A fatigue-resistant heat treatment process for ultra-high strength high-zn-content 7xxx series aluminum alloys

Abstract

The application discloses a kind of anti-fatigue heat treatment processes of super-high-strength high-Zn-content 7xxx series aluminum alloy, belongs to aluminum alloy heat treatment technical field.The process is aimed at high-Zn-content 7xxx series aluminum alloy after extrusion densification treatment heat treatment, the heat treatment process is: first two-stage solid solution treatment, after quenching treatment, then it is two-stage aging treatment to obtain super-high-strength anti-fatigue aluminum alloy.The present application two-stage solid solution improves the recrystallization degree, reduces the proportion of deformed grains, effectively improves the material uniformity;Two-stage aging process can improve the precipitation effect of precipitate phase, effectively improve the strength and fatigue strength of material.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy heat treatment technology, specifically to a fatigue-resistant heat treatment process for ultra-high strength, high Zn content 7xxx series aluminum alloys. Background Technology

[0002] Al-Zn-Mg-Cu alloys are widely used in aerospace and military fields due to their high strength, low density, and good machinability. However, the rapid development of the aerospace industry has placed higher demands on the strength and ductility of aluminum alloys. Increasing the content of alloying elements can effectively improve the strength of 7xxx series aluminum alloys, but the casting process generates a large number of micron-sized precipitates, which severely limit the elongation and fatigue performance of the material. In addition, conventional methods for preparing highly alloyed materials (spray forming / powder metallurgy) suffer from high porosity and usually require extrusion densification. During this process, the original grains are elongated to form a large number of fibrous grains. During fatigue, local stress and strain concentrations easily occur within these grains, leading to crack initiation. Therefore, there is an urgent need to develop a heat treatment process that can significantly improve the strength and fatigue strength of ultra-high strength aluminum alloys. Summary of the Invention

[0003] To address the problem of low fatigue strength in ultra-high strength aluminum alloys, the present invention aims to provide a fatigue-resistant heat treatment process for ultra-high strength, high Zn content 7xxx series aluminum alloys.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A fatigue-resistant heat treatment process for ultra-high strength, high Zn content 7xxx series aluminum alloys is disclosed. This process is for heat treatment of high Zn content 7xxx series aluminum alloys after extrusion densification. The heat treatment process is as follows: first, a two-stage solution treatment is performed, followed by quenching treatment, and then a two-stage aging treatment is performed to obtain ultra-high strength fatigue-resistant aluminum alloys.

[0006] The two-stage solution treatment includes heating the aluminum alloy multiple times and holding it at that temperature for a period of time.

[0007] Preferably, the two-stage solution treatment consists of a first-stage solution treatment and a second-stage solution treatment performed sequentially, wherein: the first-stage solution treatment temperature is 400-450℃ and the holding time is 1-4h; the second-stage solution treatment temperature is 450-500℃ and the holding time is 2-10h.

[0008] Preferably, the transfer time from the end of the solution treatment to the quenching treatment is 15 seconds, and the quenching medium is room temperature water.

[0009] Preferably, the transfer time from the end of the quenching treatment to the aging treatment is 0-2 hours, and the aging equipment is a DF-101S heat-collecting constant temperature magnetic stirrer.

[0010] The two-stage aging treatment includes a first-stage aging treatment and a second-stage aging treatment, wherein: the first-stage aging temperature is 50-100℃ and the holding time is 3-12h; the second-stage aging temperature is 100-150℃ and the holding time is 12-20h.

[0011] The high Zn content 7xxx series aluminum alloy is prepared by spray deposition or powder metallurgy, and then heat-treated after extrusion densification.

[0012] The chemical composition of the high Zn content 7xxx series aluminum alloy, by weight percentage, is: Zn 7.6-10%, Mg 1.8-3.0%, Cu 0.8-2.6%, Zr 0.08-0.3%, with the balance being Al and unavoidable impurities.

[0013] Compared with the prior art, the beneficial effects of the present invention are:

[0014] After two-stage solution treatment, the precipitated phases in the alloy can be fully dissolved, thereby improving the solution treatment effect of Zn-rich aluminum alloys and increasing the precipitation kinetics during the aging process. Furthermore, the first-stage solution treatment effectively releases residual stress generated by extrusion, dissolves low-melting-point phases, increases the supersaturated solubility of the matrix, and optimizes the solution treatment effect. Compared with single-stage solution treatment, the total solution treatment time of two-stage solution treatment is longer. Therefore, the degree of recrystallization is significantly improved, the proportion of deformed grains is reduced, and the material homogeneity is effectively improved. In addition, the two-stage aging process can improve the precipitation effect of precipitated phases; the first-stage aging preferentially precipitates atomic clusters, reducing the difficulty of subsequent metastable MgZn2 phase precipitation, improving aging efficiency, and effectively improving the strength and fatigue strength of the material. Attached Figure Description

[0015] Figure 1 This is a microstructure diagram of the spray-deposited 7055-T6 aluminum alloy prepared in Example 1.

[0016] Figure 2 This is a microstructure diagram of the spray-deposited 7055-S6 aluminum alloy prepared in Example 1.

[0017] Figure 3 The tensile curve of the spray-deposited 7055 aluminum alloy prepared in Example 1 is shown.

[0018] Figure 4 The fatigue curve of the spray-deposited 7055 aluminum alloy prepared in Example 1 is shown.

[0019] Figure 5This is a microstructure diagram of the spray-deposited 7A61-T6 aluminum alloy prepared in Example 2.

[0020] Figure 6 Microstructure of the spray-deposited 7A61-S6 aluminum alloy prepared in Example 2.

[0021] Figure 7 Tensile curve of spray-deposited 7A61 aluminum alloy prepared in Example 2.

[0022] Figure 8 Fatigue curves of spray-deposited 7A61 aluminum alloy prepared in Example 2.

[0023] Figure 9 Microstructure of the spray-deposited 7034-T6 aluminum alloy prepared in Example 3.

[0024] Figure 10 Microstructure of the spray-deposited 7034-S6 aluminum alloy prepared in Example 3.

[0025] Figure 11 Tensile curve of the spray-deposited 7034 aluminum alloy prepared in Example 3.

[0026] Figure 12 Fatigue curve of 7034 aluminum alloy prepared by spray deposition in Example 3.

[0027] Figure 13 Microstructure of the powder metallurgy 7055-T6 aluminum alloy prepared in Example 4.

[0028] Figure 14 Microstructure of the powder metallurgy 7055-S6 aluminum alloy prepared in Example 4.

[0029] Figure 15 Tensile curve of powder metallurgy 7055 aluminum alloy prepared in Example 4.

[0030] Figure 16 Fatigue curve of powder metallurgy 7055 aluminum alloy prepared in Example 4. Detailed Implementation

[0031] To further understand the present invention, the present invention is described below with reference to examples. However, the examples are only for further illustrating the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention.

[0032] The following examples illustrate the heat treatment of high Zn content 7xxx series aluminum alloys, which are prepared by spray deposition or powder metallurgy, and then subjected to extrusion densification before heat treatment.

[0033] Example 1

[0034] This embodiment focuses on the heat treatment process of 7055Al alloy (7055-T6 and 7055-S6) prepared by spray forming and subsequently densified by large deformation extrusion to eliminate porosity.

[0035] First, the box furnace is heated to 400℃, and then the 7055 alloy is placed in the solidification furnace and held for 3 hours. Then, it is heated to 500℃ at a heating rate of 10℃ / min and held for 8 hours, followed by quenching.

[0036] Secondly, after quenching, the material is transferred to an oil bath stirring furnace within 1 hour, and heated to 100°C and held for 6 hours; then heated to 120°C and held for 12 hours.

[0037] The chemical composition of the aluminum alloy is (wt%): Zn: 7.6-8.4%; Mg: 1.8-3.2%; Cu: 2.0-2.6%; Zr: 0.08-0.25%; the remainder is Al.

[0038] Example 2

[0039] This embodiment focuses on the heat treatment process of 7A61 Al alloys (7A61-T6 and 7A61-S6) prepared by spray deposition method and subsequently densified by large deformation extrusion to eliminate porosity.

[0040] First, the box furnace is heated to 400℃, and then the 7A61 alloy is placed in the solidification furnace and held for 3 hours. Then, it is heated to 500℃ at a heating rate of 10℃ / min and held for 8 hours, followed by quenching.

[0041] Secondly, after quenching, the material is transferred to an oil bath stirring furnace within 1 hour, and heated to 100℃ and held for 6 hours; then heated to 120℃ and held for 12 hours.

[0042] The chemical composition of the aluminum alloy is (wt%): Zn: 8.6-9.8%; Mg: 2.4-3.0%; Cu: 1.3-1.7%; Zr: 0.08-0.12%.

[0043] Example 3

[0044] This embodiment focuses on the heat treatment process of 7034Al alloys (7034-T6 and 7034-S6) prepared by spray deposition method and subsequently densified by large deformation extrusion to eliminate porosity.

[0045] First, the box furnace is heated to 400℃, and then the 7034 alloy is placed in the solidification furnace and held for 3 hours. Then, it is heated to 500℃ at a heating rate of 10℃ / min and held for 8 hours, followed by quenching.

[0046] Secondly, after quenching, the material is transferred to an oil bath stirring furnace within 1 hour, and heated to 100℃ and held for 6 hours; then heated to 120℃ and held for 12 hours.

[0047] The chemical composition of the aluminum alloy is (wt%): Zn: 11-12%; Mg: 2.0-3.0%; Cu: 0.8-1.2%; Zr: 0.08-0.3%; the remainder is Al.

[0048] Example 4

[0049] This embodiment focuses on the heat treatment process of 7055Al alloys (7055-T6 and 7055-S6) prepared by spray deposition method and subsequently densified by large deformation extrusion to eliminate porosity.

[0050] First, the box furnace is heated to 400℃, and then the 7055 alloy is placed in the solidification furnace and held for 3 hours. Then, it is heated to 500℃ at a heating rate of 10℃ / min and held for 8 hours, followed by quenching.

[0051] Secondly, after quenching, the material is transferred to an oil bath stirring furnace within 1 hour, and heated to 100℃ and held for 6 hours; then heated to 120℃ and held for 12 hours.

[0052] The chemical composition of the aluminum alloy is (wt%): Zn: 7.6-8.4%; Mg: 1.8-3.2%; Cu: 2.0-2.6%; Zr: 0.08-0.25%; the remainder is Al.

[0053] The heat-treated aluminum alloys from Examples 1-4 were subjected to room temperature tensile and fatigue performance tests (tensile-compression symmetrical fatigue test, R = -1, fatigue strength taken from 10). -7 (Number of cycles), and observation was performed simultaneously using EBSD. Comparative Examples 1-4 were also performed on the materials from Examples 1-4 using a conventional single-stage T6 peak aging process. The microstructure, tensile curves, and fatigue curves of the aluminum alloy materials after heat treatment in Examples 1-4 are shown below. Figure 1-16 As shown.

[0054] Table 1 shows the heat treatment process and performance test data for each embodiment and comparative example.

[0055] Table 1

[0056]

[0057] As shown in the table above, the tensile strength, yield strength, elongation, and fatigue strength of the alloys prepared in Examples 1-4 are significantly improved compared to the control group, demonstrating a clear strengthening effect. Among them, Example 4 shows the most significant strengthening effect.

[0058] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A fatigue-resistant heat treatment process for ultra-high strength, high Zn content 7xxx series aluminum alloys, characterized in that: This process is for heat treatment of high Zn content 7xxx series aluminum alloys after extrusion densification. The heat treatment process is as follows: First, a two-stage solution treatment is performed, followed by quenching, and then a two-stage aging treatment is performed to obtain an ultra-high strength fatigue-resistant aluminum alloy. The two-stage solution treatment involves first heating a box furnace to 400℃, then placing the 7055 alloy into the solution furnace and holding it at that temperature for 3 hours; then heating to 500℃ at a heating rate of 10℃ / min and holding for 8 hours, followed by quenching; then, within 1 hour after quenching, the material is transferred to an oil bath stirring furnace and heated to 100℃ and held for 6 hours; then heated to 120℃ and held for 12 hours. The chemical composition of the high Zn content 7xxx series aluminum alloy, by weight percentage, is: Zn 7.6-10%, Mg 1.8-3.0%, Cu 0.8-2.6%, Zr 0.08-0.3%, with the balance being Al and unavoidable impurities.

2. The fatigue-resistant heat treatment process for ultra-high strength, high Zn content 7xxx series aluminum alloys according to claim 1, characterized in that: The transfer time from the end of the solution treatment to the quenching treatment is 15 seconds, and the quenching medium is room temperature water.

3. The fatigue-resistant heat treatment process for ultra-high strength, high Zn content 7xxx series aluminum alloys according to claim 1, characterized in that: The transfer time from the end of the quenching treatment to the aging treatment is 0-2 hours, and the aging equipment is a DF-101S heat-collecting constant temperature magnetic stirrer.

4. The fatigue-resistant heat treatment process for ultra-high strength, high Zn content 7xxx series aluminum alloys according to claim 1, characterized in that: The high Zn content 7xxx series aluminum alloy is prepared by spray deposition or powder metallurgy, and then heat-treated after extrusion densification.

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