High-strength corrosion-resistant magnesium alloy containing stable microstructure and preparation method thereof

Abstract

The application discloses a high-strength corrosion-resistant magnesium alloy containing stable microstructure and a preparation method thereof, and belongs to the technical field of metal materials. The magnesium alloy has the following chemical components (wt.%): 1.1-1.8% of zinc, 0.2-0.35% of calcium, 0.3-0.7% of aluminum, 0.1-0.3% of manganese, 0.3-0.8% of rare earth elements RE, and the rest is magnesium. The alloy is prepared by the following steps: (1) smelting and ingot casting; (2) step homogenization treatment; (3) extrusion or rolling after extrusion; (4) solid solution heat treatment; and (5) artificial aging heat treatment. The microstructure of the magnesium alloy contains high-density microstructure which is coherent with the magnesium matrix, and the coarsening rate of the microstructure is lower than 5.32*10 ‑3 nm / h during long-time aging at 250 DEG C, and the magnesium alloy exhibits excellent three-layer structure stability. The magnesium alloy of the application has high strength and high corrosion resistance, and breaks through the technical bottleneck that the strength and corrosion resistance of traditional magnesium alloys are difficult to be considered simultaneously.

Description

Technical Field

[0001] This invention relates to the field of metallic materials technology, specifically to a high-strength, corrosion-resistant magnesium alloy with a stable microstructure and its preparation method. Background Technology

[0002] Magnesium alloys, as lightweight structural materials, possess advantages such as high specific strength and low density, making them promising for applications in the automotive, aerospace, and other fields. However, their relatively low absolute strength and poor corrosion resistance limit their widespread use as structural components. Age-induced precipitation strengthening is one of the most effective ways to improve the mechanical properties of magnesium alloys. Among various magnesium alloy systems, Mg-Zn-Ca alloys have attracted considerable attention due to their excellent aging response. However, Mg-Zn-Ca alloys still face two key technical bottlenecks in practical applications: First, the thermal stability of the aging precipitates is insufficient. During service, especially in medium- and high-temperature environments, the precipitates are prone to coarsening or transformation into equilibrium phases, leading to a significant decrease in the strengthening effect over time and insufficient long-term performance stability of the alloy. Second, there is often an "inverted relationship" between the strength and corrosion resistance of magnesium alloys. Taking traditional Mg-Zn alloys as an example, the MgZn2 phase formed during aging typically acts as a cathode phase, forming a corrosion galvanic couple with the magnesium matrix, inducing severe localized pitting corrosion. This strength-corrosion resistance mismatch also exists in Mg-Zn-Ca alloys, hindering the improvement of their overall performance. Therefore, how to improve their electrochemical properties while maintaining the long-term stability of the precipitated phase through alloy design and process control, and achieve a synergistic improvement in strength and corrosion resistance, is a pressing technical challenge that needs to be addressed. Summary of the Invention

[0003] To address the aforementioned technical challenges, this invention provides a high-strength, corrosion-resistant magnesium alloy with a stable microstructure and its preparation method. By rationally designing the alloy composition and process, a stable microstructure is formed, achieving synergistic optimization of strength and corrosion resistance.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A high-strength, corrosion-resistant magnesium alloy with a stable microstructure has the following chemical composition by mass percentage: zinc: 1.1-1.8%, calcium: 0.2-0.35%, aluminum: 0.3-0.7%, manganese: 0.1-0.3%, rare earth element RE: 0.3-0.8%, with the balance being magnesium and unavoidable impurities; wherein RE is one or more of scandium (Sc), dysprosium (Dy), and yttrium (Y), and the total amount of the unavoidable impurities is ≤0.05%.

[0005] Further, the preferred chemical composition of the magnesium alloy by mass percentage is: zinc: 1.3-1.7%, calcium: 0.22-0.3%, aluminum: 0.4-0.6%, manganese: 0.15-0.25%, and rare earth element RE: 0.4-0.7%.

[0006] Furthermore, the magnesium alloy possesses a stable microstructure that is coherent with the magnesium matrix; after aging treatment at 150-250℃ for 100-1000 h, the average size growth rate of the stable microstructure is less than 5.32 × 10⁻⁶. -3 nm / h; The stable microstructure contains RE elements. The electrode potential of the stable microstructure in the magnesium alloy is lower than that of the magnesium matrix, so that the microstructure preferentially dissolves as an anode in the corrosive medium, inducing the formation of a dense corrosion product film containing RE oxides on the alloy surface.

[0007] The stable microstructure refers to a three-layer structure, specifically, a nanoscale precipitate with a thickness of three atomic layers along the basal plane (magnesium alloy {0001} plane) in the magnesium alloy. This is a "sandwich" type three-layer structure, with the two outer layers occupied by RE and Ca atoms, while the middle layer consists of Zn, Al, and Mn atoms. Its stacking order differs from the α-Mg matrix, and the three-layer structure maintains a coherent relationship with the matrix. The density of this nanoscale precipitate is greater than 10. 24 / m -3 .

[0008] Furthermore, in the chemical composition of this magnesium alloy, the Zn / Ca mass ratio is (3~6):1. Within this range, Zn and Ca form a high-density three-layer structure in the early stage of aging. Excess Ca tends to form the Mg2Ca phase with Mg, consuming the solid solution Ca and reducing the nucleation driving force of the three-layer structure. Excess Zn easily forms a coarse MgZn2 phase, which not only reduces the number density of the three-layer structure, but also forms micro-galvanic corrosion with the matrix.

[0009] Furthermore, in the chemical composition of this magnesium alloy, the Al / Mn mass ratio is (0.8~4):1. Within this range, Al and Mn preferentially form nano-Al-Mn phases. These particles are dispersed at the grain boundaries, effectively hindering grain boundary migration through the Zener pinning effect, thus refining the grain size to below 10 μm. Excess Mn will form too much cathode Al-Mn phase, impairing corrosion resistance. Excess Al reacts with Mg to form Mg... 17 Al 12 The phase is coarse and distributed within the grains, contributing little to grain boundary pinning and worsening corrosion resistance.

[0010] Furthermore, in the chemical composition of this magnesium alloy, the RE / Zn mass ratio is (0.2~0.7):1. Within this range, RE can fully enter the three-layer structure. If RE / Zn<0.2, the RE content is insufficient, the amount entering the three-layer structure is limited, and the coarsening inhibition effect is weak. If RE / Zn>0.7, the excess RE tends to form a coarse RE-rich phase, which not only consumes the effective RE, but also acts as a new cathodic phase to accelerate corrosion.

[0011] Furthermore, the method for preparing the high-strength, corrosion-resistant magnesium alloy with a stable microstructure includes the following steps: (1) Under the protection of argon or SF6 and CO2 mixed gas, pure magnesium, pure zinc, magnesium-calcium master alloy, pure aluminum, and magnesium-manganese master alloy are added in sequence according to the chemical composition of the magnesium alloy. After melting at 680-730℃, magnesium-RE master alloy (one or more of magnesium-scandium master alloy, magnesium-dysprosium master alloy, and magnesium-yttrium master alloy) is added. The mixture is stirred evenly at 670-720℃, refined, degassed, and slag-removed. After standing and holding at the temperature for 5-30 minutes, the mixture is then poured into a mold to obtain a magnesium alloy ingot. (2) The magnesium alloy ingot obtained in step (1) is subjected to step homogenization heat treatment under argon or nitrogen protection and then air-cooled to room temperature to obtain a homogeneous magnesium alloy ingot. (3) The homogeneous magnesium alloy ingot obtained in step (2) is extruded and deformed at 270-400℃ and then cooled to room temperature to obtain an extruded profile; (4) The extruded profile obtained in step (3) is directly subjected to solution heat treatment, or the extruded profile obtained in step (3) is subjected to multiple rolling passes and then subjected to solution heat treatment; the solution heat treatment is carried out under argon or nitrogen protection, and after the solution heat treatment, it is subjected to rapid air cooling or water quenching at 60-90℃ to obtain the solution-treated profile. (5) The solid solution profile obtained in step (4) is subjected to artificial aging treatment to obtain the high-strength corrosion-resistant magnesium alloy with stable microstructure.

[0012] Further, in step (2), the stepped homogenization heat treatment is to sequentially heat the magnesium alloy ingot at 340-360℃ for 1-3 hours, 430-450℃ for 1-3 hours, and 510-530℃ for 3-5 hours.

[0013] Furthermore, in step (3), the extrusion ratio of the extrusion deformation is 25-50, and the extrusion speed is 10-35 m / min.

[0014] Further, in step (4), the multi-pass rolling process has 2-8 rolling passes, a rolling temperature of 250-350℃, and a reduction of 20-60% per pass.

[0015] Furthermore, in step (4), the solid solution heat treatment temperature is 450-510℃ and the treatment time is 30-90min.

[0016] Furthermore, in step (5), the artificial aging treatment temperature is 150-250℃ and the time is 90-300min.

[0017] The advantages and beneficial effects of this invention are as follows: 1. This invention involves adding specific rare earth elements (one or more of Sc, Dy, and Y) to magnesium alloys. These three rare earth elements can enter the microstructure (trilayer structure) of the magnesium alloy and improve the stability of the trilayer structure. For example, the coarsening rate of the trilayer structure of an alloy containing Sc / Dy / Y after aging at 200℃ for 500 hours is (2.3-5.2)×10⁻⁶. -3 nm / h, while the magnesium alloy without rare earth added evolved into a second phase after aging at 200℃ for 500h.

[0018] 2. The addition of Al and Mn to the magnesium alloy in this invention clarifies and quantifies their functional differentiation and allows them to synergize with specific RE elements: ① Al and Mn form nano-Al-Mn particles at the grain boundaries, pinning the grain boundaries and refining the grain size to below 10μm, promoting fine grain strengthening and complementing the strengthening effect of the three-layer structure; ② It was found that Mn can enter the three-layer structure and synergistically inhibit coarsening with RE elements, further reducing the coarsening rate by 30-50%; ③ Al can participate in the formation of the surface film, promoting the densification of the oxide film and further improving the corrosion resistance of the alloy.

[0019] 3. The magnesium alloy of the present invention exhibits significantly improved thermal stability of its three-layer structure. The roughening rate of the three-layer structure of the present invention is reduced by an order of magnitude compared with the prior art, indicating that the strengthening effect of the present invention can be maintained for a longer period of time under medium-high temperature (150-250℃) service conditions. This is due to the composite doping effect of Mn and Sc / Dy / Y—both of which jointly reduce the interfacial energy of the three-layer structure and hinder atomic diffusion.

[0020] 4. This invention achieves a significant leap in the strength of magnesium alloys. This remarkable increase in strength stems from the synergistic effect of the strengthening mechanisms. ① Grain refinement strengthening: Al-Mn phase pinning of grain boundaries refines grain size by 30-50%; ② Precipitation strengthening: High-density three-layer structure (>10 24 / m 3 It effectively hinders dislocation movement. For example, the room temperature yield strength of alloys containing Sc / Dy / Y is 240-320 MPa, while the yield strength of magnesium alloys without added RE is 150-240 MPa. Furthermore, due to the significantly improved stability of the three-layer structure, the yield strength of the magnesium alloy of this invention at 200°C is increased by 25-40% compared to the magnesium alloy without added RE.

[0021] 5. This invention is the first to discover that RE doping into a three-layer structure can transform the three-layer structure from a cathode to an anodic phase. Through first-principles calculations and STEM-EDS observation of the immersed transmission samples, it was found that in the corrosive medium, the RE-containing three-layer structure preferentially dissolves as an anode relative to the magnesium matrix, while the undoped RE three-layer structure acts as a cathode.

[0022] 6. This invention breaks through the technical bottleneck of the "strength-corrosion resistance inversion" in magnesium alloys, achieving a synergistic improvement in both. This breakthrough improvement in corrosion resistance stems from the unique electrochemical regulation mechanism of this invention. Firstly, there is the reversal of precipitated phase polarity: in the past, aging precipitates were mostly cathodic phases, while in this invention, the RE-doped three-layer structure acts as the anodic phase, preferentially dissolving in the corrosive medium and avoiding accelerated cathodic corrosion of the magnesium matrix. Secondly, there is the formation of a dense protective film: after the preferential dissolution of the RE-containing three-layer structure, RE... 3+ Hydrolysis deposits on the surface, forming a dense RE₂O₃ / RE(OH)₃ composite film, effectively blocking corrosive media. After aging, a RE-doped three-layer structure is formed, reducing the corrosion rate by 50-75%.

[0023] 7. The magnesium alloy preparation method of this invention has higher process tolerance and adaptability. First, in terms of process route selection, this invention provides two optional preparation routes—the conventional extrusion route and the "extrusion-rolling" combined route—which can be flexibly selected according to the shape and performance requirements of the target product, while existing technologies are usually limited to a single process route. In addition, this invention significantly reduces the alloy's sensitivity to fluctuations in the preparation process by composite doping with Mn and Sc / Dy / Y, and broadens the process window, while existing single rare earth alloys often require strict process control to achieve the expected performance. In particular, the "extrusion-rolling" combined process developed in this invention introduces new deformation energy storage during rolling and increases the nucleation sites of the three-layer structure. The synergistic effect of these two factors increases the nucleation density of the three-layer structure by more than 30% and the room temperature yield strength by 20-30%, realizing the synergistic design of "process-microstructure-property," which is another innovation of this invention. Attached Figure Description

[0024] Figure 1 The results are obtained from aberration-corrected transmission electron microscopy (TEM) measurements of the stable microstructure in the Mg-1.5Zn-0.25Ca-0.5Al-0.2Mn-0.5Y magnesium alloy prepared in Example 1.

[0025] Figure 2 The microstructure of the Mg-1.8Zn-0.75Ca-0.5Al-0.2Mn-0.5Y magnesium alloy prepared in Comparative Example 7 is shown in the EDS analysis results.

[0026] Figure 3The microstructure of the Mg-1.5Zn-0.25Ca-0.5Al-0.2Mn-1.2Y magnesium alloy prepared in Comparative Example 9 is shown in the EDS analysis results.

[0027] Figure 4 A bright-field transmission electron microscope image of the Mg-1.5Zn-0.25Ca-0.5Al-0.2Mn-0.23Y magnesium alloy prepared for Comparative Example 10. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0029] In the following examples, the raw materials for preparing magnesium alloys include: magnesium-calcium master alloy with Ca content of 21.65 wt.% and balance of Mg; magnesium-manganese master alloy with Mn content of 3.5 wt.% and balance of Mg; magnesium-scandium master alloy with Sc content of 10 wt.% and balance of Mg; magnesium-dysprosium master alloy with Dy content of 10 wt.% and balance of Mg; and magnesium-yttrium master alloy with Y content of 30 wt.% and balance of Mg. Example 1:

[0030] This embodiment describes the preparation of a high-strength, corrosion-resistant magnesium alloy with a stable microstructure: Mg-1.5Zn-0.25Ca-0.5Al-0.2Mn-0.5Y. The chemical composition of this magnesium alloy (wt.%) is: Zn: 1.5%, Ca: 0.25%, Al: 0.5%, Mn: 0.2%, Y: 0.5%, with unavoidable total impurities ≤ 0.05%, and the balance being magnesium. The specific preparation method is as follows: (1) Under the protection of SF6 and CO2 mixed gas, pure magnesium, pure zinc, magnesium-calcium master alloy, pure aluminum, and magnesium-manganese master alloy are added in sequence according to the composition ratio and heated to melt at 690°C; then magnesium-yttrium master alloy is added and stirred evenly at 680°C. After refining, degassing and slag removal, the mixture is kept at a constant temperature for 5-30 minutes and then poured into a mold to obtain magnesium alloy ingots. (2) The magnesium alloy ingot obtained in step (1) is subjected to a step homogenization heat treatment under argon protection. The steps are: 350℃ for 4 hours, 400℃ for 6 hours, and 410℃ for 8 hours. It is then air-cooled to room temperature to obtain a homogeneous magnesium alloy ingot. (3) The homogeneous magnesium alloy ingot obtained in step (2) is extruded at 320°C with an extrusion ratio of 35 and an extrusion speed of 20 m / min. After cooling to room temperature, an extruded profile is obtained. (4) The extruded profile obtained in step (3) is subjected to solution heat treatment under argon protection at a temperature of 480°C for 60 min; then it is cooled by water quenching at 75°C to obtain the solution-treated profile. (5) The solid solution profile obtained in step (4) is subjected to artificial aging treatment at a temperature of 200℃ for 150 min to obtain a high-strength corrosion-resistant Mg-1.5Zn-0.25Ca-0.5Al-0.2Mn-0.5Y magnesium alloy with a stable microstructure.

[0031] Figure 1 This is an aberration-corrected transmission electron microscope (TEM) image of the stable microstructure in the magnesium alloy prepared in this embodiment. The stable microstructure is a three-atom-thick nanoscale precipitate, formed along the {0001} plane of the magnesium alloy, exhibiting a "sandwich" type three-layer structure. Figure 1 It can be seen that the precipitated phase of the prepared magnesium alloy has a typical "sandwich" three-layer structure: the two outer layers are composed of rare earth elements Y and Ca atoms, while the middle layer is composed of Zn, Al and Mn atoms. The three-layer structure maintains a coherent relationship with the matrix.

[0032] The magnesium alloy prepared in this embodiment has a high number density of stable microstructures (three-layer structure) of 3.8 × 10⁻⁶. 24 / m 3 The average length was 9.2 nm. After aging at 200 °C for 500 hours, the average length coarsened to 10.6 nm, with a coarsening rate of 2.8 × 10⁻⁶. -3 nm / h, grain size 7.2 mm, yield strength 278 MPa at room temperature, yield strength 254 MPa at 200 °C, strength retention 91.4%, corrosion rate in 3.5 wt.% NaCl solution is 0.11 mm / y.

[0033] Comparative Example 1: The difference from Example 1 is that the magnesium alloy in this example does not contain rare earth element Y, while the remaining composition and process are the same as in Example 1. Without rare earth elements, the stability of the three-layer structure after aging is poor. After aging at 200℃ for 500 hours, the three-layer structure transforms into the second phase, with a room temperature yield strength of 235 MPa and a yield strength of 168 Pa at 200℃, maintaining a strength retention rate of 71.5%. Furthermore, since the three-layer structure does not contain RE elements, it is a cathodic phase, resulting in a corrosion rate of 0.35 mm / y after aging, significantly reducing its corrosion resistance. Example 2:

[0034] This embodiment describes the preparation of a high-strength, corrosion-resistant magnesium alloy with a stable microstructure, consisting of Mg-1.5Zn-0.25Ca-0.5Al-0.2Mn-0.5Sc. The chemical composition of this magnesium alloy (wt.%) is: Zn: 1.5%, Ca: 0.25%, Al: 0.5%, Mn: 0.2%, Sc: 0.5%, with unavoidable total impurities ≤ 0.05%, and the balance being magnesium. The preparation method is as follows: (1) Under the protection of SF6 and CO2 mixed gas, pure magnesium, pure zinc, magnesium-calcium master alloy, pure aluminum, and magnesium-manganese master alloy are added in sequence according to the composition ratio and heated to melt at 720°C; then magnesium-scandium master alloy is added and stirred evenly at 710°C. After refining, degassing and slag removal, the mixture is kept at a constant temperature for 5-30 minutes and then poured into a mold to obtain magnesium alloy ingots. (2) The magnesium alloy ingot obtained in step (1) is subjected to step homogenization heat treatment under argon protection. The steps are: 360℃ for 4 hours, 410℃ for 8 hours, and 430℃ for 10 hours. It is then air-cooled to room temperature to obtain a homogeneous magnesium alloy ingot. (3) The homogeneous magnesium alloy ingot obtained in step (2) is extruded at 300°C with an extrusion ratio of 30 and an extrusion speed of 15 m / min. After cooling to room temperature, an extruded profile is obtained. (4) The extruded profile obtained in step (3) is subjected to solution heat treatment under argon protection at a temperature of 510°C for 40 minutes; then it is rapidly cooled by air to obtain the solution-treated profile. (5) The solid solution profile obtained in step (4) is subjected to artificial aging treatment at a temperature of 200℃ for 150 min to obtain a high-strength and corrosion-resistant Mg-1.5Zn-0.25Ca-0.5Al-0.2Mn-0.5Sc magnesium alloy with a stable microstructure.

[0035] The magnesium alloy prepared in this embodiment has a high number density of three-layer structure, which is 4.1 × 10⁻⁶. 24 / m 3 The average length was 8.8 nm. After aging at 210 °C for 500 hours, the average length coarsened to 10.1 nm, with a coarsening rate of 2.6 × 10⁻⁶. -3 The strength of Sc is 91.3%, with a grain size of 6.8 μm, a yield strength of 286 MPa at room temperature, a yield strength of 261 MPa at 200 °C, and a corrosion rate of 0.14 mm / y. Sc has a smaller atomic radius, which causes greater lattice distortion after entering the trilayer structure. The trilayer structure has a slightly higher number density and slightly higher strength than the Y system; however, the Sc electrode potential (-2.03 V) is slightly higher than that of Y (-2.37 V), resulting in a slightly weaker anodic effect and a higher corrosion rate than the Y system.

[0036] Comparative Example 2: The difference from Example 2 is that no Mn element is added to the magnesium alloy in this example; the remaining composition and process are the same as in Example 2. Without Mn, the pinning effect of Al-Mn on grain boundaries is lacking, resulting in significant grain coarsening. Simultaneously, Mn cannot enter the three-layer structure to synergistically suppress coarsening, reducing the coarsening rate from 2.6 × 10⁻⁶. -3 nm / h increased to 6.2 × 10 -3The yield strength decreased by approximately 2.4 times (nm / h), but the room temperature yield strength dropped to 245 MPa, and the yield strength at 200℃ dropped to 189 MPa. Due to Mn's ability to remove Fe impurities, the corrosion resistance of the alloy without Mn deteriorated, with the corrosion rate increasing to 0.22 mm / y. This comparative example demonstrates that the addition of Mn plays an indispensable role in refining grain size, stabilizing the three-layer structure, and achieving a synergistic improvement in strength and toughness. Example 3:

[0037] This embodiment describes the preparation of a high-strength, corrosion-resistant magnesium alloy with a stable microstructure: Mg-1.5Zn-0.25Ca-0.5Al-0.2Mn-0.5Dy. The chemical composition of this magnesium alloy (wt.%) is: Zn: 1.5%, Ca: 0.25%, Al: 0.5%, Mn: 0.2%, Dy: 0.5%, with unavoidable total impurities ≤ 0.05%, and the balance being magnesium. The preparation method is as follows: (1) Under argon protection, pure magnesium, pure zinc, magnesium-calcium master alloy, pure aluminum, and magnesium-manganese master alloy are added in sequence according to the component ratio and heated to melt at 700℃; then magnesium-dysprosium master alloy is added and stirred evenly at 670℃. After refining, degassing and slag removal, the mixture is kept at a constant temperature for 5-30 minutes and then poured into a mold to obtain a magnesium alloy ingot. (2) The magnesium alloy ingot obtained in step (1) is subjected to a step homogenization heat treatment under argon gas. The steps are: 340℃ for 5 hours, 390℃ for 9 hours, and 440℃ for 5 hours. It is then air-cooled to room temperature to obtain a homogeneous magnesium alloy ingot. (3) The homogeneous magnesium alloy ingot obtained in step (2) is extruded at 350°C with an extrusion ratio of 35 and an extrusion speed of 32 m / min. After cooling to room temperature, an extruded profile is obtained. (4) The extruded profile obtained in step (3) is subjected to solution heat treatment under argon or nitrogen protection at a temperature of 490°C for 50 min; then it is cooled by water quenching at 70°C to obtain the solution-treated profile. (5) The solid solution profile obtained in step (4) is subjected to artificial aging treatment at a temperature of 195℃ for 120 min to obtain a high-strength corrosion-resistant Mg-1.5Zn-0.25Ca-0.5Al-0.2Mn-0.5Dy magnesium alloy with a stable microstructure.

[0038] The magnesium alloy prepared in this embodiment has a three-layer structure number density of 3.6 × 10⁻⁶. 24 / m 3 The average length was 9.5 nm. After aging at 195 °C for 500 hours, the average length coarsened to 11.2 nm, with a coarsening rate of 3.4 × 10⁻⁶. -3The yield strength is 7.5 mm / h, with a grain size of 7.5 mm, a room temperature yield strength of 268 MPa, a 195℃ yield strength of 242 MPa, a strength retention rate of 90.3%, and a corrosion rate of 0.13 mm / y. These results indicate that the addition of Dy element can effectively stabilize the trilayer structure, inhibit high-temperature coarsening, and significantly improve the corrosion resistance of the alloy. Its mechanism of action is similar to that of Sc and Y, further verifying the universality of the rare earth elements selected in this invention. Example 4:

[0039] This embodiment describes the preparation of a high-strength, corrosion-resistant magnesium alloy with a stable microstructure: Mg-1.5Zn-0.25Ca-0.5Al-0.2Mn-0.3Sc-0.3Y. The chemical composition of this magnesium alloy (wt.%) is: Zn: 1.5%, Ca: 0.25%, Al: 0.5%, Mn: 0.2%, Sc: 0.3%, Y: 0.3%, with unavoidable total impurities ≤ 0.05%, and the balance being magnesium. The preparation method is as follows: (1) Under the protection of SF6 and CO2 mixed gas, pure magnesium, pure zinc, magnesium-calcium master alloy, pure aluminum, and magnesium-manganese master alloy are added in sequence according to the component ratio and heated to melt at 690℃; then magnesium-scandium master alloy and magnesium-yttrium master alloy are added and stirred evenly at 680℃. After refining, degassing and slag removal, the mixture is kept at a constant temperature for 5-30 minutes and then poured into a mold to obtain magnesium alloy ingots. (2) The magnesium alloy ingot obtained in step (1) is subjected to step homogenization heat treatment under nitrogen protection. The steps are: 330℃ for 5 hours, 395℃ for 7 hours, and 435℃ for 5 hours. It is then air-cooled to room temperature to obtain a homogeneous magnesium alloy ingot. (3) The homogeneous magnesium alloy ingot obtained in step (2) is extruded at 350°C with an extrusion ratio of 40 and an extrusion speed of 32 m / min. After cooling to room temperature, an extruded profile is obtained. (4) The extruded profile obtained in step (3) is subjected to solution heat treatment under argon protection at a temperature of 510°C for 80 min; then it is rapidly cooled by air to obtain the solution-treated profile. (5) The solid solution-treated profile obtained in step (4) is subjected to artificial aging treatment at a temperature of 210℃ for 180 min to obtain a high-strength and corrosion-resistant Mg-1.5Zn-0.25Ca-0.5Al-0.2Mn-0.3Sc-0.3Y magnesium alloy with a stable microstructure.

[0040] The magnesium alloy prepared in this embodiment has a three-layer structure number density of 4.6 × 10⁻⁶. 24 / m 3 The average length was 8.2 nm. After aging at 210 °C for 500 hours, the average length coarsened to 9.4 nm, with a coarsening rate of 2.4 × 10⁻⁶. -3The grain size is 6.2 mm, yield strength is 298 MPa at room temperature and 274 MPa at 210℃, strength retention is 91.9%, and corrosion rate is 0.09 mm / y. The combined addition of Sc and Y produces a synergistic strengthening effect. Compared to single rare earth element addition, the coarsening rate of the three-layer structure is further reduced by 2.4 × 10⁻⁶. - 3 It has a strength and corrosion resistance that are superior to single rare earth systems.

[0041] Comparative Example 3: The difference from Example 4 is that 0.6% Y is added to the magnesium alloy in this example, but no Sc is added; the remaining composition and process are the same as in Example 4. The magnesium alloy prepared in this comparative example has a three-layer structure number density of 4.0 × 10⁻⁶. 24 / m 3 The average length was 9.8 nm. After aging at 210 °C for 500 hours, the average length coarsened to 11.4 nm, with a coarsening rate of 3.2 × 10⁻⁶. -3 The yield strength is 7.4 mm / h, with a grain size of 7.4 mm. The yield strength at room temperature is 286 MPa, and the yield strength at 210℃ is 262 MPa. The strength retention rate is 91.6%, and the corrosion rate is 0.12 mm / y. Compared with a single rare earth system, the three-layer structure with the addition of rare earth composites has better stability. Example 5:

[0042] This embodiment describes the preparation of a high-strength, corrosion-resistant magnesium alloy with a stable microstructure: Mg-1.5Zn-0.25Ca-0.5Al-0.2Mn-0.5Y. The chemical composition of this magnesium alloy (wt.%) is: Zn: 1.5%, Ca: 0.25%, Al: 0.5%, Mn: 0.2%, Y: 0.5%, with unavoidable total impurities ≤ 0.05%, and the balance being magnesium. The preparation method is as follows: (1) Under argon protection, pure magnesium, pure zinc, magnesium-calcium master alloy, pure aluminum, and magnesium-manganese master alloy are added in sequence according to the composition ratio and heated to melt at 700°C; then magnesium-yttrium master alloy is added and stirred evenly at 680°C. After refining, degassing and slag removal, the mixture is kept at a constant temperature for 5-30 minutes and then poured into a mold to obtain a magnesium alloy ingot. (2) The magnesium alloy ingot obtained in step (1) is subjected to step homogenization heat treatment under nitrogen protection. The steps are: 340℃ for 6 hours, 400℃ for 8 hours, and 450℃ for 9 hours. It is then air-cooled to room temperature to obtain a homogeneous magnesium alloy ingot. (3) The homogeneous magnesium alloy ingot obtained in step (2) is extruded at 305°C with an extrusion ratio of 28 and an extrusion speed of 16 m / min. After cooling to room temperature, the extruded profile is obtained. (4) The extruded profile obtained in step (3) is rolled in multiple passes, with 6 passes at a temperature of 280°C and a reduction of 30% per pass. Then, it is subjected to solution heat treatment under argon or nitrogen protection at a temperature of 510°C for 30 minutes. Subsequently, it is rapidly cooled by air to obtain the solution-treated profile. (5) The solid solution profile obtained in step (4) is subjected to artificial aging treatment at a temperature of 250℃ for 90 minutes to obtain a high-strength and corrosion-resistant Mg-1.5Zn-0.25Ca-0.5Al-0.2Mn-0.5Y magnesium alloy with a stable microstructure.

[0043] The magnesium alloy prepared in this embodiment has a three-layer structure number density of 5 × 10⁻⁶. 24 / m 3 The average length was 7.6 nm. After aging at 250 °C for 500 hours, the average length coarsened to 8.7 nm, with a coarsening rate of 2.2 × 10⁻⁶. -3 nm / h, grain size 5.6 mm, yield strength 314 MPa at room temperature, yield strength 290 MPa at 250 °C, strength retention 92.4%, corrosion rate 0.08 mm / y.

[0044] Comparative Example 4: The difference from Example 5 is that the magnesium alloy preparation process in this example does not include rolling; the remaining composition and process are the same as in Example 5. Example 5 introduced more deformation energy storage through rolling, increasing the nucleation sites of the three-layer structure. The number density of the three-layer structure was increased by approximately 30% compared to Comparative Example 4, and the yield strength was increased by approximately 20%. Example 6:

[0045] This embodiment describes the preparation of a high-strength, corrosion-resistant magnesium alloy with a stable microstructure: Mg-1.1Zn-0.2Ca-0.5Al-0.2Mn-0.5Y. The chemical composition of this magnesium alloy (wt.%) is: Zn: 1.1%, Ca: 0.2%, Al: 0.5%, Mn: 0.2%, Y: 0.5%, with unavoidable total impurities ≤ 0.05% (balance: magnesium). The preparation method is as follows: (1) Under the protection of SF6 and CO2 mixed gas, pure magnesium, pure zinc, magnesium-calcium master alloy, pure aluminum, and magnesium-manganese master alloy are added in sequence according to the composition ratio and heated to melt at 680℃; then magnesium-yttrium master alloy is added and stirred evenly at 670℃. After refining, degassing and slag removal, the mixture is kept at a constant temperature for 5-30 minutes and then poured into a mold to obtain magnesium alloy ingots. (2) The magnesium alloy ingot obtained in step (1) is subjected to step homogenization heat treatment under argon protection. The steps are: 360℃ for 4 hours, 405℃ for 6 hours, and 425℃ for 9 hours. It is then air-cooled to room temperature to obtain a homogeneous magnesium alloy ingot. (3) The homogeneous magnesium alloy ingot obtained in step (2) is extruded at 300°C with an extrusion ratio of 30 and an extrusion speed of 15 m / min. After cooling to room temperature, an extruded profile is obtained. (4) The extruded profile obtained in step (3) is subjected to solution heat treatment under argon or nitrogen protection at a temperature of 460°C for 45 min; then it is cooled by water quenching at 65°C to obtain the solution-treated profile. (5) The solid solution profile obtained in step (4) is subjected to artificial aging treatment at a temperature of 190℃ for 300 min to obtain a high-strength corrosion-resistant Mg-1.1Zn-0.2Ca-0.5Al-0.2Mn-0.5Y magnesium alloy with a stable microstructure.

[0046] The magnesium alloy prepared in this embodiment has a three-layer structure number density of 2.8 × 10⁻⁶. 24 / m 3 The average length was 10.5 nm. After aging at 190 °C for 500 hours, the average length coarsened to 12.8 nm, with a coarsening rate of 4.6 × 10⁻⁶. -3 The yield strength was 84 nm / h, grain size 8.2 mm, room temperature yield strength 242 MPa, 190℃ yield strength 216 MPa, strength retention 89.3%, and corrosion rate 0.14 mm / y. The results indicate that even when Zn and Ca contents are reduced to the lower limit, the stability of the three-layer structure remains good. Although the number density of the three-layer structure decreases, it still maintains good strength and corrosion resistance.

[0047] Comparative Example 5: The difference from Example 6 is that the Zn content in the magnesium alloy in this example is reduced from 1.1% to 0.8%, while the remaining composition and process are the same as in Example 6. This comparative example has a room temperature yield strength of 215 MPa and a corrosion rate of 0.28 mm / y. When the Zn content is below the lower limit, the nucleation driving force of the three-layer structure is insufficient, the number density of the three-layer structure is significantly reduced, and the room temperature yield strength is significantly decreased. Example 7:

[0048] This embodiment describes the preparation of a high-strength, corrosion-resistant magnesium alloy with a stable microstructure: Mg-1.5Zn-0.25Ca-0.6Al-0.15Mn-0.5Y. The chemical composition of this magnesium alloy (wt.%) is: Zn: 1.5%, Ca: 0.25%, Al: 0.6%, Mn: 0.15%, Y: 0.5%, with unavoidable total impurities ≤ 0.05%, and the balance being magnesium. The preparation method is as follows: (1) Under argon protection, pure magnesium, pure zinc, magnesium-calcium master alloy, pure aluminum, and magnesium-manganese master alloy are added in sequence according to the component ratio and heated to melt at 730°C; then magnesium-yttrium master alloy is added and stirred evenly at 720°C. After refining, degassing and slag removal, the mixture is kept at a constant temperature for 5-30 minutes and then poured into a mold to obtain a magnesium alloy ingot. (2) The magnesium alloy ingot obtained in step (1) is subjected to step homogenization heat treatment under argon protection. The steps are: 355℃ for 5 hours, 400℃ for 7 hours, and 430℃ for 10 hours. It is then air-cooled to room temperature to obtain a homogeneous magnesium alloy ingot. (3) The homogeneous magnesium alloy ingot obtained in step (2) is extruded at 340°C with an extrusion ratio of 42 and an extrusion speed of 18 m / min. After cooling to room temperature, an extruded profile is obtained. (4) The extruded profile obtained in step (3) is rolled in multiple passes, with 5 passes at a temperature of 310°C and a reduction of 35% per pass. Then, it is subjected to solution heat treatment under argon or nitrogen protection at a temperature of 460°C for 60 minutes. Subsequently, it is cooled by water quenching at 70°C to obtain the solution-treated profile. (6) The solid solution profile obtained in step (5) is subjected to artificial aging treatment at a temperature of 220℃ for 180 min to obtain a high-strength Mg-1.5Zn-0.25Ca-0.6Al-0.15Mn-0.5Y magnesium alloy with a stable microstructure.

[0049] The magnesium alloy prepared in this embodiment has a three-layer structure number density of 4 × 10⁻⁶. 24 / m 3 The average length was 8.9 nm. After aging at 220 °C for 500 hours, the average length coarsened to 10.3 nm, with a coarsening rate of 2.8 × 10⁻⁶. -3 The grain size is 6.8 mm, yield strength is 285 MPa at room temperature and 257 MPa at 220 °C, strength retention is 90.2%, and corrosion rate is 0.10 mm / y. When the Al / Mn mass ratio is 4:1, the Al-Mn phase is dispersed at the grain boundaries, refining the grains through the Zener pinning effect. Mn can also enter the three-layer structure, synergistically suppressing coarsening with Y.

[0050] Comparative Example 6: The difference from Example 7 is that the magnesium alloy in this example contains 0.3 wt.% Al and 0.4 wt.% Mn, with the remaining components and processes being the same as in Example 7. In this comparative example, the Al / Mn mass ratio is 0.75:1, exceeding the optimal range. Excessive Mn leads to the formation of too many cathodic Al-Mn phases, exacerbating microgalvanic corrosion and increasing the corrosion rate to 0.29 mm / y. Furthermore, the formation of a large amount of Al-Mn phase consumes Mn that can enter the ternary structure, resulting in weakened ternary structure stability, increased coarsening rate, and reduced high-temperature strength. Example 8:

[0051] This embodiment describes the preparation of a high-strength, corrosion-resistant magnesium alloy with a stable microstructure: Mg-1.8Zn-0.3Ca-0.5Al-0.2Mn-0.5Y. The chemical composition of this magnesium alloy (wt.%) is: Zn: 1.8%, Ca: 0.3%, Al: 0.5%, Mn: 0.2%, Y: 0.5%, with unavoidable total impurities ≤ 0.05%, and the balance being magnesium. The preparation method is as follows: (1) Under argon protection, pure magnesium, pure zinc, magnesium-calcium master alloy, pure aluminum, and magnesium-manganese master alloy are added in sequence according to the component ratio and heated to melt at 720°C; then magnesium-yttrium master alloy is added and stirred evenly at 690°C. After refining, degassing and slag removal, the mixture is kept at a constant temperature for 5-30 minutes and then poured into a mold to obtain a magnesium alloy ingot. (2) The magnesium alloy ingot obtained in step (1) is subjected to a step homogenization heat treatment under argon protection. The steps are: 350℃ for 4.5 hours, 400℃ for 5 hours, and 430℃ for 10 hours. It is then air-cooled to room temperature to obtain a homogeneous magnesium alloy ingot. (3) The homogeneous magnesium alloy ingot obtained in step (2) is extruded at 290°C with an extrusion ratio of 40 and an extrusion speed of 25 m / min. After cooling to room temperature, an extruded profile is obtained. (4) The extruded profile obtained in step (3) is subjected to solution heat treatment under argon protection at a temperature of 490°C for 50 min; then it is cooled by water quenching at 80°C to obtain the solution-treated profile. (5) The solid solution profile obtained in step (4) is subjected to artificial aging treatment at a temperature of 180℃ for 150 min to obtain a high-strength and corrosion-resistant Mg-1.8Zn-0.3Ca-0.5Al-0.2Mn-0.5Y magnesium alloy with a stable microstructure.

[0052] The magnesium alloy prepared in this embodiment has a three-layer structure number density of 3.5 × 10⁻⁶. 24 / m³, average length 9.5nm, after aging at 180℃ for 500 hours, the average length coarsens to 11.0nm, coarsening rate 3.0×10⁻³nm / h, grain size 7.5μm, room temperature yield 285MPa, 180℃ yield 256MPa, strength retention rate 89.8%, corrosion rate in 3.5% NaCl solution is 0.13mm / y.

[0053] Comparative Example 7: The difference from Example 8 is that the Ca content in this magnesium alloy is 0.75 wt.%, while the remaining components and processes are the same as in Example 8. The EDS diagram of the magnesium alloy prepared in this comparative example is shown below. Figure 2As shown, the Zn / Ca mass ratio in this comparative example is 2.4:1, which is below the optimal range. Due to the excess Ca, coarse Mg2Ca phases formed in the microstructure, consuming dissolved Ca and reducing the nucleation driving force of the ternary structure. The number density of the ternary structure significantly decreased to 1.8 × 10⁻⁶. 24 / m³. The room temperature yield strength drops to 232MPa. Example 9:

[0054] This embodiment describes the preparation of a high-strength, corrosion-resistant magnesium alloy with a stable microstructure: Mg-1.5Zn-0.25Ca-0.5Al-0.15Mn-0.5Sc. The chemical composition of this magnesium alloy (wt.%) is: Zn: 1.5%, Ca: 0.25%, Al: 0.5%, Mn: 0.15%, Sc: 0.5%, with unavoidable total impurities ≤ 0.05%, and the balance being magnesium. The preparation method is as follows: (1) Under the protection of SF6 and CO2 mixed gas, pure magnesium, pure zinc, magnesium-calcium master alloy, pure aluminum, and magnesium-manganese master alloy are added in sequence according to the composition ratio and heated to melt at 700℃; then magnesium-scandium master alloy is added and stirred evenly at 680℃. After refining, degassing and slag removal, the mixture is kept at a constant temperature for 5-30 minutes and then poured into a mold to obtain magnesium alloy ingots. (2) The magnesium alloy ingot obtained in step (1) is subjected to a step homogenization heat treatment under argon protection. The steps are: 330℃ for 5.5 hours, 395℃ for 6.5 hours, and 450℃ for 7.5 hours. It is then air-cooled to room temperature to obtain a homogeneous magnesium alloy ingot. (3) The homogeneous magnesium alloy ingot obtained in step (2) is extruded at 320°C with an extrusion ratio of 30 and an extrusion speed of 25 m / min. After cooling to room temperature, an extruded profile is obtained. (4) The extruded profile obtained in step (3) is subjected to solution heat treatment under argon protection at a temperature of 510°C for 30 minutes; then it is cooled by water quenching at 70°C to obtain the solution-treated profile. (5) The solid solution profile obtained in step (4) is subjected to artificial aging treatment at a temperature of 250℃ for 90 minutes to obtain a high-strength and corrosion-resistant Mg-1.5Zn-0.25Ca-0.5Al-0.15Mn-0.5Sc magnesium alloy with a stable microstructure.

[0055] The magnesium alloy prepared in this embodiment has a three-layer structure number density of 3.6 × 10⁻⁶. 24 / m³, average length 9.3nm, after aging at 250℃ for 500 hours, the average length coarsens to 10.8nm, coarsening rate 3.0×10⁻³nm / h, grain size 7.0μm, room temperature yield 280MPa, 250℃ yield 255MPa, strength retention rate 91.1%, corrosion rate in 3.5% NaCl solution is 0.11mm / y.

[0056] Comparative Example 8: The difference from Example 9 is that the Al content in this magnesium alloy is 0.75 wt.%, while the remaining components and process are the same as in Example 9. In the comparative example, the Al / Mn mass ratio is 5:1, exceeding the optimal range. Excess Al reacts with Mg to form coarse Mg. 17 Al 12 The phase is distributed within the grains, contributing little to grain boundary pinning, and the grains coarsen to 14.2 μm. The room temperature yield strength decreases to 238 MPa. Example 10:

[0057] This embodiment describes the preparation of a high-strength, corrosion-resistant magnesium alloy with a stable microstructure: Mg-1.5Zn-0.25Ca-0.5Al-0.2Mn-0.6Y. The chemical composition of this magnesium alloy (wt.%) is: Zn: 1.5%, Ca: 0.25%, Al: 0.5%, Mn: 0.2%, Y: 0.6%, with unavoidable total impurities ≤ 0.05%, and the balance being magnesium. The preparation method is as follows: (1) Under the protection of SF6 and CO2 mixed gas, pure magnesium, pure zinc, magnesium-calcium master alloy, pure aluminum, and magnesium-manganese master alloy are added in sequence according to the composition ratio and heated to melt at 690°C; then magnesium-yttrium master alloy is added and stirred evenly at 680°C. After refining, degassing and slag removal, the mixture is kept at a constant temperature for 20 minutes and then poured into a mold to obtain a magnesium alloy ingot. (2) The magnesium alloy ingot obtained in step (1) is subjected to step homogenization heat treatment under nitrogen protection. The steps are: 330℃ for 5 hours, 395℃ for 7 hours, and 435℃ for 5 hours. It is then air-cooled to room temperature to obtain a homogeneous magnesium alloy ingot. (3) The homogeneous magnesium alloy ingot obtained in step (2) is extruded at 350°C with an extrusion ratio of 45 and an extrusion speed of 35 m / min. After cooling to room temperature, an extruded profile is obtained. (4) The extruded profile obtained in step (3) is subjected to solution heat treatment under nitrogen protection at a temperature of 510°C for 80 minutes; then it is rapidly cooled by air to obtain the solution-treated profile. (5) The solid solution profile obtained in step (4) is subjected to artificial aging treatment at a temperature of 210℃ for 180 min to obtain a high-strength and corrosion-resistant Mg-1.5Zn-0.25Ca-0.5Al-0.2Mn-0.6Y magnesium alloy with a stable microstructure.

[0058] The magnesium alloy prepared in this embodiment has a three-layer structure number density of 4.0 × 10⁻⁶. 24 / m 3 The average length was 9.8 nm. After aging at 210 °C for 500 hours, the average length coarsened to 11.4 nm, with a coarsening rate of 3.2 × 10⁻⁶. -3 nm / h, grain size 7.4 mm, yield strength 286 MPa at room temperature, yield strength 262 MPa at 210 °C, strength retention 91.6%, corrosion rate 0.12 mm / y.

[0059] Comparative Example 9: The difference from Example 10 is that the Y content in the magnesium alloy in this example is 1.2 wt.%, while the remaining composition and process are the same as in Example 10. The EDS diagram for this comparative example is shown below. Figure 3 As shown, in this comparative example, Y / Zn = 0.8, exceeding the upper limit (>0.7). Excess Y leads to the formation of coarse rare earth-rich phases in the microstructure, consuming effective rare earth elements (RE) and accelerating corrosion as a new cathodic phase. After aging, coarse Y-rich phases were observed, and the number density of the three-layer structure decreased to 2.5 × 10⁻⁶. 24 / m³, the room temperature yield strength decreased to 246MPa, and the corrosion rate increased to 0.30mm / y.

[0060] Comparative Example 10: The difference from Example 10 is that the Y content in the magnesium alloy in this example is 0.23 wt.%, and the remaining composition and process are the same as in Example 10. In this comparative example, RE / Zn = 0.15, which is lower than the optimal range (<0.2). Due to the insufficient content of rare earth element Y, the amount entering the three-layer structure is limited, the roughening inhibition effect is weak, and the roughening rate of the three-layer structure increases after holding at 210°C for 500 hours (e.g. Figure 4 As shown in the figure, some three-layer structures are coarsened to 26 nm, which is a serious coarsening. The room temperature yield strength drops to 255 MPa, and the yield strength at 210 °C drops to 218 MPa, with a strength retention rate of 85.5%.

[0061] In summary, this invention significantly suppresses the coarsening behavior of the three-layer structure during long-term aging through the synergistic effect of rare earth elements (Sc / Dy / Y) with Zn, Ca, Al, and Mn. Under aging conditions of 150-250℃, the coarsening rate is less than 5.32 × 10⁻⁶. - 3The magnesium alloy exhibits excellent three-layer structural stability, with a yield strength of 240-320 MPa at room temperature and 210-290 MPa under medium- and high-temperature service conditions, maintaining a strength retention rate of 89-93%. Simultaneously, RE doping transforms the three-layer structure from a cathodic phase to an anodic phase, inducing the formation of a dense corrosion product film containing RE on the surface, resulting in a corrosion rate below 0.15 mm / y. This invention overcomes the technical bottleneck of traditional magnesium alloys, which struggle to simultaneously achieve both strength and corrosion resistance.

[0062] It should be particularly noted that the present invention may have many other embodiments, and all similar substitutions and modifications that do not depart from the spirit and essence of the present invention are considered to be included in the present invention.

Claims

1. A high-strength, corrosion-resistant magnesium alloy with a stable microstructure, characterized in that: The chemical composition of this magnesium alloy, by mass percentage, is as follows: Zinc: 1.1-1.8%, Calcium: 0.2-0.35%, Aluminum: 0.3-0.7%, Manganese: 0.1-0.3%, Rare Earth Elements (RE): 0.3-0.8%, with the balance being magnesium and unavoidable impurities; wherein: RE is one or more of scandium (Sc), dysprosium (Dy) and yttrium (Y), and the total amount of the unavoidable impurities is ≤0.05%.

2. The high-strength, corrosion-resistant magnesium alloy with a stable microstructure according to claim 1 or 2, characterized in that: The chemical composition of this magnesium alloy, by mass percentage, is as follows: Zinc: 1.3-1.7%, Calcium: 0.22-0.3%, Aluminum: 0.4-0.6%, Manganese: 0.15-0.25%, Rare Earth Elements (RE): 0.4-0.7%, with the balance being magnesium and unavoidable impurities.

3. The high-strength, corrosion-resistant magnesium alloy with a stable microstructure according to claim 1, characterized in that: The magnesium alloy exhibits a stable microstructure that is coherent with the magnesium matrix. After aging treatment at 150-250℃ for 100-1000 hours, the average size growth rate of the stable microstructure is less than 5.32 × 10⁻⁶. -3 nm / h; The stable microstructure contains RE elements. The electrode potential of the stable microstructure in the magnesium alloy is lower than that of the magnesium matrix, so that the microstructure preferentially dissolves as an anode in the corrosive medium, inducing the formation of a dense corrosion product film containing RE oxides on the alloy surface.

4. The high-strength, corrosion-resistant magnesium alloy with a stable microstructure according to claim 1 or 3, characterized in that: The stable microstructure refers to a three-layer structure, specifically, a nanoscale precipitate with a thickness of three atomic layers along the basal plane (magnesium alloy {0001} plane) in the magnesium alloy. This is a "sandwich" type three-layer structure, with the two outer layers occupied by RE and Ca atoms, while the middle layer consists of Zn, Al, and Mn atoms. Its stacking order differs from the α-Mg matrix, and the three-layer structure maintains a coherent relationship with the matrix. The density of this nanoscale precipitate is greater than 10. 24 / m -3 .

5. The high-strength, corrosion-resistant magnesium alloy with a stable microstructure according to claim 3, characterized in that: In this magnesium alloy, the Zn / Ca mass ratio is (3~6):1, the Al / Mn mass ratio is (0.8~4):1, and the RE / Zn mass ratio is (0.2~0.7):

1.

6. The method for preparing a high-strength, corrosion-resistant magnesium alloy with a stable microstructure according to claim 1, characterized in that: The method includes the following steps: (1) Under the protection of argon or SF6 and CO2 mixed gas, pure magnesium, pure zinc, magnesium-calcium master alloy, pure aluminum, and magnesium-manganese master alloy are added in sequence according to the chemical composition of the magnesium alloy. After melting at 680-730℃, magnesium-RE master alloy (one or more of magnesium-scandium master alloy, magnesium-dysprosium master alloy, and magnesium-yttrium master alloy) is added. The mixture is stirred evenly at 670-720℃, refined, degassed, and slag-removed. After standing and holding at the temperature for 5-30 minutes, the mixture is then poured into a mold to obtain a magnesium alloy ingot. (2) The magnesium alloy ingot obtained in step (1) is subjected to step homogenization heat treatment under argon or nitrogen protection and then air-cooled to room temperature to obtain a homogeneous magnesium alloy ingot. (3) The homogeneous magnesium alloy ingot obtained in step (2) is extruded and deformed at 270-400℃ and then cooled to room temperature to obtain the extruded profile; (4) The extruded profile obtained in step (3) is directly subjected to solution heat treatment, or the extruded profile obtained in step (3) is subjected to multiple rolling passes and then subjected to solution heat treatment; the solution heat treatment is carried out under argon or nitrogen protection, and after the solution heat treatment, it is subjected to rapid air cooling or water quenching at 60-90℃ to obtain the solution-treated profile. (5) The solid solution-treated profile obtained in step (4) is subjected to artificial aging treatment to obtain the high-strength corrosion-resistant magnesium alloy with stable microstructure.

7. The method for preparing a high-strength, corrosion-resistant magnesium alloy with a stable microstructure according to claim 6, characterized in that: In step (2), the stepped homogenization heat treatment is to sequentially heat the magnesium alloy ingot at 320-370℃ for 4-6 hours, 390-410℃ for 6-9 hours, and 430-450℃ for 5-10 hours.

8. The method for preparing a high-strength, corrosion-resistant magnesium alloy with a stable microstructure according to claim 6, characterized in that: In step (3), the extrusion ratio of the extrusion deformation is 25-50, and the extrusion speed is 10-35m / min.

9. The method for preparing a high-strength, corrosion-resistant magnesium alloy with a stable microstructure according to claim 6, characterized in that: In step (4), the rolling passes of the multi-pass rolling are 2-8, the rolling temperature is 250-350℃, and the reduction per pass is 20-60%; the solution heat treatment temperature is 450-510℃ and the treatment time is 30-90min.

10. The method for preparing a high-strength, corrosion-resistant magnesium alloy with a stable microstructure according to claim 6, characterized in that: In step (5), the artificial aging treatment temperature is 150-250℃ and the time is 90-300min.

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