A nano-biphasic low-alloy content superplastic magnesium alloy and a preparation method thereof
Magnesium alloys with nano-duplex structures formed by low-alloying elements such as Bi, Sn, Zn, and Mn have solved the problem of insufficient superplastic deformation capacity of magnesium alloys under low-alloying conditions, achieving excellent forming performance at high temperatures and feasibility for industrial production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JILIN UNIVERSITY
- Filing Date
- 2026-03-16
- Publication Date
- 2026-06-09
AI Technical Summary
Existing magnesium alloys are difficult to achieve stable fine-grained structures and high-temperature superplastic deformation capabilities under low-alloying conditions, resulting in difficulties in forming complex components. Furthermore, existing processes are complex, costly, and difficult to scale up for application.
A multi-element alloy system composed of low alloying elements such as Bi, Sn, Zn, and Mn is used to form a nano-biphase structure through reasonable melting, gravity casting, and hot extrusion processes, which inhibits grain growth and improves microstructure stability and superplasticity.
It achieves an elongation at break of ≥400% at 300℃, making it suitable for efficient extrusion molding of complex components. It features high molding stability, good microstructure uniformity, and strong performance repeatability, making it suitable for continuous industrial production.
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Figure CN122168955A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of metal material processing technology, specifically relating to a low-alloy superplastic magnesium alloy containing nano-biphase and its preparation method. Background Technology
[0002] Magnesium alloys, as lightweight structural materials, have advantages such as low density, high specific strength, high specific stiffness, excellent damping and vibration reduction performance, and recyclability, and have broad application prospects in aerospace, transportation, and electronic manufacturing. However, since magnesium alloys have a close-packed hexagonal crystal structure (HCP), the number of independent slip systems that can be activated at room temperature is limited, resulting in relatively low plastic deformation capacity. The forming of complex components usually depends on medium- and high-temperature processing. Superplastic deformation technology is an important means to achieve near-net-shape forming of complex magnesium alloy components, characterized by obtaining an elongation after fracture of >200% at high temperatures. Existing research generally believes that magnesium alloys need to meet the following conditions to obtain superplastic deformation capacity: (1) the material has a uniform and fine grain structure with an average grain size generally not greater than 8 μm; (2) this fine grain structure has good thermal stability during high-temperature deformation to avoid rapid grain growth.
[0003] Based on the above requirements, currently reported superplastic magnesium alloy systems are mostly concentrated in medium- and high-alloy content systems or magnesium alloy systems containing rare earth elements. In these alloys, a high volume fraction of second-phase particles are usually formed. During hot working, particle-induced recrystallization promotes the formation of fine-grained structures, and grain growth is inhibited through grain boundary pinning during high-temperature deformation, thereby achieving superplastic deformation capability. However, medium- and high alloying or the addition of large amounts of rare earth elements significantly increases material costs and may increase the tendency to crack during casting and extrusion, reducing the alloy's machinability. In addition, existing technical approaches to improving the superplastic deformation capability of magnesium alloys mostly rely on large plastic deformation processes such as equal channel angle extrusion, but these processes are complex, have low production efficiency, and are limited in part size, which is not conducive to large-scale industrial applications. In contrast, conventional hot extrusion has advantages such as mature technology and high efficiency, but traditional low-alloy content magnesium alloys usually lack thermally stable second-phase particles during extrusion and high-temperature deformation, resulting in rapid grain growth and difficulty in obtaining fine-grained structures and sustained high-temperature deformation capability. Therefore, achieving stable fine-grained microstructure and excellent superplastic deformation capability in magnesium alloys to meet the needs of large-scale industrial applications while ensuring a low degree of alloying and cost advantages remains a key technical problem that urgently needs to be solved. Summary of the Invention
[0004] In view of this, the purpose of this invention is to provide a low-alloy superplastic magnesium alloy containing nano-dual phases and its preparation method. The magnesium alloy obtained by this invention is a low-alloy multi-element alloy system that does not contain rare earth elements. Compared with traditional medium-high alloy or rare earth strengthened magnesium alloys, this invention achieves a synergistic improvement in extrusion formability and mechanical properties without significantly increasing the cost of raw materials. This is beneficial for obtaining a new type of extruded magnesium alloy material with high forming stability, good microstructure uniformity, strong performance repeatability, and suitability for continuous industrial production.
[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a low-alloy-content superplastic magnesium alloy containing nano-duplex phases, which is composed of the following components by mass percentage: Bi 0.5~2.0%, Sn 0.5~1.5%, Zn 0.5~1.0%, Mn 0.3~0.6%, unavoidable impurities ≤0.05%, and the balance being magnesium.
[0006] This invention also provides a method for preparing the above-mentioned superplastic magnesium alloy with high alloy content, comprising the following preparation steps: S1. Weigh the raw materials according to the stated mass percentage; The raw materials are: Pure Mg, pure Sn, pure Zn, Mg-Bi master alloy and Mg-Mn master alloy; The Bi content in the Mg-Bi master alloy is 20~30 wt.%. The Mn content in the Mg-Mn master alloy is 5~10 wt.%; S2. Preheat all raw materials, then melt pure Mg in a protective atmosphere for the first stage of heat preservation and heating, then add pure Sn, pure Zn and Mg-Mn master alloy in sequence, and further heat and melt in the second stage and mix evenly. Finally, add Mg-Bi master alloy for the third stage of heat preservation and heating, and obtain multi-element microalloyed magnesium alloy melt through stirring and refining. S3. Magnesium alloy ingots are obtained by pouring multi-component micro-alloyed magnesium alloy melt; S4. The magnesium alloy ingot is subjected to a stepped homogenization process, followed by immediate quenching to rapidly cool the alloy ingot to room temperature. Then, it undergoes pre-extrusion heat treatment and hot extrusion deformation to obtain extruded magnesium alloy rods.
[0007] Preferably, the preheating temperature in S2 is 100~250℃ and the time is 60~90 min.
[0008] Preferably, the temperature of the first stage of heat preservation in S2 is 450~500℃ and the time is 60~90 min.
[0009] Preferably, the temperature at which the temperature rises and melts in step S2 is 680~700℃.
[0010] Preferably, the temperature of the second stage of heating and melting in S2 is 700-730℃.
[0011] Preferably, the temperature for the third stage of heating and melting in S2 is 690~720℃.
[0012] Preferably, the final heat preservation time in S2 is 10~20 min.
[0013] Furthermore, the protective atmosphere in S2 is obtained by mixing CO2 and SF6 in a volume ratio of (90~99):(1-10).
[0014] Furthermore, the mold used for casting in S3 is preheated to 200~300℃.
[0015] Preferably, the method for the stepped homogenization process in S4 is as follows: First, heat the magnesium alloy ingot to 350~400℃ and hold for 1~2 hours; then heat to 420~450℃ and hold for 2~4 hours; finally heat to 480~500℃ and hold for 6~8 hours.
[0016] Furthermore, the temperature of the heat treatment before extrusion in S4 is 250~350℃, and the time is 90~120 min.
[0017] Preferably, the process parameters for hot extrusion deformation in step S4 are as follows: The extrusion ratio is 20~30:1; The extrusion exit rate is 0.6~1.2 m / min.
[0018] Furthermore, the extrusion die is preheated to 275~375°C during the extrusion process; After extrusion, the extruded magnesium alloy rod is cooled to room temperature using water cooling.
[0019] It contains at least the following beneficial technical effects: (1) The magnesium alloy obtained by this invention is a low-alloy multi-element alloy system with a total alloying element content ≤4.0wt.%, which does not contain rare earth elements. The alloy system achieves effective control over the precipitation behavior of the second phase and the stability of grain boundaries by compounding Bi, Sn, Zn, Mn and non-rare earth elements, thereby obtaining a stable fine-grained structure while maintaining a low alloying level. Compared with traditional medium- and high-alloy or rare earth-strengthened magnesium alloys, this invention achieves a synergistic improvement in extrusion formability and mechanical properties without significantly increasing raw material costs, which is beneficial for obtaining a new type of extruded magnesium alloy material with high forming stability, good microstructure uniformity, strong performance repeatability, and suitability for continuous industrial production.
[0020] (2) This invention optimizes the microstructure and mechanical properties of magnesium alloys through reasonable alloy composition design and synergistic control of smelting, gravity casting, and efficient extrusion forming processes. During hot working, Bi and Sn elements can form thermally stable Mg3Bi2 phase (melting point approximately 823℃) and Mg2Sn phase (melting point approximately 873℃), which helps maintain microstructure stability and inhibits extrusion hot cracking, thereby improving the high-temperature extrusion formability of the alloy. Furthermore, the formed Mg3Bi2 and Mg2Sn phases are symbiotically distributed in the microstructure, and the two adhere to each other at the nanoscale to form a dual-phase structure. This nano-dual-phase structure forms a stable mutual constraint relationship at the interface, which can effectively reduce the phase boundary migration rate and inhibit phase coarsening, thereby improving the thermal stability of the Mg3Bi2 and Mg2Sn phases. In addition, Zn element can promote the nucleation and precipitation of nano-phases, increase the number density of nano-dual phases, and make them more dispersed and uniformly distributed in the matrix, thereby further enhancing its inhibitory effect on grain boundary migration. In the alloy preparation process, Mn can play a role in melting and impurity removal, effectively reducing the content of harmful impurities in the melt. On the other hand, it can also form a small number of dispersed Mn particles, which helps to improve the stability of the structure.
[0021] (3) The magnesium alloy prepared by the method of the present invention is subjected to a strain rate of 1.0 × 10⁻⁶ at 300 °C. -3 ~5.0×10 -3 s -1 Under uniaxial tensile conditions, the elongation after fracture is ≥400%, exhibiting significant high-temperature superplastic deformation characteristics. During deformation, grain size growth is slow, maintaining equiaxed fine grain characteristics even under strain conditions, without significant abnormal grain growth, and the nano-biphasic particles do not show significant coarsening, demonstrating good overall thermal stability. Based on these microstructure characteristics and high-temperature deformation capabilities, the alloy is suitable for hot stretching and near-net-shape forming processes, enabling the integrated forming of complex thin-walled components, possessing clear engineering application value and promising prospects for industrialization. Attached Figure Description
[0022] Figure 1 This is a diagram of a nano-biphase structure in which the Mg3Bi2 and Mg2Sn phases are attached to the tissue. Detailed Implementation
[0023] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.
[0024] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.
[0025] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.
[0026] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.
[0027] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.
[0028] Unless otherwise specified, "room temperature" and "normal temperature" in this invention refer to 25±2℃.
[0029] Unless otherwise specified, all raw materials or instruments used in the following embodiments of the present invention are commercially available.
[0030] The raw materials used in this invention are as follows: pure Mg (purity ≥ 99.9 wt.%), pure Sn (purity ≥ 99.9 wt.%), pure Zn (purity ≥ 99.9 wt.%), Mg–Bi master alloy (Bi content 20–30 wt.%), and Mg–Mn master alloy (Mn content 5–10 wt.%).
[0031] Example 1 This embodiment uses a Mg-1.2Bi-0.8Sn-0.5Zn-0.3Mn magnesium alloy as the research object (its chemical composition by mass percentage is: Bi: 1.5wt.%, Sn: 0.8wt.%, Zn: 0.5wt.%, Mn: 0.3wt.%, unavoidable impurities ≤0.05wt.%, balance Mg); its preparation method includes the following steps: (1) According to the above alloy composition ratio, industrial pure Mg, pure Zn, pure Sn, Mg-Mn master alloy and Mg-Bi master alloy were selected as raw materials. After preheating each raw material at 200℃ for 60 min, it was smelted in a CO2 / SF6 mixed protective atmosphere. The volume ratio of CO2 to SF6 was 90:10.
[0032] First, pure magnesium is added to a crucible and held at 480°C for 60 minutes. Then, the temperature is raised to 700°C and heated until it is completely melted. Next, pure Zn, pure Sn, and Mg-Mn master alloy are added in sequence and fully melted at 725°C. The mixture is stirred evenly. Then, Mg-Bi master alloy is added and held at 710°C for 15 minutes until fully melted. The mixture is stirred evenly.
[0033] High-purity argon gas was then introduced into the melt for refining and slag removal, and ultrasonic vibration was combined to further refine the melt structure, resulting in a homogeneous multi-element microalloyed magnesium alloy melt.
[0034] (2) The magnesium alloy melt obtained in step (1) is poured into a metal mold preheated to 250°C and alloy ingots are prepared by gravity casting.
[0035] (3) The magnesium alloy ingot obtained in step (2) is subjected to homogenization heat treatment. First, the magnesium alloy ingot is heated to 350°C and held for 2 hours; then it is heated to 450°C and held for 2 hours; finally, it is heated to 480°C and held for 8 hours. Then, it is immediately quenched to rapidly cool the alloy ingot to room temperature to obtain a homogenized alloy ingot, so as to eliminate the segregation of the as-cast structure and improve the subsequent plastic processing performance.
[0036] (4) The homogeneous alloy ingot is heated to 300°C and held for 120 min, while the extrusion die is preheated to the same temperature range. Then, hot extrusion deformation is carried out under the conditions of extrusion ratio of 25:1 and extrusion exit speed of 0.8 m / min. After extrusion, it is air-cooled to room temperature to obtain extruded multi-element microalloyed magnesium alloy profile, wherein the profile is an extruded bar or profile.
[0037] The extruded Mg-1.2Bi-0.8Sn-0.5Zn-0.3Mn magnesium alloy prepared by the above process can achieve a superplastic elongation of about 400% at 300℃, exhibiting excellent high-temperature superplastic deformation capability, and is suitable for efficient extrusion forming and near-net-shape manufacturing of complex components.
[0038] Example 2 This embodiment takes a Mg-1.0Bi-1.0Sn-0.5Zn-0.3Mn magnesium alloy as an example (its chemical composition by mass percentage is: Bi: 1.0 wt.%, Sn: 1.0 wt.%, Zn: 0.5 wt.%, Mn: 0.3 wt.%, unavoidable impurities ≤0.05 wt.%, balance Mg); its preparation method includes the following steps: (1) According to the above alloy composition ratio, industrial pure Mg, pure Zn, pure Sn, Mg-Mn master alloy and Mg-Bi master alloy were selected as raw materials. After preheating each raw material at 100℃ for 75 min, it was smelted in a CO2 / SF6 mixed protective atmosphere. The volume ratio of CO2 to SF6 was 95:5.
[0039] First, pure magnesium is added to a crucible and held at 480°C for 60 minutes. Then, the temperature is raised to 700°C and heated until it is completely melted. Next, pure Zn, pure Sn, and Mg-Mn master alloy are added in sequence and fully melted at 720°C. The mixture is stirred evenly. Then, Mg-Bi master alloy is added and held at 710°C for 15 minutes until fully melted. The mixture is stirred evenly.
[0040] High-purity argon gas was then introduced into the melt for refining and slag removal, and ultrasonic vibration was combined to further refine the melt structure, resulting in a homogeneous multi-element microalloyed magnesium alloy melt.
[0041] (2) The magnesium alloy melt obtained in step (1) is poured into a metal mold preheated to 230°C and alloy ingots are prepared by gravity casting.
[0042] (3) The magnesium alloy ingot obtained in step (2) is subjected to homogenization heat treatment. First, the magnesium alloy ingot is heated to 350°C and held for 1 h; then it is heated to 450°C and held for 2 h; finally, it is heated to 500°C and held for 6 h. Then, it is immediately quenched to rapidly cool the alloy ingot to room temperature to obtain a homogenized alloy ingot, so as to eliminate the segregation of the as-cast structure and improve the subsequent plastic processing performance.
[0043] (4) The homogeneous alloy ingot is heated to 275°C and held for 90 min, while the extrusion die is preheated to the same temperature range. Then, hot extrusion deformation is carried out under the conditions of extrusion ratio of 20:1 and extrusion exit speed of 0.6 m / min. After extrusion, it is air-cooled to room temperature to obtain extruded multi-element microalloyed magnesium alloy profile, wherein the profile is an extruded bar or profile.
[0044] The extruded Mg-1.0Bi-1.0Sn-0.5Zn-0.3Mn magnesium alloy prepared by the above process can achieve a superplastic elongation of about 400% at 300℃, exhibiting excellent high-temperature superplastic deformation capability, and is suitable for efficient extrusion forming and near-net-shape manufacturing of complex components.
[0045] Example 3 This embodiment takes a Mg-0.8Bi-1.2Sn-0.5Zn-0.3Mn magnesium alloy as an example (its chemical composition by mass percentage is: Bi: 0.8 wt.%, Sn: 1.2 wt.%, Zn: 0.5 wt.%, Mn: 0.3 wt.%, unavoidable impurities ≤0.05 wt.%, balance Mg); its preparation method includes the following steps: (1) According to the above alloy composition ratio, industrial pure Mg, pure Zn, pure Sn, Mg-Mn master alloy and Mg-Bi master alloy were selected as raw materials. After preheating each raw material at 250℃ for 90 min, it was smelted in a CO2 / SF6 mixed protective atmosphere. The volume ratio of CO2 to SF6 was 99:1.
[0046] First, pure magnesium is added to a crucible and held at 480°C for 90 minutes. Then, the temperature is raised to 700°C and heated until it is completely melted. Next, pure Zn, pure Sn, and Mg-Mn master alloy are added in sequence and fully melted at 720°C. The mixture is stirred evenly. Then, Mg-Bi master alloy is added and held at 710°C for 20 minutes until fully melted. The mixture is stirred evenly.
[0047] High-purity argon gas was then introduced into the melt for refining and slag removal, and ultrasonic vibration was combined to further refine the melt structure, resulting in a homogeneous multi-element microalloyed magnesium alloy melt.
[0048] (2) The magnesium alloy melt obtained in step (1) is poured into a metal mold preheated to 270°C and alloy ingots are prepared by gravity casting.
[0049] (3) The magnesium alloy ingot obtained in step (2) is subjected to homogenization heat treatment. First, the magnesium alloy ingot is heated to 380℃ and held for 1 h; then it is heated to 450℃ and held for 2 h; finally, it is heated to 480℃ and held for 8 h, and then quenched immediately to cool the alloy ingot to room temperature to obtain a homogenized alloy ingot, so as to eliminate the segregation of the as-cast structure and improve the subsequent plastic processing performance.
[0050] (4) The homogeneous alloy ingot is heated to 300°C and held for 90 min, while the extrusion die is preheated to the same temperature range. Then, hot extrusion deformation is carried out under the conditions of extrusion ratio of 30:1 and extrusion exit speed of 1.0 m / min. After extrusion, it is air-cooled to room temperature to obtain extruded multi-element microalloyed magnesium alloy profile, wherein the profile is an extruded bar or profile.
[0051] The extruded Mg-0.8Bi-1.2Sn-0.5Zn-0.3Mn magnesium alloy prepared by the above process can achieve a superplastic elongation of about 380% at 300℃, exhibiting significant high-temperature superplastic deformation capability, and is suitable for efficient extrusion forming and near-net-shape manufacturing of complex components.
[0052] Therefore, compared with existing magnesium alloy systems that rely on high alloying or rare earth strengthening, the alloys described in Examples 1-3 of this invention, under the condition that the total content of alloying elements is ≤4.0 wt.% and contains no rare earth elements, form a nano-biphase structure combining Mg3Bi2 phase and Mg2Sn in the alloy microstructure through the composite regulation of Bi and Sn elements, as shown in Example 1. Figure 1 As shown. Figure 1 (a) shows the morphology of the nano-biphase structure formed by the combination of Mg3Bi2 phase and Mg2Sn. Figure 1 (b) to (d) are the energy dispersive spectral distributions of Mg, Bi, and Sn elements in the corresponding regions, respectively. The two-phase structure exhibits a tightly coexisting distribution, forming interfacial constraints and stabilizing effects under high-temperature conditions, effectively suppressing phase coarsening and interfacial migration behavior. Furthermore, this invention does not require large plastic deformation processes such as equal channel angle extrusion or high-pressure torsion; it can achieve high-temperature superplasticity with an elongation of approximately 400% at 300°C using only conventional melting, gravity casting, and hot extrusion forming processes. It combines adaptability to continuous industrial production with cost controllability, demonstrating significant technological advancement and application value.
[0053] The maximum solid solubility of Bi (Bi) at approximately 553 °C is about 8.87 wt.%, decreasing to below 1 wt.% below 200 °C; the maximum solid solubility of Sn (Sn) at 561 °C is about 14.48 wt.%, decreasing to about 0.45 wt.% below 200 °C. These elements exhibit high solid solubility at high temperatures, but their solubility decreases rapidly at medium and low temperatures. When Bi and Sn precipitate from the supersaturated solid solution, they form the Mg3Bi2 and Mg2Sn phases, respectively, which have higher melting points. Therefore, after high-temperature homogenization treatment, a supersaturated solid solution can be formed in the matrix, providing thermodynamic and kinetic driving forces for the attachment and precipitation of the Mg3Bi2 and Mg2Sn phases during subsequent heat treatment or hot working deformation. With a low total content of alloying elements, it is possible to obtain a high-density, size-controlled, and uniformly distributed nanoscale dual-phase structure through reasonable composition design and hot working process control, thereby regulating grain boundary migration behavior and microstructure thermal stability.
[0054] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A low-alloy-content superplastic magnesium alloy containing nano-duplex phases, characterized in that, It consists of the following components by mass percentage: Bi 0.5~2.0%, Sn 0.5~1.5%, Zn 0.5~1.0%, Mn 0.3~0.6%, unavoidable impurities ≤0.05%, and the balance being magnesium.
2. The method for preparing the low-alloy content superplastic magnesium alloy according to claim 1, characterized in that, The preparation steps include the following: S1. Weigh the raw materials according to the stated mass percentage; The raw materials are: Pure Mg, pure Sn, pure Zn, Mg-Bi master alloy and Mg-Mn master alloy; The Bi content in the Mg-Bi master alloy is 20~30 wt.%. The Mn content in the Mg-Mn master alloy is 3~10 wt.%; S2. Preheat all raw materials, then melt pure Mg in a protective atmosphere for the first stage of heat preservation and heating, then add pure Sn, pure Zn and Mg-Mn master alloy in sequence, and further heat and melt in the second stage and mix evenly. Finally, add Mg-Bi master alloy for the third stage of heat preservation and heating, and obtain multi-element microalloyed magnesium alloy melt through stirring and refining. S3. Magnesium alloy ingots are obtained by pouring multi-component micro-alloyed magnesium alloy melt; S4. The magnesium alloy ingot is subjected to a stepped homogenization process, followed by immediate quenching to rapidly cool the alloy ingot to room temperature. Then, it undergoes pre-extrusion heat treatment and hot extrusion deformation to obtain extruded magnesium alloy rods.
3. The preparation method according to claim 2, characterized in that, The preheating temperature in S2 is 100~250℃, and the time is 60~90 min.
4. The preparation method according to claim 2, characterized in that, The temperature for the first stage of heat preservation in S2 is 450~500℃, and the time is 60~90 min; the temperature for heating and melting is 680~700℃.
5. The preparation method according to claim 2, characterized in that, The temperature for the second stage of heating and melting in S2 is 700~730℃.
6. The preparation method according to claim 2, characterized in that, The temperature for the third stage of heating and melting in S2 is 690~720℃; the holding time is 10~20 min.
7. The preparation method according to claim 2, characterized in that, The step-type homogenization process in S4 is as follows: First, heat the magnesium alloy ingot to 350~400℃ and hold for 1~2 hours; then heat to 420~450℃ and hold for 2~4 hours; finally heat to 480~500℃ and hold for 6~8 hours.
8. The preparation method according to claim 2, characterized in that, The heat treatment method before extrusion in S4 is as follows: preheat the magnesium alloy ingot at 250~350℃ for 90~120 min, and preheat the extrusion die at 275~375℃.
9. The preparation method according to claim 2, characterized in that, The process parameters for hot extrusion deformation in S4 are: extrusion ratio of 20~30:1; extrusion exit speed of 0.6~1.2 m / min.