Reinforced heat treatment method for 7075 aluminum alloy

Abstract

The invention discloses a strengthening heat treatment method for 7075 aluminum alloy, and relates to the technical field of metal heat treatment. According to the method, the strength of the 7075 aluminum alloy is improved through solution treatment, dynamic quenching, composite aging treatment and ultralow-temperature strengthening, and the 7075 aluminum alloy prepared through the method not only has high strength, but also shows high hardness and has wide application prospects in the fields of automobiles, steamships and the military industry.

Description

Technical Field

[0001] This invention discloses a strengthening heat treatment method for 7075 aluminum alloy, which relates to the field of metal heat treatment technology. Background Technology

[0002] 7075 aluminum alloy is one of the most important high-strength aluminum alloys in modern industrial applications, especially in aerospace, automotive, and shipbuilding industries, where high-strength, low-density materials are required.

[0003] Aluminum alloys are susceptible to thermal stress, oxidation, and microstructural changes during manufacturing, leading to unstable performance of printed parts. The rational control of process parameters to obtain the desired microstructure and excellent mechanical properties has received considerable attention in recent years. Through appropriate heat treatment processes during manufacturing, 7075 aluminum alloy has demonstrated excellent mechanical properties in practical applications. However, the complexity of heat treatment process parameters and the uncertainty of process control have a profound impact on the material's structure and properties. Therefore, research on the heat treatment process of 7075 aluminum alloy has always been a hot topic in related research. In practical applications, heat treatment can be combined with other manufacturing technologies such as forging, rolling, and welding to form composite manufacturing technologies. Through the synergistic effect of multiple processes, the performance and stability of aluminum alloys can be further improved. Therefore, this invention employs multiple heat treatment methods to synergistically strengthen 7075 aluminum alloy, achieving optimization of the structure and properties of 7075 aluminum alloy through the synergistic control of multiple heat treatment processes. Summary of the Invention

[0004] The purpose of this invention is to provide a strengthening heat treatment method for 7075 aluminum alloy, specifically including the following steps: (1) Solution treatment: Heating 7075 aluminum alloy for solution treatment.

[0005] (2) Dynamic quenching: Quenching treatment is performed on the 7075 aluminum alloy after solution treatment.

[0006] (3) Composite aging treatment: The composite aging treatment is carried out in two stages. In the first stage, the quenched 7075 aluminum alloy is subjected to low-temperature aging treatment; in the second stage, the 7075 aluminum alloy after the first stage treatment is subjected to high-temperature aging treatment.

[0007] (4) Ultra-low temperature strengthening: The 7075 aluminum alloy after composite aging treatment is immersed in a low temperature environment for deep cryogenic strengthening treatment to obtain the strengthened 7075 aluminum alloy.

[0008] Preferably, the solution treatment temperature of 7075 aluminum alloy in step (1) is 450~490℃, and the solution treatment time is 3~6h.

[0009] Preferably, in step (2), pulse water jet technology is used to perform dynamic quenching treatment on the solution-treated 7075 aluminum alloy, wherein the circulating water pressure is 0.07MPa and the circulating water temperature is ≤25℃.

[0010] Preferably, in step (2), the quenching cooling rate of the aluminum alloy is greater than or equal to the critical threshold of the supersaturated solid solution, i.e., ≥200℃ / s.

[0011] Preferably, the conditions for the first stage of composite aging in step (3) are: heat preservation at 107~140℃ for 6 hours; and the conditions for the second stage of composite aging are: heat preservation at 175~180℃ for 8~12 hours.

[0012] Preferably, the temperature gradient difference between the two stages of composite aging treatment in step (3) is 65~75℃.

[0013] Preferably, the low-temperature environment in step (4) is a liquid nitrogen environment; the cryogenic strengthening treatment time is 3~6h. More preferably, the cryogenic strengthening treatment time of aluminum alloy is positively correlated with the liquid nitrogen immersion depth; in order to form a novel dislocation-precipitate phase interaction structure and avoid uneven performance caused by local temperature gradients, the liquid nitrogen surface should completely cover the sample during the cryogenic strengthening treatment.

[0014] Mechanism of the invention: This invention's enhanced heat treatment process achieves a significant improvement in the properties of 7075 aluminum alloy through the synergistic effect of solid solution strengthening, aging strengthening, and grain refinement strengthening. The preparation method of this invention enables the alloy to form a supersaturated solid solution with significant lattice distortion, resulting in strong interaction between fine precipitates and dislocations, a substantial increase in grain boundaries and solid solution-distorted lattice, and multi-scale synergistic effects from the formation of nano-precipitates. The synergistic combination of these processes ensures that dislocation movement simultaneously overcomes lattice distortion stress, traverses precipitate barriers, and breaks through grain boundary obstacles, thereby achieving breakthrough optimization in the strength, hardness, and fatigue resistance of the aluminum alloy.

[0015] The beneficial effects of this invention are: (1) The aluminum alloy of the present invention is hot-processed by solution treatment, so that the solute atoms and the second phase are completely dissolved into the aluminum matrix, and the composition of the alloy is more uniformly distributed.

[0016] (2) By introducing an ultra-low temperature strengthening process, the aluminum alloy strengthening heat treatment method used in this invention refines the size of the precipitated phase from 15-30 nm in conventional T6 treatment to 5-10 nm and significantly improves its distribution uniformity. This optimization is due to the lattice distortion induced by the low temperature shrinkage effect, which can effectively suppress the formation of coarse η phase, promote the uniform distribution of nanoscale η' phase, and eliminate residual stress.

[0017] (3) The aluminum alloy strengthening heat treatment method of the present invention applies a composite aging treatment process, and successfully constructs a novel nanocomposite structure by controlling the temperature rise process in a stepwise manner. This process promotes the synergistic precipitation of nano-sized MgZn2 and Al2Cu phases, forming a unique multiphase composite structure.

[0018] (4) The 7075 aluminum alloy treated by the heat treatment method of the present invention (i.e., the synergistic effect of solid solution strengthening, composite aging strengthening and grain refinement strengthening) exhibits excellent comprehensive properties: dislocation density ≥10 15 m -2 The residual stress is <50MPa. These performance improvements are attributed to the synergistic effect of the atomic cluster structure, metastable phase structure, and dislocation-precipitate phase interaction structure formed within the alloy, which together enhance the material's strength and hardness. Attached Figure Description

[0019] Figure 1 Electron micrograph of Al2Cu on 7075 aluminum alloy after strengthening treatment.

[0020] Figure 2 Electron microscopy image of Mg2Si on 7075 aluminum alloy after strengthening treatment.

[0021] Figure 3 Stress-strain curve of 7075 aluminum alloy after strengthening treatment. Detailed Implementation

[0022] The following are specific embodiments of the present invention. The embodiments and accompanying drawings are for further description of the present invention. The specific descriptions below are illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0023] Example 1 A method for strengthening heat treatment of 7075 aluminum alloy specifically includes the following steps: (1) Solution treatment: Heat the 7075 aluminum alloy to 460℃ for solution treatment and maintain for 3h.

[0024] (2) Dynamic quenching: The solution-treated 7075 aluminum alloy is subjected to dynamic quenching using pulse water jet technology. The solution-treated 7075 aluminum alloy is quenched by impact cooling with circulating water at 25℃. The circulating water pressure is 0.07MPa and the cooling rate is 200℃ / s.

[0025] (3) Composite aging treatment: The quenched 7075 aluminum alloy is first kept at 107℃ for 6 hours, and then kept at 177℃ for 8 hours.

[0026] (4) Ultra-low temperature strengthening: The 7075 aluminum alloy after composite aging treatment is completely immersed in a liquid nitrogen environment at -196℃ for 4 hours of deep cryogenic strengthening treatment to obtain the strengthened 7075 aluminum alloy.

[0027] The aluminum alloy prepared in Example 1 was cut into strips of fixed size and its hardness was tested using the Brinell hardness test method. The test results showed that the hardness of the aluminum alloy was 198.05 HB. This is because the strengthening heat treatment process of the present invention has a synergistic effect of solid solution strengthening, composite aging strengthening and grain refinement strengthening of the aluminum alloy, which significantly improves the performance of 7075 aluminum alloy.

[0028] Example 2 A method for strengthening heat treatment of 7075 aluminum alloy specifically includes the following steps: (1) Solution treatment: Heat the 7075 aluminum alloy to 450℃ for solution treatment and maintain it for 4h.

[0029] (2) Dynamic quenching: The solution-treated 7075 aluminum alloy is subjected to dynamic quenching using pulse water jet technology. The solution-treated 7075 aluminum alloy is quenched by impact cooling with circulating water at 25℃. The circulating water pressure is 0.07MPa and the cooling rate is 200℃ / s.

[0030] (3) Composite aging treatment: The quenched 7075 aluminum alloy is first kept at 110℃ for 6 hours, and then kept at 175℃ for 12 hours.

[0031] (4) Ultra-low temperature strengthening: The 7075 aluminum alloy after composite aging treatment is completely immersed in a liquid nitrogen environment at -196℃ for 3 hours of deep cryogenic strengthening treatment to obtain the strengthened 7075 aluminum alloy.

[0032] The aluminum alloy prepared in Example 2 was cut into strips of the same size as the aluminum alloy prepared in Example 1. The hardness was tested using the Brinell hardness test method. The test results showed that the aluminum alloy had excellent hardness. This is because the strengthening heat treatment process of the present invention produces a synergistic effect of solid solution strengthening, composite aging strengthening and grain refinement strengthening of the aluminum alloy, which significantly improves the performance of 7075 aluminum alloy.

[0033] Example 3 A method for strengthening heat treatment of 7075 aluminum alloy specifically includes the following steps: (1) Solution treatment: Heat the 7075 aluminum alloy to 490℃ for solution treatment and maintain it for 6h.

[0034] (2) Dynamic quenching: The solution-treated 7075 aluminum alloy is subjected to dynamic quenching using pulse water jet technology. The solution-treated 7075 aluminum alloy is quenched by impact cooling with circulating water at 25℃. The circulating water pressure is 0.07MPa and the cooling rate is 200℃ / s.

[0035] (3) Composite aging treatment: The quenched 7075 aluminum alloy is first kept at 140℃ for 6 hours, and then kept at 180℃ for 10 hours.

[0036] (4) Ultra-low temperature strengthening: The 7075 aluminum alloy after composite aging treatment is completely immersed in a liquid nitrogen environment at -196℃ for 6 hours of deep cryogenic strengthening treatment to obtain the strengthened 7075 aluminum alloy.

[0037] The aluminum alloy prepared in Example 3 was cut into strips of the same size as the aluminum alloy prepared in Example 1. The Brinell hardness test was performed, and the results showed that the aluminum alloy had excellent hardness. This is because the strengthening heat treatment process of the present invention has a synergistic effect of solid solution strengthening, composite aging strengthening and grain refinement strengthening of the aluminum alloy, which significantly improves the performance of 7075 aluminum alloy.

[0038] Example 4 A method for strengthening heat treatment of 7075 aluminum alloy specifically includes the following steps: (1) Solution treatment: Heat the 7075 aluminum alloy to 460℃ for solution treatment and maintain for 3h.

[0039] (2) Dynamic quenching: The solution-treated 7075 aluminum alloy is subjected to dynamic quenching using pulse water jet technology. The solution-treated 7075 aluminum alloy is quenched by impact cooling with circulating water at 25℃. The circulating water pressure is 0.07MPa and the cooling rate is 200℃ / s.

[0040] (3) Composite aging treatment: The quenched 7075 aluminum alloy is first kept at 107℃ for 6 hours, and then kept at 177℃ for 12 hours.

[0041] (4) Ultra-low temperature strengthening: The 7075 aluminum alloy after composite aging treatment is completely immersed in a liquid nitrogen environment at -196℃ for 4 hours of deep cryogenic strengthening treatment to obtain the strengthened 7075 aluminum alloy.

[0042] The aluminum alloy prepared in Example 4 was cut into strips of the same size as the aluminum alloy prepared in Example 1. The Brinell hardness test was performed, and the results showed that the aluminum alloy had excellent hardness. This is because the strengthening heat treatment process of the present invention has a synergistic effect of solid solution strengthening, composite aging strengthening and grain refinement strengthening of the aluminum alloy, which significantly improves the performance of 7075 aluminum alloy.

[0043] The 7075 aluminum alloy prepared in Example 4 was cut into rod-shaped tensile samples and its tensile properties were tested using a tensile testing machine. Figure 3 The stress-strain curve of the 7075 aluminum alloy prepared in Example 4 was plotted at a tensile machine speed of 1 mm / min. Table 1 shows the tensile data. As can be seen from the figure, the material is in the elastic stage when the strain is 0-0.5%, with an elastic modulus of approximately 1014 GPa. The curve then enters the yield stage, where stress increases slowly and strain increases rapidly, ranging from 0.5% to 1%, at which point the stress reaches the yield strength of approximately 595 MPa. The 1-4% strain represents the strengthening stage, during which work hardening occurs, with the highest stress reaching 627.112 MPa. Afterward, the material enters the necking and fracture stage, and the curve declines until fracture.

[0044] Table 1 Comparative Example 1 A method for strengthening heat treatment of 7075 aluminum alloy specifically includes the following steps: (1) Solution treatment: Heat the 7075 aluminum alloy to 460℃ for solution treatment and maintain for 3h.

[0045] (2) Dynamic quenching: The solution-treated 7075 aluminum alloy is subjected to dynamic quenching using pulse water jet technology. The solution-treated 7075 aluminum alloy is quenched by impact cooling with circulating water at 25℃. The circulating water pressure is 0.07MPa and the cooling rate is 200℃ / s.

[0046] (3) Aging treatment: The quenched 7075 aluminum alloy is kept at 177℃ for 14h.

[0047] (4) Ultra-low temperature strengthening: The aged 7075 aluminum alloy is completely immersed in a liquid nitrogen environment at -196℃ for 4 hours to obtain the strengthened 7075 aluminum alloy.

[0048] The aluminum alloy prepared in Comparative Example 1 was cut into strips of the same size as the aluminum alloy prepared in Example 1. The hardness was tested using the Brinell hardness test method. The test results showed that the hardness of the aluminum alloy was only 169.80 HB. This is because the aging treatment method affects the structural strengthening of the aluminum alloy. The lack of multi-stage aging treatment resulted in the 7075 aluminum alloy in this comparative example not forming a new nanocomposite structure and not forming a multiphase composite structure, resulting in low hardness and poor application performance.

[0049] Comparative Example 2 A method for strengthening heat treatment of 7075 aluminum alloy specifically includes the following steps: (1) Solution treatment: Heat the 7075 aluminum alloy to 460℃ for solution treatment and maintain for 3h.

[0050] (2) Dynamic quenching: The solution-treated 7075 aluminum alloy is subjected to dynamic quenching using pulse water jet technology. The solution-treated 7075 aluminum alloy is quenched by impact cooling with circulating water at 25℃. The circulating water pressure is 0.07MPa and the cooling rate is 200℃ / s.

[0051] (3) Composite aging treatment: The quenched 7075 aluminum alloy is first kept at 107℃ for 6 hours, and then kept at 177℃ for 8 hours.

[0052] (4) Low temperature strengthening: The aluminum alloy after composite aging treatment is completely immersed in a 25°C water flow environment and cooled for 4 hours to obtain the strengthened 7075 aluminum alloy.

[0053] The aluminum alloy prepared in Comparative Example 2 was cut into strips with the same dimensions as the aluminum alloy prepared in Example 1. The hardness was tested using the Brinell hardness test method. The test results showed that the hardness of the aluminum alloy was only 192.06 HB. This is because the strengthening treatment method will affect the structural strengthening of the aluminum alloy. The lack of cryogenic treatment resulted in the precipitate size of the aluminum alloy in this comparative example not being further refined and the distribution uniformity being poor, resulting in the low hardness of the aluminum alloy and poor application performance.

[0054] The chemical composition of 7075 aluminum alloy is shown in Table 2.

[0055] Table 2 This experiment used 7-series aluminum alloys, whose main precipitated phase is MgZn2. Figure 1 and 2 As can be seen from the energy dispersive spectroscopy (EDS) results, Al accounts for 65.8% and Cu accounts for 22.4%. The mass ratio of Al to Cu is approximately Al₂Cu. Al₂Cu is also one of the precipitates in 7-series aluminum alloys, but... Figure 2 The approximately 1:1 mass ratio of Mg to Zn in the sample is mainly due to the interference of Al2Mg3Zn3. Based on the experimental results and relevant materials, the main physical phases of 7075 aluminum alloy after the heat treatment stage are MgZn2 and Al2Cu.

[0056] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for strengthening heat treatment of 7075 aluminum alloy, characterized in that, Specifically, the following steps are included: (1) Solution treatment: Heating 7075 aluminum alloy for solution treatment; (2) Dynamic quenching: Quenching treatment is performed on the 7075 aluminum alloy after solution treatment; (3) Composite aging treatment: The composite aging treatment is carried out in two stages. In the first stage, the quenched 7075 aluminum alloy is subjected to low-temperature aging treatment. The second stage involves high-temperature aging treatment of the 7075 aluminum alloy after the first stage. (4) Ultra-low temperature strengthening: The 7075 aluminum alloy after composite aging treatment is immersed in a low temperature environment for deep cryogenic strengthening treatment to obtain the strengthened 7075 aluminum alloy.

2. The strengthening heat treatment method for 7075 aluminum alloy according to claim 1, characterized in that, In step (1), the solution treatment temperature of 7075 aluminum alloy is 450~490℃, and the solution treatment time is 3~6h.

3. The strengthening heat treatment method for 7075 aluminum alloy according to claim 1, characterized in that, In step (2), pulse water jet technology is used to perform dynamic quenching on the solution-treated 7075 aluminum alloy, wherein the circulating water pressure is 0.07MPa and the circulating water temperature is ≤25℃.

4. The strengthening heat treatment method for 7075 aluminum alloy according to claim 1, characterized in that, In step (2), the quenching cooling rate of the 7075 aluminum alloy after solution treatment is greater than or equal to the critical threshold of strengthening supersaturated solid solution, i.e., ≥200℃ / s.

5. The strengthening heat treatment method for 7075 aluminum alloy according to claim 1, characterized in that, The conditions for the first stage of composite aging in step (3) are: heat preservation at 107~140℃ for 6 hours; the conditions for the second stage of composite aging are: heat preservation at 175~180℃ for 8~12 hours.

6. The strengthening heat treatment method for 7075 aluminum alloy according to claim 1, characterized in that, The temperature gradient difference between the two stages of the composite aging treatment in step (3) is 65~75℃.

7. The strengthening heat treatment method for 7075 aluminum alloy according to claim 1, characterized in that, The low-temperature environment in step (4) is a liquid nitrogen environment; the cryogenic strengthening treatment time is 3~6h.

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