Preparation process of Al-Zn-Mg alloy

Abstract

The invention provides an Al-Zn-Mg alloy preparation process which comprises the following steps: carrying out two-stage homogenization treatment on an aluminum bar, namely firstly preserving heat at 460-480 DEG C for 10-16 hours, and then preserving heat at 480-500 DEG C for 4-10 hours; then aluminum bar solution treatment is conducted, specifically, solution treatment is conducted for 1-4 h at the temperature of 480-520 DEG C; then aluminum bar extrusion is carried out, wherein the temperature of an extrusion die is kept at 480-500 DEG C, and the extrusion speed is 5-8 m / min; two-stage quenching is carried out after extrusion forming, specifically, firstly, rapid cooling is carried out to 300-350 DEG C, and then slow cooling is carried out to the room temperature; and finally, three-stage aging treatment is conducted, specifically, in the first-stage aging treatment, heat preservation is conducted for 10-20 h at the temperature of 100-140 DEG C, in the second-stage aging treatment, heat preservation is conducted for 4-10 h at the temperature of-100 DEG C to-200 DEG C, and in the third-stage aging treatment, isothermal treatment is conducted for Compared with a conventional aluminum alloy plate, the Al-Zn-Mg alloy produced through the provided preparation technology is more uniform in alloy structure, the yield strength, the tensile strength, the compressive yield strength and other mechanical properties of the alloy are effectively improved, and the corrosion resistance of the plate is obviously improved.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy production, and in particular provides an Al-Zn-Mg alloy preparation process. Background Art

[0002] Al-Zn-Mg alloys are widely used in aerospace, rail transportation and automobile industries due to their excellent extrusion processing performance. Cu-free Al-Zn-Mg alloys are very suitable for short-process production of online quenching directly after extrusion molding due to their wide solid solution temperature range and low quenching sensitivity, which greatly promotes the application of Cu-free Al-Zn-Mg alloys in industry. At the same time, as a typical heat-treatable aluminum alloy, the type, quantity, size and distribution of the precipitated phases in the alloy grains and grain boundaries can be regulated by aging heat treatment, thereby improving the toughness and corrosion resistance of the alloy. However, with the rapid development of high-tech fields such as transportation, aerospace, etc., the demand for high-performance aluminum alloy products continues to grow, and the requirements for the strength, corrosion resistance, quality uniformity and consistency of the alloy continue to increase. There are still certain problems in the application of Al-Zn-Mg extrusion alloys in various fields. It has become an important task to optimize the heat treatment process of the alloy to meet its use requirements and give full play to its application potential.

[0003] Current technical issues include: (1) Al-Zn-Mg alloys have a key strength problem. Improving the yield strength, tensile strength and compressive yield strength of the alloy has always been a major technical challenge for Al-Zn-Mg extruded alloys.

[0004] (2) The inhomogeneity of the alloy structure and properties of Al-Zn-Mg extruded products is another difficult problem in the development of alloys. The inhomogeneity of the alloy structure seriously affects the comprehensive performance of the alloy and reduces the service life of the alloy.

[0005] (3) The quenching sensitivity of Al-Zn-Mg alloy is also one of the key factors affecting the alloy performance. Improper quenching rate selection will significantly reduce the subsequent alloy performance.

[0006] (4) Only small-sized products can be produced, with low production efficiency; poor product quality stability; and not environmentally friendly. Summary of the invention

[0007] Based on this, the present invention provides an Al-Zn-Mg alloy preparation process to improve the uniformity of the alloy structure, so as to improve the alloy's yield strength, tensile strength, compressive yield strength and other properties.

[0008] In order to achieve the above object, the present invention provides a process for preparing an Al-Zn-Mg alloy, the steps comprising: S100. Double-stage homogenization treatment of aluminum bars: first, keep at 460-480℃ for 10-16h, then keep at 480-500℃ for 4-10h; S200. Aluminum rod solution treatment: 480-520℃ solution for 1-4 h; S300. Aluminum rod extrusion process: the extrusion die is maintained at 480-500°C, and the extrusion speed is 5m / min-8m / min; S400. Two-stage quenching: first quickly cool to 300-350℃, then slowly cool to room temperature; S500. Three-level aging treatment: the first level aging treatment is 100-140℃ insulation for 10-20h, the second level aging treatment is -100--200℃ insulation for 4-10h, and the third level aging treatment is 140-200℃ isothermal for 12-24h.

[0009] Furthermore, in the double-stage homogenization process of the aluminum rod, the aluminum rod is first placed in a high-temperature furnace at 460-480°C for 10-16 hours for the first stage homogenization treatment; after the first stage homogenization treatment, it is quickly moved to 480-500°C for 4-10 hours of second stage homogenization treatment.

[0010] Furthermore, after the first stage homogenization treatment is completed and the aluminum rod is transferred to the second stage homogenization treatment, insulation measures are taken to maintain the temperature of the aluminum rod at 460-480°C.

[0011] Furthermore, during the aluminum rod extrusion process, the extrusion die is preheated to 480-500°C in advance and maintained at this temperature.

[0012] Furthermore, in the double-stage quenching process, the temperature is first cooled to 300-350° C. at a rate of 80-100° C. / s, and then cooled to room temperature at a rate of 20-40° C. / s.

[0013] Furthermore, during the first aging treatment, the material cooled to room temperature is placed in an aging furnace at a temperature of 100 to 140°C for 10 to 20 hours of aging treatment. After the first aging treatment, the material is quickly water-cooled to room temperature, and then placed in a coolant for a second aging treatment of 4 to 10 hours, and the coolant temperature is -100 to -200°C. After the second aging is completed, the material is continued to be placed in an aging furnace at a temperature of 140 to 200°C for a third aging treatment of 12 to 24 hours. After the third aging treatment, the material is cooled to room temperature by strong wind.

[0014] Compared with the prior art, the present invention has the following advantages and effects: 1. Double-stage homogenization treatment is added before solution treatment. At a higher temperature, the alloy is given enough time to fully dissolve and fuse the elements, eliminate the existing microsegregation, and lay the foundation for subsequent treatment; 2. Reduce the deformation of the entire extrusion process and ensure the quality of the extruded material by preheating and maintaining a reasonable extrusion die temperature and maintaining a reasonable extrusion speed; 3. The quenching process uses a two-stage quenching method to rapidly cool the material. Cooling at different rates within different temperature ranges can reduce the precipitation of precipitated phases and improve subsequent aging hardness; 4. The three-stage aging technology of lower temperature, ultra-low temperature and higher temperature has greatly improved the strength, hardness and corrosion resistance of the alloy. Among them, ultra-low temperature aging is a revolutionary technology, which usually uses liquid gas to cool the material and keeps it warm in a deep cold environment for a period of time. Combined with the lower temperature and higher temperature aging treatment, it can better improve the comprehensive performance of the alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which constitute a part of the specification, describe embodiments of the present disclosure and, together with the specification, are used to explain the principles of the present disclosure. With reference to the accompanying drawings, the present disclosure can be more clearly understood according to the following detailed description, in which: Figure 1 It is a process flow chart of a preparation process of an Al-Zn-Mg alloy provided; Figure 2 is a process flow chart of Example 1 of a provided Al-Zn-Mg alloy preparation process; Figure 3 is a process flow chart of Example 2 of a provided Al-Zn-Mg alloy preparation process; Figure 4 is a process flow chart of Example 3 of a provided Al-Zn-Mg alloy preparation process; Figure 5 is a process flow chart of Example 4 of a provided Al-Zn-Mg alloy preparation process; Figure 6 is a process flow chart of Example 5 of a provided Al-Zn-Mg alloy preparation process; Figure 7 is a process flow chart of the Al-Zn-Mg alloy preparation process of Comparative Example 1; Figure 8 is a process flow chart of the Al-Zn-Mg alloy preparation process of Comparative Example 2; Fig. 9 It is a process flow chart of the Al-Zn-Mg alloy preparation process of comparative example 3. DETAILED DESCRIPTION

[0016] Various exemplary embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. The description of the exemplary embodiments is merely illustrative and is in no way intended to limit the present disclosure and its application or use. The present disclosure can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to make the present disclosure thorough and complete and to fully express the scope of the present disclosure to those skilled in the art. It should be noted that unless otherwise specifically stated, the relative arrangement of the components and steps, the composition of the materials, the numerical expressions and the numerical values ​​set forth in these embodiments should be interpreted as being merely exemplary and not as limiting.

[0017] In view of the problems existing in the current alloys, the present invention creates a new heat treatment process to solve the defects in various aspects of the alloys.

[0018] like Figure 1 As shown, the present invention provides a process for preparing an Al-Zn-Mg alloy, the steps comprising: S100. Double-stage homogenization treatment of aluminum rods: first, keep at 460-480℃ for 10-16h, then keep at 480-500℃ for 4-10h. During the implementation process, the aluminum rods are first placed in a high-temperature furnace at 460-480℃ for 10-16h for the first-stage homogenization treatment. After the first-stage homogenization treatment, the rods are quickly moved to 480-500℃ for the second-stage homogenization treatment for 4-10h. The entire transfer process is kept fast to minimize the transfer time. Before the solution process, a stepped double-stage homogenization process within a reasonable temperature range is added to increase the uniformity of the overall structure of the alloy.

[0019] S200. Aluminum rod solid solution treatment: 480-520℃ solid solution for 1-4 hours. During the implementation process, the aluminum rod is quickly transferred after the homogenization process is completed, and the aluminum rod is solid solution treated at 480-520℃ for 1-4 hours. After the homogenization treatment, a higher temperature solid solution treatment is performed to ensure that the alloy elements are fully integrated and eliminate micro segregation.

[0020] S300. Aluminum rod extrusion process: the extrusion die is kept at 480-500℃, and the extrusion speed is 5-8m / min. During the implementation process, the extrusion die is preheated in advance, and the extrusion die is first heated to 480-500℃ and maintained. After the material is solution treated, the extrusion treatment is carried out quickly, and the extrusion speed is controlled at 5-8m / min, and the overall extrusion speed is kept uniform. The extrusion die is preheated in advance, and a reasonable extrusion speed is used to control the deformation of the alloy during the extrusion process, ensuring that the temperature of the alloy is in a stable state during the extrusion process.

[0021] S400. Double-stage quenching: First, quickly cool to 300-350℃, then slowly cool to room temperature; during the implementation process, after extrusion, the material is quickly cooled to 300-350℃ at a rate of 80-100℃ / s. Then cool to room temperature at a rate of 20-40℃ / s. The double-stage quenching method uses different quenching rates in different temperature ranges to quickly reduce the material temperature and reduce the generation of precipitation phases.

[0022] S500. Three-stage aging treatment: The first stage aging treatment is 100-140℃ insulation for 10-20h, the second stage aging is -100--200℃ insulation for 4-10h, and the third stage aging is 140-200℃ isothermal for 12-24h. During the implementation process, the material cooled to room temperature is placed in an aging furnace at a temperature of 100-140℃ for 10-20h aging treatment. After the aging is completed, it is quickly water-cooled to room temperature, and then placed in a coolant for 4-10h second-stage aging treatment, and the coolant temperature is -100--200℃. After the second stage aging is completed, the material is continued to be placed in an aging furnace at a temperature of 140-200℃ for 12-24h third-stage aging treatment, and finally forced air cooled to room temperature, which has good environmental protection. The three-stage aging process of lower temperature aging, ultra-low temperature aging and higher temperature aging is adopted to improve the strength of the alloy and increase the stability of performance.

[0023] In the following examples, 7046 aluminum alloy plate is used, the main components of the alloy are Al-6.6Zn-1.8Mg-0.2Cu-0.1Zr, the sample width is 200mm, the thickness is 10mm, and the length is 600mm: Example 1 like Figure 2 As shown, the steps of the Al-Zn-Mg alloy preparation process provided in Example 1 include: S110. Two-stage homogenization treatment of aluminum alloy ingots. First stage: holding temperature 470℃, holding time 12h, second stage: holding temperature 490℃, holding time 6h.

[0024] S210. After homogenization treatment, solution treatment is carried out immediately. The holding temperature is 500°C and the solution time is 2h.

[0025] S310. Preheat the extrusion die to 480°C, and quickly extrude after completing the solution treatment. Keep the temperature constant during the extrusion process and keep the extrusion rate at 6m / min.

[0026] S410. After extrusion is completed, the steel is rapidly cooled to 320°C at a rate of 100°C / s, and then cooled to room temperature at a rate of 30°C / s.

[0027] S510. Three-level aging treatment. Level 1: Insulation temperature 120℃, insulation time 12h. Level 2: Insulation temperature -150℃, insulation time 6h. Level 3: Insulation temperature 140℃, insulation time 14h.

[0028] Example 2 like Figure 3 As shown, the steps of the Al-Zn-Mg alloy preparation process provided in Example 2 include: S120. Two-stage homogenization treatment of aluminum alloy ingots. First stage: holding temperature 470℃, holding time 12h, second stage: holding temperature 490℃, holding time 6h.

[0029] S220. After homogenization treatment, solution treatment is carried out immediately. The holding temperature is 500℃ and the solution time is 2h.

[0030] S320. Preheat the extrusion die to 480°C, and quickly extrude after completing the solution treatment. Keep the temperature unchanged during the extrusion process and the extrusion rate at 6m / min.

[0031] S420. After extrusion is completed, the steel is rapidly cooled to 320°C at a rate of 100°C / s, and then cooled to room temperature at a rate of 30°C / s.

[0032] S520. Three-level aging treatment. Level 1: Insulation temperature 120℃, insulation time 12h. Level 2: Insulation temperature -150℃, insulation time 6h. Level 3: Insulation temperature 160℃, insulation time 14h.

[0033] Example 3 like Figure 4 As shown, the steps of the Al-Zn-Mg alloy preparation process provided in Example 2 include: S130. Two-stage homogenization treatment of aluminum alloy ingots. First stage: holding temperature 470℃, holding time 12h, second stage: holding temperature 490℃, holding time 6h.

[0034] S230. After homogenization treatment, solution treatment is carried out immediately. The holding temperature is 500℃ and the solution time is 2h.

[0035] S330. Preheat the extrusion die to 480°C, and quickly extrude after completing the solution treatment. Keep the temperature unchanged during the extrusion process and the extrusion rate at 6m / min.

[0036] S430. After extrusion is completed, the steel is rapidly cooled to 320°C at a rate of 100°C / s, and then cooled to room temperature at a rate of 30°C / s.

[0037] S530. Three-level aging treatment. Level 1: Insulation temperature 120℃, insulation time 12h. Level 2: Insulation temperature -150℃, insulation time 6h. Level 3: Insulation temperature 200℃, insulation time 14h.

[0038] Example 4 like Figure 5 As shown, the steps of the Al-Zn-Mg alloy preparation process provided in Example 4 include: S140. Two-stage homogenization treatment of aluminum alloy ingots. First stage: holding temperature 470℃, holding time 12h, second stage: holding temperature 490℃, holding time 6h.

[0039] S240. After homogenization treatment, solution treatment is carried out immediately. The holding temperature is 500℃ and the solution time is 2h.

[0040] S340. Preheat the extrusion die to 480°C, and quickly extrude after completing the solution treatment. Keep the temperature unchanged during the extrusion process and the extrusion rate at 6m / min.

[0041] S440. After extrusion is completed, it is quickly cooled to 320°C at a rate of 100°C / s, and then cooled to room temperature at a rate of 30°C / s.

[0042] S540. Three-level aging treatment. Level 1: Insulation temperature 120℃, insulation time 12h. Level 2: Insulation temperature -100℃, insulation time 6h. Level 3: Insulation temperature 160℃, insulation time 14h.

[0043] Example 5 like Figure 6 As shown, the steps of the Al-Zn-Mg alloy preparation process provided in Example 5 include: S150. Two-stage homogenization treatment of aluminum alloy ingots. First stage: holding temperature 470℃, holding time 12h, second stage: holding temperature 490℃, holding time 6h.

[0044] S250. After homogenization treatment, solution treatment is carried out immediately. The holding temperature is 500℃ and the solution time is 2h.

[0045] S350. Preheat the extrusion die to 480°C, and quickly extrude after completing the solution treatment. Keep the temperature unchanged during the extrusion process and the extrusion rate at 6m / min.

[0046] S450. After extrusion, the steel sheet is rapidly cooled to 320°C at a rate of 100°C / s, and then cooled to room temperature at a rate of 30°C / s.

[0047] S550. Three-level aging treatment. Level 1: Insulation temperature 120℃, insulation time 12h. Level 2: Insulation temperature -200℃, insulation time 6h. Level 3: Insulation temperature 160℃, insulation time 14h.

[0048] Comparative Example 1 like Figure 7 As shown, the steps of the Al-Zn-Mg alloy preparation process of Comparative Example 1 include: S11D. Two-stage homogenization treatment of aluminum alloy ingots. First stage: holding temperature 470℃, holding time 12h, second stage: holding temperature 490℃, holding time 6h.

[0049] S21D. After homogenization treatment, solution treatment is carried out immediately. The holding temperature is 500℃ and the solution time is 2h.

[0050] S31D. Preheat the extrusion die to 480°C, and then quickly extrude after solution treatment. Keep the temperature constant during the extrusion process and the extrusion rate at 6m / min.

[0051] S41D. After extrusion, it is quickly cooled to 320℃ at a rate of 100℃ / s, and then cooled to room temperature at a rate of 30℃ / s.

[0052] S42D.T6 aging treatment. Insulation temperature 120℃, insulation time 24h.

[0053] Comparative Example 2 like Figure 8 As shown, the steps of the Al-Zn-Mg alloy preparation process of Comparative Example 2 include: S12D. Two-stage homogenization treatment of aluminum alloy ingots. First stage: holding temperature 470℃, holding time 12h, second stage: holding temperature 490℃, holding time 6h.

[0054] S22D. After homogenization treatment, solution treatment is carried out immediately. The holding temperature is 500℃ and the solution time is 2h.

[0055] S32D. Preheat the extrusion die to 480°C, and then quickly extrude after solution treatment. Keep the temperature constant during the extrusion process and the extrusion rate at 6m / min.

[0056] S42D. After extrusion, it is quickly cooled to 320℃ at a rate of 100℃ / s, and then cooled to room temperature at a rate of 30℃ / s.

[0057] S52D.T7 aging treatment. First level: insulation temperature 120℃, insulation time 12h. Second level: insulation temperature 160℃, insulation time 14h.

[0058] Comparative Example 3 like Fig. 9 As shown, the steps of the Al-Zn-Mg alloy preparation process of Comparative Example 3 include: S13D. Single-stage homogenization treatment of aluminum alloy ingots. Holding temperature 480℃, holding time 12h.

[0059] S23D. After homogenization treatment, solution treatment is carried out immediately. The holding temperature is 500℃ and the solution time is 2h.

[0060] S33D. Preheat the extrusion die to 480°C, and then quickly extrude after solution treatment. Keep the temperature constant during the extrusion process and the extrusion rate at 6m / min.

[0061] S43D. After extrusion, it is quickly cooled to room temperature at a rate of 100℃ / s.

[0062] S53D.T6 aging treatment. Insulation temperature 120℃, insulation time 24h.

[0063] Table 1 Comparison of properties of Al-Zn-Mg alloys produced in various embodiments

[0064] Note: Mechanical properties testing standard: GB / T 228 Room temperature tensile test method for metal materials.

[0065] It can be concluded from Table 1 that the tensile strength of the Al-Zn-Mg alloy produced by the process provided by the present invention is 525-538 MPa, while the tensile strength of the Al-Zn-Mg alloy produced by the comparative example is 448-471 MPa. The tensile strength of the Al-Zn-Mg alloy produced by the process provided by the present invention is significantly improved.

[0066] The yield strength of the Al-Zn-Mg alloy produced by the process provided by the present invention is 496-504 MPa, while the tensile strength of the Al-Zn-Mg alloy produced by the comparative example is 402-422 MPa. The yield strength of the Al-Zn-Mg alloy produced by the process provided by the present invention is significantly improved.

[0067] The hardness of the Al-Zn-Mg alloy produced by the process provided by the present invention is 150-159 HV, while the hardness of the Al-Zn-Mg alloy produced by the comparative example is 121-129 HV. The hardness of the Al-Zn-Mg alloy produced by the process provided by the present invention is significantly improved.

[0068] The elongation of the Al-Zn-Mg alloy produced by the process provided by the present invention is 15% to 18%, while the elongation of the Al-Zn-Mg alloy produced by the comparative example is 8% to 11%. The productivity of the Al-Zn-Mg alloy produced by the process provided by the present invention is significantly improved, and the alloy has better elongation.

[0069] The intergranular corrosion depth of the Al-Zn-Mg alloy produced by the process provided by the present invention is 62-88 μm, while the hardness of the Al-Zn-Mg alloy produced by the comparative example is 116-187 μm. The Al-Zn-Mg alloy produced by the process provided by the present invention has better corrosion resistance.

[0070] It can be seen from the test results in Table 1 that the Al-Zn-Mg alloy preparation process provided by the present invention has significantly improved corrosion resistance, strength, hardness and elongation compared to conventional aluminum alloy plates. An Al-Zn-Mg alloy preparation process ensures high strength while also having good corrosion resistance. In addition, the above process is suitable for preparing large-size products with high production efficiency and good product quality stability.

[0071] The present invention increases the uniformity of the overall structure of the alloy by adding a step-by-step two-stage homogenization process within a reasonable temperature range before the solution process. After the homogenization treatment, a higher temperature solution treatment is performed to ensure that the alloy elements are fully fused and microsegregation is eliminated. The present invention adopts a method of preheating the extrusion die in advance, and at the same time adopts a reasonable extrusion speed to control the deformation of the alloy during the extrusion process to ensure that the temperature of the alloy is in a stable state during the extrusion process. After the extrusion is completed, a two-stage quenching method is adopted, and different quenching rates are adopted in different temperature ranges to rapidly reduce the material temperature and reduce the generation of precipitation phases. The present invention adopts a three-stage aging process of relatively low temperature aging, ultra-low temperature aging and relatively high temperature aging, thereby improving the strength of the alloy and increasing the stability of the performance. Through a series of processes, the formation of precipitation phases is reduced, the homogenization of the microstructure of the substrate is achieved, and the comprehensive performance of the alloy is greatly improved.

[0072] Although some specific embodiments of the present disclosure have been described in detail by way of examples, it should be understood by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present disclosure. It should be understood by those skilled in the art that the above embodiments may be modified or some technical features may be replaced by equivalents without departing from the scope and spirit of the present disclosure. The scope of the present disclosure is defined by the appended claims.

Claims

1. A process for preparing an Al-Zn-Mg alloy, characterized in that the steps include: S100. Double-stage homogenization treatment of aluminum bars: first, keep at 460-480℃ for 10-16h, then keep at 480-500℃ for 4-10h; S200. Aluminum rod solution treatment: 480-520℃ solution for 1-4 h; S300. Aluminum rod extrusion process: the extrusion die is maintained at 480-500°C, and the extrusion speed is 5m / min-8m / min; S400. Two-stage quenching: first quickly cool to 300-350℃, then slowly cool to room temperature; S500. Three-level aging treatment: the first level aging treatment is 100-140℃ insulation for 10-20h, the second level aging treatment is -100--200℃ insulation for 4-10h, and the third level aging treatment is 140-200℃ isothermal for 12-24h.

2. The Al-Zn-Mg alloy preparation process according to claim 1, characterized in that: In the double-stage homogenization process of the aluminum rod, the aluminum rod is first placed in a high-temperature furnace at 460-480°C for 10-16 hours for the first-stage homogenization treatment; after the first-stage homogenization treatment, it is quickly moved to 480-500°C for the second-stage homogenization treatment for 4-10 hours.

3. The Al-Zn-Mg alloy preparation process according to claim 2, characterized in that: After the first stage homogenization treatment is completed, it is transferred to the second stage homogenization treatment process, and insulation measures are taken to keep the temperature of the aluminum rod at 460-480℃.

4. The Al-Zn-Mg alloy preparation process according to claim 1, characterized in that: During the aluminum bar extrusion process, the extrusion die is preheated to 480-500°C in advance and maintained at this temperature.

5. The Al-Zn-Mg alloy preparation process according to claim 1, characterized in that: In the double-stage quenching process, the steel is first cooled to 300-350°C at a rate of 80-100°C / s, and then cooled to room temperature at a rate of 20-40°C / s.

6. The Al-Zn-Mg alloy preparation process according to claim 1, characterized in that: In the first stage aging treatment, the material cooled to room temperature is placed in an aging furnace at a temperature of 100 to 140° C. for 10 to 20 hours of aging treatment.

7. The Al-Zn-Mg alloy preparation process according to claim 1 or 6, characterized in that: After the first stage aging treatment, the material is placed in a coolant for a second stage aging treatment for 4 to 10 hours, and the coolant temperature is -100 to -200°C.

8. The Al-Zn-Mg alloy preparation process according to claim 7, characterized in that: After the first aging treatment, the material is quickly water-cooled to room temperature and then subjected to the second aging treatment.

9. The Al-Zn-Mg alloy preparation process according to claim 7, characterized in that: After the second stage aging is completed, the material is placed in an aging furnace at a temperature of 140-200°C for a third stage aging treatment for 12-24 hours.

10. The Al-Zn-Mg alloy preparation process according to claim 1 or 8, characterized in that: After the third stage aging treatment, the material is cooled to room temperature by strong wind.

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