Title:
In-line method of making T or O temper aluminum alloy sheets
Kind Code:
A1


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, US)
Tomes Jr., David Allen (Sparks, NV, US)
Timmons, David Wayne (Reno, NV, US)
Wyatt-mair, Gavin Frederick (Lafayette, CA, US)
Application Number:
11/128008
Publication Date:
09/29/2005
Filing Date:
05/12/2005
Primary Class:
International Classes:
C22C1/04; C22F1/04; (IPC1-7): C22F1/04
View Patent Images:



Primary Examiner:
MORILLO, JANELL COMBS
Attorney, Agent or Firm:
HOWMET AEROSPACE INC. (FLORHAM PARK, NJ, US)
Claims:
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° to 200° 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° F. to 350° 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° to 200° F. and reheated to a temperature range of about 250° F. to 350° 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° to 200° F. to achieve a T4 temper.

23. The method of claim 18, wherein quench quenches the strip to a temperature range of about 250° F. to 350° F. to achieve a T6 temper.

23. The method of claim 18, wherein the quench quenches strip to a temperature range of about 110° to 200° F. and reheated to a temperature range of about 250° F. to 350° 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° to 200° 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° F. to 350° 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° to 200° F. and reheated to a temperature range of about 250° F. to 350° 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° to 200° 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° F. to 350° 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° to 200° F. and reheated to a temperature range of about 250° F. to 350° 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° to 200° 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° F. to 350° 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° to 200° F. and reheated to a temperature range of about 250° F. to 350° 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° to 200° 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° F. to 350° 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° to 200° F. and reheated to a temperature range of about 250° F. to 350° 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

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

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

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° 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.

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.

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° 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° and 1200° F. for less than 120 seconds, followed by quenching, rolling and aging.

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° F., followed by recoiling the sheet.

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

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.

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.

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.

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.

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.

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

The invention is further illustrated by the following drawings in which:

FIG. 1 is a flow chart of the steps of the method of the present invention, in one embodiment;

FIG. 2 is a schematic diagram of one embodiment of the apparatus used in carrying out the method of the present invention.

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.

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.

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.

FIG. 5 is a picture of Sample 804908 (Alloy 6022 in T43 temper) after e-coating.

FIG. 6a is a picture demonstrating the grain size of Alloy 6022 rolled in-line to 0.035 inch gauge without pre-quench.

FIG. 6b is a picture demonstrating the grain size of Alloy 6022 rolled in-line to 0.035 inch gauge.

FIG. 7a depicts an as-cast structure in Alloy 6022 transverse section.

FIG. 7b consists of two pictures demonstrating the surface and shell structure of Alloy 6022 in as-cast condition in transverse section.

FIG. 7c is a picture of the center zone structure of Alloy 6022 in as-cast condition in transverse section.

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.

FIG. 8 depicts the as-cast microstructure of Al+3.5% Mg alloy in transverse direction.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

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.

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° to 900° F.

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° F. This condition is then maintained by quenching of the metal for the purpose of strengthening the final product by controlled precipitation (aging).

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.

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.

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.

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.

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.

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° 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° to 900° F., depending on alloy and temper desired. Water sprays or an air quench may be used for this purpose.

Hot or warm rolling 53 is typically carried out at temperatures within the range of about 400° to 1020° F., more preferably 700° to 1000° 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° and 850° F., more preferably 550° to 800° F., since the sheet is cooled by the rolls during rolling.

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.

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° F., preferably about 980°-1000° F. Heating is carried out for a period of about 0.1 to 3 seconds, more preferably about 0.4 to 0.6 seconds.

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° to 950 F.°, more preferably about 800°-900 F.°, 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.

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° to 250° F., preferably to about 160°-180° 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° 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° F. or below is preferred.

Products that have been annealed rather than heat-treated will be quenched, preferably air- and water-quenched, to about 110° to 720° F., preferably to about 680° to 700° F. for some products and to lower temperatures around 200° F. for other products that are subject to precipitation of intermetallic compounds during cooling, and then coiled.

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.

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.

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.

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.

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

The following examples are intended to illustrate the invention and should not be construed as limiting the invention in any way.

Example 1

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:

ElementPercentage by weight
Si0.8
Fe0.1
Cu0.1
Mn0.1
Mg0.7

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° F. for 1 second for solution heat treatment after which it was quenched to 160° 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° 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.

TABLE 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-rollin lineATCTYSUTSElongation, %
quenchTFX F.quench, F.S numberksiksiuniformtotalr valuer bar
T43 (longitudinal)
off 98011480565618.636.625.530.41.079
off100011480565819.337.223.626.71.144
Sheet from conventionaltypical17.834.521.524.50.826
ingot - T43
T43 (45° )
off 98011480565618.536.424.228.00.760
off100011480565819.637.625.429.70.725
Sheet from conventionaltypical17.033.424.526.90.602
ingot - T43
T43 (transverse)
off 98011480565618.436.222.124.50.9880.897
off100011480565819.036.723.626.30.8890.896
Sheet from conventionaltypical16.632.522.826.40.6420.668
ingot - T43
Customer requirements (min)14.019.021.00.500

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.

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.

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.

TABLE 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-rollin-linein linegaugeATChem rating
quenchanneal, F.quench, F.inchesS numberLTcomments
C710 - T43 temper
off9501600.03580490822fabricated in line
off9501600.03580490922fabricated in line
onoff1040.03580491212off-line heat treat: 1040 F./1 min.
on9201400.03580491422off-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.

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.

Response to paint-bake cycle was evaluated by holding the samples in an oven at 338° 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.

TABLE 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-rollin lineDateAgeSampleTYSUTSΔYS
quenchTFX F.quench, F.TemperSHTTestDaysIDksiksiElong %ksi
off950160T420-Aug27-Aug7804866-T16.933.823.2
T4 + PBin line7804866-T25.837.720.88.9
off950160T420-Aug27-Aug7804867-T16.834.023.0
T4 + PBin line7804867-T26.037.820.29.2
off950160T4320-Aug27-Aug7804908-T16.833.822.0
T43 + PBin line7804908-T27.639.019.510.8
off950160T4320-Aug27-Aug7804909-T16.633.825.0
T43 + PBin line7804909-T29.640.519.513.0
onoff104T4321-Aug27-Aug6804912-T18.435.224.2
T43 + PB1040/1 min6804912-T28.940.523.810.5
on920140T4322-Aug27-Aug5804914-T18.635.225.0
T43 + PB1010/1 min5804914-T30.141.122.511.5
DC ingotT43717.133.326.3
typicalT43 + PB7JIS tests30.540.926.413.4

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.

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.

Sheet at finished gauge was examined for grain size and was found to have a mean grain size of 27 □m in the longitudinal and 36 □m in the thickness direction, FIG. 6. This is substantially finer than that of 50-55 □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° 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 □m in longitudinal and 27 □m in transverse direction, which are 7 and 9 □m, respectively, finer than those observed in the sheet which had no pre-quench cooling (6a).

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 □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°-980° F. than 1060° F. that would be needed for sheet prepared from DC ingot.

TABLE 4
Characteristics of constituent particles and pores found in as -cast
samples of alloy C710 (cast number: 030820)
poresconstituents
av. diam.areaav. diam.area
location in stripμm%μm%
center, transverse0.370.370.500.143
center, longitudinal0.380.340.310.077
average0.380.360.410.11
shell, transverse0.350.210.320.23
shell, longitudinal0.330.250.280.19
average0.340.230.300.21

Notes:

1. The constituents were mainly AlFeSi phase. Small amount of Mg2Si was also seen in center zone.

2. Each result is average 20 different frames.

Example 2

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:

ElementPercentage by weight
Si0.2
Fe0.2
Cu0.1
Mn0.2
Mg3.5

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° 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° F. for 1 second for recrystallization anneal after which it was quenched to 190° 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).

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.

Sheet at finished gauge was examined for grain size and was found to have a mean grain size of 11-14 □m (ASTM 9.5). This is substantially finer than that of 16 □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.

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.

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° 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° F. with no in-line anneal. It was then cold-rolled to 0.035 inch gauge and was flash-annealed at 950° 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.

TABLE 5
Uniaxial tensile test results for Al—3.5% Mg AX alloy processed in line by the present invention.
testhot rollflow pathL
gauge,gauge,pre-rollanneal,45TYSUTSelongation. %
S numberReno cast #alloyinchinchquenchF.quench, F.Tksiksiuniformtotalr valuer barn value
805314030902BAl—3.5%0.0330.049onoffonL16.536.217.922.30.7810.9470.309
Mg4516.835.324.128.81.1200.311
T16.135.621.322.20.7660.306
805035030902BAl—3.5%0.0490.049onoffonL15.635.919.220.80.8351.05 0.314
Mg4515.435.521.722.51.2000.303
T15.835.822.426.90.9630.317
80574731021Al—3.5%0.0400.040on900190L15.235.123.225.70.7780.8640.323
Mg4514.634.823.125.30.9380.326
T14.634.723.224.50.8020.322
Alloy 5754 for comparison
DC ingot57540.036L14.629.720.422.20.9780.920.301
4514.428.921.222.00.8090.303
T14.628.919.722.41.0820.305

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

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:

ElementPercentage by weight
Si0.2
Fe0.2
Cu0.2
Mn0.3
Mg9.5

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° 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° F. for 1 second for recrystallization and spray quenching to 190° 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 ˜10 μm size.

Example 4

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:

ElementPercentage by weight
Si0.2
Fe0.2
Cu0.2
Mn0.2
Mg1.4

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).

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.

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.

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.

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.

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.

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%.

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.

The strip generally exits the caster at a range between about 900 and 1050° F., preferably at about 1000° 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° F.

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° F. to 1020° F., more preferably between 700° F. and 1000° 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.

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° and 1000° 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° to 950° F., for a period of about 0.1 to 3 seconds, more preferably about 0.4 to 0.6 seconds.

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° to 720° 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° F. for many aluminum alloys) and is continued by an air quench.

To create a T4 temper alloy, the strip is quenched to a range of about 110° to 200° F., preferably about 160° to 180° 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° to 150° F.

A T6 temper is formed by quenching the alloy after solution heat treating to about 250° to 350° 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° to 200° F. and then reheated in-line at a reheating station, up to the desired temperature of about 250° to 350° F.

An O temper may or may not include a second quench after annealing. Annealing of the strip is generally achieved at about 700° to 1050° F., more preferably about 800°-950° F. Coiling of an O temper strip is generally conducted at about 400° to 900° F., more preferably at about 670°-730° F. The strip may be quenched to the desired coiling temperatures after annealing. Alternatively, it maybe ambiently cooled to the desired temperature.

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.

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.

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.

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.

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.