METHOD OF PRODUCING A HIGH-ENERGY HYDROFORMED STRUCTURE FROM A 2XXX-SERIES ALLOY

Abstract

A method of producing an integrated monolithic aluminum structure, comprising: providing an aluminum alloy plate with a thickness of at least 38.1 mm, wherein the plate is a 2xxx-series alloy in a T3-temper and has a composition comprising, in wt. %: Cu 3.8-4.5, Mn 0.3-0.8, Mg 1.1-1.6, Si up to 0.15, Fe up to 0.20, Cr up to 0.10, Zn up to 0.25, Ti up to 0.15, Ag up to 0.10, balance aluminum; optionally pre-machining the plate to an intermediate machined structure; high-energy hydroforming the plate or intermediate structure against a rigid die forming surface having a desired curvature contour of the integrated monolithic aluminum structure, causing the plate or the intermediate structure to conform to the forming surface contour; machining or mechanical milling the high-energy formed structure to a near-final or final machined integrated monolithic aluminum structure; ageing the final integrated monolithic aluminum structure to a desired temper.

Claims

1-15. (canceled)

16. A method of producing an integrated monolithic aluminum structure, the method comprising the steps of: providing an aluminum alloy plate with a predetermined thickness of at least 31.75 mm, wherein the aluminum alloy plate is a 2xxx-series alloy provided in a T3-temper, and wherein the 2xxx-series alloy has a composition comprising, in wt. %: Cu 3.8% to 4.5%, Mn 0.3% to 0.8%, Mg 0.9% to 1.6%, Si up to 0.15%, Fe up to 0.20%, Cr up to 0.10%, Zn up to 0.25%, Ti up to 0.15%, Ag up to 0.10%, impurities and balance aluminum; optionally pre-machining of the aluminum alloy plate to an intermediate machined structure; high-energy hydroforming of the plate or optional intermediate machined structure against a forming surface of a rigid die having a contour in accordance with a desired curvature of the integrated monolithic aluminum structure, the high-energy forming causing the plate or the intermediate machined structure to conform to the contour of the forming surface to at least one of a uniaxial curvature and a biaxial curvature as a high-energy formed structure; machining or mechanical milling of the high-energy formed structure to a near-final or final machined integrated monolithic aluminum structure; and ageing of the final integrated monolithic aluminum structure to a desired temper.

17. The method according to claim 16, wherein the high-energy hydroforming step is by explosive forming.

18. The method according to claim 16, wherein the high-energy hydroforming step is by electrohydraulic forming.

19. The method according to claim 16, wherein following the high-energy forming operation, in that order, the high-energy formed structure is machined to a final machined integrated monolithic aluminum structure and then aged to a desired temper.

20. The method according to claim 16, wherein the high-energy hydroforming operation, in that order, the high-energy formed structure is aged to a desired temper and then machined to a final machined integrated monolithic aluminum structure.

21. The method according to claim 16, wherein following the high-energy hydroforming operation, the high-energy formed structure is stress-relieved, preferably by compressive forming, followed by machining and ageing to a desired temper of the integrated monolithic aluminum structure.

22. The method according to claim 16, wherein following high-energy hydroforming operation, the high-energy formed structure is stress-relieved, followed by machining and ageing to a desired temper of the integrated monolithic aluminum structure.

23. The method according to claim 22, wherein the high-energy formed structure is stress-relieved by compressive forming in a next high-energy hydroforming step.

24. The method according to claim 16, wherein the predetermined thickness of the aluminum alloy plate is at least 50.8 mm.

25. The method according to claim 16, wherein the predetermined thickness of the aluminum alloy plate is at least 63.5 mm.

26. The method according to claim 16, wherein the predetermined thickness of the aluminum alloy plate is at most 127 mm.

27. The method according to claim 26, wherein the predetermined thickness of the aluminum alloy plate is at most 114.3 mm.

28. The method according to claim 16, wherein the ageing of the integrated monolithic aluminum structure is to a desired temper selected from the group of: T3, T4, T6, and T8.

29. The method according to claim 16, wherein the ageing of the integrated monolithic aluminum structure is to a T8 temper.

30. The method according to claim 29, wherein the ageing of the integrated monolithic aluminum structure is to a T852, T87 or T89 temper.

31. The method according to claim 16, wherein the 2xxx-series aluminum alloy has a Cu-content of 3.8% to 4.3%.

32. The method according to claim 31, wherein the 2xxx-series aluminum alloy has a CU-content of 3.8% to 4.1%.

33. The method according to claim 16, wherein the pre-machining and final machining comprises high-speed machining, preferably comprises numerically-controlled machining.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The invention shall also be described with reference to the appended drawings, in which:

[0065] FIG. 1 shows a flow chart illustrating one embodiment of the method according to this invention;

[0066] FIG. 2 shows a flow chart illustrating another embodiment of the method according to this invention; and

[0067] FIGS. 3A, 3B and 3C show cross-sectional side-views of an aluminum plate progressing through stages of a forming process from a rough-shaped metal plate into a shaped, near-finally shaped and finally-shaped workpiece, according to aspects of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0068] In FIG. 1, the method comprises, in that order, a first process step of providing an 2xxx-series aluminum alloy plate material having a composition as herein described and claimed in a T3-temper and having a predetermined thickness of at least 38.1 mm, with preferred thicker gauges. In a next process step, the plate material is pre-machined (this is an optional process step) into an intermediate machined structure and subsequently high-energy hydroformed, preferably by means of explosive forming or electrohydraulic forming, into a high-energy hydroformed structure with least one of a uniaxial curvature or a biaxial curvature. Preferably, in a next process step, the intermediate product is stress relieved, more preferably in an operation including a cold compression type of operation. Then there is either machining or mechanical milling of the high-energy formed structure to a near-final or final machined integrated monolithic aluminum structure, followed by ageing of the machined integrated monolithic aluminum structure to a desired temper to develop the required strength and other engineering properties relevant for the intended application of the integrated monolithic aluminum structure.

[0069] Or in an alternative embodiment, there is firstly ageing of the intermediate integrated monolithic aluminum structure to a desired temper to develop the required strength and other engineering properties relevant for the intended application of the integrated monolithic aluminum structure, followed by machining or mechanical milling of the aged high-energy formed structure into a near-final or final machined integrated monolithic aluminum structure.

[0070] The method illustrated in FIG. 2 is closely related to the method illustrated in FIG. 1, except that in this embodiment there is a first high-energy hydroforming step, followed by performing at least a second high-energy hydroforming step the purpose of which is at least stress relief, followed by the ageing and machining as in the method illustrated in FIG. 1.

[0071] FIGS. 3A, 3B and 3C show a series in progression of exemplary drawings illustrating how an aluminum plate may be formed during an explosive forming process that can be used in the forming processes according to this invention. According to explosive forming assembly 80a, a tank 82 contains an amount of water 83. A die 84 defines a cavity 85 and a vacuum line 87 extends from the cavity 85 through the die 84 to a vacuum (not shown). Aluminum plate 86a is held in position in the die 84 via a hold-down ring or other retaining device (not shown). An explosive charge 88 is shown suspended in the water 83 via a charge detonation line 89, with charge detonation line 19a connected to a detonator (not shown). As shown in FIG. 3B, the charge 88 (shown in FIG. 3A) has been detonated in explosive forming assembly 80b creating a shock wave “A” emanating from a gas bubble “B”, with the shock wave “A” causing the deformation of the aluminum plate 86b into cavity 85 until the aluminum plate 86c is driven against (e.g., immediately proximate to and in contact with) the inner surface of die 84 as shown in FIG. 3C.

[0072] To provide proof of the principle of the invention, industrially produced plate material of three different alloys have been tested for the influence of the deformation degree on the mechanical properties in the final temper.

[0073] Plate material of the three alloys have been solution heat-treated and stretched to arrive at a T351-temper using regular industry practices. The alloy compositions are listed in Table 1. Alloy 1 is an alloy according to this invention and had a gauge of 33 mm, Alloys 2 and 3 are comparative alloys and had a gauge of respectively 25 mm and 27 mm Samples were cut from all plates and stretched at various degrees in the L-direction to simulate a subsequent deformation step by a high-energy hydroforming operation. Next all samples were artificially aged to a T8 condition and tested for its mechanical properties in the L-direction at mid-thickness (s/2) in accordance with the standard EN2002-1. The results (average over three test samples) are listed in Table 2.

TABLE-US-00002 TABLE 1 Alloy compositions of the plate material tested, all percentages are by wt. %, balance is made by aluminum and regular impurities. Element Alloy Si Fe Cu Mn Mg Ti Cr Zr Ag 1 0.07 0.03 3.9 0.55 1.30 0.031 0.001 — — 2 0.05 0.07 4.7 0.3 0.54 0.037 0.001 0.11 0.33 3 0.05 0.06 4.6 0.27 1.0 0.042 0.06 0.10 —

TABLE-US-00003 TABLE 2 Mechanical properties of the various alloy samples in T8 condition as function of the stretching degrees. Rp0.2 is the yield strength, Rm is the tensile strength, and A the elongation at fracture. Stretching Rp0.2 Rm A Alloy degree (%) [ MPa ] [ MPa ] [ % ] 1 0 455 497 11.2 2 461 502 10.8 4 460 502 11.2 6 464 503 10.8 8 466 505 10.9 10 469 509 10.3 2 0 480 517 11.1 2 475 505 12.3 4 475 504 11.3 6 480 508 11.3 8 488 515 10.9 10 495 521 10.1 3 0 445 492 13.5 2 477 505 12.4 4 495 515 11.5 6 507 521 11.7 8 517 528 10.3 10 525 535 10.2

[0074] From the results of Table 2, it can be seen that Alloy 2, being a 2xxx-series alloy having a purposive addition of silver, provides almost constant mechanical properties with increasing stretching degree. This is in conformity with what the skilled person would expect. There is a very small increase with increasing stretching degree as the skilled person would have expected, as a higher cold deformation degree would lead to small increase of tensile properties in a T8 condition.

[0075] Alloy 3 is closely related to Alloy 2 but has no purposive addition of silver. For this aluminum alloy the yield strength and ultimate tensile strength show a steadily increase with increasing stretching degree, whereas the elongation at fracture decreases. When high-energy hydroforming a plate material, depending of the geometry of the final structure, there can be considerable variation in deformation degrees. As the mechanical properties of Alloy 3 show a strong dependency of the stretching degree, this alloy is not a favorable choice for being processed via a high-energy hydroforming operation as it leads to a strong variation of the mechanical properties in the final product at final temper.

[0076] Surprisingly, Ag-free Alloy 1 shows a similar trend as Alloy 2, namely it has almost constant mechanical properties with increasing stretching degree. Also, here there is a very small increase in yield strength and tensile strength with increasing stretching degree in the final T8 temper.

[0077] Despite the lower Cu-content and the absence of Ag in Alloy 1 compared to Alloy 2, Alloy 1 shows mechanical properties close to those of Alloy 2. As Alloy 1 is also almost insensitive for variation in the deformation degree, this aluminum alloy is an ideal alloy for being processed in a high-energy hydroforming operation and provides fairly constant mechanical properties in the final product. The absence of silver makes the aluminum alloy also more cost effective than silver containing 2xxx-series alloys.

[0078] Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made without departing from the spirit or scope of the invention as herein described.

[0079] While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.