Heat treatment method for improving obdurability of aluminum-lithium alloy plate

Abstract

The invention belongs to the technical field of aluminum lithium alloy heat treatment, and provides a heat treatment method for improving the obdurability of an aluminum lithium alloy plate. The heat treatment method comprises the following steps: sequentially carrying out solid solution heat treatment, rolling pre-deformation treatment, pre-stretching treatment and artificial aging treatment on the aluminum-lithium alloy plate. According to the method, through optimized solid solution heat treatment, a second phase separated out of the aluminum lithium alloy plate in the cold deformation state is subjected to solid solution in a matrix, and a supersaturated solid solution of the aluminum lithium alloy plate is obtained; a large amount of dislocation is introduced in rolling pre-deformation, work hardening is introduced, the dislocation density is increased, and the aging precipitation power of the aluminum-lithium alloy plate is improved; residual stress in the rolling pre-deformation process is eliminated through pre-stretching treatment, and the aluminum-lithium alloy plate which is subjected to stress removal and is flat in appearance is obtained; a large number of strengthening phases such as T1 phases and theta'phases are separated out through artificial aging treatment, and strengthening and toughening of the aluminum-lithium alloy plate are achieved; the yield strength reaches 520 MPa or above, the tensile strength reaches 590 MPa or above, and the ductility reaches 8% or above.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology for aluminum-lithium alloys, and in particular to a heat treatment method for improving the strength and toughness of aluminum-lithium alloy plates. Background Technology

[0002] Aluminum-lithium alloy refers to aluminum alloys with added lithium. Lithium (Li) is the lightest metallic element, with a density of only 0.534 g / cm³. 3 Adding lithium to lightweight aluminum alloys is akin to making them even lighter. Studies show that adding 1% Li can reduce the density of aluminum alloys by 3% and increase their stiffness by 6%, while maintaining the original strength, corrosion resistance, fatigue resistance, and ductility of aluminum alloys. This has made aluminum-lithium alloys a highly competitive structural material in the aerospace field since they were first proposed in the 1920s.

[0003] To date, aluminum-lithium alloys have evolved to the third generation. Compared to the lower strength of the first-generation alloys and the poor toughness and ductility of the second-generation alloys, the third-generation alloys possess superior comprehensive mechanical properties. Third-generation aluminum-lithium alloys are Al-Cu-Li alloys, a type of age-hardening alloy. Strengthening is primarily achieved through the precipitation of a second phase during the artificial aging process. The main age-hardening phases include T1 phase (Al2CuLi), θ′ phase (Al2Cu), and δ′ phase (Al3Li). Among these, the T1 phase exhibits the strongest strengthening effect, and its contribution to alloy strength is positively correlated with the volume fraction and diameter of the T1 phase.

[0004] With the continuous development of the aerospace industry, higher requirements have been placed on the strength and toughness of aluminum-lithium alloys. In particular, the strength of aluminum-lithium alloy plates is often limited by the influence of their processing technology and deformation.

[0005] Therefore, it is urgent to study processing techniques to improve the strength and toughness of aluminum-lithium alloy sheets in order to broaden their application areas. Summary of the Invention

[0006] The purpose of this invention is to provide a heat treatment method for improving the strength and toughness of aluminum-lithium alloy plates, addressing the shortcomings of existing technologies.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a heat treatment method for improving the strength and toughness of aluminum-lithium alloy plates, comprising the following steps: The aluminum-lithium alloy sheet is subjected to solution heat treatment, rolling pre-deformation treatment, pre-stretching treatment and artificial aging treatment in sequence.

[0008] Preferably, the aluminum-lithium alloy sheet is a cold-deformed aluminum-lithium alloy sheet with a cold deformation amount of 60-84%.

[0009] Preferably, the chemical composition of the aluminum-lithium alloy plate, by mass percentage, is: Cu 3~4%, Li 0.75~1.5%, Mg 0.2~1%, Ag 0.2~1%, Mn 0.2~1%, Zr 0.05~0.25%, impurities <0.25%, and the balance being Al.

[0010] Preferably, the solution heat treatment temperature is 525~545℃ and the solution heat treatment time is 30~100min.

[0011] Preferably, the deformation amount of the rolling pre-deformation treatment is 5-25%.

[0012] Preferably, the deformation amount of the pre-stretching treatment is 2.5% to 5%.

[0013] Preferably, the temperature of the artificial aging treatment is 150~200℃, and the time of the artificial aging treatment is 4~32h.

[0014] Preferably, after the solution heat treatment, water quenching is performed first, followed by rolling pre-deformation treatment; The water quenching time is 1 to 2 minutes.

[0015] The beneficial effects of this invention are: This invention utilizes optimized solution heat treatment to dissolve the second phase precipitated in cold-deformed aluminum-lithium alloy sheets into the matrix, resulting in a supersaturated solid solution of the aluminum-lithium alloy sheet. Rolling pre-deformation introduces a large number of dislocations, leading to work hardening, increased dislocation density, and enhanced aging precipitation dynamics of the aluminum-lithium alloy sheet. Pre-stretching treatment eliminates residual stress during rolling pre-deformation, resulting in a stress-relieved aluminum-lithium alloy sheet with a smooth shape. Artificial aging treatment precipitates a large number of strengthening phases such as T1 and θ′ phases, effectively achieving the strengthening and toughening of the aluminum-lithium alloy sheet. The yield strength can reach over 520 MPa, the tensile strength over 590 MPa, and the elongation over 8%. It has low equipment requirements, high operability, and is conducive to industrial production. Attached Figure Description

[0016] Figure 1 The image shows the metallographic structure of the solid solution aluminum-lithium alloy sheet from Example 1. Figure 2 The image shows a transmission electron microscope (TEM) image of the aluminum-lithium alloy sheet after processing in Example 1, wherein (a) the electron beam along... <110> α Dark-field diagram of the incident beam, (b) electron beam along <112> α Dark field diagram of the incident light; Figure 3The graph shows a comparison of the mechanical properties of aluminum-lithium alloy plates after treatment in Examples 1-4. Detailed Implementation

[0017] This invention provides a heat treatment method for improving the strength and toughness of aluminum-lithium alloy plates, comprising the following steps: The aluminum-lithium alloy sheet is subjected to solution heat treatment, rolling pre-deformation treatment, pre-stretching treatment and artificial aging treatment in sequence.

[0018] In this invention, the aluminum-lithium alloy sheet is preferably a cold-deformed aluminum-lithium alloy sheet, and the cold deformation amount is preferably 60-84%, more preferably 65-80%, and even more preferably 70-75%.

[0019] In this invention, the preferred chemical composition of the aluminum-lithium alloy plate, by mass percentage, is as follows: Cu 3-4%, more preferably 3.2-3.8%, and even more preferably 3.4-3.6%; Li 0.75-1.5%, more preferably 1-1.3%, and even more preferably 1.1-1.2%; Mg 0.2-1%, more preferably 0.4-0.8%, and even more preferably 0.5-0.7%; Ag 0.2-1%, more preferably 0.4-0.8%, and even more preferably 0.5-0.7%; Mn 0.2-1%, more preferably 0.3-0.8%, and even more preferably 0.5-0.6%; Zr 0.05-0.25%, more preferably 0.08-0.2%, and even more preferably 0.09-0.15%; impurities <0.25%, more preferably <0.22%, and even more preferably <0.2%; the balance being Al.

[0020] In this invention, the solution heat treatment temperature is preferably 525~545℃, more preferably 530~540℃, and even more preferably 535℃; the solution heat treatment time is preferably 30~100min, more preferably 50~90min, and even more preferably 60~80min.

[0021] In this invention, the deformation amount of the rolling pre-deformation treatment is preferably 5-25%, more preferably 10-20%, and even more preferably 15-17.5%.

[0022] In this invention, the temperature of the rolling pre-deformation treatment is preferably 20~25℃, more preferably 21~24℃, and even more preferably 22~23℃.

[0023] In this invention, the deformation amount of the pre-stretching treatment is preferably 2.5-5%, more preferably 3-4.5%, and even more preferably 3.5-4%.

[0024] In this invention, the temperature of the artificial aging treatment is preferably 150~200℃, more preferably 160~180℃, and even more preferably 170~175℃; the time of the artificial aging treatment is preferably 4~32h, more preferably 8~24h, and even more preferably 12~16h.

[0025] In this invention, after the solution heat treatment is completed, it is preferable to first perform water quenching and then perform rolling pre-deformation treatment; The water quenching time is preferably 1 to 2 minutes, more preferably 1.2 to 1.8 minutes, and even more preferably 1.5 minutes.

[0026] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0027] Example 1

[0028] The chemical composition of the aluminum-lithium alloy sheet, by mass percentage, is: Cu 3.56%, Li 1.12%, Mg 0.48%, Ag 0.54%, Mn 0.36%, Zr 0.11%, with the balance being Al. The aluminum-lithium alloy sheet is a cold-deformed type, with a cold deformation rate of 75% and no edge cracking.

[0029] The heat treatment method is as follows: the aluminum-lithium alloy sheet is subjected to solution heat treatment at 535℃ for 60 minutes, followed by water quenching for 1.5 minutes to obtain the solution-treated aluminum-lithium alloy sheet; at 25℃, the solution-treated aluminum-lithium alloy sheet is subjected to pre-deformation rolling with a deformation of 15%, followed by pre-stretching with a deformation of 3%, and then artificial aging treatment at 175℃ for 16 hours.

[0030] Figure 1 The image shows the metallographic structure of the solid solution aluminum-lithium alloy sheet from Example 1. As can be seen from the image, the grains of the solid solution aluminum-lithium alloy sheet are fibrous, a typical state for rolled sheets, which is the basis for the alloy's high strength and toughness.

[0031] Figure 2 The image shows a transmission electron microscope (TEM) image of the aluminum-lithium alloy sheet after processing in Example 1, wherein (a) the electron beam along... <110> α Dark-field diagram of the incident beam, (b) electron beam along <112> α Dark field diagram of the incident light. (By...) Figure 2 It can be seen that a small amount of Al is visible in the aluminum-lithium alloy sheet after the treatment in Example 1. 20 The Cu2Mn3 phase and a large amount of uniformly dispersed T1 phase contribute the most to the precipitation strengthening of the alloy.

[0032] Example 2

[0033] The chemical composition and cold deformation of the aluminum-lithium alloy plate are the same as in Example 1.

[0034] The heat treatment method is as follows: the aluminum-lithium alloy sheet is subjected to solution heat treatment at 530℃ for 90 minutes, followed by water quenching for 2 minutes to obtain the solution-treated aluminum-lithium alloy sheet; at 25℃, the solution-treated aluminum-lithium alloy sheet is subjected to pre-deformation treatment with a deformation of 15%, followed by pre-stretching treatment with a deformation of 3%, and then artificial aging treatment at 175℃ for 16 hours.

[0035] Example 3

[0036] The chemical composition and cold deformation of the aluminum-lithium alloy plate are the same as in Example 1.

[0037] The heat treatment method is as follows: the aluminum-lithium alloy sheet is subjected to solution heat treatment at 535℃ for 60 minutes, followed by water quenching for 1.5 minutes to obtain the solution-treated aluminum-lithium alloy sheet; at 25℃, the solution-treated aluminum-lithium alloy sheet is subjected to pre-deformation rolling with a deformation of 17.5%, followed by pre-stretching with a deformation of 4%, and then artificial aging treatment at 175℃ for 16 hours.

[0038] Example 4

[0039] The chemical composition and cold deformation of the aluminum-lithium alloy plate are the same as in Example 1.

[0040] The heat treatment method is as follows: the aluminum-lithium alloy sheet is subjected to solution heat treatment at 535℃ for 60 minutes, followed by water quenching for 1.5 minutes to obtain the solution-treated aluminum-lithium alloy sheet; at 25℃, the solution-treated aluminum-lithium alloy sheet is subjected to pre-deformation rolling with a deformation of 15%, followed by pre-stretching with a deformation of 3%, and then artificial aging treatment at 180℃ for 12 hours.

[0041] Figure 3 The graph shows a comparison of the mechanical properties of aluminum-lithium alloy sheets after treatment in Examples 1-4; Figure 3 It can be seen that Examples 1 to 4 all have relatively excellent mechanical properties.

[0042] Example 5

[0043] The chemical composition of the aluminum-lithium alloy sheet, by mass percentage, is: Cu 3.62%, Li 1.01%, Mg 0.39%, Ag 0.45%, Mn 0.21%, Zr 0.09%, with the balance being Al. The aluminum-lithium alloy sheet is a cold-deformed type, with a cold deformation rate of 84% and no edge cracking.

[0044] The heat treatment method is the same as in Example 1.

[0045] Example 6

[0046] The chemical composition and cold deformation of the aluminum-lithium alloy plate are the same as in Example 5.

[0047] The heat treatment method is the same as in Example 2.

[0048] Example 7

[0049] The chemical composition and cold deformation of the aluminum-lithium alloy plate are the same as in Example 5.

[0050] The heat treatment method is the same as in Example 3.

[0051] Example 8

[0052] The chemical composition and cold deformation of the aluminum-lithium alloy plate are the same as in Example 5.

[0053] The heat treatment method is the same as in Example 4.

[0054] Example 9

[0055] The chemical composition of the aluminum-lithium alloy sheet, by mass percentage, is: Cu 3.42%, Li 1.05%, Mg 0.47%, Ag 0.42%, Mn 0.51%, Zr 0.08%, with the balance being Al. The aluminum-lithium alloy sheet is a cold-deformed type, with a cold deformation rate of 65% and no edge cracking.

[0056] The heat treatment method is the same as in Example 1.

[0057] Example 10

[0058] The chemical composition and cold deformation of the aluminum-lithium alloy plate are the same as in Example 9.

[0059] The heat treatment method is as follows: the aluminum-lithium alloy sheet is subjected to solution heat treatment at 535℃ for 60 minutes, followed by water quenching for 1.5 minutes to obtain the solution-treated aluminum-lithium alloy sheet; at 25℃, the solution-treated aluminum-lithium alloy sheet is subjected to pre-deformation rolling with a deformation of 20%, followed by pre-stretching with a deformation of 4%, and then artificial aging treatment at 175℃ for 16 hours.

[0060] Example 11

[0061] The chemical composition and cold deformation of the aluminum-lithium alloy plate are the same as in Example 9.

[0062] The heat treatment method is as follows: the aluminum-lithium alloy sheet is subjected to solution heat treatment at 545℃ for 30 minutes, followed by water quenching for 1.5 minutes to obtain the solution-treated aluminum-lithium alloy sheet; at 25℃, the solution-treated aluminum-lithium alloy sheet is subjected to pre-deformation rolling with a deformation of 20%, followed by pre-stretching with a deformation of 4%, and then artificial aging treatment at 175℃ for 16 hours.

[0063] Example 12

[0064] The chemical composition and cold deformation of the aluminum-lithium alloy plate are the same as in Example 9.

[0065] The heat treatment method is as follows: the aluminum-lithium alloy sheet is subjected to solution heat treatment at 545℃ for 30 minutes, followed by water quenching for 1.5 minutes to obtain the solution-treated aluminum-lithium alloy sheet; at 25℃, the solution-treated aluminum-lithium alloy sheet is subjected to pre-deformation rolling with a deformation of 20%, followed by pre-stretching with a deformation of 4%, and then artificial aging treatment at 165℃ for 24 hours.

[0066] Comparative Example 1

[0067] The difference from Example 1 is that the aluminum-lithium alloy sheet is a cold-deformed aluminum-lithium alloy sheet with a cold deformation amount of 90% and severe edge cracking.

[0068] Comparative Example 2

[0069] The difference from Example 5 is that the aluminum-lithium alloy sheet is a cold-deformed aluminum-lithium alloy sheet with a cold deformation amount of 90% and severe edge cracking.

[0070] Comparative Example 3

[0071] The difference from Example 9 is that the aluminum-lithium alloy sheet is a cold-deformed aluminum-lithium alloy sheet with a cold deformation amount of 90% and severe edge cracking.

[0072] Comparative Example 4

[0073] The difference from Example 1 is that the solution-treated aluminum-lithium alloy sheet was subjected to solution heat treatment at 550°C for 60 minutes.

[0074] In this comparative example, metallographic observation of the solid solution aluminum-lithium alloy sheet revealed an overheated metallographic structure.

[0075] Comparative Example 5

[0076] The difference from Example 1 is that the solution-treated aluminum-lithium alloy sheet was subjected to solution heat treatment at 500°C for 90 minutes.

[0077] In this comparative example, metallographic observation of the solid solution aluminum-lithium alloy sheet revealed that the second phase was not completely dissolved into the matrix.

[0078] Comparative Example 6

[0079] The difference from Example 1 is that the solid solution aluminum-lithium alloy sheet is subjected to a pre-deformation rolling treatment with a deformation amount of 30%, followed by a pre-stretching treatment with a deformation amount of 5%.

[0080] Comparative Example 7

[0081] The difference from Example 1 is that the solid solution aluminum-lithium alloy sheet is subjected to a pre-deformation rolling treatment with a deformation amount of 4%, followed by a pre-stretching treatment with a deformation amount of 2%.

[0082] Comparative Example 8

[0083] The difference from Example 1 is that artificial aging treatment was performed at 225°C for 12 hours.

[0084] Comparative Example 9

[0085] The difference from Example 1 is that artificial aging treatment was performed at 125°C for 24 hours.

[0086] Comparative Example 10

[0087] The difference from Example 1 is that the solid solution aluminum-lithium alloy sheet is pre-stretched with a deformation of 3%, and then artificially aged at 175°C for 16 hours.

[0088] The tensile strength, yield strength, and elongation of the aluminum-lithium alloy sheets treated in Examples 1-12 and Comparative Examples 1-10 were tested according to GB / T 228.1-2010. The test results are shown in Table 1.

[0089] Table 1 Performance Test Results

[0090] As shown in Table 1, the aluminum-lithium alloy plates treated in Examples 1-12 exhibit high yield strength, tensile strength, and elongation, demonstrating excellent strength and toughness. In Comparative Examples 1-3, the cold-deformed aluminum-lithium alloy plates showed a cold deformation of up to 90%, indicating significant cold deformation and severe edge cracking. After the same heat treatment as in Example 1, they exhibited excellent yield strength and tensile strength, but extremely low elongation. Comparative Examples 4 and 5 adjusted the solution heat treatment temperature. Comparative Example 4 underwent solution heat treatment at a high temperature of 550℃, resulting in over-burning of the metallographic structure, leading to a significant decrease in both yield strength and tensile strength. Comparative Example 5 underwent solution heat treatment at a lower temperature of 500℃, but the second phase did not completely dissolve into the matrix, failing to achieve the solution strengthening effect, and both yield strength and tensile strength were significantly reduced. These results indicate that a suitable solution heat treatment temperature is crucial for effective solution strengthening. At the specified temperature, the metallographic structure remains intact, and the second phase is completely dissolved into the matrix. Comparative Examples 6 and 7 adjusted the amount of pre-deformation during rolling. High-deformation pre-deformation significantly reduced the yield strength, tensile strength, and elongation of Comparative Example 6. Low-deformation pre-deformation maintained a higher elongation, but the yield strength and tensile strength remained low. Comparative Examples 8 and 9 changed the temperature of the artificial aging treatment. High-temperature artificial aging at 225℃ maintained high yield strength and tensile strength, but the elongation decreased sharply. Low-temperature artificial aging at 125℃ maintained a higher elongation, but the yield strength and tensile strength remained low. Comparative Example 10 omitted the pre-deformation rolling treatment, greatly reducing the dislocations introduced before aging heat treatment, maintaining a high elongation, but significantly reducing strength.

[0091] As can be seen from the above embodiments, the present invention provides a heat treatment method for improving the strength and toughness of aluminum-lithium alloy plates. The method utilizes aluminum-lithium alloy plates with a specific deformation morphology, which undergo solution heat treatment, rolling pre-deformation treatment, pre-stretching treatment, and artificial aging treatment. The optimized solution heat treatment process allows the second phase to dissolve into the matrix, forming a supersaturated solid solution. Rolling pre-deformation increases dislocation density and enhances the precipitation dynamics during aging. Pre-stretching treatment eliminates residual stress, and artificial aging treatment precipitates strengthening phases, thereby achieving the strengthening and toughening of the aluminum-lithium alloy plate. By rationally controlling the specific conditions of solution heat treatment, rolling pre-deformation treatment, pre-stretching treatment, and artificial aging treatment, the yield strength of the aluminum-lithium alloy plate reaches above 520 MPa, the tensile strength reaches above 590 MPa, and the elongation reaches above 8%.

[0092] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A heat treatment method for improving the strength and toughness of aluminum-lithium alloy plates, characterized in that, It includes the following steps: The aluminum-lithium alloy sheet is subjected to solution heat treatment, rolling pre-deformation treatment, pre-stretching treatment and artificial aging treatment in sequence.

2. The heat treatment method according to claim 1, characterized in that, The aluminum-lithium alloy sheet is a cold-deformed aluminum-lithium alloy sheet with a cold deformation amount of 60~84%.

3. The heat treatment method according to claim 1 or 2, characterized in that, The chemical composition of the aluminum-lithium alloy plate, by mass percentage, is: Cu 3~4%, Li 0.75~1.5%, Mg 0.2~1%, Ag 0.2~1%, Mn 0.2~1%, Zr 0.05~0.25%, impurities <0.25%, and the balance is Al.

4. The heat treatment method according to claim 3, characterized in that, The solution heat treatment temperature is 525~545℃, and the solution heat treatment time is 30~100min.

5. The heat treatment method according to claim 4, characterized in that, The deformation amount of the pre-deformation rolling process is 5-25%.

6. The heat treatment method according to claim 4 or 5, characterized in that, The deformation amount of the pre-stretching treatment is 2.5~5%.

7. The heat treatment method according to claim 6, characterized in that, The temperature for the artificial aging treatment is 150~200℃, and the time for the artificial aging treatment is 4~32h.

8. The heat treatment method according to claim 1 or 7, characterized in that, After the solution heat treatment is completed, water quenching is performed first, followed by rolling pre-deformation treatment; The water quenching time is 1 to 2 minutes.

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