High-zn magnesium alloy based on two-stage corrosion-resistant barrier and preparation method thereof

Abstract

This invention discloses a high-Zn magnesium alloy based on a dual-level corrosion barrier, formed by injection casting, and its preparation method, belonging to the field of magnesium alloy materials and metallurgical technology. Addressing the corrosion resistance bottleneck caused by the porous surface film and strong cathodic activity of the grain boundary second phase in high-Zn injection-cast magnesium alloys, a novel dual-level corrosion barrier design is proposed. Through optimized design of major and micro elements, optimized injection casting process, and synergistic control of precise heat treatment regime, a dual-level corrosion barrier consisting of a dense surface passivation layer and a fine network of weak cathodic phases is constructed. The magnesium alloy prepared by this invention, after immersion in 3.5 wt.% NaCl solution for 7 days, exhibits a weight loss corrosion rate ≤0.70 mm / year and a hydrogen evolution rate ≤0.40 mL / cm² / day, demonstrating significantly superior corrosion resistance compared to existing commercially available high-Zn magnesium alloys. It is suitable for applications such as 3C, drones, robots, and automobiles, where both corrosion resistance and lightweighting are required.

Description

Technical Field

[0001] This invention relates to the fields of magnesium alloy materials and metallurgical technology, and in particular to a high-Zn magnesium alloy based on a dual-level corrosion barrier by injection casting and its preparation method. Background Technology

[0002] Magnesium alloys, as the lightest metallic structural materials, possess advantages such as low density, high specific strength, high thermal conductivity, and recyclability, showing broad application prospects in fields such as automotive lightweighting, electronic equipment, and aerospace. Injection casting, as a key process for near-net-shape forming of magnesium alloys, features high production efficiency, high forming precision, and dense microstructure, making it the core manufacturing method for commercial magnesium alloy structural components.

[0003] In injection-cast magnesium alloy systems, while high Zn (≥6.0 wt.%) systems can significantly improve mechanical properties through solid solution and precipitation strengthening, their corrosion resistance becomes increasingly problematic. On one hand, surface protection is limited: because Zn has a weaker oxygen affinity than Mg, and Zn... 2+ With Mg 2+ With similar radii, it is difficult to improve the density of the MgO film through lattice doping effects. The naturally occurring corrosion product film is in a loose state (PBR<1), which cannot effectively block the penetration of corrosive media. On the other hand, the internal electrochemical environment is unbalanced: the sub-rapid solidification process of injection casting leads to severe grain boundary segregation of Zn elements, forming a coarse, strongly cathodic second phase, which exacerbates the uneven distribution of solute and the potential gradient between the grains and grain boundaries, and severely induces microgalvanic corrosion. Therefore, how to construct a dual-level corrosion-resistant barrier of "dense surface passivation layer" and "internal electrochemical barrier" through the synergistic coupling control of composition design, injection casting process optimization and precise heat treatment is the key technical challenge to improve the long-term corrosion stability of injection-cast high-Zn magnesium alloys. Summary of the Invention

[0004] In view of this, the present invention provides a high-Zn magnesium alloy based on a dual-level corrosion barrier and its preparation method, aiming to solve the corrosion resistance bottleneck caused by the loose surface film and strong cathodic activity of the second phase at the grain boundaries in high-Zn system injection-cast magnesium alloys.

[0005] Therefore, the present invention provides the following technical solution:

[0006] On one hand, the present invention provides a method for preparing high-Zn magnesium alloy by injection casting based on a dual-level corrosion-resistant barrier, the method comprising: A Mg-Zn-Al high-Zn system was adopted, with trace elements Ca and RE added; Weigh each raw material according to the composition ratio, and melt each raw material to obtain magnesium alloy melt; The magnesium alloy melt is shot-cast to obtain a shot-cast magnesium alloy; The shot-cast magnesium alloy is subjected to a medium-temperature short-time solution treatment to induce partial remelting of the residual liquid phase, transforming the coarse weak cathode second phase into a discontinuous fine network weak cathode phase, forming an internal electrochemical barrier. The medium-temperature short-time solution treatment includes heating the shot-cast magnesium alloy to 310-330 ℃ at a heating rate of 5-10 ℃ / min, holding it at that temperature for 5-20 h under argon protection, and then air-cooling it to obtain a solution-treated magnesium alloy. The solid solution magnesium alloy is subjected to precise aging treatment to induce corrosion-resistant elements to segregate towards the surface and grain boundaries, forming a dense surface passivation film, and finally constructing a two-level corrosion-resistant barrier. The precise aging treatment includes heating the solid solution magnesium alloy to 175-185 ℃ at a heating rate of 3-5 ℃ / min, holding it at that temperature for 1-3 h, and then air cooling it to room temperature.

[0007] Further, each raw material is weighed according to the component ratio, including: by weight percentage, the main element Zn / Al ratio is 1.2~5, the trace elements Ca are 0.1%~0.5%, Mn are 0.1%~0.5%, RE are 0.1%~0.5%, and the balance is Mg and impurities; the content of harmful impurities among the impurities is: Fe≤0.02%, Ni≤0.005%, Cu≤0.005%.

[0008] Furthermore, Zn 6.0%~10.0%, Al 2.0%~5.0%.

[0009] Furthermore, RE can be one or both of Ce and Sm.

[0010] Further, the raw materials are weighed according to the composition ratio, and the raw materials are smelted to obtain a magnesium alloy melt, including: Weigh out pure Mg ingots, pure Zn ingots, pure Al ingots, Mg-Ca, Mg-Mn and Mg-RE master alloys according to the composition ratio; melt the pure Mg ingots at 680 ℃ in a protective gas environment of SF6 and CO2, then raise the temperature to 720~740 ℃, add the remaining alloy raw materials in sequence and hold for 20~30 minutes; refine at 720~730 ℃ for 5~8 minutes, let stand for 30~40 minutes and then remove the slag to obtain magnesium alloy melt.

[0011] Furthermore, the volume ratio of SF6 to CO2 in the SF6 and CO2 mixed protective gas is 1:60 to 1:80.

[0012] Further, the magnesium alloy melt is shot-cast to obtain a shot-cast magnesium alloy, comprising: The magnesium alloy melt was cast into an ingot, and fine particles with a particle size of 1.2~1.6 mm were prepared by shearing with a granulator. The magnesium alloy was prepared by using an injection casting machine with the screw speed set at 50~150 r / min, the injection casting temperature at 600~620 ℃, the injection casting rate at 1~4 m / s, the mold temperature at 230~290 ℃, and the holding time at 3~5 s.

[0013] In another aspect, the present invention also provides a high Zn magnesium alloy prepared by the above-mentioned injection casting method based on a dual-level corrosion barrier.

[0014] Advantages and positive effects of the present invention: This invention employs a dual-level corrosion-resistant barrier constructed using a medium-temperature short-time solution treatment and a precise aging treatment, consisting of an internal electrochemical barrier and a dense surface passivation film. The medium-temperature short-time solution treatment avoids grain coarsening and precisely controls the remelting of the coarse second phase at grain boundaries into a discontinuous fine network phase. Precise aging promotes the selective segregation of corrosion-resistant elements, forming a dense passivation film containing Al₂O₃, RE₂O₃, and Zn(OH)₂ on the surface, achieving efficient and low-energy-consumption corrosion-resistant modification. In the dual-level corrosion-resistant barrier, the dense structure of the surface passivation barrier effectively blocks Cl₂. - Corrosive media can penetrate the interior; the fine network of weak cathodic phases significantly weakens the microgalvanic corrosion effect, blocks the corrosion propagation path, and transforms the corrosion failure mode into uniform corrosion, thus greatly improving long-term corrosion resistance and stability.

[0015] The preparation process in this invention is highly compatible and suitable for industrial-scale production. The preparation process does not require complex surface treatment, and the process is simplified and environmentally friendly. It can produce complex structural parts with high precision and dense structure, and is widely applicable to the dual requirements of corrosion resistance and lightweight in the automotive, electronic equipment, aerospace and other fields.

[0016] Meanwhile, the composition design in this invention is adapted to the characteristics of the high-Zn system. The synergy between high Zn and Al ensures the matrix strengthening effect and provides solute support for oxide film densification. The two also form a Mg-Zn-Al phase, laying the foundation for weak cathodic modification. Ca and RE elements significantly purify the melt and inhibit the segregation of harmful impurities at grain boundaries, reducing micro-electrochemical inhomogeneity. Mn element effectively improves the allowable limit of Fe and significantly weakens the microcouple effect in the non-equilibrium structure of injection casting. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a SEM image of a high-Zn magnesium alloy injection-cast based on a dual-level corrosion barrier in an embodiment of the present invention. Detailed Implementation

[0019] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0020] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0021] This invention utilizes a synergistic control of composition design, injection casting solidification, and precise heat treatment to construct a surface passivation film and an internal fine-network weak cathode phase, such as... Figure 1 As shown, the prepared high-Zn magnesium alloy, after being immersed in 3.5 wt.% NaCl solution for 7 days, exhibited a weight loss corrosion rate ≤0.70 mm / year and a hydrogen evolution rate ≤0.40 mL / cm² / day. This effectively addresses the two core issues of porous surface film and strong cathodic second phase at grain boundaries in high-Zn magnesium alloys.

[0022] Example 1 A method for preparing high-Zn magnesium alloy by injection casting based on a dual-level corrosion-resistant barrier, the specific steps of which are as follows: S11. Composition Design: By mass percentage, Zn 10.0%, Al 2%, Ca 0.3%, Mn 0.2%, Ce 0.2%, Sm 0.1%, with the balance being Mg; impurity content is strictly controlled: Fe 0.015%, Ni 0.003%, Cu 0.002%; the calculated Zn / Al ratio in this embodiment is 5.0. S12. Material Preparation and Smelting: Weigh 20 kg of raw materials, including 8.6 kg of pure Mg ingots, 2.0 kg of pure Zn ingots, 0.40 kg of pure Al ingots, 3.0 kg of Mg-20Ca master alloy, 4.0 kg of Mg-10Mn master alloy, 1.33 kg of Mg-30Ce master alloy, and 0.67 kg of Mg-30Sm master alloy. Under a protective gas mixture of SF6 and CO2 (volume ratio 1:70), add the pure Mg ingots to the smelting furnace, melt at 680 ℃, then raise the temperature to 730 ℃, add the remaining raw materials in sequence, and hold for 25 min. Raise the temperature to 725 ℃ and refine for 6 min. After standing for 35 min, remove the slag to obtain the magnesium alloy melt. S13. Injection casting: The magnesium alloy melt is cast into an ingot and sheared into fine particles of 1.4~1.6 mm by a granulator; an injection casting machine is used with the screw speed set at 100 r / min, the injection temperature at 610 ℃, the injection rate at 2.5 m / s, the mold temperature at 260 ℃, and the holding time at 4 s to prepare the injection-cast magnesium alloy. The weak cathode second phase is formed by modification with corrosion-resistant elements, which provides support for the preparation of the internal corrosion-resistant barrier.

[0023] S14. Medium-temperature short-time solution treatment: The cast magnesium alloy is heated to 320 ℃ at a heating rate of 8 ℃ / min, protected by argon gas, held at this temperature for 12 h, and then air-cooled to room temperature. S15. Precision aging treatment: The solution-treated magnesium alloy is heated to 180℃ at a heating rate of 4℃ / min, held for 2 hours, and then air-cooled to room temperature to obtain a high Zn corrosion-resistant magnesium alloy formed by injection casting.

[0024] Corrosion resistance of the high-Zn magnesium alloy prepared in Example 1: After immersion in 3.5wt.% NaCl solution for 7 days, the weight loss corrosion rate was 0.70 mm / year and the hydrogen evolution rate was 0.40 mL / cm² / day; Dual-barrier characteristics: The surface chemical passivation barrier is mainly composed of MgO, Al2O3, Ce2O3, Zn(OH)2, etc., and the internal fine network is mainly composed of Mg-Zn phase, containing some Mg-Zn-Al phase, which is discontinuously distributed.

[0025] In this embodiment, the Zn / Al ratio is 5.0 (within the upper limit of the scope defined by this invention), with a high Zn content and a low Al content. At this ratio, the solid solution strengthening effect of Zn is fully utilized, but the contribution of Al to the densification of the surface passivation film is relatively limited—insufficient Al results in a low Al2O3 content in the surface passivation film, leading to slightly poorer film density and insufficient inhibition of Cl. -The corrosion resistance is relatively low due to the intrusion of Al, with a small amount of Mg-Zn-Al phase forming internally, and the Mg-Zn phase being dominant. The weak cathodic modification effect is limited, resulting in a lower corrosion resistance compared to the embodiments of this invention. However, it is still significantly better than conventional high-Zn magnesium alloys without added Ca and RE elements and without optimized Zn / Al ratios. This phenomenon indicates that an excessively high Zn / Al ratio, due to insufficient Al, weakens the density of the surface passivation film and the synergistic corrosion resistance effect of the internal weak cathodic phase, leading to a decrease in corrosion resistance.

[0026] Example 2 A method for preparing high-Zn magnesium alloy by injection casting based on a dual-level corrosion-resistant barrier, the specific steps of which are as follows: S21. Composition Design: By mass percentage, Zn 6%, Al 5%, Ca 0.2%, Mn 0.3%, Ce 0.3%, with the balance being Mg and unavoidable impurities; Impurity content control: Fe 0.012%, Ni 0.002%, Cu 0.003%; S22. Material Preparation and Smelting: Weigh 20 kg of raw materials, including 7.8 kg of pure magnesium ingots, 1.2 kg of pure zinc ingots, 1.0 kg of pure aluminum ingots, 2.0 kg of Mg-20Ca master alloy, 6.0 kg of Mg-10Mn master alloy, and 2.0 kg of Mg-30Ce master alloy; mix protective gases at a volume ratio of 1:65, melt the pure magnesium ingots at 680 ℃, raise the temperature to 720 ℃ and add the remaining raw materials, hold for 20 min; refine at 720 ℃ for 5 min, let stand for 30 min and then remove the slag; S23. Shot casting: The ingot is sheared into fine particles of 1.2~1.4 mm. The shot casting parameters are: screw speed 80 r / min, shot casting temperature 600 ℃, shot casting rate 1.8 m / s, mold temperature 230 ℃, and holding time 3 s to prepare shot-cast magnesium alloy. The weak cathode second phase is formed by modifying with corrosion-resistant elements to provide support for the preparation of the internal corrosion-resistant barrier.

[0027] S24. Medium-temperature short-time solution treatment: heating rate 5 ℃ / min, holding at 310 ℃ for 8 h, Ar gas protection, air cooling to room temperature; S25. Precise aging treatment: heating rate 3 ℃ / min, holding at 175 ℃ for 3 h, then air cooling to room temperature.

[0028] Corrosion resistance of the high-Zn magnesium alloy prepared in Example 2: After immersion in 3.5wt.% NaCl solution for 7 days, the weight loss corrosion rate was 0.55 mm / year and the hydrogen evolution rate was 0.25 mL / cm² / day; Dual-barrier characteristics: The surface passivation film is mainly composed of MgO, Al2O3, Ce2O3, Zn(OH)2, etc., and the internal fine network is composed of Mg-Zn-Al and Mg-Zn phases, which are discontinuously distributed.

[0029] In this embodiment, the Zn / Al ratio is 1.2 (within the lower limit of the scope defined by this invention), with a high Al content and a low Zn content. The advantages of Al are fully utilized—Al, as a corrosion-resistant strengthening element, can significantly promote the formation of Al2O3 in the surface passivation film. Al2O3 has excellent chemical stability, effectively densifying the surface passivation film and improving the film's resistance to Cl. - The alloy exhibits strong resistance to corrosive media, and the Al and Zn elements synergistically form a large amount of Mg-Zn-Al phase. This phase has lower cathodic activity than the pure Mg-Zn phase, which can further weaken the internal micro-galvanic corrosion effect. However, due to the low Zn content, the solid solution strengthening effect is slightly weaker. Nevertheless, the corrosion resistance is significantly improved compared to Example 1, indicating that it is appropriate to reduce the Zn / Al ratio and increase the Al content. This can improve the corrosion resistance of the alloy by optimizing the density of the surface passivation film and the composition of the internal second phase.

[0030] Example 3 A method for preparing high-Zn magnesium alloy by injection casting based on a dual-level corrosion-resistant barrier, the specific steps of which are as follows: S31. Composition Design: By mass percentage, Zn 9%, Al 4%, Ca 0.4%, Mn 0.4%, Sm 0.3%, with the balance being Mg and unavoidable impurities; Impurity content control: Fe 0.018%, Ni 0.004%, Cu 0.004%; S32. Material preparation and smelting: Weigh 20 kg of raw materials, 3.4 kg of pure magnesium ingots, 1.8 kg of pure zinc ingots, 0.8 kg of pure aluminum ingots, 4.0 kg of Mg-20Ca master alloy, 8.0 kg of Mg-10Mn master alloy, and 2.0 kg of Mg-30Sm master alloy; mix protective gas at a volume ratio of 1:75, add the raw materials at 740 ℃, and hold for 30 min; refine at 730 ℃ for 8 min, let stand for 40 min, and then remove the slag; S33. Injection casting: Fine particle size 1.4~1.5 mm, injection casting parameters: screw speed 130 r / min, injection casting temperature 620 ℃, injection casting rate 3.5 m / s, mold temperature 280 ℃, holding time 5 s, to prepare injection cast magnesium alloy; a weak cathode second phase is formed by modification with corrosion-resistant elements, providing support for the preparation of internal corrosion-resistant barrier.

[0031] S34. Medium-temperature short-time solution treatment: heating rate 10 ℃ / min, holding at 330 ℃ for 18 h, Ar gas protection, air cooling to room temperature; S35, Precise Aging Treatment: Heating rate 5 ℃ / min, hold at 185 ℃ for 1.5 h, then air cool to room temperature.

[0032] The properties of the high-Zn magnesium alloy prepared in Example 3, corrosion resistance: after immersion in 3.5wt.% NaCl solution for 7 days, the weight loss corrosion rate was 0.60 mm / year, and the hydrogen evolution rate was 0.30 mL / cm² / day.

[0033] In this embodiment, the Zn / Al ratio is 2.25 (within the middle range defined by this invention). The balanced ratio of Zn and Al elements achieves synergistic effects, representing a superior Zn / Al ratio in this invention. On one hand, the appropriate Zn content fully leverages solid solution strengthening, ensuring the alloy's mechanical properties while providing sufficient solute for the formation of internal Mg-Zn and Mg-Zn-Al phases. On the other hand, a suitable amount of Al promotes the formation of Al2O3 in the surface passivation film, significantly improving the film's density and stability, effectively blocking corrosive media intrusion. Simultaneously, Al, in synergistic with Zn, regulates the morphology of the internal second phase, resulting in a more uniform and discontinuous distribution of the fine-mesh weak cathode phase, further weakening the micro-galvanic corrosion effect. Therefore, the corrosion resistance of this embodiment is at the middle level of the three embodiments, balancing corrosion resistance and mechanical properties, fully demonstrating the advantages of a reasonable Zn / Al ratio within the range of 1.2 to 5.0.

[0034] Comparative example (conventional high-Zn magnesium alloy) A high-Zn magnesium alloy was prepared using a conventional injection casting process. The composition was Zn 8.0 wt.%, Al 3.5 wt.%, Mn 0.2 wt.%, with the balance being Mg and impurities (Fe 0.015 wt.%, Ni 0.003 wt.%, Cu 0.002 wt.%). No Ca or RE elements were added, and no medium-temperature short-time solution treatment or precise aging treatment was performed. The calculated Zn / Al ratio of the comparative example was approximately 2.29. Although this is close to the Zn / Al ratio of Example 3, its corrosion resistance is significantly lower than that of the embodiments of this invention due to the absence of Ca and RE trace elements and the lack of precise heat treatment control.

[0035] The properties of conventional high-Zn magnesium alloys are as follows: Corrosion resistance: After immersion in 3.5wt.% NaCl solution for 7 days, the weight loss corrosion rate is 1.50 mm / year, and the hydrogen evolution rate is 1.00 mL / cm² / day.

[0036] The comparison shows that the high Zn magnesium alloy prepared by the present invention has improved corrosion resistance compared with conventional high Zn magnesium alloys through the dual-level corrosion resistance barrier design of "surface passivation layer and fine network weak cathode phase", effectively solving the corrosion resistance bottleneck of high Zn magnesium alloy system by injection casting.

[0037] The core corrosion resistance mechanism of this invention lies in: 1. Surface passivation barrier: Based on an alloying composition design strategy using corrosion-resistant elements (Al, Ca, RE, etc.), the distribution of corrosion-resistant solutes is controlled to promote the formation and densification of the surface passivation layer. With a PBR value greater than 1, it can effectively block Cl... - It inhibits the dissolution of the matrix by preventing the intrusion of corrosive media.

[0038] 2. Internal fine network weak cathode phase barrier: The medium-temperature short-time solution treatment causes the coarse grain boundary second phase in the shot-cast state to melt back into a discontinuous fine network phase. After modification with major and trace elements, the cathode activity is significantly reduced, weakening the microgalvanic corrosion effect. At the same time, it physically blocks the corrosion propagation path and improves long-term corrosion resistance stability.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for producing a high-Zn magnesium alloy by a two-stage corrosion-resistant barrier-based injection molding, characterized by, The method includes: A Mg-Zn-Al high-Zn system was adopted, with trace elements Ca and RE added; The raw materials are weighed according to the composition ratio and smelted to obtain a magnesium alloy melt. The raw materials weighed according to the composition ratio include: by weight percentage, the main element Zn / Al ratio is 1.2~5, trace elements Ca 0.1%~0.5%, Mn 0.1%~0.5%, RE 0.1%~0.5%, and the balance is Mg and impurities; the content of harmful impurities is: Fe≤0.02%, Ni≤0.005%, Cu≤0.005%; Zn 6.0%~10.0%, Al 2.0%~5.0%. The magnesium alloy melt is shot-cast to obtain a shot-cast magnesium alloy; The shot-cast magnesium alloy is subjected to a medium-temperature short-time solution treatment to induce partial remelting of the residual liquid phase, transforming the coarse weak cathode second phase into a discontinuous fine network weak cathode phase, forming an internal electrochemical barrier. The medium-temperature short-time solution treatment includes heating the shot-cast magnesium alloy to 310-330 ℃ at a heating rate of 5-10 ℃ / min, holding it at that temperature for 5-20 h under argon protection, and then air-cooling it to obtain a solution-treated magnesium alloy. The solid solution magnesium alloy is subjected to precise aging treatment to induce corrosion-resistant elements to segregate towards the surface and grain boundaries, forming a dense surface passivation film, and finally constructing a two-level corrosion-resistant barrier. The precise aging treatment includes heating the solid solution magnesium alloy to 175-185 ℃ at a heating rate of 3-5 ℃ / min, holding it at that temperature for 1-3 h, and then air cooling it to room temperature.

2. The method for preparing high-Zn magnesium alloy by injection casting based on a dual-level corrosion barrier according to claim 1, characterized in that, RE can be one or both of Ce and Sm.

3. The method for preparing high-Zn magnesium alloy by injection casting based on a dual-level corrosion barrier according to claim 1, characterized in that, Weigh each raw material according to the composition ratio, and melt each raw material to obtain a magnesium alloy melt, including: Weigh out pure Mg ingots, pure Zn ingots, pure Al ingots, Mg-Ca, Mg-Mn and Mg-RE master alloys according to the composition ratio; melt the pure Mg ingots at 680 ℃ in a protective gas environment of SF6 and CO2, then raise the temperature to 720~740 ℃, add the remaining alloy raw materials in sequence and hold for 20~30 minutes; refine at 720~730 ℃ for 5~8 minutes, let stand for 30~40 minutes and then remove the slag to obtain magnesium alloy melt.

4. The method for preparing high-Zn magnesium alloy by injection casting based on a dual-level corrosion barrier according to claim 3, characterized in that, The volume ratio of SF6 to CO2 in the SF6 and CO2 mixed protective gas is 1:60 to 1:

80.

5. The method for preparing high-Zn magnesium alloy by injection casting based on a dual-level corrosion barrier according to claim 1, characterized in that, The magnesium alloy melt is shot-cast to obtain a shot-cast magnesium alloy, comprising: The magnesium alloy melt was cast into an ingot, and fine particles with a particle size of 1.2~1.6 mm were prepared by shearing with a granulator. The magnesium alloy was prepared by using an injection casting machine with the screw speed set at 50~150 r / min, the injection casting temperature at 600~620 ℃, the injection casting rate at 1~4 m / s, the mold temperature at 230~290 ℃, and the holding time at 3~5 s.

6. A high-Zn magnesium alloy prepared by the injection casting method based on a dual-level corrosion barrier as described in any one of claims 1 to 5.

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