[0164] The aluminum alloy sheet has properties that are
particularly useful for body stock. When the aluminum alloy sheet
is to be used as body stock, the alloy sheet preferably has an
as-rolled yield strength of at least about 37 ksi and more
preferably at least about 38 ksi, and most preferably at least
about 39 ksi but no more than about 43 ksi and more preferably no
more than about 42 ksi, and most preferably no more than about 41
ksi. The as-rolled tensile strength preferably is at least about 40
ksi, more preferably at least about 42 ksi, and most preferably at
least about 42.5 ksi but no more than about 47 ksi, more preferably
no more than about 46 ksi, and most preferably no more than about
45 ksi. The aluminum alloy sheet 128 should have an elongation of
at least about 3% and more preferably at least about 4%.
[0165] To produce acceptable drawn and ironed container bodies,
aluminum alloy sheet 128 used as body stock should have a low
earing percentage. Preferably, the aluminum alloy sheet 128,
according to the present invention, has a tested earing of no more
than about 2.0% and more preferably no more than about 1.9% and
most preferably no more than about 1.8%.
[0166] Container bodies fabricated from the aluminum alloy sheet
128 of the embodiment of the present invention have relatively high
strengths. The container bodies have a minimum dome reversal
strength of at least about 90 psi and more preferably at least
about 93 psi at current commercial thicknesses. The column strength
of the container bodies preferably is at least about 200 psi and
more preferably at least about 230 psi.
[0167] FIG. 9 depicts yet another embodiment of a process that is
particularly useful for producing body stock. In this embodiment,
the process includes no heating step before or during hot rolling,
a hot mill annealing step 300, an intermediate annealing step 304,
and a stabilize annealing step 308. This process produces aluminum
sheet 312 having superior physical properties that is particularly
useful for body stock. It has been discovered that this process can
produce aluminum alloy sheet 312 having a relatively low earing;
can avoid work hardening during fabrication of the sheet (by a
bodymaker) into container bodies and thereby inhibit split flanges
and incomplete trim off bodymakers and increase physical properties
(i.e., the as-rolled yield and tensile strengths) by varying the
soak time and temperature of the stabilize anneal 308.
[0168] The relationship between stabilize anneal soak time and
temperature and the physical properties of the sheet 312 is
believed to be the result of the chemistry and the relatively fine
grain size of the sheet 312. The grain size is particularly fine
for an induction heater in the intermediate annealing step. The
relationship is surprising and unexpected for a sheet having the
above-described chemistry. The process permits sheet to be produced
according to a variety of differing specifications simply by
altering the soak time and/or temperature of the stabilize
anneal.
[0169] Referring to FIG. 9, a melt of the aluminum alloy
composition is formed and continuously cast 20 to provide a cast
strip 24. The nozzle tip size preferably ranges from about 10 to
about 25 mm and more preferably from about 10 to about 20 mm, with
a maximum tip size of 17.5 mm being most preferred. The reduction
in tip size to 17.5 mm or less can provide an reduction in the
tested earing for the sheet 312 of 0.2% or more and obtain an
increase of 1 Ksi in tensile and yield strength relative to
aluminum alloy sheet produced by other processes.
[0170] The cast strip 24 is hot rolled 160 to form a hot rolled
strip 164. In the hot rolling step 160, the cast strip 24 is
preferably reduced in thickness by an amount of at least about 50%,
more preferably at least about 55%, and most preferably at least
about 68% but no more than about 45%, more preferably no more than
about 90%, and most preferably no more than about 95% to a gauge
preferably ranging from about 0.065 to about 0.120 inches and more
preferably from about 0.085 to about 0.110 inches. The lowering of
the gauge of the hot rolled strip from 0.105 inches to the range of
about 0.065 to about 0.090 can provide further reductions in the
tested earing of the sheet 312, improved surface grain size, and
increased strength properties.
[0171] The hot rolled strip 164 is hot mill annealed 300 in a batch
or continuous heater to form a hot mill annealed strip 316. The
continuous heater can be a gas-fired, infrared, or an induction
heater.
[0172] The temperature and duration of the anneal depend upon the
type of furnace employed. The strip is preferably intermediate
annealed at a minimum temperature of about 650.degree. F. (i.e.,
about 343.degree. C.) and more preferably about 700.degree. F.
(i.e., about 371.degree. C.), and preferably at a maximum
temperature of about 900.degree. F. (i.e., about 482.degree. C.)
and more preferably of no more than about 850.degree. F. (i.e.,
about 454.degree. C.). For an induction heater, the minimum
temperature is preferably about 900.degree. F., and the maximum
temperature is preferably about 1,000.degree. F. For continuous
heaters, the annealing time for any portion of the strip is
preferably a maximum of about 1 minute, more preferably about 30
seconds, and most preferably about 20 seconds and a minimum of
about 2 seconds. For batch heaters, the annealing time is
preferably a minimum of about 2 hours and is preferably a maximum
of about 3 hours.
[0173] Referring again to FIG. 9, the hot mill annealed strip 316
is allowed to cool and then subjected to cold rolling 320 to form a
partially cold rolled strip 324. In the cold rolling step 320, the
thickness of the strip 316 is preferably reduced by at least about
50% and more preferably at least about 60% but no more than about
70% and more preferably no more than about 65%. Preferably, the
reduction to intermediate gauge is performed in 1 to 2 passes. The
minimum gauge of the partially cold rolled strip 324 is preferably
about 0.013 inches, and the maximum gauge is preferably about 0.030
inches.
[0174] The partially cold rolled strip 324 is intermediate annealed
304 to form an intermediate annealed strip 328. The intermediate
annealing step 304 can be performed in a continuous or batch
heater. The preferred continuous heater is an induction heater,
with a transflux induction heater being most preferred. The minimum
temperature of the anneal 304 using an induction heater preferably
is about 750.degree. F., more preferably about 800.degree. F., and
most preferably about 950.degree. F. The maximum temperature of the
anneal 304 is preferably about 1,050.degree. F., more preferably
about 1,000.degree. F., and most preferably about 1,020.degree. F.
The duration of the anneal is as set forth above. For a batch
heater, the strip 324 is preferably intermediate annealed 304 at a
minimum temperature of at least about 650.degree. F. (i.e., about
343.degree. C.) and more preferably at least about 825.degree. F.
(i.e., about 440.degree. C.), and preferably at a maximum
temperature of no more than about 900.degree. F. (i.e., about
482.degree. C.) and more preferably of no more than about
1,000.degree. F. (i.e., about 537.degree. C.). The soak time at the
annealing temperature for a batch heater preferably ranges from
about 2 to about 3 hours and for a continuous heater, particularly
an induction heater, from about 2 to about 30 seconds.
[0175] The annealed strip 328 can be cooled, such as by quenching,
and/or a nitrogen purge, after annealing.
[0176] After cooling, the annealed strip 328 is subjected to cold
rolling 332 to form cold rolled strip 336. The amount of reduction
in cold rolling depends upon the type of heater used in the
intermediate anneal 304. For a continuous heater, particularly an
induction heater, the preferred reduction in thickness of the
annealed strip 328 is at least about 20% and more preferably at
least about 25% but no more than about 55% and more preferably no
more than about 60% and more preferably no more than about 65% to a
gauge ranging from about 0.013 to about 0.009 inches in one pass.
For a batch heater, the preferred reduction in thickness of the
strip 328 is at least about 40% and more preferably at least about
50% but no more than about 70% and more preferably no more than
about 65% to a gauge ranging from about 0.013 to about 0.009 inches
in one pass. An annealed strip 328 that has been intermediate
annealed in an induction heater is much more sensitive to increases
in earing from subsequent cold work than an annealed strip 328 that
has been intermediate annealed in a batch heater. Accordingly, cold
rolling reductions for induction annealed strips are less than
those for batch annealed strips. The cold rolled strip 336 is
subjected to a stabilize anneal 308 to form aluminum alloy sheet
312. A batch or continuous heater can be employed in the stabilize
anneal 308. The cold rolled strip 336 is preferably stabilize
annealed 308 at a minimum temperature of at least about 300.degree.
F. (i.e., about 146.degree. C.) and more preferably at least about
325.degree. F. (i.e., about 162.degree. C.), and preferably at a
maximum temperature of no more than about 500.degree. F. (i.e.,
about 260.degree. C.) and more preferably of no more than about
550.degree. F. (i.e., about 287.degree. C.). The most preferred
temperature is about 350.degree. F. (i.e., about 176.degree. C.).
The annealing time for a batch heater preferably ranges from about
2 to about 3 hours and for a continuous heater, particularly an
induction heater, from about 2 to about 30 seconds.
[0177] An aluminum alloy composition that is particularly useful
for body stock in this embodiment includes:
[0178] (i) Manganese, preferably in an amount of at least about
0.85 wt %, more preferably at least about 0.9 wt %, and most
preferably at least about 0.95 wt % but no more than about 1.2 wt
%, more preferably no more than about 1.1 wt %, and most preferably
no more than about 1.1 wt %.
[0179] (ii) Magnesium, preferably in an amount of at least about
0.9 wt %, more preferably at least about 1.0 wt %, and most
preferably at least about 1.0 wt % but preferably no more than
about 1.5 wt %, more preferably no more than about 1.4 wt %, and
most preferably no more than about 1.35 wt %.
[0180] (iii) Copper, preferably in amount of at least about 0.20 wt
%, and more preferably at least about 0.40 wt % but preferably no
more than about 0.60 wt % and more preferably no more than about
0.55 wt %.
[0181] (iv) Iron, preferably in an amount of at least about 0.35 wt
% and more preferably at least about 0.40 wt % but preferably no
more than about 0.50 wt % and more preferably no more than about
0.60 wt %.
[0182] (v) Silicon, preferably in an amount of at least about 0.3
wt % but no more than about 0.5 wt % and more preferably no more
than about 0.4 wt %.
[0183] A particularly useful aluminum alloy composition for body
stock using this process includes the following constituents:
[0184] (i) Manganese in an amount of at least about 0.85 but no
more than about 1.2 wt %.
[0185] (ii) Magnesium in an amount of at least about 0.85 but no
more than about 1.5 wt %.
[0186] (iii) Copper in an amount of at least about 0.20 but no more
than about 0.60 wt %.
[0187] (iv) Iron in an amount of at least about 0.20 but no more
than about 0.60 wt %.
[0188] (v) Silicon in an amount of at least about 0.30 but no more
than about 0.50 wt %.
[0189] The aluminum alloy sheet 312 has properties that are
particularly useful for body stock. When the aluminum alloy sheet
312 is to be used as body stock, the alloy sheet preferably has a
final yield strength of at least about 37 ksi and more preferably
at least about 37.5 ksi, and most preferably at least about 38.5
ksi but no more than about 45 ksi and more preferably no more than
about 43 ksi, and most preferably no more than about 42.5 ksi. The
final tensile strength preferably is at least about 40 ksi, more
preferably at least about 41 ksi, and most preferably at least
about 43 ksi but no more than about 47 ksi, more preferably no more
than about 46.5 ksi, and most preferably no more than about 46.0
ksi. The aluminum alloy sheet 312 should have a final elongation of
at least about 3% and more preferably at least about 4%.
[0190] To produce acceptable drawn and ironed container bodies,
aluminum alloy sheet 312 used as body stock should have a low
earing percentage. Preferably, the aluminum alloy sheet 312,
according to the present invention, has a tested earing of no more
than about 2.5% and more preferably no more than about 2.2% and
most preferably no more than about 2%. An induction heater can
provide a lower earing percentage because the induction heater uses
a lower reduction in the cold rolling step 332. Preferably,
aluminum alloy sheet 312 produced using an induction heater has a
tested earing of no more than about 2.0% and more preferably no
more than about 1.9%.
[0191] Container bodies fabricated from the aluminum alloy sheet
312 of the embodiment of the present invention have relatively high
strengths. The container bodies have a minimum dome reversal
strength of at least about 90 psi and more preferably at least
about 93 psi at current commercial thicknesses. The column strength
of the container bodies preferably is at least about 210 psi and
more preferably at least about 230 psi.
[0192] In accordance with yet another embodiment of the present
invention, a method is provided for fabricating an aluminum alloy
sheet in which the initial cold rolling step is performed in the
absence of an annealing step after hot rolling and before the first
cold rolling step and/or in which the reductions in strip thickness
between intermediate anneals and after the last intermediate anneal
are maintained at or below a specified level to avoid full hard
conditions. The first intermediate annealing step is performed
after the first cold rolling step, and the second intermediate
annealing step is performed after the subsequent cold rolling step.
The method generally includes the steps of:
[0193] (i) forming an aluminum alloy melt;
[0194] (ii) continuously casting the alloy melt to form a cast
strip;
[0195] (iii) optionally heating the cast strip before hot
rolling;
[0196] (iv) hot rolling the cast strip to form a hot rolled
strip;
[0197] (v) cooling the hot rolled strip to a temperature below the
recrystallization temperature of the hot rolled strip;
[0198] (vi) cold rolling the hot rolled strip to form a partially
cold rolled strip;
[0199] (vii) annealing, preferably in a batch anneal, the partially
cold rolled strip to form a first intermediate annealed strip;
and
[0200] (viii) further cold rolling the first intermediate cold mill
strip to form a further cold rolled strip;
[0201] (ix) further annealing, either in a continuous or a batch
anneal, the further cold rolled strip to form a second intermediate
annealed strip; and
[0202] (x) forming the second intermediate annealed strip into the
aluminum alloy sheet. As desired, after annealing step (ix) the
second intermediate annealed strip can be further cold rolled
and/or stabilize annealed to form the aluminum alloy sheet.
[0203] The elimination of the annealing step directly after the hot
rolling step and the performance of two separate annealing steps
only after cold rolling steps offer a number of advantages,
particularly when the resulting sheet is employed in the
fabrication of containers such as cans. The containers produced
from the aluminum alloy sheet can have a reduced degree of earing
and a reduction in the occurrence of split flanges and sidewalls in
containers produced from the sheet. The plug diameter can be within
an acceptable tolerance of the specified plug diameter. Containers
produced from the sheet can have a significantly reduced incidence
of bulging in the container necked/flange sidewalls compared to
containers produced from aluminum alloy sheet having different
compositions and/or produced by other processes. It is believed
that the alloy sheet of the present invention typically experiences
less work hardening during fabrication of containers from the sheet
than other continuously cast alloys and comparable to direct chill
or ingot cast sheet. For instance, work hardening can occur when
cans come off the canmaker and are heated to elevated temperatures
to dry the paint on the can. As noted, the reductions in strip
thickness between the two intermediate annealing steps and after
the final intermediate annealing step are each maintained below the
level required for the strip to realize a full hard state. The
annealing of a thinner gauge of sheet (i.e., annealing which is
performed only after cold rolling steps) compared to annealing in
previous embodiments (i.e., which is performed after casting and
before hot rolling and again after cold rolling) increases the
amount of reduction which can be satisfactorily achieved with each
cold roll pass and thus can eliminate one or more cold rolling
passes relative to previous embodiments. Finally, the physical
properties of the sheet of this embodiment can experience
significantly less reduction during fabrication relative to the
reduction in physical properties of other alloy sheets during
fabrication. In canmaking applications, for example, existing
continuously cast alloy sheets can suffer a reduction in physical
properties of as much as 4 lbs or more in buckle strength and 20
lbs or more in column strength, after heating the sheet in deco/IBO
ovens.
[0204] The aluminum alloy sheet produced by the above-described
method can have a number of desirable properties, especially for
can making applications. By way of example, the sheet can have an
as-rolled ultimate tensile strength of at least about 42.5 ksi; an
as-rolled yield tensile strength of at least about 38.5 ksi; an
earing ranging of no more than about 2.0%; and/or an as-rolled
elongation of more than about 4%.
[0205] While not wishing to be bound by any theory, it is believed
that the maintenance of all cold mill reductions, e.g., the cold
mill reductions between the first and second intermediate annealing
steps and after the second intermediate annealing step to produce
finished gauge sheet, to levels that are less than that required to
realize full hard properties in the sheet during fabrication is an
important factor in the improved properties, particularly reduced
earing. The present invention maintains total cold mill reductions
between the first and second intermediate anneal steps, and after
the second intermediate anneal step, preferably less than about 73%
to prevent the sheet from acquiring full hard properties. Because
of the relatively fine grain size of continuously cast sheet
compared to direct chill cast sheet, continuously cast sheet has a
significantly higher rate of increase in earing for a given percent
reduction in the cold mill.
[0206] An aluminum alloy that is particularly useful for this
process comprises (a) preferably from about 0.85 to about 1.20 and
more preferably from about 0.95 to about 1.10 wt % manganese, (b)
preferably from about 0.85 to about 1.50 and more preferably from
about 1.3 to about 1.45 wt % magnesium, (c) preferably from about
0.20 to about 0.60 and more preferably from about 0.28 to about
0.40 wt % copper, (d) preferably from about 0.30 to about 0.50 and
more preferably from about 0.25 to about 0.35 wt % silicon, and (e)
preferably from about 0.20 to about 0.60 and more preferably from
about 0.40 to about 0.45 wt % iron, with the balance being aluminum
and incidental additional materials and impurities. The incidental
additional materials and impurities are preferably limited to about
0.05 wt % each, and the sum total of all incidental additional
materials and impurities preferably does not exceed about 0.15 wt
%.
[0207] The aluminum alloy sheet is preferably made by continuous
casting and more preferably by any of the processes described
above. Preferably, the sheet has an after-bake yield tensile
strength of at least about 37.0 ksi, more preferably at least about
38.0 ksi and more preferably at least about 39.0 ksi. The sheet
preferably has an earing of less than about 2.0%, more preferably
less than about 1.8% and most preferably no more than about 1.6%.
The sheet preferably has an elongation of more than about 4% and
more preferably more than about 4.5%. Finally, the sheet preferably
has an after-bake ultimate tensile strength of at least about 42.5
ksi, more preferably at least about 43.0 ksi and more preferably at
least about 43.5 ksi.
[0208] With continuing reference to FIG. 10, in the process the
continuously cast strip 24 is produced in a casting cavity having a
preferred tip diameter ranging from about 17 to about 19 mm and
subjected to hot rolling as described previously to form the hot
rolled strip 40. The hot mill preferably reduces the thickness of
the cast strip in one or more passes by at least about 70% and more
preferably by at least about 80%. The gauge of the cast strip
preferably ranges from about 0.50 inches to about 0.95 inches while
the gauge of the hot rolled strip ranges from about 0.060 to about
0.140 inches. The hot rolled strip preferably exits the hot mill at
a temperature ranging from about 500 to about 750.degree. F. It is
preferred that the total reduction of the cast strip be realized in
two to three passes with two passes being most preferred.
[0209] As an optional step, the continuously cast strip 24 can be
heated 28 as described above to form a heated strip 32. The heated
strip 32 is then hot rolled 36 to form the hot rolled strip 40.
[0210] The hot rolled strip 40 passes directly to a cooling step
400 before the first cold rolling step to form a cooled strip 404.
The hot rolled strip 40 is allowed to cool before cold rolling to a
temperature less than the recrystallization temperature of the hot
rolled strip. Preferably, the hot rolled strip 40 is allowed to
cool for a sufficient period of time to produce a hot rolled sheet
having a temperature ranging from about 75 to about 140.degree. F.
Generally, the hot rolled strip 40 is cooled for about 48 hours.
The strip is preferably not quenched or otherwise solution heat
treated.
[0211] In the first cold rolling step 408, the cooled strip 404 is
passed between cold rollers, as necessary, to form a cold rolled
strip 412 at an intermediate gauge. Preferably, the intermediate
gauge ranges from about 0.050 to about 0.090 inches and more
preferably from about 0.055 to about 0.088 inches. The total
reduction preferably is less than about 65% and more preferably
ranges from about 20% to about 45% and more preferably from about
25 to about 40% through the cold rollers. It is preferred that the
total sheet reduction be realized in two passes or less, with a
single pass being most preferred.
[0212] When the desired intermediate anneal gauge is reached
following the first cold rolling step 408, the cold rolled strip
412 is breakdown or first intermediate annealed 416 in a batch
anneal oven to form a first intermediate annealed strip 420 and
reduce the residual cold work and lower the earing of the aluminum
sheet. The first intermediate anneal 416 is preferably a heat soak
anneal. Preferably, the strip 412 is intermediate annealed at a
minimum temperature of at least about 700.degree. F. and more
preferably at a minimum of at least about 800.degree. F., and
preferably at a maximum temperature of about 900.degree. F. and
most preferably at a maximum temperature of about 850.degree. F.
The most preferred annealing temperature is about 825.degree. F.
The annealing soak time is preferably a minimum of at least about
0.5 hours and is more preferably a minimum of at least about 1 hour
with about 3 hours being most preferred.
[0213] Preferably, the first intermediate annealed strip 420 is
allowed to cool to a temperature less than the recrystallization
temperature of the strip prior to additional cold rolling steps.
The preferred temperature for cold rolling ranges from about 75 to
about 140.degree. F. The cooling time typically is 48 hours. As
will be appreciated, the strip can be force cooled in a
significantly shorter time by injecting nitrogen gas into the batch
anneal oven to reduce the sheet temperatures to about 250.degree.
F. However, the strip is preferably not subjected to solution heat
treatment.
[0214] After the strip 420 has cooled to ambient temperature, a
further cold rolling step 424 is used, as necessary, to form a
further cold rolled strip 428 having a smaller intermediate gauge.
Preferably, the intermediate gauge ranges from about 0.015 to about
0.040 inches and more preferably from about 0.020 to about 0.030
inches. It is preferred that the thickness of the strip be reduced
in total by less than 73%, more preferably by no more than about
71%, and more preferably by no more than about 70%. It is preferred
that the total reduction be realized in two passes or less, with a
single pass being preferred.
[0215] By maintaining all reductions between anneal points below
the level necessary to realize full hard conditions (i.e., about
73% or higher), the earing is maintained at relatively low levels.
As will be appreciated, the earing of a strip is directly related
to the amount of cold work the strip experiences. The reduction in
the final cold rolling step is selected to realize the desired
strength properties in the final aluminum alloy sheet.
[0216] The further cold rolled strip 428 is annealed a second time
or second intermediate annealed 432, preferably in a continuous or
batch anneal oven, to form a second intermediate annealed strip
436. The anneal can be a heat soak anneal or a continuous anneal,
such as in an induction heater. Preferably, the annealing
temperature for a batch heater ranges from about 600 to about
900.degree. F., more preferably from about 650 to about 750.degree.
F. The most preferred temperature is about 705.degree. F. The
annealing or soak time preferably is at least about 0.5 hrs and
more preferably about 2 hrs, with about 3 hrs being most preferred.
Preferably the annealing temperature for a continuous heater ranges
from about 700 F to about 1050 F, with about 950 F being more
preferred. The annealing or soak time preferably ranges from about
2 seconds to about 2.5 minutes and more preferably from about 3 to
about 10 seconds.
[0217] Preferably, the second intermediate annealed strip 436 is
allowed to cool to a temperature less than the recrystallization
temperature of the strip prior to a final cold rolling step 440.
The preferred temperature for cold rolling ranges from about 75 to
about 140.degree. F. The cooling time typically is about 48 hours.
As will be appreciated, the strip can be force cooled in a
significantly shorter time by injecting the nitrogen gas into the
batch annealing oven to reduce the sheet temperatures to about
250.degree. F. However, the strip is preferably not subjected to
solution heat treatment.
[0218] Finally, a final cold rolling step 440 is used to impart the
final properties to a final cold rolled strip 444. Generally, the
final gauge is specified and therefore the desired percent
reduction for the final cold rolling step 440 is determined. The
percent reductions in the other cold rolling steps and the hot
rolling step are back calculated based upon the final desired
gauge. As noted, the back calculation is performed such that the
total cold mill reductions before the first intermediate annealing
step 416, between the first and second intermediate annealing steps
416 and 432, and after the second intermediate annealing step 432
are each less than the level required to realize full hard
conditions.
[0219] In a preferred embodiment, the total reduction to final
gauge is from about 40% to 70%, more preferably from about 50% to
about 60% and most preferably from about 55% to about 65% in the
step. Preferably, the reduction is realized through a single pass.
When the strip is fabricated for drawn and ironed container bodies,
the final gauge can be, for example, from about 0.010 to about
0.014 inches. The final cold rolling step is preferably conducted
at a temperature ranging from about 75.degree. F. to about
120.degree. F. (incoming strip temperature) The process can include
a stabilizing anneal step 452 to impart desired properties to the
aluminum alloy sheet 448. The stabilizing anneal step 452 can be
performed in either a batch or continuous heater. As noted above,
the continuous heater can include an induction heater. The
temperature for the stabilizing anneal preferably ranges from about
120 to about 205 C and more preferably from about 145 to about 175
C (for a batch heater) and preferably ranges from about 145 to
about 260 C and more preferably from about 200 to about 235 C (for
a continuous heater).
[0220] The aluminum alloy sheet 448 produced from the above-noted
alloy by this process is especially useful for drawn and ironed
container bodies. When the aluminum alloy sheet is to be fabricated
into drawn and ironed container bodies, the alloy sheet preferably
has an as-rolled yield tensile strength of at least about 37.5 ksi,
more preferably at least about 38.0 ksi, and most preferably at
least about 38.5 ksi. The maximum as-rolled yield tensile strength
is no more than about 40.0 ksi. Preferably, the after-bake yield
tensile strength is at least about 36.0 ksi, more preferably at
least about 37.0 ksi, and most preferably is at least about 38.0
ksi, and preferably is not greater than about 39.5 ksi. The
aluminum alloy sheet preferably has an as rolled ultimate tensile
strength of at least about 42.5 ksi, more preferably at least about
43.0 ksi and most preferably at least about 43.5 ksi and preferably
less than about 45.0 ksi. The after-bake ultimate tensile strength
is preferably at least about 42.5 ksi, more preferably at least
about 43.0 ksi and most preferably at least about 43.5 ksi, and
preferably not greater than about 44.0 ksi. Preferably, the
aluminum alloy sheet has an earing of less than about 2%, more
preferably less than about 1.8% and most preferably less than about
1.6%. The earing typically ranges from about 1.5% to about 1.7%.
The sheet preferably has an after-bake elongation of at least about
4.5%, more preferably at least about 5.0% and most preferably at
least about 5.5%. The sheet preferably has an as-rolled elongation
of at least about 4.0%, more preferably at least about 4.5%, and
most preferably at least about 5.0%. Further, container bodies
fabricated from the alloy of the present invention have a minimum
dome reversal strength of at least about 90 psi and more preferably
at least about 95 psi at current commercial thickness.
EXAMPLE 1
[0221] Tests were conducted to compare sheet produced by a variety
of processes including the process of the present invention. The
goals of the tests included: (i) determine the feasibility of
replacing the hot mill batch anneal using a solenoidal heater
located in front of the first hot mill stand to cause
self-annealing of the strip after hot milling is complete; (ii)
determine the feasibility of replacing the intermediate batch
anneal with a continuous anneal using a transflux induction heater
(TFIH); and (iii) confirm prior test results that it is possible to
eliminate one cold mill pass and hot mill anneal by exiting the hot
mill at 0.065 inch gauge. Referring to Tables I and II, samples
29-31, 32-33, 34, 35, 36-37, 38, 39-42, and 43-44 are sample
groupings based on the process used to produce the sample. As used
in Table VI, "TFIH" refers to a transflux induction heater,
"Heater" refers to a continuous solenoidal heater, and "Batch"
refers to a batch gas fired heater. The chemical weight percent
compositions of the samples are shown in Table I. The composition
is the same as that for body stock. The continuous anneal test
results, namely earing, ultimate tensile strength, yield tensile
strength, and elongation, and process used to produce coils from
the samples are presented in Table II for each sample.
1TABLE 1 Sample Si Fe Cu Mn Mg No. (wt %) (wt %) (wt %) (wt %) (wt
%) 29 0.39 0.538 0.404 1.06 1.333 30 0.383 0.532 0.4 1.058 1.316 32
0.394 0.546 0.405 1.064 1.334 39 0.421 0.57 0.419 1.045 1.335 40
0.39 0.547 0.405 1.064 1.334 44 0.395 0.541 0.405 1.061 1.336 34
0.392 0.551 0.408 1.073 1.339 35 0.379 0.538 0.398 1.048 1.303 36
0.397 0.554 0.409 1.054 1.322 37 0.388 0.543 0.403 1.063 1.337 38
0.386 0.542 0.404 1.076 1.334 31 and 41-43 0.387 0.562 0.463 1.055
1.339
[0222]
2TABLE II Sample HM gauge Heater Hot Mill CM Batch Intermediate
Anneal Finish gauge No. (Inches) on/off Anneal Pass Anneal CM Pass
Batch/TFIH (Inches) 29 0.105 off none .062" yes/825.degree. F.
.025" Batch 0.0112 30 0.105 off none .062" yes/825.degree. F. .025"
Batch 0.0112 31 0.105 Not available none .062" yes/825.degree. F.
.025" Batch 0.0112 32 0.105 off none .062" yes/825.degree. F. .025"
TFIH 0.0112 31 0.105 Not available none .062" yes/825.degree. F.
.025" TFIH 0.0112 39 0.105 off yes/825.degree. F. .050" no .025"
Batch 0.0112 40 0.105 off yes/825.degree. F. .050" no .025" Batch
0.0112 41 0.105 Not available yes/825.degree. F. .045" no .025"
Batch 0.0112 41 0.105 Not available yes/825.degree. F. .045" no
.025" Batch 0.0112 44 0.105 off yes/825.degree. F. .050" no .025"
TFIH 0.0112 42 0.105 Not available yes/825.degree. F. .045" no
.025" TFIH 0.0112 34 0.065 on none none none .025" Batch 0.0112 35
0.065 on none none none .025" TFIH 0.0112 36 0.105 on none .050"
none .025" Batch 0.0112 37 0.105 on none .050" none .025" Batch
0.0112 38 0.105 on none .050" none .025" TFIH 0.0112
[0223] For samples 34-38, a solenoidal heater was located before
the first stand of the hot mill. The heater raised the tab
temperature a maximum of 160.degree. F. at a casting speed of 16.4
fpm and a slab thickness of 19.0 mm. Table VIII illustrates test
results for coils produced utilizing this process
configuration.
[0224] The solenoidal heater was found to have the following
advantages: (i) at lower gauges of the cast strip, elimination of
the need for a hot mill anneal at 825.degree. F. for 3 hours; (ii)
reduction of the hot mill stand amps and loads when the exit gauge
from the hot mill is reduced; (iii) increase in the amount of heat
transferred to the cast strip when the cast strips are thinner than
19 mm (i.e., thinner cast strips cool more quickly, which can
increase the loads and amps and therefore limit the exit gauge that
can be realized without applying excessive power to the hot mill);
and (iv) removal of striations in the hot mill strip.
[0225] As shown in Table VIII, Samples 36-38 produced using the
solenoidal heater at the hot mill exit gauge of 0.105-inch gauge
were undesirable. Microstructure confirmed that the coils produced
using this exit gauge did not recrystallize. This is further
confirmed in the final gauge earing/mechanical property data. While
not wishing to be bound by any theory, it is believed that the cast
strip gauge is too thick for the amount of time available in the
solenoidal heater and the power usage. This, in combination with
the chemistry of the samples, complicates recrystallization.
Another reason could be the higher intrastand gauge of 0.22 mm
versus 0.19 mm seen on the 0.65-inch gauge material. The higher
intrastand gauge and intrastand temperature maintained the cast
strip above the temperature above the recrystallization point
before the second hot mill stand.
[0226] In the case of coils fabricated using the solenoidal heater
and an exit gauge of 0.65 inch, the material reacted as a
self-anneal hotband and recrystallized. Referring to Tables VII and
VIII, for example, Samples 29 and 34 both recrystallized. Sample
29, which was fabricated without the solenoidal heater, exited the
hot mill at 0.105-inch gauge and was cold rolled to 0.062-inch
gauge. It then received a batch anneal at 825.degree. F. for 3
hours of soak time, which caused recrystallization. The total
anneal cycle time was 12 to 18 hours of soak time. In contrast,
Sample 34 exited the hot mill at 0.065-inch gauge with the
solenoidal heater at 30% of available power. Sample 34 received no
batch anneal after the first cold rolling pass. Unlike Sample 29,
which received three cold mill passes, Sample 34 received only two
cold mill passes. The data illustrates that when both samples were
given a batch anneal at 0.025-inch gauge after the second cold
rolling pass and before the finished cold rolling pass, there was a
very minor difference in properties.
[0227] In short, the minor difference in properties indicates that
a solenoidal heater could be placed in front of the hot mill and,
using an exit gauge of 0.65 inches or lower, a cold mill pass and
the hot mill anneal could both be eliminated while maintaining
acceptable properties.
[0228] Regarding the comparison of an intermediate batch anneal
against an intermediate continuous anneal using an induction
heater, Tables II through VIII present the results. The pilot line
using the transflux induction heater could only accept a 14.5-inch
wide strip and was limited to a maximum of 1,000 lbs. of incoming
weight. The TFIH anneal temperature was 950.degree. F. as compared
to 705.degree. F. for the batch anneal. The reason for the
temperature difference is due to the total exposure time which is
considerably less for the TFIH compared to the batch anneal. The
total exposure time of the strip in the TFIH was about 2-6
seconds.
[0229] It is evident from the Tables that the final earing is
aggravated by the use of a continuous intermediate anneal as
compared to a batch anneal. The magnitude of the earing varied,
depending upon the process used to produce the material.
[0230] The TFIH increases the as-rolled mechanical properties of
the sheet by an average of about 3.0 ksi in tensile strength and
3.5 ksi in yield strength. An important issue is the increase of
tensile and yield strengths when the TFIH coils are subjected to
further heating. Normally when as-rolled material is heated in the
temperature range of 325.degree. to 400.degree. F., the mechanical
properties will be decreased significantly in yield strength and
slightly in the tensile strength and increased in percent
elongation. In the case of the coils produced by a process using a
TFIH, tensile and yield strengths and percent elongation are
increased as the coils are heated. This phenomena is illustrated in
Table VII and FIGS. 11 and 12. The increase in tensile and yield
strengths from heating is as much as 5 ksi with a 325.degree. F./1
hour stabilize anneal and 7 ksi with an after-bake temperature of
400.degree. F. for 10 minutes. The increase continues until a
stabilized temperature of about 400.degree. F. is realized.
3 TABLE III If "O" Hot Hot Mill heater Caster Heater Heater Inter-
Mill Hot Mill Hot Mill Stand Stand is off Exit Entry Exit stand
Exit Stand Stand Stand Stand 1 2 Sample Heater Temp Temp Temp Temp
Temp 1 2 1 2 Gauge Gauge No. KW* (.degree. F.) (.degree. F.)
(.degree. F.) (.degree. F.) (.degree. F.) Amps Amps Load Load
(Inches) (Inches) 45 0 1030 935 904 775 655 1460 1290 1018 970
0.225 0.105 46 40 1025 940 1004 798 645 1350 1210 890 911 0.23
0.105 47 30 1023 958 954 794 717 1420 1440 998 1070 0.19 0.065 48
30 1030 953 959 801 700 1400 1460 1085 1024 0.19 0.065 49 40 1040
970 984 803 658 1300 1210 898 951 0.19 0.065 50 40 1039 963 989 800
652 1290 1220 870 943 0.22 0.105 51 40 1034 960 999 799 655 1280
1220 896 947 0.22 0.105 52 0 1015 948 911 750 647 1480 1250 1010
982 0.22 0.105 53 0 905 768 652 1500 1280 1049 981 0.22 0.105 54 0
958 910 767 647 1490 1250 1029 970 0.22 0.105 55 0 952 908 767 650
1490 1260 1032 985 0.22 0.105 56 0 960 910 766 645 1480 1250 1022
980 0.22 0.105 Caster Speed was 16.4 feet per minute. Caster tip
size was 19 millimeters.
[0231]
4 TABLE IV Finish Inter- Ga As rolled 325/hr 400/10 mediate Sample
Earing Uts YTS El Uts YTS El Uts YTS El Anneal No. (%) (ksi) (ksi)
(%) (ksi) (ksi) (%) (ksi) (ksi) (%) Type 36 2.53 43.34 41.62 2.67
44.71 39.64 5.41 43.55 37.81 5.45 Batch 37 2.88 43.62 41.83 3.14
44.69 39.91 4.69 43.2 37.94 5.5 Batch Average 2.71 43.48 41.73 2.91
44.70 39.78 5.05 43.38 37.88 5.48 Earing (%) 34 1.72 41.94 40.12
3.26 43.71 38.6 5.58 42.47 36.9 5.48 Batch 35 2.66 45.06 44.53 2.43
50.42 44.48 7.87 49.95 44.19 7.6 TFIH Diff 0.94 3.12 4.41 -0.8 6.71
5.88 2.29 7.48 7.29 2.12 Samples 34 & 35
[0232]
5 TABLE V Finish Ga Surface As rolled 325/1 hr. 400/10 2nd Anneal
Sample Earing Grain Uts YTS El Uts YTS El Uts YTS El Gauge No. (%)
Rating (ksi) (ksi) (%) (ksi) (ksi) (%) (ksi) (ksi) (%) (Inches)
Type 29 1.76 3 42.8 40.78 3.63 44.19 38.84 5.35 42.75 36.89 5.78
0.025 Batch 30 1.97 2.25 42.25 40.54 3.49 43.97 38.54 5.39 42.55
36.65 6.08 0.025 Batch Average 29 1.865 2.625 42.53 40.66 3.56
44.08 38.69 5.37 42.65 36.77 5.93 & 30 31 1.35 1.5 41.91 39.6
3.6 43.41 38.19 5.34 42.1 36.91 5.63 0.025 Batch Diff Average
-0.515 -1.125 -.062 -1.06 0.04 -0.67 -0.5 -0.03 -0.55 0.14 -0.3 29
& 30 and Sample 31 32 2.06 6 45.09 43.97 2.49 49.23 43.04 7.2
47.51 41.1 7.01 0.025 TFIH 33 2.14 5 44.54 43.61 2.5 48.57 42.8
6.85 48.47 42.66 7.12 0.025 TFIH Average 32 2.1 5.5 44.82 43.79
2.495 48.9 42.92 7.025 47.99 41.88 7.065 & 33 Diff Samples 0.08
-1 -0.55 -0.36 0.01 -0.24 -0.35 -0.35 0.96 1.56 0.11 32 & 33
Diff Average 0.195 3.375 2.565 3.31 -1.07 5.15 4.35 1.83 4.86 4.33
1.08 29 & 30 and Sample 32 Diff Samples 0.79 3.5 2.63 4.01 -1.1
5.16 4.61 1.51 6.37 5.75 1.49 31 and 32
[0233]
6 TABLE VI Finish Ga Surface As rolled 325/1 hr. 400/10 2nd Anneal
Sample Earing Grain Uts YTS El Uts YTS El Uts YTS El Gauge No. (%)
Rating (ksi) (ksi) (%) (ksi) (ksi) (%) (ksi) (ksi) (%) (Inches)
Type 39 1.61 3.5 41.87 40.08 3.2 43.63 38.85 5.23 42.16 36.52 5.37
0.025 Batch 40 1.68 3.5 42.17 40.59 2.86 44.05 38.67 5.97 42.86
36.95 5.91 0.025 Batch Avg. 1.65 3.50 42.02 40.34 3.03 43.84 38.76
5.60 42.51 36.74 5.64 Samples 39 & 40 41 1.78 4 42.18 40.58
3.34 44.22 39.01 5.74 43.04 37.23 5.84 0.025 Batch 42 2.14 3.5
42.45 40.84 3.17 44.46 39.1 5.69 43.22 37.44 5.84 0.025 Batch Avg.
1.96 3.75 42.32 40.71 3.255 44.34 39.06 5.715 43.13 37.34 5.84
Samples 41 & 42 43 2.58 8 45.3 44.14 2.46 48.32 42.96 6.37
47.46 41.86 6.81 0.025 TFIH 44 2.58 8 45.15 44.11 3.17 49.02 43
6.87 48.06 42.24 7.23 0.025 TFIH Diff Sample 0.93 4.5 3.13 3.78
0.14 5.18 4.24 1.27 5.55 5.51 1.59 44 & Avg. Samples 38 &
40 Diff Sample 0.62 4.25 2.985 3.43 -0.8 3.98 3.905 0.655 4.33
4.525 0.97 43 & Avg. Samples 34 & 35
[0234]
7 TABLE VII Finish Ga Surface As rolled 325/1 hr. 400/10 Sample
Earing Grain Uts YTS El Uts YTS El Uts YTS El No. (%) Rating (ksi)
(ksi) (%) (ksi) (ksi) (%) (ksi) (ksi) (%) Heater 29 1.76 3 42.8
40.78 3.63 44.19 38.84 5.35 42.75 36.89 5.78 N/A 30 1.97 2.25 42.25
40.54 3.49 43.97 38.54 5.39 42.55 36.55 6.08 N/A 31 1.35 1.5 41.91
39.6 3.6 43.41 38.19 5.34 42.1 36.91 5.63 N/A 32 2.06 6 45.09 43.97
2.49 49.23 43.04 7.2 47.51 41.1 7.01 N/A 33 2.14 5 44.54 43.61 2.5
48.57 42.8 6.85 48.47 42.66 7.12 N/A 34 1.72 3 41.94 40.12 3.26
43.71 38.6 5.58 42.47 36.9 5.48 Y 35 3.04 7 45.06 44.53 2.43 50.42
44.48 7.87 49.95 44.19 7.6 Y 36 2.53 2.5 43.34 41.62 2.67 44.71
39.64 5.41 43.55 37.81 5.45 Y 37 3.36 2.25 43.62 41.83 3.14 44.69
39.91 4.69 43.2 37.94 5.5 Y 38 2.41 8 47.24 45.46 3.95 52.16 46.38
8.19 50.01 44.56 7.94 Y 39 1.61 3.5 41.87 40.08 3.2 43.63 38.85
5.23 42.16 36.52 5.37 N/A 40 1.68 3.5 42.17 40.59 2.86 44.05 38.67
5.97 42.86 36.95 5.91 N/A 41 1.78 4 42.18 40.58 3.34 44.22 39.01
5.74 43.04 37.23 5.84 N/A 42 2.14 3.5 42.45 40.84 3.17 44.46 39.1
5.69 43.22 37.44 5.84 N/A 43 2.58 8 45.3 44.14 2.46 48.32 42.96
6.37 47.46 41.86 6.81 N/A 44 2.58 8 45.15 44.11 3.17 49.02 43 6.87
48.06 42.24 7.23 N/A 1st ANNEAL 2nd (INTERMEDIATE) ANNEAL HM TIME
Sample GA GA TEMP TIME GA TEMP (Hrs=H No. (In) (In) TYPE (.degree.
F.) (Hrs.) (In) TYPE (.degree. F.) Sec=S) 29 0.105 0.062 Batch 825
3 0.025 Batch 705 13 H 30 0.105 0.062 Batch 825 3 0.025 Batch 705
13 H 31 0.105 0.062 Batch 825 3 0.025 Batch 705 13 H 32 0.105 0.062
Batch 825 3 0.025 TFIH 950 2 S 33 0.105 0.062 Batch 825 3 0.025
TFIH 950 2 S 34 0.065 0.065 N/A 800 0.025 Batch 705 13 H 35 0.065
0.065 N/A 800 0.025 TFIH 950 2 S 36 0.105 0.105 N/A 800 0.025 Batch
705 13 H 37 0.105 0.105 N/A 800 0.025 Batch 705 13 H 38 0.105 0.105
N/A 800 0.025 TFIH 950 2 S 39 0.105 0.105 Batch 825 3 0.025 Batch
705 13 H 40 0.105 0.105 Batch 825 3 0.025 Batch 705 13 H 41 0.105
0.105 Batch 825 3 0.025 Batch 705 13 H 42 0.105 0.105 Batch 825 3
0.025 Batch 705 13 H 43 0.105 0.105 Batch 825 3 0.025 TFIH 950 2 S
44 0.105 0.105 Batch 825 3 0.025 TFIH 950 2 S
[0235]
8TABLE VIII Sam- ple Ultimate Tensile Strength (ksi) Yield Tensile
Strength (ksi) % Elongation No. 275.degree. F. 325.degree. F.
375.degree. F. 425.degree. F. 475.degree. F. 275.degree. F.
325.degree. F. 375.degree. F. 425.degree. F. 475.degree. F.
275.degree. F. 325.degree. F. 375.degree. F. 425.degree. F.
475.degree. F. 29 43.06 43.92 42.67 38.41 36.08 39.62 38.61 36.95
33.19 30.73 4.06 5.42 5.53 4.99 4.66 39 42.38 43.32 42.23 37.53
35.8 39.11 38.04 36.56 32.17 30.08 4.29 5.6 5.95 5.67 6.74 31 42.28
43.23 42.37 37.88 35.9 38.97 38.03 36.63 32.58 30.09 3.74 5.41 5.67
5.57 6.64 34 42.6 43.71 42.64 38.5 36.39 39.47 38.59 37.11 33.54
31.1 3.96 5.35 5.95 5.09 5.8 35 47.58 51.53 48.24 46.2 40.28 43.86
45.72 42.63 41.23 35.45 5.14 7.64 7.26 6.02 5.14 37 46.54 49.02
49.7 46.27 38.88 42.68 43.03 43.68 40.84 33.2 4.89 6.86 7.7 6.42
6.27 31 46.82 49.86 48.51 44.27 38.84 43.02 44.06 42.73 38.92 33.34
4.91 7.05 7.67 6.4 5.95 Earing (%) 275.degree. F. 325.degree. F.
425.degree. F. 29 1.98 1.86 1.97 39 1.68 1.7 1.85 31 1.4 1.46 1.43
34 1.95 2.18 2.02 35 2.65 3.25 2.47 37 2.23 2.68 2.32 31 2.45 2.26
2.2
[0236] Based upon the foregoing, the test results indicate that:
(i) one cold mill pass and the hot mill anneal can be eliminated by
introducing a solenoidal heater and exit strip gauge of 0.65 inch
or less with an intermediate batch anneal; and (ii) the TFIH used
at the intermediate anneal point (with a 55% final reduction)
increases the final earing by at least 0.6%, which is not
acceptable. The same process, when introduced to temperatures of
325 to 400.degree. F. increases the overall mechanical properties
(i.e., tensile and yield strengths) by 5 to 7 ksi which also is not
acceptable in a can plant where the IBO and deco ovens would, in
fact, make the can too strong to be necked and flanged.
EXAMPLE 2
[0237] Further experiments were performed to examine the properties
of aluminum alloy sheet produced according to the process of FIG.
9. Samples 70 and 71 were produced using a tip size of 17.5 mm and
a batch heater in the intermediate anneal (with the annealing
temperature being 825 F) while samples 72 and 73 were produced
using a tip size of 19.0 mm and a transflux induction heater in the
intermediate anneal (with the annealing temperature being 950 F).
All of the samples were produced using a hot rolling reduction of
60%, a hot mill annealing temperature of about 825 F, a cold
rolling reduction in the first pass of about 60% and in the second
pass of about 50-65%, and a stabilize anneal temperature of about
350 F.
[0238] The cold rolling reductions to finish gauge for the samples
were different. The reduction for sample 70 was 55%, for sample 71
was 50%, for sample 72 was 30%, and for sample 73 was 35%.
[0239] The properties of the samples are as follows:
9 Sample 70 Before Stabilize Anneal Tensile strength 41.8 ksi Yield
strength 39.51 ksi Elongation 3.39% Earing 1.8% After Stabilize
Anneal Tensile strength 45.19 Yield strength 39.49 Elongation 6.4%
Sample 71 Before Stabilize Anneal Tensile strength 40.49 ksi Yield
strength 38.65 ksi Elongation 3.33% Earing 1.7% After Stabilize
Anneal Tensile strength 44.78 Yield strength 38.95 Elongation 6.8%
Sample 72 Before Stabilize Anneal Tensile strength 43.8 ksi Yield
strength 42.78 ksi Elongation 1.55% Earing 1.5% After Stabilize
Anneal Tensile strength 47.82 Yield strength 41.75 Elongation 7.24%
Sample 73 Before Stabilize Anneal Tensile strength 44.46 ksi Yield
strength 41.13 ksi Elongation 4.51% Earing 1.6% After Stabilize
Anneal Tensile strength 48.02 Yield strength 40.98 Elongation
8.5%
[0240] As can be seen from the above results, both batch and
intermediate annealed samples provided acceptable properties for
body stock. The tensile and yield strength and the elongation were
increased by the stabilize anneal. The highest tensile and yield
strengths and elongations were for the samples that were produced
using an induction heater in the intermediate anneal followed by a
stabilize anneal.
EXAMPLES 3-11
[0241] To illustrate the advantages of aluminum alloy sheet of the
present invention relative to aluminum alloy sheet produced by
other continuous casting and ingot casting processes, a number of
aluminum alloys were formed into sheets. In the tests, six samples
of 3000 series alloys produced by other continuous casting or ingot
casting processes were compared with three 3000 series alloys
produced according to the method of the present invention. The
results are presented in Tables IX (A) and (B).
10TABLE IX(A) Sample Alloy Composition As rolled After Bake #
Designation Si Cu Fe Mn Mg UTS YTS Elong. Earing % UTS YTS EL 11
5349D 0.38 0.43 0.28 1.14 1.81 42.8 39.5 3.2 1.4 42.5 37.2 5.6 12
3304B 0.19 0.37 0.41 0.81 1.2 42.3 38.8 4.1 1.7 42.3 37.1 5.1 13
3304C 0.21 0.55 0.41 1.04 1.3 43.9 39.9 4.4 1.8 43.1 37.8 5.3 14
3304F 0.21 0.55 0.41 0.83 1.36 43.3 39.1 4.4 1.8 42.6 37.3 5.3 15
3304CSV 0.38 0.57 0.47 1.05 1.33 43.5 40.1 4.59 2.6 43.3 37.6 5.87
16 3304CSV(mod) 0.38 0.57 0.46 1.04 1.35 42.8 38.9 4.99 1.7 42 36.3
5.58 17 3304CJ(mod) 0.42 0.598 0.5 1.06 1.42 43.2 39.3 4.7 1.6 42.7
37 5.8 18 3304CJ(mod) 0.42 0.59 0.5 1.03 1.448 43.25 39.6 4.6 1.7
42.7 37 5.7 19 Comparative AA3004 44.1 40.08 6.74 1.8 41.1 37.28
5.88
[0242]
11 TABLE IX(B) Hot Total cold Cold mill Total cold roll Cold mill
Total mill roll red % first red % from second final Sample anneal
to (first) anneal first anneal point to anneal cold mill # temp
anneal point temp second anneal point temp red % 74 825 74 N/A N/A
705 45 75 825 53 N/A N/A 705 65 76 825 75 N/A N/A 705 60 77 825 75
N/A N/A 705 60 78 825 74 N/A N/A 705 60 79 N/A 41 825 60 705 55 80
N/A 33 825 60 705 55 81 N/A 42 825 60 705 55 82 620 F. self anneal
391% total cold work to finish gauge
[0243] The balance of the composition in each sample was aluminum.
Samples 74-81 were continuously cast in a block caster and then
continuously hot rolled. Samples 74-78 were annealed, cold rolled,
annealed a second time, and cold rolled to form the aluminum alloy
sheet. In accordance with the process of the present invention,
samples 79-81 were cold rolled, annealed, cold rolled, annealed,
and cold rolled to form the aluminum alloy sheet. The various
anneals were each for about 3 hours. Samples 74, 76-79, and 82 were
fabricated into cans on conventional canmaking equipment and the
canmaking behavior of the samples determined.
[0244] Table X illustrates the results of testing the processed
sheets.
12 TABLE X BODYSTOCK PRODUCT PROGRESSION SAM- NECKING/ PLE ALLOY
SCORING BUCKLE FLANGING EARING 74 5349D Severe Fair Very Poor 1.7%
76 3304C Severe Good Poor 2.4% 77 3304F Fair Fair Fair 2.4% 78 3304
CSV Good Good Fair 2.6% 79 3304 (MOD) Good Good Good 1.7% 82
Comparative 2.0%
[0245] Samples 74 and 76-77 produced scored cans and demonstrated
poor necking/flange behavior. Samples 74 and 77 further
demonstrated a fair buckle strength while sample 76 demonstrated
poor earing. Sample 77 exhibited fair qualities in can scoring,
buckle strength, and necking/flange behavior but a very poor
earing. In sharp contrast, sample 79, which was fabricated by the
process of the present invention had a low degree of can scoring
and acceptable buckle strength, necking/flange behavior, and
earing. Sample 82, which was produced by ingot casting techniques
and is considered high quality canmaking stock, in fact had a
higher earing than sample 79.
[0246] Samples 78 and 79 were compared to sample 82, which is high
quality canmaking sheet prepared by ingot casting techniques. The
various sheet samples were formed into cans. The results are
presented in Table XI below.
13 TABLE XI BODYMAKER After-Deco/IBO Ovens UTS YTS Elong. UTS YTS
Elong. SAMPLE ALLOY (ksi) (ksi) (%) (ksi) (ksi) (%) 78 3304 CSV
51.10 47.50 0.90 47.00 40.10 2.90 79 3304 CSV 48.95 45.66 1.08
44.34 38.43 3.76 (modified) 82 3004/3104 48.96 45.06 1.63 43.25
38.67 3.82 (Compara- tive)
[0247] The ultimate tensile strength (UTS), yield tensile strength
(YTS), and elongation (Elong) were measured after the container
exited the bodymaker and after the container exited the deco step.
The deco step or after bake step included heating the alloy sheet
to about 400.degree. F. for about 10 minutes. The bodymaker samples
are the mechanical properties of the container thick wall in a
transverse direction.
[0248] Sample 78 exhibited a greater UTS and YTS and lower
elongation than sample 79 after the bodymaker and the after-deco
step. Sample 79 exhibited more elongation than sample 78,
especially after the deco step. In fact, the properties of sample
79 mirrored the properties of sample 82, which, as noted above, is
considered high quality canmaking stock, in both UTS and YTS after
the bodymaker and deco step and in elongation after the deco step.
The differences in physical properties of samples 79 and 82 in each
of these categories were within testing error of one another.
Sample 82, however, did have a measurably higher elongation than
sample 16 after the bodymaker. Nonetheless, sample 79 has canmaking
properties similar to sample 82. This is a surprising and
unexpected result for continuously cast aluminum alloy sheet which
has significantly more cold work than ingot cast sheet.
[0249] While various embodiments of the present invention have been
described in detail, it is apparent that modifications and
adaptations of those embodiments will occur to those skilled in the
art. It is to be expressly understood that such modifications and
adaptations are within the spirit and scope of the present
invention.
* * * * *