U.S. patent application number 11/128008 was filed with the patent office on 2005-09-29 for in-line method of making t or o temper aluminum alloy sheets.
Invention is credited to Timmons, David Wayne, Tomes, David Allen JR., Unal, Ali, Wyatt-Mair, Gavin Frederick.
Application Number | 20050211350 11/128008 |
Document ID | / |
Family ID | 37431700 |
Filed Date | 2005-09-29 |
United States Patent
Application |
20050211350 |
Kind Code |
A1 |
Unal, Ali ; et al. |
September 29, 2005 |
In-line method of making T or O temper aluminum alloy sheets
Abstract
A method of making aluminum alloy sheet in a continuous in-line
process is provided. A continuously-cast aluminum alloy strip is
optionally quenched, hot or warm rolled, annealed or heat-treated
in-line, optionally quenched, and preferably coiled, with
additional hot, warm or cold rolling steps as needed to reach the
desired gauge. The process can be used to make aluminum alloy sheet
of T or O temper having the desired properties, in a much shorter
processing time. The T or O temper may be selected by annealing the
strip to achieve an O temper or solution heat treating the strip to
achieve a T temper, and, if a T temper is desired, quenching the
strip subsequent to the solution heat treating. The invention
further provides a hot or warm rolling step wherein the strip is
substantially reduces to a final thickness about 10-65% from a
casting thickness.
Inventors: |
Unal, Ali; (Export, PA)
; Tomes, David Allen JR.; (Sparks, NV) ; Timmons,
David Wayne; (Reno, NV) ; Wyatt-Mair, Gavin
Frederick; (Lafayette, CA) |
Correspondence
Address: |
Eric A. Lerner
Eckert Seamans Cherin & Mellott, LLC
44th Floor
600 Grant Street
Pittsburgh
PA
15219
US
|
Family ID: |
37431700 |
Appl. No.: |
11/128008 |
Filed: |
May 12, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11128008 |
May 12, 2005 |
|
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|
10782027 |
Feb 19, 2004 |
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Current U.S.
Class: |
148/694 |
Current CPC
Class: |
C22F 1/05 20130101; C22F
1/04 20130101; C22F 1/047 20130101 |
Class at
Publication: |
148/694 |
International
Class: |
C22F 001/04 |
Claims
We claim:
1. A method of manufacturing T or O temper aluminum alloy sheet in
an in-line sequence comprising the steps of: (i) providing a thin
cast aluminum alloy strip having a first thickness; (ii) quenching
the strip with a first quench to a hot or warm rolling temperature;
(iii) hot or warm rolling the strip to a final thickness that is
about 10-65% reduced from the first thickness; (iv) selectively
proceeding according to a first set of criteria depending on
whether a T or O temper is desired, and (v) quenching the strip
with a second quench if a T temper is desired.
2. The method of claim 1, wherein the first set of criteria
comprises solution heat treating for a T temper.
3. The method of claim 1, wherein the first set of criteria
comprises annealing the strip for an O temper.
4. The method of claim 1, further comprising the step of quenching
the strip with the second quench if an O temper is desired.
5. The method of claim 1, further comprising the step of not
quenching the strip with the second quench if an O temper is
desired.
6. The method of claim 1, wherein the second quench quenches the
strip to a temperature in the range of about 110.degree. to
200.degree. F. to achieve a T4 temper.
7. The method of claim 1, wherein the second quench quenches the
strip to a temperature in the range of about 250.degree. F. to
350.degree. F. to achieve a T6 temper.
8. The method of claim 1, wherein the second quench quenches the
strip to a temperature in the range of about 110.degree. to
200.degree. F. and reheated to a temperature range of about
250.degree. F. to 350.degree. F. to achieve a T6 temper.
9. The method of claim 1, wherein the second quench is an air
quench.
10. The method of claim 1, wherein the second quench is a
combination air and water quench.
11. The method of claim 1, wherein the aluminum alloy includes
manganese up to 0.25 weight percent.
12. The method of claim 1, wherein the strip as cast from the
caster has a first thickness in a range of about 0.06-0.15
inches.
13. The method of claim 1, wherein the strip after the hot or warm
rolling step has a final thickness in a range of about 0.02-0.13
inches.
14. The method of claim 1, further including the step of tension
leveling the strip after step (v).
15. The method of claim 1, further including the step of coiling
the strip after step (v).
16. The method of claim 1, wherein a total time for the method to
be performed is between the range of about 10 and 50 seconds.
17. The method of claim 1, wherein the aluminum strip after step
(v) is characterized by sufficient strength to permit tension to be
applied to the strip.
18. A method of manufacturing T or O temper aluminum alloy sheet in
an in-line sequence comprising the steps of: (i) providing a thin
cast aluminum alloy strip having a first thickness; (ii) hot or
warm rolling the strip to a final thickness that is about 10-65%
reduced from the first thickness of the strip as cast; (iii)
selectively proceeding according to a first set of criteria
depending whether a T or O temper is desired, and (iv) quenching
the strip with a quench if a T temper is desired
19. The method of claim 18, wherein the first set of criteria
comprises solution heat treating for a T temper.
20. The method of claim 18, wherein the first set of criteria
comprises annealing the strip for an O temper.
21. The method of claim 18, further comprising the step of
quenching the strip if an O temper is desired.
22. The method of claim 18, further comprising the step of not
quenching the strip if an O temper is desired.
23. The method of claim 18, wherein the quench quenches the strip
to a temperature range of about 110.degree. to 200.degree. F. to
achieve a T4 temper.
23. The method of claim 18, wherein quench quenches the strip to a
temperature range of about 250.degree. F. to 350.degree. F. to
achieve a T6 temper.
23. The method of claim 18, wherein the quench quenches strip to a
temperature range of about 110.degree. to 200.degree. F. and
reheated to a temperature range of about 250.degree. F. to
350.degree. F. to achieve a T6 temper.
23. The method of claim 18, wherein the quench is an air
quench.
23. The method of claim 18, wherein the quench is a combination air
and water quench.
24. The method of claim 18, wherein the aluminum alloy includes
manganese up to 0.25 weight percent.
25. The method of claim 18, wherein the strip as cast from the
caster has a thickness in a range of about 0.06-0.15 inches.
26. The method of claim 18, wherein the strip after the hot or warm
rolling step has a thickness in a range of about 0.02-0.13
inches.
27. The method of claim 18, further including the step of tension
leveling the strip after step (iv).
28. The method of claim 18, further including the step of coiling
the strip after step (iv).
29. The method of claim 18, wherein a total time for the method to
be performed is between the range of about 10 and 50 seconds.
30. The method of claim 18, wherein the aluminum strip after step
(v) is characterized by sufficient strength to permit tension to be
applied to the strip.
31. A method of manufacturing T or O temper aluminum alloy sheet in
an in-line sequence comprising the steps of: (i) providing a thin
cast aluminum alloy strip having a first thickness, wherein the
aluminum alloy includes up to 0.25 weight percent of manganese;
(ii) optionally quenching the strip with a first quench to a hot or
warm rolling temperature; (iii) hot or warm rolling the strip to a
final thickness; (iv) step of selectively proceeding according to a
first set of criteria depending on whether a T or O is temper
desired, and (v) quenching the strip with a second quench if a T
temper is desired.
32. The method of claim 31, wherein the first set of criteria
comprises solution heat treating for a T temper.
33. The method of claim 31, wherein the first set of criteria
comprises annealing the strip for an O temper.
34. The method of claim 31, further comprising the step of
quenching the strip with the second quench if an O temper is
desired.
35. The method of claim 31, further comprising the step of not
quenching the strip with the second quench if an O temper is
desired.
36. The method of claim 31, wherein the second quench quenches the
strip to a temperature range of about 110.degree. to 200.degree. F.
to achieve a T4 temper.
37. The method of claim 31, wherein the second quench quenches the
strip to a temperature range of about 250.degree. F. to 350.degree.
F. to achieve a T6 temper.
38. The method of claim 31, wherein the second quench quenches the
strip to a temperature range of about 110.degree. to 200.degree. F.
and reheated to a temperature range of about 250.degree. F. to
350.degree. F. to achieve a T6 temper.
39. The method of claim 31, wherein the second quench is an air
quench.
40. The method of claim 31, wherein the second quench is a
combination air and water quench.
41. The method of claim 31, wherein the strip as cast from the
caster has a thickness in a range of about 0.06-0.15 inches.
42. The method of claim 31, wherein the strip after the hot or warm
rolling step has a thickness in a range of about 0.02-0.13
inches.
43. The method of claim 31, further including the step of tension
leveling the strip after step (v).
44. The method of claim 31, further including the step of coiling
the strip after step (v).
45. The method of claim 31, wherein the strip has a first thickness
after casting and a final thickness after the hot or warm rolling,
the final thickness that is about 10-65% reduced from the first
thickness.
46. The method of claim 31, wherein a total time for the method to
be performed is between the range of about 10 and 50 seconds.
47. The method of claim 31, wherein the aluminum strip after step
(v) is characterized by sufficient strength to permit tension to be
applied to the strip.
48. A method of manufacturing auto body parts made from T or O
temper aluminum alloy sheet comprising the steps of: (i) providing
a thin cast aluminum alloy strip having a first thickness; (ii)
optionally quenching the strip with a first quench to a hot or warm
rolling temperature; (iii) hot or warm rolling the strip to a final
thickness that is about 10-65% reduced from the first thickness;
(iv) selectively proceeding according to a first set of criteria
depending on whether a T or O temper is desired, (v) quenching the
strip with a second quench if a T temper is desired, and (vi)
forming the T or O tempers into auto body panels or
reinforcements.
49. The method of claim 48, wherein the first set of criteria
comprises solution heat treating for a T temper.
50. The method of claim 48, wherein the first set of criteria
comprises annealing the strip for an O temper.
51. The method of claim 48, further comprising the step of
quenching the strip with the second quench if an O temper is
desired.
52. The method of claim 48, further comprising the step of not
quenching the strip with the second quench if an O temper is
desired.
53. The method of claim 48, wherein the second quench quenches the
strip to a temperature in the range of about 110.degree. to
200.degree. F. to achieve a T4 temper.
54. The method of claim 48, wherein the second quench quenches the
strip to a temperature in the range of about 250.degree. F. to
350.degree. F. to achieve a T6 temper.
55. The method of claim 48, wherein the second quench quenches the
strip to a temperature in the range of about 110.degree. to
200.degree. F. and reheated to a temperature range of about
250.degree. F. to 350.degree. F. to achieve a T6 temper.
56. The method of claim 48, wherein the aluminum alloy includes
manganese up to 0.25 weight percent.
57. The method of claim 48, wherein the strip as cast from the
caster has a first thickness in a range of about 0.06-0.15
inches.
58. The method of claim 48, wherein the strip after the hot or warm
rolling step has a final thickness in a range of about 0.02-0.13
inches.
59. The method of claim 48, further including the step of tension
leveling the strip after step (v).
60. The method of claim 48, further including the step of coiling
the strip after step (v).
61. The method of claim 48, wherein a total time for the method to
be performed is between the range of about 10 and 50 seconds.
62. The method of claim 48, wherein the aluminum strip after step
(v) is characterized by sufficient strength to permit tension to be
applied to the strip.
63. A method of manufacturing T or O temper aluminum alloy sheet
without cold rolling in an in-line sequence comprising the steps
of: (i) providing a thin cast aluminum alloy strip having a first
thickness; (ii) optionally quenching the strip with a first quench
to a hot or warm rolling temperature; (iii) hot or warm rolling the
strip to a final thickness; (iv) selectively proceeding according
to a first set of criteria depending on a whether a T or O temper
is desired, (v) quenching the strip with a second quench if a T
temper is desired, and (vi) coiling the temper without cold rolling
prior to the coiling.
64. The method of claim 63, wherein the first set of criteria
comprises solution heat treating for a T temper.
65. The method of claim 63, wherein the first set of criteria
comprises annealing the strip for an O temper.
66. The method of claim 63, further comprising the step of
quenching the strip with the second quench if an O temper is
desired.
67. The method of claim 63, further comprising the step of not
quenching the strip with the second quench if an O temper is
desired.
68. The method of claim 63, wherein the second quench quenches the
strip to a temperature in the range of about 110.degree. to
200.degree. F. to achieve a T4 temper.
69. The method of claim 63, wherein the second quench quenches the
strip to a temperature in the range of about 250.degree. F. to
350.degree. F. to achieve a T6 temper.
70. The method of claim 63, wherein the second quench quenches the
strip to a temperature in the range of about 110.degree. to
200.degree. F. and reheated to a temperature range of about
250.degree. F. to 350.degree. F. to achieve a T6 temper.
71. The method of claim 63, wherein the strip has a first thickness
after casting and a final thickness after the hot or warm rolling,
the final thickness that is about 10-65% reduced from the first
thickness.
72. The method of claim 63, wherein a total time for the method to
be performed is between the range of about 10 and 50 seconds.
73. The method of claim 63, wherein the aluminum strip after step
(v) is characterized by sufficient strength to permit tension to be
applied to the strip.
74. A method of manufacturing T or O temper aluminum alloy sheet in
an in-line sequence comprising the steps of: (i) providing a thin
cast aluminum alloy strip having a first thickness; (ii) optionally
quenching the strip with a first quench to a hot or warm rolling
temperature; (iii) hot or warm rolling the strip to a thickness in
at least one hot or warm rolling station to a final thickness that
is about 10-65% reduced from the first thickness; (iv) selectively
proceeding according to a first set of criteria depending on
whether a T or O temper is desired, and (v) quenching the strip
with a second quench if a T temper is desired.
75. The method of claim 74, wherein the first set of criteria
comprises solution heat treating for a T temper.
76. The method of claim 74, wherein the first set of criteria
comprises annealing the strip for an O temper.
77. The method of claim 74, further comprising the step of
quenching the strip with the second quench if an O temper is
desired.
78. The method of claim 74, further comprising the step of not
quenching the strip with the second quench if an O temper is
desired.
79. The method of claim 74, wherein the second quench quenches the
strip to a temperature in the range of about 110.degree. to
200.degree. F. to achieve a T4 temper.
80. The method of claim 1, wherein the second quench quenches the
strip to a temperature in the range of about 250.degree. F. to
350.degree. F. to achieve a T6 temper.
81. The method of claim 74, wherein the second quench quenches the
strip to a temperature in the range of about 110.degree. to
200.degree. F. and reheated to a temperature range of about
250.degree. F. to 350.degree. F. to achieve a T6 temper.
82. The method of claim 74, wherein a total time for the method to
be performed is between the range of about 10 and 50 seconds.
83. The method of claim 74, wherein the aluminum strip after step
(v) is characterized by sufficient strength to permit tension to be
applied to the strip.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The instant application is a continuation-in-part
application claiming priority from U.S. application Ser. No.
10/782,027, filed Apr. 19, 2004.
FIELD OF THE INVENTION
[0002] The present invention relates to a method of making aluminum
alloy sheet in a continuous in-line process. More specifically, a
continuous process is used to make aluminum alloy sheet of T or O
temper having the desired properties, with the minimum number of
steps and shortest possible processing time.
BACKGROUND INFORMATION
[0003] Conventional methods of manufacturing of aluminum alloy
sheet for use in commercial applications such as auto panels,
reinforcements, beverage containers and aerospace applications
employ batch processes which include an extensive sequence of
separate steps. Typically, a large ingot is cast to a thickness of
up to about 30 inches and cooled to ambient temperature, and then
stored for later use. When an ingot is needed for further
processing, it is first "scalped" to remove surface defects. Once
the surface defects have been removed, the ingot is preheated to a
temperature of about 1040.degree. F. for a period of 20 to 30
hours, to ensure that the components of the alloy are properly
distributed throughout the metallurgical structure. It is then
cooled to a lower temperature for hot rolling. Several passes are
applied to reduce the thickness of the ingot to the required range
for cold rolling. An intermediate anneal or a self-anneal is
typically carried out on the coil. The resulting "hot band" is then
cold-rolled to the desired gauge and coiled. For non-heat-treated
products, the coil is further annealed in a batch step to obtain
O-temper. To produce heat-treated products, the coiled sheet is
subjected to a separate heat treatment operation, typically in a
continuous heat-treat line. This involves unwinding the coil,
solution heat treatment at a high temperature, quenching and
recoiling. The above process, from start to finish, can take
several weeks for preparing the coil for sale, resulting in large
inventories of work in progress and final product, in addition to
scrap losses at each stage of the process.
[0004] Because of the lengthy processing time in this flow path,
numerous attempts have been made to shorten it by elimination of
certain steps, while maintaining the desired properties in the
finished product.
[0005] For example, U.S. Pat. No. 5,655,593 describes a method of
making aluminum alloy sheet where a thin strip is cast (in place of
a thick ingot) which is rapidly rolled and continuously cooled for
a period of less than 30 seconds to a temperature of less than
350.degree. F. U.S. Pat. No. 5,772,802 describes a method in which
the aluminum alloy cast strip is quenched, rolled, annealed at
temperatures between 600.degree. and 1200.degree. F. for less than
120 seconds, followed by quenching, rolling and aging.
[0006] U.S. Pat. No. 5,356,495 describes a process in which the
cast strip is hot-rolled, hot-coiled and held at a hot-rolled
temperature for 2-120 minutes, followed by uncoiling, quenching and
cold rolling at less than 300.degree. F., followed by recoiling the
sheet.
[0007] None of the above methods disclose or suggest the sequence
of steps of the present invention. There continues to be a need to
provide a continuous in-line method of making heat-treated (T
temper) and annealed (O temper) sheet having the desired properties
in a shorter period of time, with less or no inventory and less
scrap losses.
SUMMARY OF THE INVENTION
[0008] The present invention solves the above need by providing a
method of manufacturing aluminum alloy sheet in a continuous
in-time sequence comprising (i) providing a continuously-cast
aluminum alloy strip as feedstock; (ii) optionally quenching the
feedstock to the preferred hot rolling temperature; (iii) hot or
warm rolling the quenched feedstock to the required thickness, (iv)
annealing or solution heat-treating the feedstock in-line,
depending on alloy and temper desired; and (v) optionally,
quenching the feedstock. Preferably, additional steps include
tension leveling and coiling.
[0009] This method allows the elimination of many steps and much
processing time, and yet still results in an aluminum alloy sheet
having all of the desired properties. Both heat-treated and O
temper products are made in the same production line which takes
about 30 seconds to convert molten metal to finished coil. It is an
object of the present invention, therefore, to provide a continuous
in-line method of making aluminum alloy sheet having properties
similar to or exceeding those provided with conventional
methods.
[0010] It is an additional object of the present invention to
provide a continuous in-line method of making aluminum alloy sheet
more quickly so as to minimize waste and processing time.
[0011] It is a further object of the present invention to provide a
continuous in-line method of making aluminum alloy sheet, in a more
efficient and economical process.
[0012] It is a further object of the present invention to provide a
method of manufacturing T or O temper aluminum alloy sheet in an
in-line sequence comprising (i) providing a thin cast aluminum
alloy strip having a first thickness; (ii) quenching the strip with
a first quench to a hot or warm rolling temperature; (iii) hot or
warm rolling the strip to a final thickness that is about 10-65%
reduced from the first thickness; (iv) selectively proceeding
according to a first set of criteria depending on whether a T or O
temper is desired, and (v) quenching the strip with a second quench
if a T temper is desired.
[0013] These and other objects of the present invention will become
more readily apparent from the following figures, detailed
description and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The invention is further illustrated by the following
drawings in which:
[0015] FIG. 1 is a flow chart of the steps of the method of the
present invention, in one embodiment;
[0016] FIG. 2 is a schematic diagram of one embodiment of the
apparatus used in carrying out the method of the present
invention.
[0017] FIG. 3 is an additional embodiment of the apparatus used in
carrying out the method of the present invention. This line is
equipped with four rolling mills to reach a finer finished
gauge.
[0018] FIG. 4a is a graph demonstrating the equi-biaxial stretching
performance of 6022-T43 sheet (0.035 inch gauge) made in-line
compared with sheet made from DC ingot and heat-treated
off-line.
[0019] FIG. 4b is a graph demonstrating the equi-biaxial stretching
performance of 6022-T4 Alloy made in-line compared with sheet made
from DC ingot and heat-treated off-line.
[0020] FIG. 5 is a picture of Sample 804908 (Alloy 6022 in T43
temper) after e-coating.
[0021] FIG. 6a is a picture demonstrating the grain size of Alloy
6022 rolled in-line to 0.035 inch gauge without pre-quench.
[0022] FIG. 6b is a picture demonstrating the grain size of Alloy
6022 rolled in-line to 0.035 inch gauge.
[0023] FIG. 7a depicts an as-cast structure in Alloy 6022
transverse section.
[0024] FIG. 7b consists of two pictures demonstrating the surface
and shell structure of Alloy 6022 in as-cast condition in
transverse section.
[0025] FIG. 7c is a picture of the center zone structure of Alloy
6022 in as-cast condition in transverse section.
[0026] FIG. 7d consists of two pictures demonstrating pores and
constituents (mainly AlFeSi particles) in the center zone of Alloy
6022 cast structure in transverse section.
[0027] FIG. 8 depicts the as-cast microstructure of Al+3.5% Mg
alloy in transverse direction.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0028] The present invention provides a method of manufacturing
aluminum alloy sheet in a continuous in-line sequence comprising:
(i) providing a continuously-cast thin aluminum alloy strip as
feedstock; (ii) optionally, quenching the feedstock to the
preferred hot or warm rolling temperature; (iii) hot or warm
rolling the quenched feedstock to the desired final thickness; (iv)
annealing or solution heat-treating the feedstock in-line,
depending on alloy and temper desired; and (v) optionally,
quenching the feedstock, after which it is preferably
tension-leveled and coiled. This method results in an aluminum
alloy sheet having the desired dimensions and properties. In a
preferred embodiment, the aluminum alloy sheet is coiled for later
use. This sequence of steps is reflected in the flow diagram of
FIG. 1, which shows a continuously-cast aluminum alloy strip
feedstock 1 which is optionally passed through shear and trim
stations 2, optionally quenched for temperature adjustment 4,
hot-rolled 6, and optionally trimmed 8. The feedstock is then
either annealed 16 followed by suitable quenching 18 and optional
coiling 20 to produce O temper products 22, or solution heat
treated 10, followed by suitable quenching 12 and optional coiling
14 to produce T temper products 24. As can be seen in FIG. 1, the
temperature of the heating step and the subsequent quenching step
will vary depending on the desired temper.
[0029] As used herein, the term "anneal" refers to a heating
process that causes recrystallization of the metal to occur,
producing uniform formability and assisting in earing control.
Typical temperatures used in annealing aluminum alloys range from
about 600.degree. to 900.degree. F.
[0030] Also as used herein, the term "solution heat treatment"
refers to a metallurgical process in which the metal is held at a
high temperature so as to cause the second phase particles of the
alloying elements to dissolve into solid solution. Temperatures
used in solution heat treatment are generally higher than those
used in annealing, and range up to about 1060.degree. F. This
condition is then maintained by quenching of the metal for the
purpose of strengthening the final product by controlled
precipitation (aging).
[0031] As used herein, the term "feedstock" refers to the aluminum
alloy in strip form. The feedstock employed in the practice of the
present invention can be prepared by any number of continuous
casting techniques well known to those skilled in the art. A
preferred method for making the strip is described in U.S. Pat. No.
5,496,423 issued to Wyatt-Mair and Harrington. Another preferred
method is as described in co-pending applications Ser. Nos.
10/078,638 (now U.S. Pat. No. 6,672,368) and 10/377,376, both of
which are assigned to the assignee of the present invention. The
continuously-cast aluminum alloy strip preferably ranges from about
0.06 to 0.25 inches in thickness, more preferably about 0.08 to
0.14 inches in thickness. Typically, the cast strip will have a
width up to about 90 inches, depending on desired continued
processing and the end use of the sheet.
[0032] Referring now to FIG. 2, there is shown schematically a
preferred apparatus used in carrying out a preferred embodiment of
the method of the present invention. Molten metal to be cast is
held in melter holders 31, 33 and 35, is passed through troughing
36 and is further prepared by degassing 37 and filtering 39. The
tundish 41 supplies the molten metal to the continuous caster 45.
The metal feedstock 46 which emerges from the caster 45 is moved
through optional shear 47 and trim 49 stations for edge trimming
and transverse cutting, after which it is passed to a quenching
station 51 for adjustment of rolling temperature. The shear station
is operated when the process in interrupted; while running, shear
is open.
[0033] After optional quenching 51, the feedstock 46 is passed
through a rolling mill 53, from which it emerges at the required
final thickness. The feedstock 46 is passed through a thickness
gauge 54, a shapemeter 55, and optionally trimmed 57, and is then
annealed or solution heat-treated in a heater 59.
[0034] Following annealing/solution heat treatment in the heater
59, the feedstock 46 passes through a profile gauge 61, and is
optionally quenched at quenching station 63. Additional steps
include passing the feedstock 46 through a tension leveler to
flatten the sheet at station 65, and subjecting it to surface
inspection at station 67. The resulting aluminum alloy sheet is
then coiled at the coiling station 69. The overall length of the
processing line from the caster to the coiler is estimated at about
250 feet. The total time of processing from molten metal to coil is
therefore about 30 seconds.
[0035] Any of a variety of quenching devices may be used in the
practice of the present invention. Typically, the quenching station
is one in which a cooling fluid, either in liquid or gaseous form
is sprayed onto the hot feedstock to rapidly reduce its
temperature. Suitable cooling fluids include water, air, liquefied
gases such as carbon dioxide, and the like. It is preferred that
the quench be carried out quickly to reduce the temperature of the
hot feedstock rapidly to prevent substantial precipitation of
alloying elements from solid solution.
[0036] In general, the quench at station 51 reduces the temperature
of the feedstock as it emerges from the continuous caster from a
temperature of about 1000.degree. F. to the desired hot or warm
rolling temperature. In general, the feedstock will exit the quench
at station 51 with a temperature ranging from about 400.degree. to
900.degree. F., depending on alloy and temper desired. Water sprays
or an air quench may be used for this purpose.
[0037] Hot or warm rolling 53 is typically carried out at
temperatures within the range of about 400.degree. to 1020.degree.
F., more preferably 700.degree. to 1000.degree. F. The extent of
the reduction in thickness affected by the hot rolling step of the
present invention is intended to reach the required finish gauge.
This typically involves a reduction of about 55%, and the as-cast
gauge of the strip is adjusted so as to achieve this reduction. The
temperature of the sheet at the exit of the rolling station is
between about 300.degree. and 850.degree. F., more preferably
550.degree. to 800.degree. F., since the sheet is cooled by the
rolls during rolling.
[0038] Preferably, the thickness of the feedstock as it emerges
from the rolling station 53 will be about 0.02 to 0.15 inches, more
preferably about 0.03 to 0.08 inches.
[0039] The heating carried out at the heater 59 is determined by
the alloy and temper desired in the finished product. In one
preferred embodiment, for T tempers, the feedstock will be solution
heat-treated in-line, at temperatures above about 950.degree. F.,
preferably about 980.degree.-1000.degree. F. Heating is carried out
for a period of about 0.1 to 3 seconds, more preferably about 0.4
to 0.6 seconds.
[0040] In another preferred embodiment, when O temper is desired,
the feedstock will require annealing only, which can be achieved at
lower temperatures, typically about 700.degree. to 950 F..degree.,
more preferably about 800.degree.-900 F..degree., depending upon
the alloy. Again, heating is carried out for a period of about 0.1
to 3 seconds, more preferably about 0.4 to 0.6 seconds.
[0041] Similarly, the quenching at station 63 will depend upon the
temper desired in the final product. For example, feedstock which
has been solution heat-treated will be quenched, preferably air and
water quenched, to about 110.degree. to 250.degree. F., preferably
to about 160.degree.-180.degree. F. and then coiled. Preferably,
the quench at station 63 is a water quench or an air quench or a
combined quench in which water is applied first to bring the
temperature of the sheet to just above the Leidenfrost temperature
(about 550.degree. F. for many aluminum alloys) and is continued by
an air quench. This method will combine the rapid cooling advantage
of water quench with the low stress quench of airjets that will
provide a high quality surface in the product and will minimize
distortion. For heat treated products, an exit temperature of
200.degree. F. or below is preferred.
[0042] Products that have been annealed rather than heat-treated
will be quenched, preferably air- and water-quenched, to about
110.degree. to 720.degree. F., preferably to about 680.degree. to
700.degree. F. for some products and to lower temperatures around
200.degree. F. for other products that are subject to precipitation
of intermetallic compounds during cooling, and then coiled.
[0043] Although the process of the invention described thus far in
one embodiment having a single step hot or warm rolling to reach
the required final gauge, other embodiments are contemplated, and
any combination of hot and cold rolling may be used to reach
thinner gauges, for example gauges of about 0.007-0.075 inches. The
rolling mill arrangement for thin gauges could comprise a hot
rolling step, followed by hot and/or cold rolling steps as needed.
In such an arrangement, the anneal and solution heat treatment
station is to be placed after the final gauge is reached, followed
by the quench station. Additional in-line anneal steps and quenches
may be placed between rolling steps for intermediate anneal and for
keeping solute in solution, as needed. The pre-quench before hot
rolling needs to be included in any such arrangements for
adjustment of the strip temperature for grain size control. The
pre-quench step is a pre-requisite for alloys subject to hot
shortness.
[0044] FIG. 3 shows schematically an apparatus for one of many
alternative embodiments in which additional heating and rolling
steps are carried out. Metal is heated in a furnace 80 and the
molten metal is held in melter holders 81, 82. The molten metal is
passed through troughing 84 and is further prepared by degassing 86
and filtering 88. The tundish 90 supplies the molten metal to the
continuous caster 92, exemplified as a belt caster, although not
limited to this. The metal feedstock 94 which emerges from the
caster 92 is moved through optional shear 96 and trim 98 stations
for edge trimming and transverse cutting, after which it is passed
to an optional quenching station 100 for adjustment of rolling
temperature.
[0045] After quenching 100, the feedstock 94 is passed through a
hot rolling mill 102, from which it emerges at an intermediate
thickness. The feedstock 94 is then subjected to additional hot
milling 104 and cold milling 106, 108 to reach the desired final
gauge.
[0046] The feedstock 94 is then optionally trimmed 110 and then
annealed or solution heat-treated in heater 112. Following
annealing/solution heat treatment in the heater 112, the feedstock
94 optionally passes through a profile gauge 113, and is optionally
quenched at quenching station 114. The resulting sheet is subjected
to x-ray 116, 118 and surface inspection 120 and then optionally
coiled.
[0047] Suitable aluminum alloys for heat-treatable alloys include,
but are not limited to, those of the 2XXX, 6XXX and 7XXX Series.
Suitable non-heat-treatable alloys include, but are not limited to,
those of the 1XXX, 3XXX and 5XXX Series. The present invention is
applicable also to new and non-conventional alloys as it has a wide
operating window both with respect to casting, rolling and in-line
processing.
EXAMPLES
[0048] The following examples are intended to illustrate the
invention and should not be construed as limiting the invention in
any way.
Example 1
[0049] In-line fabrication of a heat-treatable alloy. A
heat-treatable aluminum alloy was processed in-line by the method
of the present invention. The composition of the cast was selected
from the range of 6022 Alloy that is used for auto panels. The
analysis of the melt was as follows:
1 Element Percentage by weight Si 0.8 Fe 0.1 Cu 0.1 Mn 0.1 Mg
0.7
[0050] The alloy was cast to a thickness of 0.085 inch at 250 feet
per minute speed and was processed in line by hot rolling in one
step to a finish gauge of 0.035 inches, followed by heating to a
temperature of 980.degree. F. for 1 second for solution heat
treatment after which it was quenched to 160.degree. F. by means of
water sprays and was coiled. Samples were then removed from the
outermost wraps of the coil for evaluation. One set of samples was
allowed to stabilize at room temperature for 4-10 days to reach T4
temper. A second set was subjected to a special pre-aging treatment
at 180.degree. F. for 8 hours before it was stabilized. This
special temper is called T43. The performance of the samples was
evaluated by several tests that included response to hemming,
uniaxial tension, equi-biaxial stretching (hydraulic bulge) and
aging in an auto paint-bake cycle. The results obtained were
compared with those obtained on sheet of the same alloy made by the
conventional ingot method. Deformed samples from the hydraulic
bulge test were also subjected to a simulated auto painting cycle
to check for surface quality and response to painting. In all
respects, the sheet fabricated in-line by the present method
performed as well as or better than that from the ingot method.
2TABLE 1 Tensile properties of 6022-T43 sheet fabricated in line by
the present method. Measurements were made after nine days of
natural aging on ASTM specimens. Cast number: 031009. pre-roll in
line ATC TYS UTS Elongation, % quench TFX F. quench, F. S number
ksi ksi uniform total r value r bar T43 (longitudinal) off 980 114
805656 18.6 36.6 25.5 30.4 1.079 off 1000 114 805658 19.3 37.2 23.6
26.7 1.144 Sheet from conventional typical 17.8 34.5 21.5 24.5
0.826 ingot - T43 T43 (45.degree. ) off 980 114 805656 18.5 36.4
24.2 28.0 0.760 off 1000 114 805658 19.6 37.6 25.4 29.7 0.725 Sheet
from conventional typical 17.0 33.4 24.5 26.9 0.602 ingot - T43 T43
(transverse) off 980 114 805656 18.4 36.2 22.1 24.5 0.988 0.897 off
1000 114 805658 19.0 36.7 23.6 26.3 0.889 0.896 Sheet from
conventional typical 16.6 32.5 22.8 26.4 0.642 0.668 ingot - T43
Customer requirements (min) 14.0 19.0 21.0 0.500 Notes: 1. T43
temper was obtained by holding samples at 180 F. for 8 hours in a
separate furnace after fabrication The time between fabrication and
entry of samples into furnace was less than 10 minutes.
[0051] Results of the tensile testing are shown in Table 1 for T43
temper sheet in comparison with those typical for sheet made from
ingot. It is noted that in all respects, the properties of the
sheet made by the present method exceeded the customer requirements
and compared very well with those for conventional sheet in the
same temper. With respect to the isotropy of the properties as
measured by the r values, for example, the sheet of the present
method obtained 0.897 compared to 0.668 for ingot. In these tests,
a generally higher strain hardening coefficient of 0.27 (compared
to 0.23 for ingot) was also found. Both of these two findings are
important because they suggest that the sheet of the present method
is more isotropic and better able to resist thinning during forming
operations. Similar observations applied also to T4 temper sheet
samples.
[0052] Flat hemming tests were done after 28 days of room
temperature aging. In these tests, a pre-stretch of 11% was applied
compared to 7% required in customer specifications. Even under
these more severe conditions, all samples obtained ail acceptable
rating of 2 or 1, Table 2. In similar testing, sheet made from
ingot shows an average of 2-3 in the longitudinal hems and 2 in
transverse hems. This suggests that the sheet fabricated in-line
has superior hemmability. Some samples were solution heat-treated
off-line in a salt bath after fabrication. When tested, these
samples, too, showed excellent hemming performance as seen in Table
2.
3TABLE 2 Flat hem rating (at 11% pre-stretch) after 28 days' of
natural aging for alloy 6022 at 0.035 inch gauge (cast number:
030820) pre-roll in-line in line gauge ATC hem rating quench
anneal, F. quench, F. inches S number L T comments C710 - T43
temper off 950 160 0.035 804908 2 2 fabricated in line off 950 160
0.035 804909 2 2 fabricated in line on off 104 0.035 804912 1 2
off-line heat treat: 1040 F./1 min. on 920 140 0.035 804914 2 2
off-line heat treat: 1010 F./1 min. Conventional ingot sheet - T43
temper "2-3" 2 Notes: 1. T43 temper was obtained by holding samples
at 180 F. for 8 hours in a separate furnace after fabrication The
time between fabrication and entry of samples into furnace was less
than 10 minutes. 2. Requirement for hemming: A rating of 2 or less
at 7% pre-stretch.
[0053] In equi-biaxial stretching by hydraulic bulge, the
performance of the sheet made in line was comparable to those of
sheet made from ingot as seen in stress strain curves in FIGS. 4a
and 4b. This observation applied both in T4 and in T43 temper. The
performance in this test was particularly important because it is
known that continuous-cast materials typically do not perform well
in this test due to the presence of center line segregation of
coarse intermetallic particles.
[0054] Response to paint-bake cycle was evaluated by holding the
samples in an oven at 338.degree. F. for a duration of 20 minutes
(Nissan cycle). The tensile yield strength of the samples increased
by up to 13 ksi by this treatment, Table 3. In all cases, the
required minimum of 27.5 ksi was met easily in the T43 temper. The
overall response in this temper was comparable to the average
performance of sheet made from DC ingot. As expected, the T4 temper
samples were somewhat unsatisfactory in this respect.
4TABLE 3 Paint bake response of alloy C710 produced in Reno at
rolled gauge of 0.035 inches. Cast number: 030820. Nissan/Toyota
paint bake cycle: 2% stretch, 338 F./20 minutes. TYS required: 27.5
ksi min. Natural pre-roll in line Date Age Sample TYS UTS .DELTA.YS
quench TFX F. quench, F. Temper SHT Test Days ID ksi ksi Elong %
ksi off 950 160 T4 20-Aug 27-Aug 7 804866-T 16.9 33.8 23.2 T4 + PB
in line 7 804866-T 25.8 37.7 20.8 8.9 off 950 160 T4 20-Aug 27-Aug
7 804867-T 16.8 34.0 23.0 T4 + PB in line 7 804867-T 26.0 37.8 20.2
9.2 off 950 160 T43 20-Aug 27-Aug 7 804908-T 16.8 33.8 22.0 T43 +
PB in line 7 804908-T 27.6 39.0 19.5 10.8 off 950 160 T43 20-Aug
27-Aug 7 804909-T 16.6 33.8 25.0 T43 + PB in line 7 804909-T 29.6
40.5 19.5 13.0 on off 104 T43 21-Aug 27-Aug 6 804912-T 18.4 35.2
24.2 T43 + PB 1040/1 min 6 804912-T 28.9 40.5 23.8 10.5 on 920 140
T43 22-Aug 27-Aug 5 804914-T 18.6 35.2 25.0 T43 + PB 1010/1 min 5
804914-T 30.1 41.1 22.5 11.5 DC ingot T43 7 17.1 33.3 26.3 typical
T43 + PB 7 JIS tests 30.5 40.9 26.4 13.4 Notes: 1. Samples were
held at 180 F. for 8 hours for the T43 temper (quench aged). 2.
Samples 804912 and 804914: Laboratory solution heat treat was
carried out in a salt bath under conditions indicated followed by
water quenching.
[0055] The deformed hydraulic bulge specimens were inspected for
surface quality and were found to show no undesirable features such
as orange peel, blisters, etc. Selected bulge samples were
subjected to a simulated auto-paint cycle. FIG. 5 shows excellent
painted surface quality with no paint brush lines, blisters or
linear features.
[0056] Sheet at finished gauge was examined for grain size and was
found to have a mean grain size of 27 .quadrature.m in the
longitudinal and 36 .quadrature.m in the thickness direction, FIG.
6. This is substantially finer than that of 50-55 .quadrature.m
typical for sheet made from ingot. Since a fine grain size is
recognized to be generally beneficial, it is likely that a part of
the good/superior properties of the sheet made by the present
method was due to this factor. It was found that even finer grain
size could be obtained in the present method by rapidly cooling the
strip to about 700.degree. F. before it is rolled. This effect is
illustrated in FIGS. 6a and 6b where the two samples are shown side
by side. The grain size of the cooled sample (6b) was 20
.quadrature.m in longitudinal and 27 .quadrature.m in transverse
direction, which are 7 and 9 .quadrature.m, respectively, finer
than those observed in the sheet which had no pre-quench cooling
(6a).
[0057] Samples of as-cast strip were quenched and examined
metallographically to further understand the benefits of thin strip
casting. The samples showed the three-layered structure
characteristic of the Alcoa strip casting process, FIG. 7a. The
surfaces of the strip were clean (no liquation, blisters or other
surface defects) with a fine microstructure, FIG. 7b. Unlike the
material continuously cast by Hazelett belt casters or roll
casters, the strip of the present method showed no centerline
segregation of coarse intermetallic compounds. On the contrary, the
last liquid to solidify had formed fine second phase particles
between grains in a center zone that covered about 25% of the
section, FIG. 7c. This absence of a marked centerline segregation
in the present method provided the good mechanical properties
observed, especially in the equi-biaxial stretch tests. Most of the
second phase particles observed were AlFeSi phase with an average
size <1 .quadrature.m, FIG. 7d. Some Mg2Si particles were seen
in the center zone of the sample, but none was noted in the outer
"shells", FIG. 7b. This suggested that the rapid solidification in
the caster was able to keep the solute in solution in the outer
zones of the structure. This factor, combined with the fine overall
microstructure of the strip (see Table 4), enabled the complete
dissolution of all solute at substantially lower solution heat
treatment temperatures of 950.degree.-980.degree. F. than
1060.degree. F. that would be needed for sheet prepared from DC
ingot.
5TABLE 4 Characteristics of constituent particles and pores found
in as -cast samples of alloy C710 (cast number: 030820) pores
constituents av. diam. area av. diam. area location in strip .mu.m
% .mu.m % center, transverse 0.37 0.37 0.50 0.143 center,
longitudinal 0.38 0.34 0.31 0.077 average 0.38 0.36 0.41 0.11
shell, transverse 0.35 0.21 0.32 0.23 shell, longitudinal 0.33 0.25
0.28 0.19 average 0.34 0.23 0.30 0.21 Notes: 1. The constituents
were mainly AlFeSi phase. Small amount of Mg.sub.2Si was also seen
in center zone. 2. Each result is average 20 different frames.
Example 2
[0058] In-line fabrication of a non-heat treatable alloy. A
non-heat-treatable aluminum alloy was processed by the method of
the present invention. The composition of the cast was selected
from the range of the 5754 Alloy that is used for auto inner panels
and reinforcements. The analysis of the melt was as follows:
6 Element Percentage by weight Si 0.2 Fe 0.2 Cu 0.1 Mn 0.2 Mg
3.5
[0059] The alloy was cast to a strip thickness of 0.085 inch at 250
feet per minute speed. The strip was first cooled to about
700.degree. F. by water sprays placed before the rolling mill,
after which it was immediately processed in-line by hot rolling in
one step to a finish gauge of 0.040 inches, followed by heating to
a temperature of 900.degree. F. for 1 second for recrystallization
anneal after which it was quenched to 190.degree. F. by means of
water sprays and was coiled. The performance of the samples was
evaluated by uniaxial tensile tests and by limiting dome height
(LDH).
[0060] Results of the tensile testing are shown in Table 5. The TYS
and elongation of the sample in the longitudinal direction were
15.2 ksi and 25.7%, respectively, well above the minimum of 12 ksi
and 17% required for Alloy 5754. UTS value was 35.1 ksi, in the
middle of the range specified as 29-39 ksi. In the limiting dome
height test, a value of 0.952 inch was measured that met the
required minimum of 0.92 inch. These values compared well with
typical properties reported for sheet prepared from DC ingot. Sheet
of the present invention had a higher elongation, higher UTS and
higher strain hardening coefficient n. A higher anisotropy value r
was expected, but was not verified in the testing of this sample.
The r value was 0.864 compared to 0.92 for DC sheet.
[0061] Sheet at finished gauge was examined for grain size and was
found to have a mean grain size of 11-14 .quadrature.m (ASTM 9.5).
This is substantially finer than that of 16 .quadrature.m typical
for sheet made from ingot. Since a fine grain size is recognized to
be generally beneficial, it is likely that a part of the
good/superior properties of the sheet made by the present method
was due to this factor.
[0062] Samples of as-cast strip were quenched and examined
metallographically. Despite differences in chemical composition,
the as-cast samples showed the same three-layered structure as that
described above for Alloy 6022, FIG. 8. This confirms that the
three-layered fine microstructure that enables in-line processing
of the strip described in this invention, is a characteristic of
the Alcoa strip casting process.
[0063] Variations of the fabrication path were also investigated.
In one test, 0.049 inch gauge sheet was fabricated in-line without
the in-line anneal, Table 5. The sample was then flash-annealed
off-line in a salt bath at 975.degree. F. for 15 s followed by
water quenching. That sample showed similar properties and a high r
value comparable to those described above for sheet fabricated with
in-line anneal. This equivalence conformed that in-line fabrication
is able to develop the full properties of the alloy in O-temper. In
another test, the strip was hot rolled in-line to 0.049 inch gauge
and was quenched to 160.degree. F. with no in-line anneal. It was
then cold-rolled to 0.035 inch gauge and was flash-annealed at
950.degree. F. for 15 seconds, Table 5. That sheet, too, developed
good mechanical properties. These observations suggested that hot
and cold rolling could be combined with an-in line final anneal to
make sheet of a wide range of thickness of O-temper products by the
present invention.
7TABLE 5 Uniaxial tensile test results for Al--3.5% Mg AX alloy
processed in line by the present invention. test hot roll flow path
L gauge, gauge, pre-roll anneal, 45 TYS UTS elongation. % S number
Reno cast # alloy inch inch quench F. quench, F. T ksi ksi uniform
total r value r bar n value 805314 030902B Al--3.5% 0.033 0.049 on
off on L 16.5 36.2 17.9 22.3 0.781 0.947 0.309 Mg 45 16.8 35.3 24.1
28.8 1.120 0.311 T 16.1 35.6 21.3 22.2 0.766 0.306 805035 030902B
Al--3.5% 0.049 0.049 on off on L 15.6 35.9 19.2 20.8 0.835 1.05
0.314 Mg 45 15.4 35.5 21.7 22.5 1.200 0.303 T 15.8 35.8 22.4 26.9
0.963 0.317 805747 31021 Al--3.5% 0.040 0.040 on 900 190 L 15.2
35.1 23.2 25.7 0.778 0.864 0.323 Mg 45 14.6 34.8 23.1 25.3 0.938
0.326 T 14.6 34.7 23.2 24.5 0.802 0.322 Alloy 5754 for comparison
DC ingot 5754 0.036 L 14.6 29.7 20.4 22.2 0.978 0.92 0.301 45 14.4
28.9 21.2 22.0 0.809 0.303 T 14.6 28.9 19.7 22.4 1.082 0.305 Notes
1. AA registered requirement for 5754: TYS = 12 ksi min. (L). UTS =
29-39 ksi (L). Elongotion: 17% min(L). LDH = 0.92 inches min. 2.
Samples 805314 and 805035 were annelaed off-line in a salt bath at
950 F. and 975 F., respectively, for 15 seconds following which
they were quenched in water.
Example 3
[0064] In-line fabrication of a non-heat-treatable ultra high Mg
alloy. An Al-10% Mg alloy was processed by the method of the
present invention. The composition of the melt was as follows:
8 Element Percentage by weight Si 0.2 Fe 0.2 Cu 0.2 Mn 0.3 Mg
9.5
[0065] The alloy was cast to a strip thickness of 0.083 inch at 230
feet per minute speed. The strip was first cooled to about
650.degree. F. by water sprays placed before the rolling mill. It
was then immediately hot-rolled in-line in one step to a finish
gauge of 0.035 inch followed by an anneal at 860.degree. F. for 1
second for recrystallization and spray quenching to 190.degree. F.
The sheet was then coiled. Performance of the sheet in O-temper was
evaluated by uniaxial tensile tests on ASTM-4 d samples removed
from the last wraps of the coil. In the longitudinal direction, the
samples showed TYS and UTS values of 32.4 and 58.7 ksi,
respectively. These very high strength levels, higher by about 30%
than those reported for similar alloys, were accompanied by high
elongation: 32.5% total elongation and 26.6% uniform elongation.
The samples showed very fine grain structure of .about.10 .mu.m
size.
Example 4
[0066] In-line fabrication of a recyclable auto sheet alloy. An
Al-1.4% Mg alloy was processed by the method of the present
invention. The composition of the melt was as follows:
9 Element Percentage by weight Si 0.2 Fe 0.2 Cu 0.2 Mn 0.2 Mg
1.4
[0067] The alloy was cast to a strip thickness of 0.086 inch at 240
feet per minute speed. It was rolled to 0.04 inch gauge in one
step, flash annealed at 950 F, following which it was water
quenched and coiled. The quenching of the rolled sheet was done in
two different ways to obtain O temper and T temper by different
settings of the post quench 63. For the T temper, the strip was
pre-quenched by quench 53 to about 700 F before warm-rolling to
gauge and was post-quenched to 170 F (sample #: 804995 in Table 6).
In a second case, the sheet was post quenched to around 700 F and
was warm coiled to create O temper. The O-temper coil was done both
by warm rolling (sample: 804997) and by hot rolling (sample:
804999).
[0068] Performance of the sheet was evaluated by uniaxial tensile
tests on ASTM-4 d samples and by hydraulic bulge test. In the T
temper, the sheet showed tensile yield strength, ultimate tensile
strength and elongation values well above the requirements for
alloy 5754 in O-temper and as good as those available in sheet made
by the conventional ingot method, Table 6. In the hydraulic bulge
test, too, the performance of the T temper AX-07 was very close to
that of alloy 5754, FIG. 8. This suggests that AX-07 in T temper
made by the method of the present invention can be used to replace
the 5754 sheet in inner body parts and reinforcements in auto
applications. Such a replacement would have the advantage of making
those parts recyclable into the 6xxx series alloys, by virtue of
the lower Mg content, used in outer skin parts of autos without the
need for separation.
[0069] Samples were also tested in O-temper made by the present
method. In that temper, the strength levels were lower, around 8.8
ksi yield strength and 23 ksi tensile strength. The performance in
the hydraulic bulge test improved equaling that of conventional
5754 as may be seen in FIG. 8. This temper thus offers a material
that would be formed more easily at lower press loads.
[0070] In a preferred embodiment of the method shown in FIG. 1, the
present invention provides a method of manufacturing T or O temper
aluminum alloy sheet in a continuous in-line sequence comprising:
(i) casting a thin aluminum alloy strip having a first thickness;
(ii) optionally quenching the strip to a hot or warm rolling
temperature; (iii) hot or warm rolling the strip to substantially a
final thickness about 10-65% reduced from the first thickness; (iv)
selectively annealing the strip to achieve an O temper or solution
heat treating the strip to achieve a T temper; and, (v) if a T
temper is desired, quenching the strip subsequent to the solution
heat treating.
[0071] The alloys selected for casting can vary widely depending on
the final product and temper desired, for example, series 1XXX,
2XXX, 3XXX, 5XXX, 6XXX or 7XXX alloys. For example, a composition
selected for a particular 6022 alloy typically used for auto panels
would have, by percent weight, 0.8 Si, 0.1 Fe, 0.1 Cu, 0.1 Mn and
0.7 Mg, the remainder Aluminum. Either low or high manganese levels
may be crystallized utilizing the techniques of the present
invention. For example, manganese levels lower than 0.25 wt. % may
be used if desired, but higher levels may be used if desired as
well.
[0072] The strip is thin-cast from the caster to a thickness
between about 0.06 and 0.15 inches, preferably between 0.08 and
0.13 inches. The speed of the caster corresponds to the thickness
of the strip as cast, such that the greater the thickness of the
strip, the slower the casting speed. For example, the strip may
emerge from the caster at a speed of about 260 feet per minute to
form a strip with 0.08 thickness, and a speed of about 150 feet per
minute to form a strip with 0.13 thickness, with intermediate
thicknesses formed by intermediate speeds.
[0073] The strip is preferably thin-cast such that the final
thickness of the strip is about 10-65% reduced from the first
thickness. This is to be contrasted with prior art casting
processes, which produce a final thickness reduced about 80% from
the first thickness. Thickness of the strip as cast can be
determined by deciding what the desired gauge thickness of the
temper is and working backward. Thus, if the final gauge of the T
or O temper is 0.07 inches, the thickness of the strip as cast can
be adjusted to 0.11 inches, with the hot or warm rolling step
adjusted to reduce the strip by 36.3%.
[0074] The thin casting size, in addition to the rapid speed of the
steps of the method facilitated by the in-line process, enables the
solute of the strip to stay in solution throughout the process.
Essentially, the thin size allows the molten material to rapidly
solidify, thereby keeping solute of the material from falling out
of solution. The rapid solidification in the caster improves
surface quality of the strip by reducing blemishes, blisters or
other defects on the surface of the strip, as shown in FIG. 7b.
Further, as shown in FIG. 7c, there is no centerline segregation of
coarse inter-metallic compounds.
[0075] The strip generally exits the caster at a range between
about 900 and 1050.degree. F., preferably at about 1000.degree. F.
Following casting, the strip is preferably quenched with a first
quench. The grain size of the strip, and of the final T or O
temper, is finer if the strip is quenched prior to the hot or warm
rolling step as opposed to not quenching. Most preferably, the
strip exits the quench at about 400 to 900.degree. F.
[0076] After the preferred first quench, the strip is immediately
fed into a single hot or warm rolling stand. Hot or warm rolling is
typically carried out at temperatures within the range of about
400.degree. F. to 1020.degree. F., more preferably between
700.degree. F. and 1000.degree. F. The final thickness of the
strip, after the hot or warm rolling step, is about 10-65% reduced
as compared to the first thickness of the strip as cast. Typical
final thickness is about 0.02 to 0.13 inches, most preferably about
0.03 and 0.08 inches. The reduction of the thin cast strip is
preferably done in a single in-line rolling pass, thereby
increasing the speed and reducing the cost generally associated
with multiple rolling stands. The single rolling stand provides the
benefit of reducing initial capital investment in the system and
reducing processing time of the strip. While most preferably only
one rolling stand is included in the continuous in-line process,
other rolling stations may be included in the processes if the
final thickness of the temper is about 10-65% reduced. In such
multiple rolling stations, the final thickness of the sheet is
reduced by 10-65% at each station until the desired final thickness
is reached.
[0077] After hot rolling, the strip is preferably annealed for an O
temper or solution heat treated for a T temper. To form a T temper,
the strip is preferably solution heat treated about 980.degree. and
1000.degree. F., for a period of about 0.1 to 3 seconds, more
preferably about 0.4 to 0.6 seconds. To form an O temper, the strip
is preferably annealed about 700.degree. to 950.degree. F., for a
period of about 0.1 to 3 seconds, more preferably about 0.4 to 0.6
seconds.
[0078] A second quenching step can be employed after the annealing
or solution heat treating, if desired. This quenching step, or lack
thereof, helps guide the alloy to its final temper of T4, T5, T6,
T8, O, or other temper desired known by one skilled in the art of
heat treating aluminum. The strip that has been solution heat
treated is preferably rapidly quenched to between about 110.degree.
to 720.degree. F. by air, or by a combination of air and water,
wherein the water is applied to first bring the temperature of the
sheet to about the Leidenfrost temperature (about 550.degree. F.
for many aluminum alloys) and is continued by an air quench.
[0079] To create a T4 temper alloy, the strip is quenched to a
range of about 110.degree. to 200.degree. F., preferably about
160.degree. to 180.degree. F. The alloy may further be permitted to
cool after the quench, such that the alloy is preferably coiled at
a temperature range of about 130.degree. to 150.degree. F.
[0080] A T6 temper is formed by quenching the alloy after solution
heat treating to about 250.degree. to 350.degree. F. The aging step
occurs during the cooling of the coil from the coiling temperature
to room temperature. The quenching is done in the same manner and
rate as the quenching to form the T4 alloy, preferably by air or a
combination of air and water. Generally, the rate of cooling to
form a T6 temper is the same as the rate to form a T4 temper.
However, the cooling is conducted for a shorter length of time to
provide the higher final temperature. In alternate embodiments, the
alloy could be heated down to about 110.degree. to 200.degree. F.
and then reheated in-line at a reheating station, up to the desired
temperature of about 250.degree. to 350.degree. F.
[0081] An O temper may or may not include a second quench after
annealing. Annealing of the strip is generally achieved at about
700.degree. to 1050.degree. F., more preferably about
800.degree.-950.degree. F. Coiling of an O temper strip is
generally conducted at about 400.degree. to 900.degree. F., more
preferably at about 670.degree.-730.degree. F. The strip may be
quenched to the desired coiling temperatures after annealing.
Alternatively, it maybe ambiently cooled to the desired
temperature.
[0082] After the second quench, the resultant strip has tension,
wherein tension is defined as a state where the strip has
solidified to a point that it possesses the strength needed to
permit the placing of tension onto it. Significantly, the
stabilizing effects of cold rolling are not required in order to
produce tension. Thus, the alloy may be tension leveled prior to
coiling without first stabilizing the alloy through additional
steps such as cold rolling. After optionally tension leveling, the
alloy is preferably coiled. Coiling can be performed by any means
known in the art.
[0083] The method of the invention, beginning with casting and
ending with second quench or anneal, is completed is 10 to 50
seconds, most preferably in about 20-30 seconds. (The short time is
enabled through the single in-line sequence, the rapid formation
and solidification of the strip in the caster, the limitation of a
rolling step to a single rolling step, and the lack of need for a
final cold rolling step to develop tension in the alloy. The short
time period enables the creation of T or O tempers with
dramatically reduced cost by substantially decreasing the energy
per unit created and the amount of equipment required to perform
the method.
[0084] As shown in FIG. 5, the surface quality of the T or O temper
alloys produced by the invention is improved over the prior art,
with no paint brush lines, blisters or linear features. The high
surface quality is achieved in part through the short formation
time of the T or O temper from casting to completion, the rapid
increase and decrease of temperature, and the decreased number of
rolling stations.
[0085] The tempers of the invention match the strength of alloys
most advantageously used in auto panels and reinforcements, such as
6XXX and 5XXX series alloys disclosed in examples 1 and 2, while
costing substantially less to form. The estimated cost of producing
T or O tempers that favorably compare in strength to 6XXX and 5XXX
alloys is about 40% less than the production cost of those alloys.
Among other anticipated use of tempers created by the invention
herein is within the aerospace industry, typically alloys in the
2XXX, 6XXX and 7XXX series. Further, additional objects can be
derived from the invention from the above series, as well as the
1XXX or 3XXX series. The strip of the desired T or O temper
produced by the present invention can be formed into auto body
parts, auto body reinforcements, aerospace panels or other products
by any means known in the art.
[0086] Whereas particular embodiments of this invention have been
described above for purposes of illustration, it will be evident to
those skilled in the art that numerous variations of the details of
the present invention may be made without departing from the
invention as defined in the appending claims.
* * * * *