A method for improving anisotropy of an Al-Zn-Mg-Cu alloy sheet

Abstract

The application discloses a method for improving anisotropy of Al-Zn-Mg-Cu alloy plate, which comprises sequentially performing annealing treatment, three-stage solid solution treatment and regression re-aging treatment on the Al-Zn-Mg-Cu alloy plate, wherein the annealing treatment is performed at 180-460 DEG C for 60-80 h and then air-cooled to room temperature. The aluminum alloy plate is annealed by using reasonable annealing treatment conditions, so as to eliminate residual stress in the aluminum alloy plate and simultaneously cause recrystallization, and the three-stage solid solution treatment and the regression re-aging treatment are cooperated, compared with a traditional process, the anisotropy of mechanical properties of the aluminum alloy plate is significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of Al-Zn-Mg-Cu alloy sheet processing, specifically relating to a method for improving the anisotropy of Al-Zn-Mg-Cu alloy sheets to meet the isotropic mechanical properties of Al-Zn-Mg-Cu alloys required by aerospace and other fields. Background Technology

[0002] In recent years, with the rapid development of the aerospace and transportation industries, there has been a greater demand for energy consumption, while also placing significant pressure on environmental protection. Therefore, lightweighting of aircraft and automobiles is inevitable. Al-Zn-Mg-Cu alloys possess a series of advantages, including low density, high specific strength, high specific stiffness, and good corrosion resistance. They can reduce product weight and energy consumption while ensuring product quality, making them widely applicable and irreplaceable in aerospace and transportation fields. However, other applications, such as spacecraft or high-speed rail, are limited by the anisotropy of mechanical properties. Therefore, it is necessary to study the anisotropy of the mechanical properties of Al-Zn-Mg-Cu alloys.

[0003] To meet the requirements of use under different conditions, the anisotropy of alloys must be reduced. Adjusting the alloy composition and strengthening process are the main methods to improve alloy performance. For the fabrication of aluminum alloy devices, deformation and annealing are commonly used. Deformation produces new microstructures with elongated or recrystallized grains, thereby altering the properties of the final material. Simultaneously, as deformation occurs, dislocation density increases, and the stored energy can be released through recrystallization during annealing. The planar anisotropy index (IPA) is one of the important indicators for evaluating the anisotropy of alloy mechanical properties. Its main principle is to test the difference in mechanical property indicators (yield strength is used in this invention) in different directions of the alloy; a higher value indicates more severe anisotropy.

[0004] To date, research on the isotropic mechanical properties of Al-Zn-Mg-Cu alloys has not been established, which to some extent restricts the development of my country's aerospace, weaponry, and transportation industries. Therefore, improving the anisotropic mechanical properties of Al-Zn-Mg-Cu alloys is of significant practical importance. Summary of the Invention

[0005] The purpose of this invention is to address the problem of large anisotropy in the mechanical properties of existing Al-Zn-Mg-Cu alloys by providing a method to improve the anisotropy of Al-Zn-Mg-Cu alloy plates.

[0006] The objective of this invention is achieved through the following technical solution: A method for improving the anisotropy of Al-Zn-Mg-Cu alloy plates, characterized by comprising a pretreatment and a post-treatment, wherein the pretreatment is annealing and the post-treatment is a subsequent strengthening heat treatment. The subsequent strengthening heat treatment is a three-stage solution treatment + re-aging process.

[0007] The annealing process involves holding the sample at 180-460℃ for 60-80 hours, followed by air cooling to room temperature.

[0008] The three-stage solution treatment is as follows: the annealed Al-Zn-Mg-Cu alloy plate is held at 445-455℃ for 0.25-0.75h for the first stage of solution treatment; the furnace temperature is increased to 455-465℃ and held for 0.25-0.75h for the second stage of solution treatment; the temperature is further increased to 465-475℃ and held for 0.25-0.75h for the third stage of solution treatment; then it is water quenched to room temperature, with a quenching transfer time of less than 5s.

[0009] The re-aging treatment is as follows: the solution-treated Al-Zn-Mg-Cu alloy plate is held at 110-130℃ for 20-30 hours for the first aging treatment; then it is held at 180-210℃ for 0.25-1 hour for the second aging treatment; then it is held at 110-130℃ for 20-30 hours for the third aging treatment; finally, it is water-quenched to room temperature with a quenching transfer time of less than 5 seconds.

[0010] The composition of the Al-Zn-Mg-Cu alloy, by mass percentage, is as follows: Zn 5.10~6.10%, Mg 2.10~2.90%, Cu 1.20~2.00%, Fe 0.00~0.50%, Mn 0.00~0.30%, Cr 0.18~0.28%, Si 0.00~0.40%, total impurity elements ≤0.15%, and the balance is Al.

[0011] The beneficial effects of this invention are: (1) The present invention performs annealing treatment on Al-Zn-Mg-Cu alloy plates, which is beneficial to reduce hardness and improve machinability; reduce residual stress, stabilize dimensions, reduce deformation and crack tendency; refine grains, adjust microstructure, and eliminate microstructure defects.

[0012] (2) The present invention uses reasonable annealing temperature and annealing time to anneal the aluminum alloy sheet to eliminate residual stress in the aluminum alloy sheet and recrystallize at the same time. Combined with the three-stage solution treatment + re-aging process, it significantly improves the anisotropy of the mechanical properties of the aluminum alloy sheet compared with the traditional process.

[0013] (3) This invention employs a three-stage solution treatment process. As the solution temperature increases, fewer components remain in the alloy. Increasing the solution temperature can significantly improve its performance. However, excessively high solution temperatures can lead to overheating and deterioration of the alloy's performance. The three-stage solution treatment process can avoid overheating and allow the components to dissolve more completely. Attached Figure Description

[0014] Figure 1 Metallographic images of Examples 1-3 (ac) and Comparative Example (d); scale bar 100 μm. Detailed Implementation

[0015] The present invention will be further described below with reference to embodiments and comparative examples. The composition of the Al-Zn-Mg-Cu alloy, by mass percentage, is as follows: Zn 5.10~6.10%, Mg 2.10~2.90%, Cu 1.20~2.00%, Fe 0.00~0.50%, Mn 0.00~0.30%, Cr 0.18~0.28%, Si 0.00~0.40%, total impurity elements ≤0.15%, and the balance is Al. Example 1

[0016] The Al-Zn-Mg-Cu alloy plate with a thickness of about 3 mm was first annealed by heating in the furnace to 200℃ for 72 h, followed by air cooling to room temperature. Then, a three-stage solution treatment was performed: 450℃ / 0.5 h + 460℃ / 0.5 h + 470℃ / 0.5 h. After solution treatment, the sample was water quenched to room temperature with a quenching transfer time of less than 5 s. Finally, a re-aging treatment was performed by heating to 120℃ / 24 h + 200℃ / 45 min + 120℃ / 24 h. After aging, the sample was water quenched to room temperature with a quenching transfer time of less than 5 s. Example 2

[0017] The Al-Zn-Mg-Cu alloy plate with a thickness of about 3 mm was first annealed by furnace heating to 300℃ / 72h, followed by air cooling to room temperature; then it was subjected to a three-stage solution treatment of 450℃ / 0.5h + 460℃ / 0.5h + 470℃ / 0.5h, after which the sample was water quenched to room temperature with a quenching transfer time of less than 5s; finally, it was subjected to a re-aging treatment of heating to 120℃ / 24h + 200℃ / 45min + 120℃ / 24h, after which the sample was water quenched to room temperature with a quenching transfer time of less than 5s. Example 3

[0018] The Al-Zn-Mg-Cu alloy plate with a thickness of about 3 mm was first annealed by furnace heating to 450℃ / 72h, followed by air cooling to room temperature; then it was subjected to a three-stage solution treatment of 450℃ / 0.5h + 460℃ / 0.5h + 470℃ / 0.5h, after which the sample was water quenched to room temperature with a quenching transfer time of less than 5s; finally, it was subjected to a re-aging treatment of heating to 120℃ / 24h + 200℃ / 45min + 120℃ / 24h, after which the sample was water quenched to room temperature with a quenching transfer time of less than 5s. Comparative Example

[0019] A 3mm thick Al-Zn-Mg-Cu alloy plate was subjected to a three-stage solution treatment: 450℃ / 0.5h + 460℃ / 0.5h + 470℃ / 0.5h. After solution treatment, the sample was water-quenched to room temperature with a quenching transfer time of less than 5s. Finally, a regression aging treatment was performed, which involved heating to 120℃ / 24h + 200℃ / 45min + 120℃ / 24h. After aging, the sample was water-quenched to room temperature with a quenching transfer time of less than 5s.

[0020] The tensile specimens used in both the examples and comparative examples were selected by wire cutting at angles of 0°, 45°, and 90° to the rolling direction. The commonly used formula for calculating the interplane anisotropy index (IPA) is shown below:

[0021] Among them, S Max S represents the maximum yield strength in different directions; Min S represents the minimum yield strength in different directions; Mid The yield strength is defined as the value between the maximum and minimum values ​​in different directions, where N is the number of test directions; in this paper, N=3. The Al-Zn-Mg-Cu alloys prepared in the examples and comparative examples were tested according to the method for determining the tensile strength at room temperature of metallic materials in GB / T 228.1-2010. Each sample was tested three times to ensure the accuracy of the experimental data. The yield strength and interplanar anisotropy index (IPA) of the Al-Zn-Mg-Cu alloys in the examples and comparative examples are shown in Table 1.

[0022] Table 1. Yield strength and interplanar anisotropy index (IPA) of embodiments and comparative examples of the present invention.

[0023] A comparison of the yield strength test results of Examples 1-3 and the comparative example shows that the embodiments of the present invention can significantly improve the isotropic mechanical properties of the alloys compared with the comparative example. Examples 1-3 are further compared with each other, with Example 2 being the preferred embodiment of the present invention.

[0024] The above embodiments and comparative examples are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. For those skilled in the art, any improvements and substitutions made based on the technical solutions of the present invention without creative effort shall fall within the protection scope of the present invention.

Claims

1. A method for improving the anisotropy of Al-Zn-Mg-Cu alloy plates, characterized in that, Al-Zn-Mg-Cu alloy plates were subjected to annealing, three-stage solution treatment and re-aging treatment in sequence to obtain Al-Zn-Mg-Cu alloy plates with reduced anisotropy. The annealing temperature is 180-460℃, the annealing time is 60-80h, and the annealing is followed by air cooling to room temperature. The three-stage solution treatment is as follows: the annealed Al-Zn-Mg-Cu alloy plate is held at 445-455℃ for 0.25-0.75h for the first stage of solution treatment; the furnace temperature is increased and held at 455-465℃ for 0.25-0.75h for the second stage of solution treatment; the temperature is further increased and held at 465-475℃ for 0.25-0.75h for the third stage of solution treatment; then it is water quenched to room temperature, with a quenching transfer time of less than 5s. The re-aging treatment is as follows: the solution-treated Al-Zn-Mg-Cu alloy plate is held at 110-130℃ for 20-30 hours for the first aging treatment; then held at 180-210℃ for 0.25-1 hour for the second aging treatment; then held at 110-130℃ for 20-30 hours for the third aging treatment; finally, it is water-quenched to room temperature with a quenching transfer time of less than 5 seconds. The composition of the Al-Zn-Mg-Cu alloy, by mass percentage, is as follows: Zn 5.10~6.10%, Mg 2.10~2.90%, Cu 1.20~2.00%, Fe 0.00~0.50%, Mn 0.00~0.30%, Cr 0.18~0.28%, Si 0.00~0.40%, total impurity elements ≤0.15%, and the balance is Al.

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