Manufacturing method of Al-Zn-Mg-Cu series aluminum alloy sheet and aluminum alloy sheet

Abstract

The present invention discloses a method for manufacturing an Al-Zn-Mg-Cu series aluminum alloy sheet, including the following steps: (1) manufacturing an Al-Zn-Mg-Cu series aluminum alloy ingot; (2) sequentially performing homogenization treatment, hot rolling, cold rolling, solution quenching and aging treatment on the Al-Zn-Mg-Cu series aluminum alloy ingot to obtain a T6 state aluminum alloy sheet; (3) performing heating, warm forming, in-mold quenching, pre-aging treatment, and baking painting treatment on the T6 state aluminum alloy sheet to obtain a finished aluminum alloy sheet. Further, the present invention also discloses an Al-Zn-Mg-Cu series aluminum alloy sheet manufactured by the above manufacturing method. The Al-Zn-Mg-Cu series aluminum alloy sheet designed by the present invention has its production process and process parameters standardized, and the Al-Zn-Mg-Cu series aluminum alloy sheet manufactured by the manufacturing method has high tensile strength, yield strength and elongation rate, can be applied to automobiles, and has good prospects for generalization and practical value.

Description

Technical Field

[0001] Technical Field The present invention relates to an aluminum alloy sheet and a method for manufacturing the same, and particularly to a 7000 series aluminum alloy sheet and a method for manufacturing the same.

Background Art

[0002] Background Art As is well known, the density of aluminum is about 1 / 3 of that of steel, and it is the most widely used lightweight material at present. Aluminum alloy materials are lightweight materials with rapid application and maturing technology. In recent years, the usage amount of aluminum alloy materials in automobiles has shown a continuous increasing trend.

[0003] Compared with steel materials, aluminum alloy materials have many advantages such as high thermal conductivity, good corrosion resistance, and excellent processing performance. Although their strength is not as high as that of high-strength steel, through technical improvements, aluminum alloy materials can completely meet the requirements for vehicle lightweighting in terms of strength. Moreover, since the energy absorption performance of aluminum alloy materials is about twice that of steel, the collision safety of automobiles can be effectively improved. Therefore, in the automotive field, using aluminum alloy materials instead of conventional steel materials is an important development trend in vehicle lightweighting technology.

[0004] In the current prior art, aluminum alloys for automobile bodies mainly include the 2000 series (Al-Cu series), 5000 series (Al-Mg series), 6000 series (Al-Mg-Si series), and a small amount of the 7000 series (Al-Zn-Mg series or Al-Zn-Mg-Cu series). Among them, the Al-Zn-Mg-Cu series aluminum alloy is also called the 7000 series aluminum alloy material. After quenching and aging treatment, very high strength and toughness can be obtained, and due to its low density, many automobile manufacturers have begun to consider using this 7000 series aluminum alloy material instead of high-strength steel sheets for the manufacture of automobile parts such as B-pillars and damper reinforcing ribs of automobiles. For example, in the prior art, there is a 7000 series aluminum alloy that can be used for the manufacture of automobile safety devices, and the strength of this alloy is twice that of the conventional aluminum alloy for bumpers. This 7000 series aluminum alloy material can reduce the mass of the automobile body compared with high-strength steel materials and can ensure the safety of passengers to the greatest extent.

[0005] However, the 7000 series aluminum alloy in the quenched state has poor plasticity at room temperature, so it shows strong brittleness and hardness, and it is difficult to directly form more complex parts by general forming methods. Therefore, generally, it is necessary to anneal this 7000 series aluminum alloy sheet to improve the plasticity of the material, and then perform quenching and aging treatment after forming.

[0006] According to research, the conventional treatment method adopted is very complex in process, has a long subsequent heat treatment time, cannot meet the requirements of mass production of parts in the automobile industry, is easy to deform, and has a certain impact on the size of parts.

[0007] Meanwhile, currently, researchers' studies on warm forming mainly focus on aluminum alloy materials such as 5000 series and 6000 series that do not require heat treatment, as well as some magnesium alloy materials. The research on warm forming of heat-treatable 7000 series aluminum alloy materials is relatively less. Although there are individual studies, they all remain at the experiments of warm forming and their mechanical theories, the research on warm formability, and the simulation research on the warm forming process. In the current prior art, there is still no clear process technology targeting 7000 series aluminum alloy sheets for automobiles.

[0008] Therefore, in order to solve the problems that the room temperature formability of the conventional 7000 series aluminum alloy for automobiles is poor and the heat-treated samples after forming are prone to deformation, the inventors designed a manufacturing method for a new Al-Zn-Mg-Cu series aluminum alloy sheet belonging to the 7000 series aluminum alloy sheet. The process principle provided by the manufacturing method can not only be applied to this Al-Zn-Mg-Cu series aluminum alloy material, but also to all other aluminum alloys that can be strengthened by heat treatment, such as 2000 series, 6000 series, and other 7000 series aluminum alloy materials.

Summary of the Invention

Problems to be Solved by the Invention

[0009] Content of the Invention One object of the present invention is to provide a manufacturing method for a new Al-Zn-Mg-Cu series aluminum alloy sheet. The manufacturing method for the Al-Zn-Mg-Cu series aluminum alloy sheet adopts a reasonable process design, can improve the formability of the aluminum sheet, and can meet the usage requirements and lightweight requirements of automotive sheets. At the same time, the manufactured Al-Zn-Mg-Cu series aluminum alloy sheet has high tensile strength, yield strength, and elongation rate, can meet the requirements for the material strength and toughness of automotive sheets, and thus can overcome the drawbacks of the prior art.

Means for Solving the Problems

[0010] To achieve the above object, the manufacturing method of an Al-Zn-Mg-Cu series aluminum alloy sheet provided by the present invention includes the following steps: (1) Manufacturing an Al-Zn-Mg-Cu series aluminum alloy ingot; (2) Sequentially performing homogenization treatment, hot rolling, cold rolling, solution quenching treatment, and artificial aging treatment on the Al-Zn-Mg-Cu series aluminum alloy ingot to obtain a T6 state aluminum alloy sheet; (3) Performing heating, warm forming, in-die quenching, preliminary aging treatment, and baking painting treatment on the T6 state aluminum alloy sheet to obtain a finished aluminum alloy sheet.

[0011] In the current prior art, the forming process of traditional aluminum alloy sheets is to perform solution quenching and aging treatment on the aluminum alloy sheets and then obtain finished products by hot press forming. This process has poor formability and cannot be applied to Al-Zn-Mg-Cu series alloys.

[0012] In the present invention, in order to solve the problems that the room temperature formability of 7000 series aluminum alloys is poor and the heat-treated samples after forming are prone to deformation, the inventors have conducted extensive research. As a result, they have found that a new process integrating warm forming and quenching (solution heat treatment - forming - cold die quenching, abbreviated as the HFQ process) can be used to process 7000 series aluminum alloys.

[0013] The warm forming process is a process that combines the processes of hot forming and heat treatment. It can be applied to the forming of aluminum alloy sheet structural parts with complex shapes and high strength, contributing to the improvement of the formability of aluminum alloys. When attempting to use 7000 series high-strength aluminum alloys in the automotive field, it is necessary to significantly improve production efficiency. The warm forming process is expected to be an optimal process for the production of 7000 series high-strength aluminum alloys in the automotive manufacturing field.

[0014] However, in the conventional general warm forming process flow, it is common to perform warm forming and in-die quenching on a solutionized (W state) aluminum alloy sheet. Although this warm forming process has good formability, it still does not exert the strength limit because a part of the supersaturated solid solution decomposes during the in-die quenching process, affecting the precipitation of subsequent age-hardening phases.

[0015] Therefore, different from the above conventional warm forming process, in the present invention, the inventors creatively designed a process flow of homogenization treatment, hot rolling, cold rolling, solution quenching treatment, artificial aging treatment, heating, warm forming, in-die quenching, pre-aging treatment, and baking paint treatment for the manufactured Al-Zn-Mg-Cu series (i.e., 7000 series) aluminum alloy ingot and sequentially performed them, thereby obtaining a finished Al-Zn-Mg-Cu series aluminum alloy sheet.

[0016] In the present invention, by combining the process flows of step (2) and step (3), the process according to the present application becomes far superior to the above prior art process. This process designed according to the present invention adds an artificial aging treatment process after the solution quenching treatment compared with the conventional warm forming process.

[0017] The warm forming process adopted in the present invention first heats the Al-Zn-Mg-Cu series alloy sheet manufactured by cold rolling to the solution treatment temperature, and then holds it at the solution treatment temperature for a predetermined time to sufficiently dissolve solute atoms into the α-aluminum matrix, and quickly transports the sufficiently solutionized Al-Zn-Mg-Cu series alloy sheet to the mold for press forming and holds the pressure in the mold for quenching. Correspondingly, after the solution quenching treatment is completed, finally, the formed product is subjected to artificial aging treatment to control the formation of precipitates and ensure its strength.

[0018] However, the main reasons for holding the pressure in the mold for quenching are, firstly, to prevent the formation of coarse precipitates, especially their precipitation at grain boundaries, by rapid quenching, and secondly, to avoid deformation of the formed product during the quenching process.

[0019] This novel warm forming process designed by the present invention not only improves the formability of aluminum alloy materials, but also reduces the rebound of aluminum alloy materials, and can meet the production requirements of complex-shaped aluminum alloy automotive body exterior parts that require high precision and high strength.

[0020] It should be noted that after the completion of step (2), in step (3), it is necessary to perform rapid heating solution treatment, followed by warm forming and in-mold quenching on the artificially aged (T6 state) aluminum alloy sheet. This process not only has good formability, but also can exert the strength limit of the Al-Zn-Mg-Cu alloy system. This is because after rapid heating solution treatment, some fine strengthening phases still exist in the Al-Zn-Mg-Cu alloy system, and these strengthening phases can play a reinforcing role in the subsequent rapid preliminary aging treatment process.

[0021] It should be explained that in the present invention, the purpose of artificial aging treatment is to decompose the supersaturated solid solution with unstable profile after quenching by holding it at a predetermined temperature for a predetermined time, so as to significantly increase the strength and hardness of the alloy.

[0022] For Al-Zn-Mg-Cu series aluminum alloys, when only high strength is required, adopting a single-stage aging regime can obtain the T6 state. After aging treatment, its strengthening phases are mainly GP zones and a small amount of transition phases (η' phase), and the strength reaches the peak.

[0023] Furthermore, in the manufacturing method according to the present invention, the mass percentage content ratio of chemical elements of the Al-Zn-Mg-Cu series aluminum alloy ingot is: Cu: 1.6 - 2.2%, Mg: 1.8 - 2.4%, Zn: 6.0 - 8.6%, Zr: 0.10 - 0.16%, 0 < Ti ≤ 0.10%, 0 < Mn ≤ 0.05%, 0 < Cr ≤ 0.04%, and the balance is Al and inevitable impurities.

[0024] In some embodiments, the Ti content is 0 < Ti ≤ 0.06%. In some embodiments, the Ti content is 0.01 ≤ Ti ≤ 0.10%. In some embodiments, the Ti content is 0.04 ≤ Ti ≤ 0.10%. In some embodiments, the Ti content is 0.04 ≤ Ti ≤ 0.06%.

[0025] In some embodiments, the Mn content is 0.01 ≤ Mn ≤ 0.05%. In some embodiments, the Cr content is 0.005 ≤ Cr ≤ 0.04%. In some embodiments, the Cr content is 0.005 ≤ Cr ≤ 0.01%.

[0026] In the present invention, the Al-Zn-Mg-Cu series aluminum alloy ingot is optimized and designed, and the design principle of each chemical element is as follows.

[0027] Cu: In the Al-Zn-Mg-Cu series aluminum alloy ingot according to the present invention, by adding the Cu element, the stress corrosion resistance, cracking performance, strength performance, fatigue resistance performance and processing performance of the alloy can be improved, the fluidity of the alloy can be increased, the strengthening effect of the second-stage aging in two-stage aging can be enhanced, processing defects can be reduced, and the crack propagation rate of the alloy in a corrosive medium can be decreased. The Cu element can dissolve in the GP zone to make the GP zone more stable and delay its aging precipitation. Also, the Cu atoms can dissolve in η and η', reducing the potential difference between the intragranular and grain boundary of the crystal, and improving the corrosion resistance of the alloy. Moreover, an increase in the content of the Cu element increases the tendency of the material to have welding hot cracks and leads to a decrease in welding performance. Therefore, when designing the composition of the Al-Zn-Mg-Cu series aluminum alloy, various performance indicators of the alloy should be comprehensively considered, an appropriate Cu content should be selected, and by controlling the mass percentage content of the Cu element to 1.6 - 2.2%, the welding performance of the alloy can be balanced.

[0028] Of course, in some preferred embodiments, in order to obtain better implementation effects, the mass percentage content of the Cu element may be further controlled to 1.8-2.2%.

[0029] Mg, Zn: In the Al-Zn-Mg-Cu series aluminum alloy ingot according to the present invention, the alloying elements Zn and Mg can improve the yield strength and fracture toughness of the alloy by precipitating from the alloy matrix to form the strengthening phase η'(MgZn2) phase. If the content of the Zn element in the alloy is too low, the strength of the alloy will be insufficient. However, if the content of the Zn element in the alloy is too high, the toughness of the alloy will be low and the formability will be poor. According to the research of the present inventors, only when the contents of the Zn and Mg elements fall within a certain critical range, the age hardening effect can be achieved in the alloy matrix. When the content exceeds the maximum value of the critical range, even if the contents of the Zn and Mg elements are increased, the age hardening effect cannot be improved. However, when the contents of Zn and Mg are below the minimum value of the critical range, the age hardening effect disappears. Therefore, when the Zn / Mg ratio falls within the range of 2.6-3.3, the age precipitation phase of the alloy can be distributed finely and dispersedly, and the age treatment process can also proceed rapidly. Therefore, in the present invention, the mass percentage content of the Mg element is controlled to 1.8-2.4%, and the mass percentage content of the Zn element is controlled to 6.0-8.6%.

[0030] Of course, in some preferred embodiments, in order to obtain better implementation effects, the mass percentage content of the Mg element may be controlled to 2.0-2.4%, and the mass percentage content of the Zn element may be controlled to 6.1-7.8%.

[0031] Zr: In the Al-Zn-Mg-Cu series aluminum alloy ingot according to the present invention, the fine and dispersed precipitate phases formed by trace transition elements Mn, Cr, and Zr can improve the yield strength and tensile strength of the alloy, and by suppressing recrystallization, a fine deformed substructure-containing grain structure can be obtained, and this structure contributes to the improvement of the fracture toughness of the alloy and improves the toughness by causing intragranular fracture in the alloy. Alloys containing Mn and Cr elements have significantly higher corrosion resistance than alloys without Mn and Cr. These elements contribute to the increase in the recrystallization temperature of the alloy and prevent the progress of the recrystallization process during hot deformation and subsequent quenching heating. Moreover, low contents of Cr and Mn do not form any harmful coarse phases. Of course, the most effective is the addition of Zr, which can increase the recrystallization temperature of the aluminum alloy both after hot deformation and after cold deformation, and enables the obtaining of a non-recrystallized structure after heat treatment. Therefore, in the present invention, in order to further improve the strength of the Al-Zn-Mg-Cu series alloy, Zr element is added as an essential element, and the mass percentage content of Zr is controlled to be 0.10 - 0.16%.

[0032] Of course, in some preferred embodiments, in order to obtain better implementation effects, the mass percentage content of Zr element may be further controlled to be 0.10 - 0.13%.

[0033] The Zr element can combine with the Al element to form the Al3Zr intermetallic compound. This intermetallic compound has two structural forms: one is Al3Zr directly precipitated from the melt, which has a tetragonal crystal structure and can significantly refine the as-cast grains of the alloy; the other is spherical particles precipitated during the ingot homogenization process, which has an LI2 structure and is in a co-lattice relationship with the matrix, and has the effect of strongly suppressing recrystallization during the hot working process. By adding a small amount of Zr, the strength, fracture toughness, and stress corrosion resistance of the aluminum alloy can be improved. Also, since Zr has low hardenability, Zr can also improve the hardenability and weldability of the alloy.

[0034] In summary, in this Al-Zn-Mg-Cu series aluminum alloy designed according to the present invention, the addition of trace amounts of Cr, Mn, Ti, and Zr has a strong grain refinement effect, and the ingot structure of the Al-Zn-Mg-Cu series aluminum alloy produced therefrom is uniform and fine equiaxed crystals. As the grain refinement mechanism of this design, the atomic clusters containing Cr and Mn that are completely co-lattice with α(Al) replace TiB as the "matrix" for the joint nucleation of Al3Ti and Al3Zr, so that both Ti and Zr can contribute to the grain refinement process. In the heterogeneous nucleation process, Al3Ti nucleates through the co-lattice atomic clusters, Al3(Ti,Zr) nucleates through Al3Ti, and α(Al) nucleates through Al3(Ti,Zr).

[0035] Furthermore, in the manufacturing method according to the present invention, the mass percentage content of the chemical elements of the Al-Zn-Mg-Cu series aluminum alloy ingot further satisfies at least one of the following: Cu: 1.8 - 2.2%, Mg: 2.0 - 2.4%, Zn: 6.1 - 7.8%, Zr: 0.10 - 0.13%.

[0036] Furthermore, in the manufacturing method according to the present invention, the inevitable impurities of the Al-Zn-Mg-Cu series aluminum alloy ingot include at least one of the following: Si ≤ 0.10%, Fe ≤ 0.15%, and the total amount of other impurity elements ≤ 0.100%.

[0037] In the Al-Zn-Mg-Cu series aluminum alloy ingot according to the present invention, both Si and Fe are impurity elements in the aluminum alloy. Impurity elements such as Si and Fe are harmful elements that cannot be avoided in the melting process of the Al-Zn-Mg-Cu series aluminum alloy ingot, and can form coarse brittle phases with high melting points (such as Al7Cu2Fe) in the alloy matrix. These phases will be arranged in a string-like manner along the deformation direction during the processing and deformation process. There is a high-energy phase interface between them and the matrix, and it is difficult for them to deform coherently. After applying force, microcracks are likely to occur. If stress is continuously applied, the microcracks will coalesce and grow, developing into macroscopic cracks, the crack propagation speed will increase, and the plasticity and fracture toughness of the alloy will decrease.

[0038] For example, when the Fe element dissolves in Al, it forms FeAl3, and by refining the recrystallized grains, the performance of the alloy can be improved. However, due to the large potential difference between FeAl3 and the Al matrix, it leads to a decrease in the corrosion resistance of the alloy. Also, for example, when Mn is added to the aluminum alloy ingot, (Fe,Mn)Al6 is formed in the alloy, thereby reducing the potential difference between FeAl3 and Al and improving the corrosion resistance of the alloy.

[0039] Therefore, in order to ensure the performance and quality of the aluminum alloy, it is necessary to strictly control the mass percentage content of the above impurity elements, and control the total amount of other impurity elements to ≤0.100% and the mass percentage content of each other individual impurity element to ≤0.030%. Thereby, the content of coarse second phases containing impurity elements such as Si and Fe in the alloy can be reduced, and finally, the fracture toughness of the alloy can be improved and the crack propagation speed can be decreased.

[0040] When technically acceptable, in order to obtain an aluminum alloy with better performance and quality, the content of impurity elements in the Al-Zn-Mg-Cu series aluminum alloy ingot should be reduced as much as possible.

[0041] In some preferred embodiments, in order to obtain better implementation effects and bring better quality to the produced Al-Zn-Mg-Cu series aluminum alloy ingots, more preferably, it may be controlled such that Si < 0.08% and Fe < 0.10%.

[0042] Furthermore, in the manufacturing method according to the present invention, in step (2), for the homogenization treatment, a three-stage homogenization treatment is adopted. However, for the first-stage homogenization treatment, it is held at a temperature of 418 - 430 °C for 5 - 8 h, for the second-stage homogenization treatment, it is held at a temperature of 460 - 468 °C for 8 - 12 h, and for the third-stage homogenization treatment, it is held at a temperature of 470 - 480 °C for 20 - 24 h.

[0043] In step (2) of the present invention, the purpose of performing the homogenization treatment on the Al-Zn-Mg-Cu series aluminum alloy ingot is to eliminate dendritic segregation and compositional segregation, obtain a solid solution with uniformly distributed solute atoms, and reduce the coarse second phase which is the nucleation mechanism of recrystallization PSN.

[0044] The two-stage homogenization treatment can obtain the best age hardening effect. However, due to the high-temperature holding stage at 473 °C in the secondary homogenization treatment regime, it brings about a certain degree of aggregation and growth phenomena of the insoluble Fe-containing phase (Al7Cu2Fe) and S (Al2CuMg) phase. These coarse and brittle second phases are difficult to deform, which not only reduces the strength of the alloy but also inhibits the movement of dislocations and reduces the plasticity of the alloy.

[0045] The purpose of adopting the three-stage homogenization treatment in the present invention is to obtain fine, dispersed, and uniformly distributed Al3Zr particles by adopting the three-stage homogenization treatment. According to the dislocation bypass mechanism in which the second phase that is difficult to deform inhibits the movement of dislocations, the smaller the radius and distribution interval of the Al3Zr particles that are difficult to deform and the more dispersed they are, the greater the critical shear stress that the dislocations need to overcome to move further. As a result, the stronger the effect of inhibiting the movement of dislocations, the higher the strength of the alloy. In addition, the finely dispersed Al3Zr particles can prevent the occurrence of recrystallization, retain the deformed substructure, and refine the crystal grain size. Therefore, the dislocation slip distance can be shortened, the intersection of dislocations on different slip planes and the stress concentration caused by the accumulation of dislocations at the crystal grain boundaries can be reduced, and the plasticity of the aluminum alloy material can be improved. Further, the three-stage homogenization treatment can also spheroidize the S(Al2CuMg) phase.

[0046] Furthermore, in the manufacturing method according to the present invention, in step (2), the hot rolling includes the following steps: heating the ingot to 430-440 °C and holding for 90-120 min, and then performing multi-pass hot rolling alternately in the longitudinal and transverse directions, and controlling the total hot rolling deformation amount to be ≥85%. Control the rolling end temperature to be ≥380 °C, for example, 380-400 °C.

[0047] In the above technical solution of the present invention, performing the hot process alternately in the longitudinal and transverse directions means controlling the rolling direction of the hot rolling alternately along the length direction and the width direction of the sheet material. By performing rolling alternately in the longitudinal and transverse directions, the sheet material size required for subsequent warm forming can be obtained, and good mechanical properties in the thickness direction can be obtained.

[0048] In the hot rolling process, the starting rolling temperature of hot rolling is about 85 - 90% of the melting point temperature of the alloy. However, it is necessary to consider the influence of low melting point phases such as the S (Al2CuMg) phase and T (AlZnMgCu) phase in the Al-Zn-Mg-Cu system. If the hot rolling temperature is too high, grain coarsening and melting of grain boundary low melting point substances are likely to occur, leading to overheating and overburning of the ingot to be heated, as well as cracks and crushing during hot rolling. If the hot rolling temperature is too low, non-uniform deformation of the ingot is caused, the rolling load is increased, the tendency of edge cracks during ingot rolling is increased, and normal rolling is affected. As can be seen from these, since the height of the hot rolling temperature affects the heat resistance and room temperature mechanical properties of the material, in order to ensure the performance of the aluminum alloy material, in the present invention, the starting rolling temperature of hot rolling may be controlled at 430 - 440°C.

[0049] Correspondingly, in the hot rolling process, the finishing rolling temperature of hot rolling is determined according to the type II recrystallization diagram of the alloy. The finishing rolling temperature during block rolling of hot rolling of Al-Zn-Mg-Cu system aluminum alloy is usually controlled above the recrystallization temperature. Therefore, in the present invention, the finishing rolling temperature may be controlled at ≧380°C.

[0050] Furthermore, in the hot rolling process, the total rolling deformation amount needs to be selected according to the characteristics of the Al-Zn-Mg-Cu system aluminum alloy itself. The larger the total rolling deformation amount, the more uniform the structure of the material and the better the performance. When the total rolling deformation amount is controlled at 85% or more, rolled plates with the best structure can be obtained.

[0051] Also, in the hot rolling process, the pass reduction rate needs to be selected considering the high temperature performance, bite conditions, product quality requirements, etc. of the Al-Zn-Mg-Cu system alloy, and the pass reduction rate varies depending on the rolling stage. In the first stage of rolling, it may be rolled in 3 - 5 passes with a low pass reduction rate (for example, 30% or less); in the middle stage of rolling, the pass reduction rate may reach 45% or more; in the final stage of rolling, generally the pass reduction rate is reduced (for example, to 30% or less), so that good plate shape, thickness variation and surface quality can be obtained.

[0052] Furthermore, in the manufacturing method according to the present invention, in step (2), the cold rolling includes the following steps: First, the hot rolled sheet is air-cooled to room temperature, then multi-pass cold rolling is performed, and the total cold rolling deformation amount is controlled to be ≧ 75%. In some embodiments, the thickness of the cold rolled steel sheet is 1.5 to 2.5 mm.

[0053] Furthermore, in the manufacturing method according to the present invention, in step (2), a two-stage solution heat treatment is adopted for the solution heat quenching treatment. However, as the first-stage solution heat treatment, it is held at a temperature of 445 to 450 °C for 20 to 30 minutes, and as the second-stage solution heat treatment, it is held at a temperature of 475 to 478 °C for 10 to 20 minutes and then directly water granulated.

[0054] In the above technical solution of the present invention, the purpose of the two-stage solution heat treatment process is to reduce and make the second phase in the aluminum alloy matrix obtained in this process less and more uniform. In the solution heat treatment of the Al-Zn-Mg-Cu series aluminum alloy, before overburning occurs, the higher the solution heat treatment temperature, the higher the concentration of alloying elements dissolved, the higher the concentration of supersaturated solid solution in the alloy after quenching, and the higher the strength after aging. And with the second-stage solution heat treatment, when the holding time at a temperature of 475 to 478 °C becomes longer, a phenomenon of gradual growth of crystal grains appears in the microstructure of the aluminum alloy, and the growth of crystal grains reduces the strength of the alloy. Therefore, in order to improve the solution heat treatment degree of the alloy, it is necessary to control the holding time of the second solution heat treatment so that it is not too long.

[0055] In the above two-stage solution heat treatment process provided by the present invention, the first-stage solution heat treatment temperature is lowered to promote the diffusion of non-equilibrium phases, and the second-stage solution heat treatment temperature is raised to promote the increase of element concentration in the alloy structure, increase the concentration of the solution heat treated supersaturated solid solution, dissolve more of the coarse second phase in the alloy into the aluminum matrix, and finally obtain an alloy material with good mechanical properties. Correspondingly, the solution heat treatment time should not be too long. If it is too long, recrystallization and crystal grain growth will occur to a greater extent, affecting the performance of the material.

[0056] In the above step (2) of the present invention, through solution treatment, the Al-Zn-Mg-Cu alloying elements are dissolved into the matrix as much as possible, and the primary phase remaining in the alloy and the secondary phase formed during homogenization annealing or deformation are removed as much as possible. Thereby, a large amount of lower structure and fine grain structure can be included in the microstructure of the product after solution treatment. By optimizing the solution regime, the aluminum alloy can obtain excellent strength and toughness performance. Subsequently, through precipitation aging treatment, the strength and toughness of the aluminum alloy product can be further enhanced.

[0057] Correspondingly, quenching means cooling the alloy from the solid solution state to room temperature by rapid cooling, whereby the high-temperature structure of the alloy can be retained in a metastable state. For all heat treatments in which the structure changes during the cooling process, by reasonably controlling the cooling rate, a desired structure can be obtained.

[0058] In the present invention, during the quenching and cooling process of the Al-Zn-Mg-Cu series aluminum alloy, a predetermined quenching rate should be ensured. Rapid quenching can suppress the nucleation and growth of precipitates during the quenching process, keep solute atoms in the solid solution without forming the secondary phase, thereby ensuring the realization of high material strength. Therefore, in the present invention, quenching can be performed by water atomization, and the quenching transfer time can be controlled within 10 s.

[0059] Furthermore, in the manufacturing method according to the present invention, in step (2), the quenching transfer time (that is, the transfer time for transferring from the heat treatment furnace to the cooling water) is controlled within 10 s, for example, 5-10 s.

[0060] Furthermore, in the manufacturing method according to the present invention, in step (2), as the artificial aging treatment, it is kept warm at a temperature of 185-205 °C for 30-60 min.

[0061] It should be noted that in the prior art, the aging temperature of the 7000 series aluminum alloy in the T6 state is usually controlled at 100-150 °C, and the holding time is usually 8-36 h.

[0062] In the present invention, the microstructure and properties of high-strength Al-Zn-Mg-Cu series aluminum alloys are closely related. The properties of the alloy are mainly affected by the size, type, and distribution of the precipitation phases in the alloy microstructure. The microstructure of Al-Zn-Mg-Cu series aluminum alloys mainly consists of three parts, namely, intragranular precipitation phases (mpt), grain boundary precipitation phases (GBP), and precipitation-free zones (PFZ) near the grain boundaries. Among them, the intragranular precipitation phases (mpt) play a decisive role in the strength of the alloy. The GP zones and η' phases precipitated by aging treatment have a higher strengthening effect than the coarse equilibrium phase η phase.

[0063] Generally, the aging precipitation sequence of 7000 series ultra-high-strength aluminum alloys is usually considered to be supersaturated solid solution (ss)-GP zone-η' transition phase (MgZn2)-η equilibrium phase (MgZn2). Therefore, considering the influence of the number, distribution, and size of GP zones, η' phases, η phases, T phases, and other second phases on the alloy properties, how to adjust the number, distribution, and size of these phases is the key to artificial aging treatment.

[0064] During the aging treatment process, the aging temperature has a great influence on the precipitation of alloy precipitates. Depending on the aging temperature, the critical nucleation size, type, and aggregation growth rate of the precipitation phases are different. When the aging temperature is low, initially, the precipitation of the alloy precipitation phase is fast, and the aging strengthening effect of the alloy is obvious. However, in the later stage, the precipitation and growth of the precipitation phase become slow. Low-temperature aging can obtain higher strength, but it takes a long time to reach the peak of aging. As the aging temperature increases, the diffusion coefficient of solute atoms increases, the precipitation rate of the precipitation phase increases, and a higher aging temperature is also more favorable for the formation of the transition phase η' phase and the equilibrium phase η phase. As the aging temperature of the alloy gradually increases, the time for the hardness of the alloy to reach the peak becomes shorter.

[0065] Therefore, in the present invention, when optimizing the artificial aging treatment process, a high-temperature short-time aging treatment regime is adopted, and the aluminum alloy sheet can be held at a temperature in the range of 185 to 205 °C for 30 to 60 min. According to this regime, the peak of aging can be reached quickly, and the strength of the aluminum alloy sheet is maximized.

[0066] Furthermore, in the manufacturing method according to the present invention, in step (3), the heating is rapid solution heat treatment, and it is held at a temperature of 460 to 477 °C for 5 to 10 min. Preferably, the heating adopts contact heating.

[0067] In the above technical solution of the present invention, setting the solution heat treatment temperature in the range of 460 to 477 °C is because the dissolution temperatures of the S (Al2CuMg) phase and T (AlZnMgCu) phase in the Al-Zn-Mg-Cu series aluminum alloy are in this range. On the other hand, it is also to avoid the problem of overburning due to too high a temperature during rapid solution heat treatment.

[0068] In an embodiment, as the heating means, contact heating may be adopted. Furthermore, in the manufacturing method according to the present invention, in step (3), as the pre-aging treatment, it is held at a temperature of 75 to 100 °C for 30 to 60 min.

[0069] In the present invention, treating the Al-Zn-Mg-Cu series alloy sheet by the pre-aging process is to ensure that natural aging does not occur in the aluminum alloy, and pre-aging must be performed within 30 min after the solution treatment. Inhibiting the natural aging process by the pre-aging treatment essentially means inhibiting the formation of atomic clusters and GP zones in the Al-Zn-Mg-Cu series alloy. At the same time, the pre-aging can also promote the nucleation of low-temperature precipitation phases, and the strength improvement in the subsequent baking paint stage depends on the nucleation of these precipitation phases.

[0070] Furthermore, in the manufacturing method according to the present invention, in step (3), as the baking painting treatment, it is kept warm at a temperature of 170 to 190 °C (for example, 180 to 190 °C) for 20 to 40 minutes.

[0071] In the present invention, the baking painting treatment (Paint Baking) corresponds to artificial aging. By the T4P + PB (preliminary aging + baking painting treatment), a large amount of fine and dense precipitation phases can be obtained, and the atomic clusters and GP zones in the precipitation phases increase significantly. Compared with the temperature of natural aging, the temperature of baking painting is higher, and the unstable phases in the T4P state structure continue to nucleate and precipitate, further improving the strength, that is, it shows obvious baking painting hardening.

[0072] In the above technical solution, the preferably designed baking painting process takes into account the requirements of the baking painting process, but is also set in accordance with the process characteristics of the Al-Zn-Mg-Cu series aluminum alloy that reaches the peak of aging at high temperature in a short time.

[0073] Correspondingly, another object of the present invention is to provide an Al-Zn-Mg-Cu series aluminum alloy sheet. The Al-Zn-Mg-Cu series aluminum alloy sheet is easy to produce, and has high tensile strength, yield strength and high elongation rate, can meet the requirements for the material strength and toughness of automotive sheets, can be efficiently applied to the automotive manufacturing industry to meet the requirements of vehicle weight reduction, and has good application prospects.

[0074] To achieve the above object, the Al-Zn-Mg-Cu series aluminum alloy sheet provided by the present invention is manufactured by the manufacturing method of the Al-Zn-Mg-Cu series aluminum alloy sheet according to the present invention.

[0075] Furthermore, in the Al-Zn-Mg-Cu series aluminum alloy sheet according to the present invention, its performance is that the tensile strength is 610 to 650 MPa, the yield strength is 580 to 630 MPa, and the elongation rate is ≥ 15.0%.

[0076] Furthermore, in the Al-Zn-Mg-Cu series aluminum alloy sheet according to the present invention, its performance is as follows: the tensile strength is 612 - 647 MPa, the yield strength is 580 - 630 MPa, and the elongation is ≧15.0%.

[0077] Furthermore, in the Al-Zn-Mg-Cu series aluminum alloy sheet according to the present invention, its performance is as follows: the tensile strength Rm is 612 - 647 MPa, the yield strength Rp0.2 is 586 - 623 MPa, and the elongation A is 15.4 - 17.2%.

[0078] The manufacturing method of the Al-Zn-Mg-Cu series aluminum alloy sheet according to the present invention has the following advantages and beneficial effects compared with the prior art: In order to solve the problems that the room temperature formability of the conventional 7000 series aluminum alloy for automobiles is poor and the heat-treated samples after forming are prone to deformation, the inventors have designed a new manufacturing method for the Al-Zn-Mg-Cu series aluminum alloy sheet.

[0079] The manufacturing method of the Al-Zn-Mg-Cu series aluminum alloy sheet adopts a reasonable process design, and its production process and process parameters are standardized. Moreover, it can significantly improve the formability and comprehensive mechanical properties of the manufactured Al-Zn-Mg-Cu series aluminum sheet, meet the requirements for the use of automotive sheets, and overcome the drawbacks of the prior art.

[0080] The Al-Zn-Mg-Cu series aluminum alloy sheet is easy to produce, has high tensile strength, yield strength and high elongation, can meet the requirements for the material strength and toughness of automotive sheets, can be efficiently applied to the automotive manufacturing industry to meet the requirements of vehicle weight reduction, and has good application prospects.

[0081] In one embodiment, the mechanical properties of the Al-Zn-Mg-Cu series aluminum alloy sheet are as follows: the tensile strength is 610-650 MPa, the yield strength is 580-630 MPa, and the elongation is ≧15.0%. The mechanical properties of the Al-Zn-Mg-Cu series aluminum alloy sheet manufactured by such a manufacturing method are significantly improved compared with those of the conventional 7000 series aluminum alloy sheet.

[0082] In addition, the process principle provided by the manufacturing method can not only be applied to this Al-Zn-Mg-Cu series aluminum alloy material, but also be applied to all other aluminum alloys that can be strengthened by heat treatment, such as 2000 series, 6000 series and other 7000 series aluminum alloy materials, and has good prospects for generalization and practical value.

Brief Description of the Drawings

[0083]

Figure 1

Embodiments for Carrying out the Invention

[0084] Specific Embodiments Hereinafter, based on specific examples and drawings, the manufacturing method of the Al-Zn-Mg-Cu series aluminum alloy sheet and the aluminum alloy sheet according to the present invention will be further interpreted and described, but such interpretation and description do not unduly limit the technical solution of the present invention.

[0085] Examples 1-6 and Comparative Examples 1-2 In the present invention, the chemical compositions of the Al-Zn-Mg-Cu series aluminum alloy sheets according to Examples 1-6 are shown in Table 1 below. The chemical compositions of the Al-Zn-Mg-Cu series aluminum alloy sheets according to Examples 1-6 are shown in Table 1.

[0086]

Table 1

[0087] Correspondingly, based on the above chemical composition design, in the present invention, the Al-Zn-Mg-Cu series aluminum alloy sheets according to Examples 1 to 6 were all manufactured by the following steps: (1) Compounded according to the chemical composition shown in Table 1, melted in a melting furnace, refined, and then an Al-Zn-Mg-Cu series aluminum alloy ingot was cast.

[0088] (2) The obtained Al-Zn-Mg-Cu series aluminum alloy ingot was sequentially subjected to homogenization treatment, hot rolling, cold rolling, solution quenching treatment, and artificial aging treatment to obtain a T6 state Al-Zn-Mg-Cu series aluminum alloy sheet: Homogenization treatment: The aluminum alloy ingot was put into a homogenization furnace for homogenization treatment, and a three-stage homogenization treatment regime was adopted. Specifically, for the first-stage homogenization treatment, it was held at a temperature of 418 - 430°C for 5 - 8 h, for the second-stage homogenization treatment, it was held at a temperature of 460 - 468°C for 8 - 12 h, and for the third-stage homogenization treatment, it was held at a temperature of 470 - 480°C for 20 - 24 h, and then forced water-cooled to room temperature to obtain a homogenized aluminum alloy ingot; Hot rolling: The aluminum alloy ingot was heated to 430 - 440°C and held for 90 - 120 min, and then subjected to multi-pass hot rolling alternately in the longitudinal and transverse directions. The total hot rolling deformation amount was controlled to be ≥85%, and the rolling end temperature was controlled to be ≥380°C to obtain a hot-rolled sheet with a final thickness of 6 mm; Cold rolling: First, the hot-rolled sheet was air-cooled to room temperature, and then multi-pass cold rolling was performed to 1.5 - 2.5 mm, and the total cold rolling deformation amount was controlled to be ≥75%; Solution quenching treatment: The cold-rolled sheet was subjected to two-stage solution treatment. Specifically, for the first-stage solution treatment, it was held at a temperature of 445 - 450°C for 20 - 30 min, and for the second-stage solution treatment, it was held at a temperature of 475 - 478°C for 10 - 20 min, and then direct water atomization was performed; however, the quenching transfer time was controlled within 10 s; Artificial aging treatment: The solutionized and quenched sheet material was transported into an aging furnace for artificial aging treatment. The sheet material was held at a temperature of 185 - 205 °C for 30 - 60 minutes to obtain an Al-Zn-Mg-Cu series aluminum alloy sheet material in the T6 state.

[0089] (3) The obtained Al-Zn-Mg-Cu series aluminum alloy sheet material in the T6 state was subjected to heating, warm forming, in-mold quenching, preliminary aging treatment, and baking painting treatment to obtain a finished Al-Zn-Mg-Cu series aluminum alloy sheet material: Heating: The Al-Zn-Mg-Cu series aluminum alloy sheet material in the T6 state obtained by artificial aging was held at a temperature of 460 - 477 °C for 5 - 10 minutes, and then warm forming and in-mold quenching were directly carried out; Preliminary aging treatment: For the Al-Zn-Mg-Cu series aluminum alloy sheet material after warm forming and in-mold quenching, preliminary aging treatment should be carried out within a short time so that an Al-Zn-Mg-Cu series aluminum alloy sheet material in the T4P state can be obtained. As the preliminary aging process, the sheet material was held at a temperature of 75 - 100 °C for 30 - 60 minutes, and then baking painting treatment was carried out; Baking painting treatment: The sheet material was held at a temperature of 170 - 190 °C for 20 - 40 minutes to obtain an aluminum alloy sheet material in the T4P + PB state.

[0090] In the present invention, this Al-Zn-Mg-Cu series aluminum alloy sheet material designed according to Examples 1 - 6 is all 7055 aluminum alloy sheet material, and the processes related to the Al-Zn-Mg-Cu series aluminum alloy sheet material according to Examples 1 - 6 all meet the requirements of the specifications designed by the present invention.

[0091] The specific process parameters in the above processes and steps of the Al-Zn-Mg-Cu series aluminum alloy sheet material according to Examples 1 - 6 are shown in Tables 2-1, 2-2, and 2-3.

[0092]

Table 2-1

[0093]

Table 2-2

[0094]

Table 2-3

[0095] To further illustrate the mechanical properties of the Al-Zn-Mg-Cu series aluminum alloy sheets according to Examples 1 to 6 of the present invention, samples were respectively taken from the obtained finished Al-Zn-Mg-Cu series aluminum alloy sheets according to Examples 1 to 6, and the mechanical properties of the aluminum alloy sheets of the finished products of each example could be measured. The measurement results of the relevant mechanical properties are shown in Table 3 below.

[0096] The measurement means of the relevant mechanical properties were as follows: Tensile test: Tensile test specimens were prepared according to the GB / T 228.1-2010 standard, and the numerical values of the yield strength, tensile strength, and elongation rate of the Al-Zn-Mg-Cu series aluminum alloy sheets according to each example were measured and obtained.

[0097] Correspondingly, in order to prove that the Al-Zn-Mg-Cu series aluminum alloy sheets according to Examples 1 to 6 manufactured by the manufacturing method according to the present invention have excellent mechanical properties, the inventors further cited two types of 7000 series aluminum alloy materials in the prior art, namely Comparative Example 1 and Comparative Example 2, for comparison.

[0098] Comparative Example 1 is an Al-Mg-Cu-Zn series aluminum alloy sheet derived from the patent technical document with the publication number CN104862551A and the publication date of August 26, 2015. Its mechanical properties after T4P + artificial aging are shown in Table 3.

[0099] Comparative Example 2 is a 7075 aluminum alloy hot press forming sheet derived from the patent technical document with the publication number CN107686954A and the publication date of February 13, 2018. Its mechanical properties in the T6 state are shown in Table 3.

[0100] The measurement results of the mechanical properties of the finished Al-Zn-Mg-Cu series aluminum alloy plates according to Examples 1 to 6 and the aluminum alloy plates of the finished products according to Comparative Examples 1 to 2 are shown in Table 3.

[0101]

Table 3

[0102] As shown in Table 3, in the present invention, the finished Al-Zn-Mg-Cu series aluminum alloy plates according to Examples 1 to 6 have high mechanical properties, with their tensile strength Rm being 612 to 647 MPa, their yield strength Rp0.2 being 586 to 623 MPa, and their elongation rate A being 15.4 to 17.2%.

[0103] As can be seen by comparing the finished Al-Zn-Mg-Cu series aluminum alloy plates according to Examples 1 to 6 with the aluminum alloy plates of the finished products according to Comparative Examples 1 to 2, the mechanical properties of the finished Al-Zn-Mg-Cu series aluminum alloy plates according to Examples 1 to 6 were more than 30% higher than those of the aluminum alloy plates of the finished products according to Comparative Example 1. This is mainly because the process route adopted in the present invention is different from that of Comparative Example 1. The fundamental reason is that the present invention adopts the plate after T6 heat treatment and performs warm forming, so that the basis of precipitation strengthening can be obtained in advance, and by combining with the reinforcement treatment by baking painting in the subsequent stage, high strength and toughness performance can be brought to the material.

[0104] To sum up, the production process and process parameters of the manufacturing method of the Al-Zn-Mg-Cu series aluminum alloy for automobiles designed according to the present invention are very standardized, and the comprehensive performance of the products manufactured thereby is significantly improved, meeting the requirements of automobiles for high-performance aluminum alloys.

[0105] The process principle provided by the present invention can be applied not only to this 7000 series Al-Zn-Mg-Cu series aluminum alloy material, but also to any other heat-treatable aluminum alloy materials, such as 2000 series, 6000 series, and other 7000 series aluminum alloy materials.

[0106] Figure 1 conceptually shows a process flowchart of a method for manufacturing an Al-Zn-Mg-Cu series aluminum alloy sheet according to the present invention.

[0107] As shown in Figure 1, in the present invention, when an Al-Zn-Mg-Cu series aluminum alloy sheet is melted and cast according to a designed chemical element composition, a corresponding Al-Zn-Mg-Cu series aluminum alloy ingot is obtained. When homogenization treatment, hot rolling, cold rolling, solution quenching treatment, and artificial aging treatment are sequentially performed on the Al-Zn-Mg-Cu series aluminum alloy ingot, a T6 state aluminum alloy sheet is obtained.

[0108] Based on the obtained T6 state aluminum alloy sheet, when further heating, warm forming, in-mold quenching, pre-aging treatment, and baking painting treatment are performed, a finished aluminum alloy thin sheet in the T4P+PB state is obtained.

[0109] In addition, the combination of each technical feature in the present application is not limited to the combination described in the claims of the present application or the combination described in the specific embodiments. As long as they do not conflict with each other, all the technical features described in the present application can be freely combined or joined in any form.

[0110] Furthermore, it should also be noted that the above-mentioned examples are only specific examples of the present invention. The present invention is not limited to the above-mentioned examples, and it is obvious that any similar changes or modifications that can be directly derived or easily conceived by those skilled in the art from the disclosure content of the present invention are included in the protection scope of the present invention.

Claims

1. A method for manufacturing an Al-Zn-Mg-Cu series aluminum alloy sheet, characterized by comprising the following steps: (1) Producing an Al-Zn-Mg-Cu series aluminum alloy ingot; (2) Sequentially performing homogenization treatment, hot rolling, cold rolling, solution quenching treatment, and artificial aging treatment on the Al-Zn-Mg-Cu series aluminum alloy ingot to obtain a T6 state aluminum alloy sheet; (3) Performing heating, warm forming, in-mold quenching, preliminary aging treatment, and baking painting treatment on the T6 state aluminum alloy sheet to obtain a finished aluminum alloy sheet.

2. The mass percentage content ratio of the chemical elements of the Al-Zn-Mg-Cu series aluminum alloy ingot is: Cu: 1.6 - 2.2%, Mg: 1.8 - 2.4%, Zn: 6.0 - 8.6%, Zr: 0.10 - 0.16%, 0 < Ti ≤ 0.10%, 0 < Mn ≤ 0.05%, 0 < Cr ≤ 0.04%, and the balance is Al and inevitable impurities The manufacturing method according to Claim 1, characterized in that.

3. The mass percentage content of the chemical elements of the Al-Zn-Mg-Cu series aluminum alloy ingot further satisfies at least one of the following, the manufacturing method according to Claim 2, characterized in that: Cu: 1.8 - 2.2%, Mg: 2.0 - 2.4%, Zn: 6.1 - 7.8%, Zr: 0.10 - 0.13%.

4. The inevitable impurities of the Al-Zn-Mg-Cu series aluminum alloy ingot include at least one of the following: Si ≤ 0.10%, Fe ≤ 0.15%, and the total amount of other impurity elements ≤ 0.100%; preferably, Si < 0.08%, Fe < 0.1%, and the mass of each of the other impurity elements is ≤ 0.030%, the manufacturing method according to Claim 1, characterized in that.

5. In step (2), for the homogenization treatment, a three-stage homogenization treatment is adopted. However, for the first-stage homogenization treatment, it is held at a temperature of 418 - 430 °C for 5 - 8 h, for the second-stage homogenization treatment, it is held at a temperature of 460 - 468 °C for 8 - 12 h, and for the third-stage homogenization treatment, it is held at a temperature of 470 - 480 °C for 20 - 24 h, the manufacturing method according to Claim 1, characterized in that.

6. In step (2), the hot rolling includes the following steps: heating the ingot to 430 - 440 °C, holding for 90 - 120 min, and then performing multi-pass hot rolling alternately in the longitudinal and transverse directions, controlling the total hot rolling deformation amount to be ≥ 85% and the final rolling temperature to be ≥ 380 °C. The manufacturing method according to claim 1 is characterized by this.

7. In step (2), the cold rolling includes the following steps: first, air-cool the hot rolled sheet to room temperature, and then perform multi-pass cold rolling, controlling the total cold rolling deformation amount to be ≥ 75%. The manufacturing method according to claim 1 is characterized by this.

8. In step (2), a two-stage solution heat treatment is adopted for the solution quenching treatment. Specifically, for the first-stage solution heat treatment, hold at a temperature of 445 - 450 °C for 20 - 30 min, and for the second-stage solution heat treatment, hold at a temperature of 475 - 478 °C for 10 - 20 min, and then directly perform water granulation. The manufacturing method according to claim 1 is characterized by this.

9. In step (2), the quenching transfer time is controlled within 10 s. The manufacturing method according to claim 8 is characterized by this.

10. In step (2), for the artificial aging treatment, hold at a temperature of 185 - 205 °C for 30 - 60 min. The manufacturing method according to claim 1 is characterized by this.

11. In step (3), the heating is rapid solution heating, holding at a temperature of 460 - 477 °C for 5 - 10 min; preferably, the heating adopts contact heating. The manufacturing method according to claim 1 is characterized by this.

12. In step (3), for the pre-aging treatment, hold at a temperature of 75 - 100 °C for 30 - 60 min. The manufacturing method according to claim 1 is characterized by this.

13. In step (3), for the baking paint treatment, hold at a temperature of 170 - 190 °C for 20 - 40 min. The manufacturing method according to claim 1 is characterized by this.

14. An Al-Zn-Mg-Cu series aluminum alloy sheet manufactured by the manufacturing method according to any one of claims 1 - 13.

15. The performance of the Al-Zn-Mg-Cu series aluminum alloy sheet according to claim 14 is characterized in that the tensile strength is 610 - 650 MPa, the yield strength is 580 - 630 MPa, and the elongation is ≥ 15.0%.

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