In-situ nano-biphase reinforced Al-Zn-Mg-Cu-Y alloy and high-pressure preparation method thereof

Abstract

This invention discloses an in-situ nano-duplex reinforced Al-Zn-Mg-Cu-Y alloy. The chemical composition of the alloy, by mass percentage, comprises: Zn 4-8%, Mg 1.2-2.8%, Cu 1.2-2.0%, Y 0.1-0.6%, and Al 86.6-93.5%, with the total mass percentage of each chemical component being 100%. The alloy microstructure contains uniformly distributed nano-scale η-phase and nano-scale T-phase. This invention also discloses a high-pressure preparation method for the above-mentioned in-situ nano-duplex reinforced Al-Zn-Mg-Cu-Y alloy, comprising the following steps: subjecting the billet to high-temperature and high-pressure treatment to obtain the in-situ nano-duplex reinforced Al-Zn-Mg-Cu-Y alloy. This invention adds rare earth element Y and combines this with high-temperature and high-pressure treatment to form uniformly distributed nano-scale η-phase and nano-scale T-phase in-situ within the alloy microstructure.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy technology, and in particular to an in-situ nano-duplex reinforced Al-Zn-Mg-Cu-Y alloy and its high-pressure preparation method. Background Technology

[0002] Al-Zn-Mg-Cu aluminum alloys are widely used in aerospace, transportation, and other fields due to their high specific strength. Under conventional casting processes, the microstructure of this alloy mainly consists of coarse α-Al dendrites and network eutectic phases (such as Mg(Zn,Al,Cu)2 phase) distributed along grain boundaries, while inevitably containing casting defects such as porosity and shrinkage. These coarse second phases and defects are prone to becoming crack initiation sites under stress, severely limiting the compressive strength and hardness of the alloy. In addition, the strengthening phases precipitated after traditional solution aging treatment are of a single type, making it difficult to achieve multi-phase synergistic strengthening, and the distribution of strengthening phases is uneven, resulting in limited precipitation strengthening effect. Although adding microalloying elements such as Zr and Sc or using methods such as rapid solidification and large plastic deformation can refine the microstructure or improve the distribution of precipitated phases to some extent, these methods are often complex, require high-end equipment, are expensive, or are difficult to prepare large-size samples, and the strengthening effect is singular. Therefore, there is an urgent need to develop a new method that can generate high-density, uniformly distributed multi-type nanoscale reinforcing phases in situ within the alloy, while eliminating casting defects and achieving microstructural densification, so as to significantly improve the hardness and compressive strength of Al-Zn-Mg-Cu alloys. Summary of the Invention

[0003] Based on the technical problems existing in the background technology, this invention proposes an in-situ nano-duplex strengthened Al-Zn-Mg-Cu-Y alloy and its high-pressure preparation method; this invention adds rare earth Y to the Al-Zn-Mg-Cu alloy and combines it with high temperature and high pressure treatment to significantly refine the coarse second phase of the alloy, and forms uniformly distributed nano-scale η phase and nano-scale T phase in situ in the alloy microstructure, which greatly improves the mechanical properties of the alloy.

[0004] This invention proposes an in-situ nano-duplex reinforced Al-Zn-Mg-Cu-Y alloy, wherein the chemical composition of the alloy, by mass percentage, comprises: Zn 4-8%, Mg 1.2-2.8%, Cu 1.2-2.0%, Y 0.1-0.6%, and Al 86.6-93.5%, with the total mass percentage of each chemical component being 100%. The alloy microstructure contains uniformly distributed nanoscale η phase and nanoscale T phase.

[0005] Preferably, the chemical composition of the alloy, by mass percentage, includes: Zn 5.6%, Mg 2.5%, Cu 1.6%, Y 0.5%, with the balance being Al.

[0006] Preferably, the chemical composition of the alloy, by mass percentage, includes: Zn 6.5%, Mg 2.5%, Cu 2.0%, Y 0.5%, with the balance being Al.

[0007] Preferably, the nanoscale η phase is Mg(Zn, Al, Cu)2.

[0008] Preferably, the volume fraction of the nanoscale η phase in the alloy microstructure is 3-4%; more preferably, it is 3.51%.

[0009] Preferably, the average particle size of the nanoscale η phase is 20-25 nm; more preferably, it is 22.62 nm.

[0010] Preferably, the nanoscale η phase is in the form of strips.

[0011] Preferably, the nanoscale T phase is Mg. 32 (Al, Zn) 49 .

[0012] Preferably, the volume fraction of nanoscale T phase in the alloy microstructure is 1.4-1.6%; more preferably, it is 1.55%.

[0013] Preferably, the average particle size of the nanoscale T phase is 10-15 nm; more preferably, it is 12.67 nm.

[0014] Preferably, the nanoscale T phase is in the form of particles.

[0015] Preferably, the Y element is distributed in the alloy structure in the form of intermetallic compounds.

[0016] Preferably, the intermetallic compound formed by the Y element is Al8Cu4Y, which has a strengthening effect in the alloy structure.

[0017] Preferably, the volume fraction of the intermetallic compound formed by Y element in the alloy structure is 2-2.5%; more preferably, it is 2.35%.

[0018] Preferably, the matrix of the alloy structure is an α-Al matrix.

[0019] Preferably, the in-situ nano-dual-phase reinforced Al-Zn-Mg-Cu-Y alloy has a room temperature compressive strength ≥700MPa and a Vickers hardness ≥205 under a test force of 0.2kg.

[0020] The present invention also proposes a high-pressure preparation method for the above-mentioned in-situ nano-dual-phase strengthened Al-Zn-Mg-Cu-Y alloy, comprising the following steps: subjecting the billet to high-temperature and high-pressure treatment to obtain the in-situ nano-dual-phase strengthened Al-Zn-Mg-Cu-Y alloy; The high-temperature and high-pressure treatment involves a pressure of 1-4 GPa, a temperature of 800-1100℃, and a time of 3-4 hours. The chemical composition of the billet is the same as that of the above-mentioned in-situ nano-duplex reinforced Al-Zn-Mg-Cu-Y alloy.

[0021] The pressure can be 1, 2, 3 or 4 GPa, and the temperature can be 800, 900, 1000 or 1100℃.

[0022] The mechanism by which rare earth element Y is added to Al-Zn-Mg-Cu alloy and combined with high-temperature and high-pressure treatment to form nanoscale η-phase and nanoscale T-phase is as follows: 1) Pressure introduces far more excess vacancies than conventional quenching. High pressure "freezes" vacancies much more efficiently than atmospheric pressure quenching, and vacancies have almost no chance of annihilation, remaining nearly intact at room temperature. The "solute trapping" effect under high pressure results in extremely high concentrations of Zn, Mg, and Cu in the α-Al matrix, far exceeding the levels achievable by conventional solid solution treatment, providing a huge driving force for precipitation. Furthermore, the increased number of vacancies under high pressure leads to a high nucleation rate and rapid cooling. Since it falls within the scope of solidification rather than heat treatment, the system can bypass or rapidly pass through the metastable GP and η' phase regions, directly precipitating a high-density, thermodynamically more stable nanoscale η phase. 2) High-pressure forced solid solution greatly increases the probability of various chemical composition fluctuations at the atomic scale, changing the local Zn / Mg / Cu ratio, which may be more conducive to the formation of the T phase. In addition, the alloy contains Y element and has phases such as Al8Cu4Y. These Y-containing phases will stick or consume Cu / other solutes during solid solution / high pressure, changing the local effective Zn / Mg / Cu ratio. Furthermore, the growth of the η phase will consume a large number of surrounding Zn and Mg atoms, and the local composition of the adjacent η phase region is more inclined to be rich in Mg and Al, which just meets the stoichiometric requirements of the T phase. For the above reasons, the high-density T phase can be uniformly and diffusely precipitated in the region between the η phases. 3) When η-phase particles and T-phase particles are close to each other, their diffusion fields (solute depletion regions) will overlap and interfere with each other. The growth of one phase will consume solute atoms that might have flowed to the other phase, thereby inhibiting the growth of the other. This competitive relationship effectively inhibits the excessive growth of either side and together limits their size to the nanoscale.

[0023] Preferably, the blanks are assembled into components and then subjected to high temperature and high pressure treatment.

[0024] Preferably, the assembly includes: a blank with an external insulating layer, a graphite tube, a graphite sheet, and a conductive sealing sheet. The blank with the external insulating layer is placed inside the graphite tube, the graphite sheet seals both ends of the graphite tube, and the conductive sealing sheet is placed outside the graphite sheet and seals both ends of the graphite tube.

[0025] The blanks, graphite tubes, graphite sheets, and conductive sealing sheets in the above-mentioned assembly are all dried at 240°C and kept dry at 100°C for later use.

[0026] Graphite sheets and conductive sealing sheets serve to provide heating during high-temperature and high-pressure heat treatment.

[0027] The above-mentioned assembly was placed in an octahedral pyrophyllite block and transferred to a high-pressure pressurization device for high-temperature and high-pressure treatment; the above-mentioned octahedral pyrophyllite block is a pressure transmission carrier commonly used in high-temperature and high-pressure treatment.

[0028] After high-temperature and high-pressure treatment, heating is stopped and pressure is released, and the mixture is cooled to room temperature in a high-pressure pressurization device.

[0029] Preferably, raw materials of various chemical components are taken, smelted and cast in a protective gas atmosphere to obtain billets.

[0030] Preferably, the protective gas is at least one of argon and sulfur hexafluoride.

[0031] Preferably, the melting temperature is 740-760℃.

[0032] Preferably, the casting temperature is 715-725℃.

[0033] Preferably, the raw materials for each chemical component are Al ingots, Mg ingots, Zn granules, Al-Cu master alloys, and Al-Y master alloys.

[0034] The purity of the above-mentioned pure Al ingots, pure Mg ingots, and Zn particles is all above 99.9%; the Cu content of the above-mentioned Al-Cu master alloy can be 40wt%; and the Y content of the above-mentioned Al-Y master alloy can be 20wt%.

[0035] The above casting can directly produce a blank of the target size; or it can cast a part and then cut it into blanks of the target size; the blanks can be ground and then further processed.

[0036] Beneficial effects: 1. This invention adds rare earth element Y to the Al-Zn-Mg-Cu alloy. The segregation of rare earth Y atoms at grain boundaries and phase boundaries effectively pins interfacial movement. Furthermore, combined with high-temperature and high-pressure heat treatment, the extremely high pressure significantly inhibits atomic diffusion and grain boundary migration during melt solidification, resulting in an ultra-fine solidification structure with submicron or even nanometer-scale grains. Nanoscale η-phase and nanoscale T-phase are formed in situ within the alloy structure, achieving a two-phase strengthened alloy. This gives the alloy excellent mechanical properties; the refined structure and nanoscale strengthening work synergistically to significantly improve the alloy's hardness and compressive strength. Moreover, the ultra-high pressure environment almost completely eliminates defects such as porosity and shrinkage cavities common in casting processes, achieving atomic-scale densification of the material and further enhancing the alloy's mechanical properties.

[0037] 2. The high-temperature and high-pressure process parameters of this invention can be well integrated with existing casting equipment, and are easy to upgrade and implement on the basis of existing industrial equipment. The process has good reproducibility, which is conducive to large-scale production. The ultra-high pressure technology integrates the complex multi-process of traditional aluminum alloy (melting, casting, homogenization, hot working, heat treatment) into a unified near-net-shape forming process. The transformation from raw materials to high-performance dense components is completed in a single process cycle, which greatly simplifies the process, improves efficiency and reduces energy consumption. Attached Figure Description

[0038] Figure 1 The images show SEM images of the alloys obtained in Comparative Examples 1-3 and Example 1, where a is Comparative Example 1, b is Example 1, c is Comparative Example 3, and d is Comparative Example 2.

[0039] Figure 2 The image shows a TEM image of the alloy obtained in Example 1, where ab is a bright-field photograph of the nanoparticle phase and cd is the alloy diffraction pattern.

[0040] Figure 3 This is a TEM image of the alloy obtained in Comparative Example 2.

[0041] Figure 4 The room temperature compression curves are for the alloys prepared in Example 1 and Comparative Examples 1-3. Detailed Implementation

[0042] The technical solution of the present invention will now be described in detail through specific embodiments.

[0043] The chemical composition formulations and high-temperature and high-pressure processing parameters of the billets obtained in Examples 1-5 and Comparative Examples 1-3 are shown in Table 1.

[0044] Table 1 Chemical composition formula (by mass percentage) and high-temperature and high-pressure treatment process parameters

[0045] The high-pressure preparation methods of Examples 1-5 and Comparative Examples 1-3 above include the following steps: After holding the crucible at 450℃ for 30 minutes, pure Al ingots (Al content 99.99wt%), pure Zn granules (Zn content 99.99wt%), Al-Cu master alloy (copper content 40wt%), and Al-Y master alloy (Y content 20wt%) were added under an Ar protective atmosphere. The crucible was then heated to 750℃ until the raw materials were completely melted. During this process, mechanical stirring with a graphite stirring rod was used to promote the melting of the raw materials and ensure uniform composition. When the melt temperature was maintained at 740℃, pure Mg ingots (Mg content 99.99wt%) were added under an Ar protective atmosphere until they were completely melted. When the melt temperature was maintained at 740℃ again and no bubbles were observed, slag removal was performed. When the melt temperature dropped to 720℃, pouring was carried out. During pouring, a certain flow rate of Ar gas was maintained for protection. After pouring, the Ar gas was turned off, and the mixture solidified to obtain the casting. The casting was then wire-cut into pieces with dimensions of Φ5×6.8 mm. The blank is made of mm, and the surface is polished for later use; The blank is coated with an insulating layer and then embedded in a graphite tube. Graphite sheets are used to seal both ends of the graphite tube, and then conductive sealing sheets are used to seal both ends of the graphite tube to obtain an assembly. The assembly is placed in an octahedral pyrophyllite block and then transferred to a high-pressure pressurization device. The pressure is increased at a constant rate to a predetermined pressure. While maintaining the predetermined pressure, the sample is heated to a predetermined temperature to melt it and held at that temperature for a predetermined time. Then, the heating is stopped and the pressure is released. The sample is cooled to room temperature in the high-pressure pressurization device to obtain an in-situ nano-nano dual-phase reinforced Al-Zn-Mg-Cu-Y alloy.

[0046] Detection The alloys from Example 1 and Comparative Example 1 were tested, and the results are as follows: Figure 1-2 As shown.

[0047] Figure 1 The images show SEM images of the alloys obtained in Comparative Examples 1-3 and Example 1, where a is Comparative Example 1, b is Example 1, c is Comparative Example 3, and d is Comparative Example 2.

[0048] Depend on Figure 1 It can be seen that the alloy of Comparative Example 1 is mainly composed of α-Al phase, Mg(Zn,Al,Cu)2 phase and Al8Cu4Y phase; compared with Comparative Example 3, the morphology of α-Al phase and Mg(Zn,Al,Cu)2 phase did not change significantly. The alloy of Comparative Example 2 is similar to that of Example 1, mainly composed of α-Al phase, a small amount of intergranular phase and small-sized spherical phase within the grains, but the number of spherical phases is reduced compared to Example 1; The alloy in Comparative Example 3 is mainly composed of α-Al phase and Mg(Zn,Al,Cu)2 phase; The alloy in Example 1 is mainly composed of α-Al phase, a small amount of intergranular phase and small-sized spherical phase within the grains. It can be seen that the dendritic morphology of the α-Al phase disappears and the volume fraction of the second phase is also significantly reduced.

[0049] Figure 2 The image shows a TEM image of the alloy obtained in Example 1, where ab is a bright-field photograph of the nanoparticle phase and cd is the alloy diffraction pattern.

[0050] Figure 3 This is a TEM image of the alloy obtained in Comparative Example 2.

[0051] Depend on Figure 2-3 It can be seen that the Al-Zn-Mg-Cu-Y alloy in Example 1 generated a high-density nanophase under high pressure conditions. Figure 3 Compared to Comparative Example 2, the precipitate phase of Comparative Example 2 is mainly composed of large-sized, strip-shaped η phase, while the precipitate phase of Example 1 is mainly composed of large-sized and sparse strip-shaped η phase and small-sized and high-density granular T phase, and both η phase and T phase are at the nanoscale. In the in-situ nano-duplex reinforced Al-Zn-Mg-Cu-Y alloy described in Example 1, nanoscale η phase and nanoscale T phase are uniformly distributed; The nanoscale η phase is Mg(Zn, Al, Cu)2, the volume fraction of the nanoscale η phase in the alloy structure is 3.51%, the average particle size of the nanoscale η phase is 22.62 nm, and the nanoscale η phase is in strip shape; Nanoscale T phase is Mg 32 (Al, Zn) 49 The volume fraction of nano-sized T phase in the alloy structure is 1.55%, the average particle size of the nano-sized T phase is 12.67 nm, and the nano-sized T phase is granular. The alloy microstructure also contains intermetallic compounds formed by Y element, with the composition Al8Cu4Y and a volume fraction of 2.35%; the matrix of the alloy microstructure is an α-Al matrix.

[0052] Comparing Example 1 with Comparative Examples 1-3, it is shown that adding Y alone cannot eliminate the coarse network eutectic, and high-pressure treatment alone is not enough to generate a two-phase structure of nanoscale η phase and nanoscale T phase. Only by adding rare earth Y to the Al-Zn-Mg-Cu alloy and combining it with high-temperature and high-pressure treatment can the coarse second phase in the alloy be eliminated, and at the same time, a uniformly distributed nanoscale η phase and nanoscale T phase are formed in situ in the alloy structure.

[0053] The formation of nanoscale η-phase and nanoscale T-phase in in-situ nano-duplex strengthened Al-Zn-Mg-Cu-Y alloy is due to the following reasons: Pressure introduces far more excess vacancies than conventional quenching. High pressure "freezes" vacancies far more efficiently than atmospheric pressure quenching, and vacancies have almost no chance of annihilation, remaining nearly intact at room temperature. The solute trapping effect under high pressure results in extremely high concentrations of Zn, Mg, and Cu in the α-Al matrix, far exceeding the levels achievable by conventional solution treatment, providing a huge driving force for precipitation. Furthermore, the increased vacancies under high pressure lead to a high nucleation rate and rapid cooling. Since it falls within the scope of solidification rather than heat treatment, the system can bypass or rapidly pass through the metastable GP and η' phase regions, directly precipitating a high-density, thermodynamically more stable nanoscale η phase. High-pressure forced solid solution greatly increases the probability of various chemical composition fluctuations at the atomic scale, changing the local Zn / Mg / Cu ratio, which may be more conducive to the formation of the T phase. The alloy contains phases such as Al8Cu4Y, which contain Y and will stick or consume Cu / other solutes during solid solution / high pressure, changing the local effective Zn / Mg / Cu ratio. In addition, the growth of the η phase will consume a large number of surrounding Zn and Mg atoms, and the local composition of the central region will be more Mg-rich and Al-rich, which exactly meets the stoichiometric requirements of the T phase. For the above reasons, the high-density T phase can be uniformly and diffusely precipitated in the region between the η phases. The extreme supersaturated solid solution generated by high pressure provides a huge, global phase transformation driving force for any possible precipitated phase; this means that the η phase and T phase have a strong tendency to precipitate at any location in the entire α-Al matrix; when the η phase and T phase are close to each other, their diffusion fields (solute depletion regions) will overlap and interfere with each other; the growth of one phase will consume solute atoms that might otherwise flow to the other phase, thereby inhibiting the growth of the other. This competitive relationship effectively inhibits the excessive growth of either one, and together they restrict each other's size to the nanoscale, ultimately resulting in an in-situ nano-duplex reinforced alloy.

[0054] The alloys of Example 1 and Comparative Examples 1-3 were tested for their room temperature compressive strength, and the results are as follows: Figure 4 As shown.

[0055] Figure 4 The room temperature compression curves are for the alloys prepared in Example 1 and Comparative Examples 1-3.

[0056] Depend on Figure 4 It can be seen that the room temperature compressive strength of Example 1 is ≥700MPa, which is much higher than that of Comparative Examples 1-3.

[0057] Alloys from Examples 1-5 and Comparative Examples 1-3 were tested for Vickers hardness under a test force of 0.2 kg. The results are shown in Table 2.

[0058] Table 2 Performance Test Results

[0059] As can be seen from Table 2, the in-situ nano-dual-phase reinforced Al-Zn-Mg-Cu-Y alloy of the present invention has excellent hardness.

[0060] The significant improvement in room temperature compressive strength and hardness of the in-situ nano-dual-phase reinforced Al-Zn-Mg-Cu-Y alloy provided by this invention indicates that the introduction of rare earth element Y and the synergistic effect of high-pressure preparation conditions successfully generated a nanoscale dual-phase reinforcement system composed of η and T phases in situ within the alloy, achieving microstructure refinement and densification. Compared with similar alloys under traditional processes, the room temperature compressive strength of this invention is increased by 40%, and the hardness is increased by 98%.

[0061] 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. An in-situ nano-duplex reinforced Al-Zn-Mg-Cu-Y alloy, characterized in that, The chemical composition of the alloy, by mass percentage, includes: Zn 4-8%, Mg 1.2-2.8%, Cu 1.2-2.0%, Y 0.1-0.6%, Al 86.6-93.5%, and the total mass percentage of each chemical component is 100%. The alloy microstructure contains uniformly distributed nanoscale η phase and nanoscale T phase.

2. The in-situ nano-duplex reinforced Al-Zn-Mg-Cu-Y alloy according to claim 1, characterized in that, The nanoscale η phase is Mg(Zn, Al, Cu)2; preferably, the volume fraction of the nanoscale η phase in the alloy structure is 3-4%; preferably, the average particle size of the nanoscale η phase is 20-25 nm; preferably, the nanoscale η phase is in the form of strips.

3. The in-situ nano-duplex reinforced Al-Zn-Mg-Cu-Y alloy according to claim 1 or 2, characterized in that, Nanoscale T phase is Mg 32 (Al, Zn) 49 Preferably, the volume fraction of nanoscale T phase in the alloy microstructure is 1.4-1.6%; preferably, the average particle size of nanoscale T phase is 10-15 nm; preferably, the nanoscale T phase is granular.

4. The in-situ nano-duplex reinforced Al-Zn-Mg-Cu-Y alloy according to any one of claims 1-3, characterized in that, Y element is distributed in the alloy structure in the form of intermetallic compounds; preferably, the composition of the intermetallic compounds formed by Y element is Al8Cu4Y; preferably, the volume fraction of the intermetallic compounds formed by Y element in the alloy structure is 2-2.5%.

5. The in-situ nano-duplex reinforced Al-Zn-Mg-Cu-Y alloy according to any one of claims 1-4, characterized in that, The matrix of the alloy structure is an α-Al matrix.

6. The in-situ nano-duplex reinforced Al-Zn-Mg-Cu-Y alloy according to any one of claims 1-5, characterized in that, The in-situ nano-duplex reinforced Al-Zn-Mg-Cu-Y alloy has a room temperature compressive strength ≥700MPa and a Vickers hardness ≥205 under a test force of 0.2 kg.

7. A high-pressure preparation method for the in-situ nano-nano dual-phase reinforced Al-Zn-Mg-Cu-Y alloy as described in any one of claims 1-6, characterized in that, The process includes the following steps: subjecting the billet to high-temperature and high-pressure treatment to obtain an in-situ nano-duplex strengthened Al-Zn-Mg-Cu-Y alloy; The high-temperature and high-pressure treatment involves a pressure of 1-4 GPa, a temperature of 800-1100℃, and a time of 3-4 hours. The chemical composition of the billet is the same as that of the in-situ nano-duplex reinforced Al-Zn-Mg-Cu-Y alloy described in any one of claims 1-6.

8. The high-pressure preparation method for the in-situ nano-dual-phase reinforced Al-Zn-Mg-Cu-Y alloy according to claim 7, characterized in that, After the blanks are assembled into components, they are subjected to high temperature and high pressure treatment.

9. The high-pressure preparation method for the in-situ nano-dual-phase reinforced Al-Zn-Mg-Cu-Y alloy according to claim 8, characterized in that the assembly... include: The components include a blank with an external insulating layer, a graphite tube, a graphite sheet, and a conductive sealing sheet. The blank with the external insulating layer is placed inside the graphite tube, the graphite sheet seals both ends of the graphite tube, and the conductive sealing sheet is placed outside the graphite sheet and seals both ends of the graphite tube.

10. The high-pressure preparation method of the in-situ nano-duplex reinforced Al-Zn-Mg-Cu-Y alloy according to any one of claims 7-9, characterized in that, Raw materials of various chemical compositions are taken, smelted and cast in a protective gas atmosphere to obtain billets; preferably, the protective gas is at least one of argon and sulfur hexafluoride; preferably, the smelting temperature is 740-760℃; preferably, the casting temperature is 715-725℃; preferably, the raw materials of various chemical compositions are Al ingots, Mg ingots, Zn granules, Al-Cu master alloy and Al-Y master alloy.

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