Heat-treatment-free corrosion-resistant high-toughness die-casting magnesium alloy and preparation method thereof

Abstract

The invention relates to the field of metal materials, and discloses a heat-treatment-free corrosion-resistant high-toughness die-casting magnesium alloy and a preparation method thereof, and the magnesium alloy comprises the following elements: Al, Sm, Ce, Mn, Ca and the balance of Mg. According to the invention, Al solid solution strengthening is carried out, rare earth elements Sm and Ce are utilized to form a dispersively-distributed thermally-stable second phase, Ca is added to effectively inhibit a Mg17Al12 phase and form a high-stability Al2Ca phase, Mn is added to remove Fe impurities, and the as-cast obdurability and corrosion resistance of the alloy are effectively improved. The preparation method comprises the following steps: melting pure magnesium, cooling, adding an intermediate alloy, introducing high-purity argon to remove gas and impurities, and finally controlling injection parameters in a vacuum environment to form. Solution aging heat treatment is not needed, air holes and deformation are avoided, the alloy with the tensile strength larger than or equal to 250 MPa and the corrosion rate smaller than or equal to 0.3 mm / year is finally obtained, high toughness and excellent corrosion resistance are both considered, and the method is suitable for low-cost production.

Description

Technical Field

[0001] This invention relates to the field of metallic materials, specifically to a heat-treasure-free corrosion-resistant high-strength and tough die-cast magnesium alloy and its preparation method. Background Technology

[0002] In the automotive parts manufacturing sector, high-pressure die casting has become the mainstream forming process due to its advantages such as high production efficiency, high level of automation, and good economics. In particular, the application of integrated die casting technology can reduce the number of molds, shorten the production cycle, and lower manufacturing costs. Furthermore, the simplification of the manufacturing process facilitates better control over part quality. However, this advanced process places higher demands on material properties, especially for large integrated die-cast structural parts. Developing heat-free alloys that combine high strength, toughness, and corrosion resistance has become crucial for solving production challenges.

[0003] For traditional die-cast alloys, heat treatment is usually a necessary process to ensure that their mechanical properties meet design requirements. However, the heat treatment process can easily cause thermal deformation of parts, seriously affecting dimensional accuracy. Especially for large-sized integrated die-cast parts, deformation caused by heat treatment is often difficult to completely repair through subsequent straightening processes, and high-temperature treatment can also induce surface bulging or internal cracking of the casting, leading to increased scrap rates and a sharp increase in production costs. In contrast, heat-treatment-free alloys can meet the requirements for use in the as-cast state, effectively avoiding the above-mentioned heat treatment defects, while reducing production steps, energy consumption, and carbon emissions.

[0004] Furthermore, magnesium alloys, as lightweight structural materials, are chemically reactive and prone to corrosion in humid atmospheres or industrial environments, limiting their widespread application in automotive chassis and body structural components. Current technologies typically employ the addition of alloying elements to promote the formation of a dense oxide layer on the magnesium alloy surface, thereby improving corrosion resistance. However, the addition of large amounts of alloying elements, especially rare earth elements, not only increases raw material costs but also reduces the fluidity of the magnesium alloy melt, deteriorates casting process performance, and even adversely affects the overall mechanical properties of the alloy. If low-speed filling processes such as gravity casting are used, it is difficult to avoid problems such as poor casting density, numerous porosity defects, and insufficient strength. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a heat-treasure-free corrosion-resistant high-strength and high-toughness die-cast magnesium alloy and its preparation method. This solves the technical problems that existing die-cast magnesium alloys cannot achieve both high strength and toughness and excellent corrosion resistance in a heat-treasure-free state, and that traditional heat treatment processes easily lead to die-cast parts deformation, poor dimensional accuracy, and high production costs.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: a heat-treasure-free corrosion-resistant high-strength and tough die-cast magnesium alloy and its preparation method.

[0007] In a first aspect, the present invention provides a heat-treatable, corrosion-resistant, high-strength and tough die-cast magnesium alloy, employing the following technical solution: A heat-treatable, corrosion-resistant, high-strength, and tough die-cast magnesium alloy, wherein the elemental composition of the magnesium alloy, by mass percentage, is as follows: Al: 7.5~8.5wt.%; Sm: 0.15~0.25wt.%; Ce: 0.15~0.25wt.%; Mn: 0.15~0.25wt.%; Ca: 0~1.5wt.%; Unavoidable impurities content ≤0.02wt.%; The balance is Mg.

[0008] By adopting the above technical solution, this invention achieves synergistic effects of various elements through specific multi-element microalloying composition design. Specifically, controlling the Al content within the range of 7.5–8.5 wt.% ensures the solid solution strengthening effect of the matrix. By adding trace amounts of rare earth elements Sm and Ce, utilizing their low solid solubility in the magnesium matrix, they preferentially react with Al during solidification to form thermally stable Al-RE intermetallic compounds, which refine the primary α-Mg grains and pin grain boundaries. This improves the alloy's yield strength while enhancing high-temperature thermal stability and inhibiting grain growth to maintain good toughness. The addition of Mn removes Fe impurities from the melt, reducing the tendency for microgalvanic corrosion caused by impurity elements and improving the corrosion resistance of the matrix. The addition of Ca increases the ignition temperature of the magnesium melt during the smelting stage and reduces oxide inclusions. Furthermore, it forms a continuous network of Al2Ca phase in the solidification structure, which can block corrosion propagation channels. The above-mentioned composition allows the alloy to obtain a fine-grained structure and dispersed strengthening phases in the as-cast state, achieving a balance between high strength, high toughness and corrosion resistance under heat treatment-free conditions.

[0009] Preferably, the elemental composition of the magnesium alloy, by mass percentage, is as follows: Al: 7.8~8.2wt.%; Sm: 0.18~0.22wt.%; Ce: 0.18~0.22wt.%; Mn: 0.18~0.22wt.%; Ca: 0.8~1.2wt.%; Unavoidable impurities content ≤0.02wt.%; The balance is Mg.

[0010] By adopting the above technical solution, the Ca content is controlled within the range of 0.8 to 1.2 wt.%, which can regulate the morphology of the Al2Ca phase, making it present as a fine continuous network distribution. This avoids the formation of coarse blocky phases due to excessive Ca content, which would reduce the plasticity of the alloy. At this point, the comprehensive mechanical properties and corrosion resistance of the alloy reach a better level.

[0011] Preferably, the mass ratio of Sm to Ce is 0.8:1 to 1.2:1; or, the sum of the mass percentages of Sm and Ce is 0.3 to 0.5 wt.%.

[0012] By adopting the above technical solution, the addition of mixed rare earth elements has a better strengthening effect than that of single rare earth elements, utilizing the lattice distortion effect caused by the difference in atomic radii of Sm and Ce. Controlling the ratio of the two to be close to 1:1 helps to form a multi-element rare earth phase, improves the thermal stability of the second phase particles, and enhances the pinning ability of grain boundaries.

[0013] Secondly, the present invention provides a method for preparing a heat-treasure-free corrosion-resistant, high-strength, and tough die-cast magnesium alloy, employing the following technical solution: A method for preparing a heat-treasure-free, corrosion-resistant, high-strength, and tough die-cast magnesium alloy includes the following steps: S1. Select pure magnesium ingots, pure aluminum ingots, magnesium-samarium master alloy, magnesium-cerium master alloy, magnesium-manganese master alloy and magnesium-calcium master alloy, and weigh the raw materials according to the elemental composition ratio of the magnesium alloy; grind the pure magnesium ingots and melt them in a sealed resistance furnace. During the melting process, a protective gas is introduced. After the pure magnesium ingots are completely melted, the furnace is kept warm to obtain pure magnesium melt. S2. After the pure magnesium melt cools down, add the pure aluminum ingot, magnesium samarium master alloy, magnesium cerium master alloy, magnesium manganese master alloy and magnesium calcium master alloy, keep it warm until the master alloy melts, remove slag, stir evenly and let it stand to obtain the first mixed melt. S3. High-purity argon gas is introduced into the first mixed melt, and the mixture is continuously stirred to remove gas and impurities. After standing, the slag is removed to obtain the second mixed melt. S4. Under vacuum conditions, the pouring temperature, injection speed and pressure are controlled to inject the second mixed melt into a mold with a set mold temperature for die casting to obtain a heat-free corrosion-resistant high-strength and tough die-cast magnesium alloy.

[0014] By adopting the above technical solutions, the preparation process has been optimized for easily oxidized and highly reactive alloy systems. In the melting stage, a temperature control strategy of melting pure magnesium at high temperature and adding easily oxidized intermediate alloys at lower temperatures reduces the burn-off rate of rare earth and calcium elements, ensuring the accuracy of the alloy composition and reducing the formation of oxide inclusions. In the melt treatment stage, high-purity argon gas is introduced and stirred, utilizing the bubble rising process to remove hydrogen and fine inclusions from the melt, reducing the porosity of the die casting. In the forming stage, a negative pressure environment is established in the mold cavity using vacuum die casting technology, reducing air entrapment during the filling process. Combined with high-pressure, high-speed filling and mold temperature control, the alloy melt rapidly solidifies to form a dense chilled layer structure, thereby directly obtaining a high-performance as-cast product.

[0015] Preferably, in step S1, the protective gas is a mixture of sulfur hexafluoride and carbon dioxide; the temperature after melting is controlled at 705-715°C, and the holding time is 45-65 minutes.

[0016] By adopting the above technical solution, a dense protective film is formed on the surface of the melt by a mixture of sulfur hexafluoride and carbon dioxide, which isolates the air and prevents the magnesium liquid from burning; the melting temperature and holding time are controlled to ensure that the pure magnesium ingot is fully melted and the temperature is uniform, while avoiding grain coarsening caused by prolonged high temperature.

[0017] Preferably, in step S1, the magnesium-samarium master alloy is Mg-35Sm alloy, the magnesium-cerium master alloy is Mg-30Ce alloy, the magnesium-manganese master alloy is Mg-3Mn alloy, and the magnesium-calcium master alloy is Mg-20Ca alloy.

[0018] By adopting the above technical solution and using intermediate alloys instead of pure metals, it is possible to reduce the melting temperature, shorten the melting time, and improve the diffusion rate and distribution uniformity of high-melting-point elements and easily oxidized elements in the magnesium matrix.

[0019] Preferably, in step S2, the temperature at which the intermediate alloy is added is 680–690°C; the holding time is 10–20 min; and the settling time is 5–10 min.

[0020] By adopting the above technical solution, the material is added in a lower temperature range to reduce element loss; the static operation utilizes the density difference to separate the slag from the melt and allow it to float, thus achieving preliminary purification of the melt.

[0021] Preferably, in step S3, the continuous stirring time is 0.5 to 2 minutes; and the flow rate of the high-purity argon gas is controlled at 2 to 5 L / min.

[0022] By adopting the above technical solution, the stirring time and argon flow rate are controlled within a reasonable range, which not only ensures the degassing effect, but also avoids the rupture and entrapment of the oxide film on the surface of the melt due to vigorous stirring or the splashing of the melt due to excessive gas flow.

[0023] Preferably, in step S4, the casting temperature is 685–715°C; the vacuum level of the vacuum environment is 45–55 mbar; the injection speed is 4–8 m / s; the pressure is 45–65 MPa; and the temperature of the mold is controlled at 240–290°C.

[0024] By adopting the above technical solution, the above process parameters constitute a suitable die casting window. Higher injection speed and pressure are beneficial to improving the density of the casting. A suitable vacuum degree can reduce porosity defects. Combined with mold temperature control of cooling rate, it promotes the formation of non-equilibrium solidification structure, thereby improving the mechanical properties of the casting.

[0025] This invention provides a heat-treasure-free, corrosion-resistant, high-strength, and tough die-cast magnesium alloy and its preparation method. It possesses the following beneficial effects: 1. This invention incorporates Ca and rare earth elements Sm and Ce into magnesium-aluminum alloys. The rare earth elements react with aluminum to generate a second phase with high thermal stability, which not only refines the as-cast microstructure but also hinders dislocation movement through grain boundary pinning effect. This multi-element microalloying design allows the alloy to achieve a good balance of high strength and high toughness in the as-cast state without solution aging heat treatment, thereby improving the mechanical properties of die-cast parts.

[0026] 2. This invention improves corrosion resistance through the purifying effect of Mn and the microstructure regulation of Ca. Mn can effectively remove impurity iron from the melt and reduce the self-corrosion tendency of the matrix; while an appropriate amount of Ca forms a continuous network of Ca-containing second phase at the grain boundaries, which can effectively block the propagation path of the corrosive medium, thereby improving the corrosion resistance of magnesium alloys.

[0027] 3. The alloy material provided by this invention has excellent die-casting process performance. Combined with vacuum die casting and step-by-step melting processes, it reduces porosity and oxide inclusion defects inside the casting, resulting in a dense microstructure in the die-cast parts. Because this alloy has heat-free properties, it avoids the porosity and dimensional deformation problems caused by high-temperature heat treatment in traditional magnesium alloys. While ensuring product dimensional accuracy, it shortens the production cycle and reduces energy consumption and manufacturing costs. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the preparation examples, examples, and test examples. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Examples 1-3: Example 1: This embodiment provides a heat-treasure-free corrosion-resistant high-strength and tough die-cast magnesium alloy and its preparation method, including the following steps: S1. Weigh the raw materials according to the following composition percentages: Al: 8.0 wt.%, Sm: 0.2 wt.%, Ce: 0.2 wt.%, Mn: 0.2 wt.%, Ca: 0 wt.%, unavoidable impurities ≤ 0.02 wt.%, with the balance being Mg. Grind the selected pure magnesium ingots and then melt them in a sealed resistance furnace. During the melting process, a mixture of sulfur hexafluoride and carbon dioxide is introduced as a protective gas. After melting at 710℃, the temperature is held for 50-60 minutes to obtain pure magnesium melt. S2. After the temperature of the pure magnesium melt drops to 685℃, add pure aluminum ingots, magnesium samarium master alloy, magnesium cerium master alloy and magnesium manganese master alloy, keep it at the temperature for 10-15 minutes, and after the master alloy melts, remove slag, stir evenly, and let it stand for 5-10 minutes to obtain the first mixed melt. S3. High-purity argon gas is introduced into the first mixed melt and stirred continuously for 1 minute to remove gas and impurities. After standing for 5-10 minutes, slag is removed to obtain the second mixed melt. S4. Under the conditions of pouring temperature of 690-710℃, vacuum degree of 50mbar, injection speed of 5-7m / s, pressure of 50-60MPa and mold temperature controlled at 250-280℃, the second mixed melt is die-cast to obtain a heat-free corrosion-resistant high-strength and tough die-cast magnesium alloy.

[0030] Example 2: This embodiment provides a heat-treasure-free corrosion-resistant high-strength and tough die-cast magnesium alloy and its preparation method, including the following steps: S1. Weigh the raw materials according to the following composition percentages: Al: 8.0 wt.%, Sm: 0.2 wt.%, Ce: 0.2 wt.%, Mn: 0.2 wt.%, Ca: 1.0 wt.%, unavoidable impurities ≤ 0.02 wt.%, and the balance being Mg. Grind the selected pure magnesium ingots and then melt them in a sealed resistance furnace. During the melting process, a mixture of sulfur hexafluoride and carbon dioxide is introduced as a protective gas. After melting at 710℃, the temperature is held for 50-60 minutes to obtain pure magnesium melt. S2. After the temperature of the pure magnesium melt drops to 685℃, add pure aluminum ingots, magnesium samarium master alloy, magnesium calcium master alloy, magnesium cerium master alloy and magnesium manganese master alloy, keep it at the temperature for 10-15 minutes, and after the master alloy melts, remove slag, stir evenly, and let it stand for 5-10 minutes to obtain the first mixed melt. S3. High-purity argon gas is introduced into the first mixed melt and stirred continuously for 1 minute to remove gas and impurities. After standing for 5-10 minutes, slag is removed to obtain the second mixed melt. S4. Under the conditions of pouring temperature of 690-710℃, vacuum degree of 50mbar, injection speed of 5-7m / s, pressure of 50-60MPa and mold temperature controlled at 250-280℃, the second mixed melt is die-cast to obtain a heat-free corrosion-resistant high-strength and tough die-cast magnesium alloy.

[0031] Example 3: This embodiment provides a heat-treasure-free corrosion-resistant high-strength and tough die-cast magnesium alloy and its preparation method, including the following steps: S1. Weigh the raw materials according to the following composition percentages: Al: 8.0 wt.%, Sm: 0.2 wt.%, Ce: 0.2 wt.%, Mn: 0.2 wt.%, Ca: 1.4 wt.%, unavoidable impurities ≤ 0.02 wt.%, and the balance being Mg. After grinding the selected pure magnesium ingots, melt them in a sealed resistance furnace. During the melting process, a mixture of sulfur hexafluoride and carbon dioxide is introduced as a protective gas. After melting at 710℃, the temperature is held for 50-60 minutes to obtain pure magnesium melt. S2. After the temperature of the pure magnesium melt drops to 685℃, add pure aluminum ingots, magnesium samarium master alloy, magnesium calcium master alloy, magnesium cerium master alloy and magnesium manganese master alloy, keep it at the temperature for 10-15 minutes, and after the master alloy melts, remove slag, stir evenly, and let it stand for 5-10 minutes to obtain the first mixed melt. S3. High-purity argon gas is introduced into the first mixed melt and stirred continuously for 1 minute to remove gas and impurities. After standing for 5-10 minutes, slag is removed to obtain the second mixed melt. S4. Under the conditions of pouring temperature of 690-710℃, vacuum degree of 50mbar, injection speed of 5-7m / s, pressure of 50-60MPa and mold temperature controlled at 250-280℃, the second mixed melt is die-cast to obtain a heat-free corrosion-resistant high-strength and tough die-cast magnesium alloy.

[0032] Test example: Test method: Room temperature tensile property test: Standard tensile specimens die-cast from Examples 1 to 3 were used and tested according to GB / T228.1-2010 "Metallic materials, tensile testing—Part 1: Test at room temperature". The testing equipment was an electronic universal testing machine, and the loading speed was set to 10. -3 / s. Test parameters include tensile strength and elongation after fracture. The average value of 5 parallel specimens is taken for each test group.

[0033] Corrosion resistance test: The corrosion rate of the alloy was tested using the full immersion hydrogen evolution method. The die-cast samples were cut to specified dimensions, polished, cleaned, dried, and weighed to obtain their initial dimensions. The samples were then suspended and immersed in a 3.5 wt.% NaCl aqueous solution at 25°C for 14 days. The hydrogen evolution corrosion rate of the samples was calculated by measuring the volume change of the 3.5 wt.% NaCl solution in the burette.

[0034] The formula for calculating the corrosion rate is: P H =2.279V H , where P H (mm / year) represents the hydrogen evolution corrosion rate of the alloy, V H (mL·cm) -2 ·day -1 ( ) represents the rate at which hydrogen gas is released from the alloy.

[0035] Test results: Table 1: Test results of mechanical and corrosion resistance properties of die-cast magnesium alloys prepared in Examples 1-3 Results Analysis and Conclusions: Based on the data in Table 1 and the microstructure evolution mechanism of the alloy, the effectiveness of this technical solution is analyzed as follows: Example 1 served as the basic control group, with a tensile strength of 250 MPa, an elongation of 10%, and a corrosion rate of 0.315 mm / year. In this system, rare earth elements and Mn elements mainly formed Al-RE and Al-Mn type second phases, which played a certain strengthening role in the matrix and endowed the alloy base with corrosion resistance.

[0036] In Example 2, the addition of 1.0 wt.% Ca increased the tensile strength to 255 MPa, reduced the corrosion rate to 0.279 mm / year (the lowest among the three groups), and decreased the elongation to 7.1%. Mechanistic analysis suggests that the addition of Ca suppressed the low-potential β... Mg 17 Al 12The precipitation of the second phase promoted the formation of the thermally stable Al2Ca phase at the grain boundaries. This second phase pinned the grain boundaries, refined the matrix structure, and thus improved strength and corrosion resistance. Although the increase in the amount of the second phase led to a slight decrease in elongation, this composition achieved optimal corrosion resistance while maintaining high strength, indicating that 1.0 wt.% Ca can effectively improve the compactness of the surface oxide film and inhibit corrosion propagation.

[0037] In Example 3, increasing the Ca content to 1.4 wt.% further improved the tensile strength to 260 MPa and the elongation to 8.0%, but the corrosion rate increased sharply to 2.891 mm / year. This abrupt change indicates that corrosion resistance severely deteriorates when the Ca content exceeds a critical value. The reason is that excessive Ca leads to coarsening of the continuous network Al2Ca phase at the grain boundaries. The coarse second phase has a potential difference with the magnesium matrix, resulting in severe microgalvanic corrosion and accelerating matrix dissolution.

[0038] In summary, while high Ca content yields the highest strength, it sacrifices corrosion resistance. Controlling the Ca content to around 1.0 wt.% allows for strength enhancement through grain refinement and second-phase strengthening, while simultaneously preventing micro-galvanic corrosion caused by second-phase coarsening, thus achieving the optimal balance between strength and corrosion resistance.

Claims

1. A heat-treasure-free, corrosion-resistant, high-strength, and tough die-cast magnesium alloy, characterized in that, The elemental composition of the magnesium alloy, by mass percentage, is as follows: Al: 7.5~8.5wt.%; Sm: 0.15~0.25wt.%; Ce: 0.15~0.25wt.%; Mn: 0.15~0.25wt.%; Ca: 0~1.5wt.%; Unavoidable impurities content ≤0.02wt.%; The balance is Mg.

2. The heat-treasure-free, corrosion-resistant, high-strength and tough die-cast magnesium alloy according to claim 1, characterized in that, The preferred elemental composition of the magnesium alloy, expressed as a percentage by mass, is as follows: Al: 7.8~8.2wt.%; Sm: 0.18~0.22wt.%; Ce: 0.18~0.22wt.%; Mn: 0.18~0.22wt.%; Ca: 0.8~1.2wt.%; Unavoidable impurities content ≤0.02wt.%; The balance is Mg.

3. The heat-treasure-free, corrosion-resistant, high-strength, and tough die-cast magnesium alloy according to claim 1, characterized in that, The mass ratio of Sm to Ce is 0.8:1 to 1.2:

1.

4. A method for preparing the heat-treasure-free corrosion-resistant high-strength and tough die-cast magnesium alloy according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Select pure magnesium ingots, pure aluminum ingots, magnesium-samarium master alloy, magnesium-cerium master alloy, magnesium-manganese master alloy and magnesium-calcium master alloy, and weigh the raw materials according to the elemental composition ratio of the magnesium alloy; grind the pure magnesium ingots and melt them in a sealed resistance furnace. During the melting process, a protective gas is introduced. After the pure magnesium ingots are completely melted, the furnace is kept warm to obtain pure magnesium melt. S2. After the pure magnesium melt cools down, add the pure aluminum ingot, magnesium samarium master alloy, magnesium cerium master alloy, magnesium manganese master alloy and magnesium calcium master alloy, keep it warm until the master alloy melts, remove slag, stir evenly and let it stand to obtain the first mixed melt. S3. High-purity argon gas is introduced into the first mixed melt, and the mixture is continuously stirred to remove gas and impurities. After standing, the slag is removed to obtain the second mixed melt. S4. Under vacuum conditions, the pouring temperature, injection speed and pressure are controlled to inject the second mixed melt into a mold with a set mold temperature for die casting to obtain a heat-free corrosion-resistant high-strength and tough die-cast magnesium alloy.

5. The method for preparing a heat-treatable, corrosion-resistant, high-strength, and tough die-cast magnesium alloy according to claim 4, characterized in that, In step S1, the protective gas is a mixture of sulfur hexafluoride and carbon dioxide; the temperature after melting is controlled at 705-715°C, and the holding time is 45-65 minutes.

6. The method for preparing a heat-treasure-free, corrosion-resistant, high-strength, and tough die-cast magnesium alloy according to claim 4, characterized in that, In step S1, the magnesium-samarium master alloy is Mg-35Sm alloy, the magnesium-cerium master alloy is Mg-30Ce alloy, the magnesium-manganese master alloy is Mg-3Mn alloy, and the magnesium-calcium master alloy is Mg-20Ca alloy.

7. The method for preparing a heat-treasure-free corrosion-resistant, high-strength, and tough die-cast magnesium alloy according to claim 4, characterized in that, In step S2, the temperature at which the intermediate alloy is added is 680–690°C; the holding time is 10–20 min; and the settling time is 5–10 min.

8. The method for preparing a heat-treasure-free, corrosion-resistant, high-strength and tough die-cast magnesium alloy according to claim 4, characterized in that, In step S3, the stirring time is 0.5 to 2 minutes; the flow rate of the high-purity argon gas is controlled at 2 to 5 L / min.

9. The method for preparing a heat-treatable, corrosion-resistant, high-strength, and tough die-cast magnesium alloy according to claim 4, characterized in that, In step S4, the pouring temperature is 685–715°C; the vacuum level of the vacuum environment is 45–55 mbar.

10. The method for preparing a heat-treasure-free, corrosion-resistant, high-strength and tough die-cast magnesium alloy according to claim 4, characterized in that, In step S4, the injection speed is 4-8 m / s; the pressure is 45-65 MPa; and the temperature of the mold is controlled at 240-290℃.

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