High-strength corrosion-resistant low-alloying Mg-Zn-Nd-Ca-Sn-Zr alloy and preparation method thereof

Abstract

The invention discloses a high-strength corrosion-resistant low-alloying Mg-Zn-Nd-Ca-Sn-Zr alloy and a preparation method thereof, and relates to the technical field of magnesium alloys, the alloy comprises the following components in percentage by weight: 0.7-1.2% of Zn, 0.4-0.7% of Nd, 0.1-0.6% of Ca, 0.1-0.4% of Sn, 0.3-0.6% of Zr, less than or equal to 3% of Zn, less than or equal to 3% of Nd, less than or equal to 3% of Ca, less than or equal to 3% of Sn and less than or equal to 3% of Zr, and the balance of Mg and inevitable impurity elements. The alloy is prepared in the mode that an atmosphere protection crucible resistance furnace is adopted for smelting, a magnesium alloy cast ingot is obtained through pouring, and then two-stage solution treatment, forward extrusion pre-deformation treatment, severe plastic deformation treatment and stress aging treatment are conducted. The magnesium alloy has high strength and excellent corrosion resistance, and the strength and the corrosion resistance can be matched so that the strength requirement and the corrosion resistance requirement can be met at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium alloys, and particularly relates to a high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy and a preparation method thereof. Background Art

[0002] The significance of bone health for people's daily life is self-evident. Sports injuries, degenerative bone diseases, and autoimmune bone diseases all seriously affect human healthy life. With the development of orthopedic treatment technologies, a safer and more reliable new type of bone implant material is currently being sought.

[0003] Due to its advantages such as low density, degradability, good biocompatibility, and appropriate elastic modulus, compared with traditional alloy implant materials such as stainless steel, titanium alloy, and copper alloy, magnesium alloy can avoid secondary surgery and the harm to the human body caused by the release of harmful ions during the service period of the material in the human body. Moreover, the production cost of magnesium alloy is low, which can reduce the medical cost of patients. For the above reasons, magnesium alloy shows great potential in clinical medicine as a biomedical alloy, and is currently regarded as a new type of degradable biomedical material and is expected to be widely used in the medical field.

[0004] The standard potential of magnesium is relatively low and its chemical properties are active, so its magnesium alloy is prone to relatively severe galvanic corrosion. Among them, the magnesium matrix often acts as the anode to lose electrons and undergo an oxidation reaction, while the second phase, impurities, etc. act as the cathode to participate in the reduction reaction. Traditional high-performance magnesium alloys usually have a relatively high content of alloying elements. The alloy strength is improved by forming more precipitation strengthening phases, and the corrosion resistance of the alloy is enhanced by the hindrance effect of the continuous network second phase precipitated at the grain boundaries. However, due to the relatively high content of alloying elements in traditional high-performance magnesium alloys, there is still strong galvanic corrosion, which will have a negative impact on the corrosion resistance of the alloy, resulting in too fast a corrosion rate of the magnesium alloy. Moreover, the network continuous second phase will deteriorate the mechanical properties of the alloy, and it is difficult to match the strength and corrosion resistance after alloying, and it cannot meet the strength requirements and corrosion resistance requirements at the same time, seriously affecting the practical application of magnesium alloys. Summary of the Invention

[0005] To solve some or all of the technical problems existing in the above-mentioned prior art, the present invention provides a high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy and a preparation method thereof.

[0006] The technical solution of the present invention is as follows: In the first aspect, a high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy is provided, including the following components by weight percentage: Zn: 0.7 - 1.2%, Nd: 0.4 - 0.7%, Ca: 0.1 - 0.6%, Sn: 0.1 - 0.4%, Zr: 0.3 - 0.6%, and Zn + Nd + Ca + Sn + Zr ≤ 3%, with the balance being Mg and unavoidable impurity elements.

[0007] In some alternative embodiments, the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy comprises the following components by weight percentage: Zn: 1.0%, Nd: 0.7%, Ca: 0.5%, Sn: 0.2%, Zr: 0.3%, with the balance being Mg and unavoidable impurity elements.

[0008] In some alternative embodiments, the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy is prepared by at least the following steps: According to the components and weight percentages of the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy, put the raw materials into a crucible resistance furnace, melt at 700 - 750 °C, and use a CO 2 and SF 6 mixed gas as the protective gas during melting, and then pour the melt to obtain a magnesium alloy ingot. The raw materials include: pure Mg, pure Zn, Mg-Nd master alloy, Mg-Ca master alloy, Mg-Sn master alloy, and Mg-Zr master alloy; Subject the magnesium alloy ingot to double-stage solution treatment, cutting treatment, forward extrusion pre-deformation treatment, severe plastic deformation treatment, and stress aging treatment in sequence to obtain a magnesium alloy finished product. The double-stage solution treatment adopts a double-stage solution treatment of 450 °C × 2 h + 500 °C × 0.5 h. The cutting treatment is used to cut the magnesium alloy ingot into round bars of specified dimensions. The extrusion temperature of the forward extrusion pre-deformation treatment is 300 - 350 °C, and the extrusion ratio is 4:1. The severe plastic deformation treatment adopts spiral torsion extrusion, with an extrusion temperature of 300 - 350 °C, a torsion angle of 180°, an extrusion rate of 5 - 10 mm / min, and two extrusion passes. In the stress aging treatment, the stress type is tensile stress, the stress value is 75 MPa, the aging temperature is 150 °C, and the aging time is 1 - 2 h.

[0009] In some alternative embodiments, the purity of pure Mg is above 99.99 wt.%, and the purity of pure Zn is above 99.99 wt.%.

[0010] In a second aspect, there is also provided a method for preparing the above-mentioned high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy, and the preparation method at least comprises the following steps: According to the composition and weight percentage of the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy, the raw materials are put into a crucible resistance furnace, melted at 700-750 °C, and CO 2 and SF 6 mixed gas is used as the protective gas during melting, and then the melt is poured to obtain a magnesium alloy ingot. The raw materials include: pure Mg, pure Zn, Mg-Nd master alloy, Mg-Ca master alloy, Mg-Sn master alloy and Mg-Zr master alloy; The magnesium alloy ingot is successively subjected to double-stage solution treatment, cutting treatment, forward extrusion pre-deformation treatment, severe plastic deformation treatment and stress aging treatment to obtain a magnesium alloy finished product. The double-stage solution treatment adopts a double-stage solution treatment of 450 °C × 2 h + 500 °C × 0.5 h. The cutting treatment is used to cut the magnesium alloy ingot into round bars of specified dimensions. The extrusion temperature of the forward extrusion pretreatment is 300-350 °C, and the extrusion ratio is 4:1. The severe plastic deformation treatment adopts spiral torsion extrusion, the extrusion temperature is 300-350 °C, the torsion angle is 180°, the extrusion rate is 5-10 mm / min, and the extrusion pass is two passes. In the stress aging treatment, the stress type is tensile stress, the stress value is 75 MPa, the aging temperature is 150 °C, and the aging time is 1-2 h.

[0011] In some alternative embodiments, according to the composition and weight percentage of the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy, the raw materials are put into a crucible resistance furnace, melted at 700-750 °C, and CO 2 and SF 6 mixed gas is used as the protective gas during melting, and then the melt is poured to obtain a magnesium alloy ingot, including: Step 1.1, according to the composition and weight percentage of the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy, determine the dosages of pure Mg, pure Zn, Mg-Nd master alloy, Mg-Ca master alloy, Mg-Sn master alloy and Mg-Zr master alloy; Step 1.2, preheat the crucible, stirring rod and slag skimmer to 200-250 °C, take them out and brush them with a pre-prepared coating, and the coating is a mixed solution of zinc oxide and water glass; Step 1.3, put pure Mg and pure Zn into the crucible, heat it up to 700 °C and keep it warm, and during this period, introduce CO 2 and SF 6The mixed gas. After all the pure Mg and pure Zn are melted, the temperature is raised to 730 °C. Subsequently, an Mg-Sn master alloy is added and held for 15 min. After melting, the temperature is raised to 750 °C. Subsequently, an Mg-Nd master alloy is added and held for 15 min. After melting, the temperature is lowered to 740 °C. Subsequently, an Mg-Zr master alloy is added and stirred for 1 min to prevent the Mg-Zr master alloy from depositing at the bottom of the melt, and held for 15 min. After melting, an Mg-Ca master alloy is added. After all the metal is melted, the surface scum is skimmed off, a refining agent is added for impurity removal, quickly stirred for 1 min, and then allowed to stand for 20 min; Step 1.4, skim off the scum above the melt, pour the melt into a mold preheated to 200 - 250 °C at a uniform speed to complete casting, and demold and take out the magnesium alloy ingot after cooling to room temperature.

[0012] In some alternative embodiments, the purity of pure Mg is above 99.99 wt.%, and the purity of pure Zn is above 99.99 wt.%.

[0013] In some alternative embodiments, the magnesium alloy ingot is successively subjected to double-stage solution treatment, cutting treatment, forward extrusion pre-deformation treatment, severe plastic deformation treatment, and stress aging treatment to obtain a magnesium alloy product, including: Step 2.1, perform double-stage solution treatment on the magnesium alloy ingot. The temperature of the first-stage solution treatment is 450 °C and the time is 2 h, the temperature of the second-stage solution treatment is 500 °C and the time is 0.5 h, and the cooling method is water cooling at 25 °C for both; Step 2.2, cut the magnesium alloy ingot after double-stage solution treatment into round bars with a diameter of a specified size; Step 2.3, perform forward extrusion pre-deformation treatment on the round bar. The extrusion temperature is 300 - 350 °C and the extrusion ratio is 4:1 to obtain a round bar with a diameter half of the specified size; Step 2.4, cut the round bar after forward extrusion pre-deformation treatment into a cuboid with a cross-section of the required size, put it into a screw torsion extrusion die for severe plastic deformation extrusion. The extrusion temperature is 300 - 350 °C, the torsion angle is 180°, the extrusion rate is 5 - 10 mm / min, the extrusion pass is two passes, and water quenching is performed after each extrusion pass. After water quenching, it is put into the screw torsion extrusion die and heated to the extrusion temperature and held for 10 min before the next extrusion pass; Step 2.5, perform stress aging treatment on the specimen obtained after severe plastic deformation extrusion with a tensile stress type, a stress value of 75 MPa, an aging temperature of 150 °C, and an aging time of 1 - 2 h to obtain a magnesium alloy product.

[0014] In some alternative embodiments, the specified size is 30 mm.

[0015] In some alternative embodiments, the required size is 10 mm × 10 mm.

[0016] The main advantages of the technical solution of the present invention are as follows: The high-strength, corrosion-resistant, low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy and its preparation method of the present invention regulate a fine-grained structure with a uniform and fine distribution of precipitation phases through microalloying, two-stage solution treatment, severe plastic deformation treatment, and stress aging treatment. By using grain refinement strengthening, precipitation strengthening, and weakening the basal texture, the strength and plasticity of the alloy are improved. At the same time, the compactness of the surface film of the magnesium alloy is improved by using the characteristics of fine grains and uniform distribution of fine second phases, the corrosion mode of the magnesium alloy is changed, and the tendency of local pitting corrosion on the surface of the magnesium alloy is reduced, achieving a synergistic improvement in the strength, plasticity, and corrosion resistance of the alloy, realizing the matching of the strength and corrosion resistance of the magnesium alloy to simultaneously meet the strength requirements and corrosion resistance requirements. A high-strength, corrosion-resistant, low-alloyed magnesium alloy with a strength greater than 320 MPa, an average corrosion rate of 0.1 - 0.2 mm / year, and an elongation of more than 20% can be obtained. Moreover, the content of alloying elements in the magnesium alloy is low, which can further reduce the raw material cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, and constitute a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 is the metallographic microstructure diagram of the magnesium alloy obtained in Example 2 of the present invention; Figure 2 is the microstructure diagram of the magnesium alloy obtained in Example 2 of the present invention under a scanning electron microscope; Figure 3 is the stress-strain curve diagram of the magnesium alloy obtained in Example 2 of the present invention; Figure 4 is the morphology diagram of the magnesium alloy obtained in Example 2 of the present invention after soaking for 300 hours and removing corrosion products; Figure 5 is the hydrogen evolution curve diagram of the magnesium alloy obtained in Example 2 of the present invention; Figure 6 is the average corrosion rate diagram of the magnesium alloys obtained in Examples 1 - 3 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the scope of protection of the present invention.

[0019] The technical solutions provided by the embodiments of the present invention are described in detail below.

[0020] In a first aspect, an embodiment of the present invention provides a high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy. The high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy comprises the following components by weight percentage: Zn: 0.7-1.2%, Nd: 0.4-0.7%, Ca: 0.1-0.6%, Sn: 0.1-0.4%, Zr: 0.3-0.6%, and Zn+Nd+Ca+Sn+Zr≤3%, with the balance being Mg and inevitable impurity elements.

[0021] In the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy provided by the embodiment of the present invention, adding alloying elements Zn, Nd, Ca, Sn, and Zr to the magnesium alloy and controlling the contents of the alloying elements within the above ranges are one of the key factors for achieving high strength and corrosion resistance of the magnesium alloy. Among them, the action mechanisms of each element are as follows: Zn element is one of the essential elements for the human body and has special physiological functions. Alloying with Zn element can increase the corrosion potential of the magnesium alloy in body fluid, reduce the corrosion tendency, and lower the corrosion rate. At the same time, Zn has good solution aging strengthening effect. Adding Zn element also helps to improve the mechanical properties of the magnesium alloy. However, if the added Zn element is excessive, redundant MgZn phase will be generated, and the MgZn phase will enhance the galvanic corrosion effect as the cathode, deteriorating the corrosion resistance of the alloy; if the added Zn element is too little, the solution strengthening effect will be reduced and the mechanical properties of the alloy will decline. Therefore, the content of Zn element is controlled at 0.7-1.2%.

[0022] As one of the light rare earth elements, the microalloying of light rare earth Nd element can significantly refine the microstructure of as-cast alloy as heterogeneous nucleation sites. The solubility of Nd element in Mg is 3.6%, which will cause lattice distortion in the magnesium matrix, leading to the interaction between dislocations and rare earth atoms and improving the alloy strength. The precipitation strengthening effect of Nd element is good in the low-alloy system. During subsequent aging, uniform and fine precipitate phases can precipitate, hinder dislocation slip, and improve the alloy strength. At the same time, the fine and uniform distribution of precipitate phases can improve the surface potential distribution of the alloy and reduce the tendency of galvanic corrosion of the alloy. On the other hand, due to the loose and porous corrosion product film of magnesium alloy, severe pitting corrosion is likely to occur. By adding Nd element, a dense oxide can be formed in the product layer, improving the protection ability of the corrosion product film to the matrix and being beneficial to improving the corrosion resistance of the alloy. However, due to the low solubility of Nd element in Mg, if the added Nd element is excessive, a continuous network of Mg 12 Nd phase will be formed, and the continuous network of Mg 12 Nd phase at the grain boundary will become a potential crack source, having a negative impact on the strength of the alloy. Moreover, the continuous network distribution of Mg 12 Nd phase will exacerbate the galvanic corrosion effect and deteriorate the corrosion resistance of the alloy. If the added Nd element is too little, the precipitation kinetics of precipitate phases will decrease, the aging strengthening effect will be reduced, and the mechanical properties will decline. Therefore, the content of Nd element is controlled at 0.4 - 0.7%.

[0023] Ca element has excellent biocompatibility and can improve the composition of the corrosion product layer. The Ca-containing corrosion product formed in body fluid can effectively protect the matrix. However, due to the low solubility of Ca element in Mg, if the added Ca element is excessive, a brittle phase Mg 2 Ca will be generated, reducing the toughness of the alloy. If the added Ca element is too little, the protection of the Ca element to the corrosion product layer will be reduced, and the corrosion resistance of the alloy will decline. Therefore, the content of Ca element is controlled at 0.1 - 0.6%.

[0024] The diffusion rate of Sn element is relatively fast, and it will segregate at the grain boundary. With the extension of the immersion time, Sn atoms will dissolve at the grain boundary and then form SnO 2 oxide attached to the corrosion product layer, thus increasing the compactness of the product film. Appropriate Sn alloying can improve the corrosion resistance of the alloy. At the same time, Sn element has a good aging strengthening effect, and Mg 2 Sn precipitate phases can be formed after aging, which has an obstructive effect on dislocation slip. However, if the added Sn element is excessive, the galvanic corrosion effect will be exacerbated, deteriorating the corrosion resistance of the alloy. If the added Sn element is too little, the SnO formed by the Sn element segregated at the grain boundary 2As the oxide decreases, the protection of the corrosion product layer decreases, and the corrosion resistance of the alloy deteriorates. Therefore, the Sn content is controlled within 0.1 - 0.4%.

[0025] The Zr element does not form a phase with Mg. Adding Zr element in combination can become heterogeneous nucleation sites during the solidification of the alloy, promoting the nucleation rate and thus refining the grains, and further improving the strength and corrosion resistance of the magnesium alloy. However, if the added Zr element is excessive, too many discretely distributed α-Zr particles will become potential crack sources, deteriorating the alloy strength, exacerbating the galvanic corrosion tendency of the alloy, and also deteriorating the corrosion resistance of the alloy; if the added Zr element is too little, the effect of refining the grains is not obvious. Therefore, the content of the Zr element is controlled to be 0.3 - 0.6%.

[0026] Since there will be strong galvanic corrosion in the magnesium alloy when the content of alloying elements in the magnesium alloy is relatively high, which will have a negative impact on the corrosion resistance of the alloy and lead to too fast a corrosion rate of the magnesium alloy. Therefore, controlling the total amount of alloying elements Zn, Nd, Ca, Sn, and Zr added to the magnesium alloy to be below 3% can further reduce the corrosion tendency and improve the corrosion resistance of the magnesium alloy.

[0027] More preferably, the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy provided by the embodiments of the present invention comprises the following components by weight percentage: Zn: 1.0%, Nd: 0.7%, Ca: 0.5%, Sn: 0.2%, Zr: 0.3%, and the balance is Mg and inevitable impurity elements.

[0028] Furthermore, in the embodiments of the present invention, the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy is prepared by at least the following steps: According to the components and weight percentages of the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy, the raw materials are put into a crucible resistance furnace and melted at 700 - 750 °C, and CO 2 and SF 6 mixed gas is used as the protective gas during melting, and then the melt is poured to obtain a magnesium alloy ingot. The raw materials include: pure Mg, pure Zn, Mg-Nd master alloy, Mg-Ca master alloy, Mg-Sn master alloy, and Mg-Zr master alloy; The magnesium alloy ingot is successively subjected to double-stage solution treatment, cutting treatment, forward extrusion pre-deformation treatment, severe plastic deformation treatment, and stress aging treatment to obtain a finished magnesium alloy. The double-stage solution treatment adopts a double-stage solution treatment of 450°C × 2h + 500°C × 0.5h. The cutting treatment is used to cut the magnesium alloy ingot into round bars of specified dimensions. The extrusion temperature of the forward extrusion pre-deformation treatment is 300 - 350°C, and the extrusion ratio is 4:1. The severe plastic deformation treatment adopts Screw Twist Extrusion (STE), the extrusion temperature is 300 - 350°C, the torsion angle is 180°, the extrusion rate is 5 - 10 mm / min, and the number of extrusion passes is two. In the stress aging treatment, the stress type is tensile stress, the stress value is 75 MPa, the aging temperature is 150°C, and the aging time is 1 - 2h.

[0029] In the embodiments of the present invention, since the total amount of alloying elements Zn, Nd, Ca, Sn, and Zr in the magnesium alloy is controlled below 3%, the content of alloying elements in the magnesium alloy is relatively low. On the one hand, the inhibition effect on the grain growth of the as-cast alloy is not strong, resulting in coarse grains of the as-cast alloy, and the second phase precipitated in the as-cast state is prone to segregation at the grain boundaries, which is likely to cause strong galvanic corrosion. On the other hand, the precipitation driving force and precipitation strengthening effect of the second phase are relatively weak, and the amount of the second phase is small, resulting in insufficient alloy strength. Therefore, on the basis of the above-defined types and contents of alloying elements, by combining double-stage solution treatment, forward extrusion pre-deformation treatment, severe plastic deformation, and stress aging treatment, the grains are refined, the precipitation amount of the second phase is increased, and its distribution is improved, so that the prepared magnesium alloy has a fine-grained structure with uniform and fine precipitate phases. By combining fine grain strengthening and precipitation strengthening, while improving the strength of the magnesium alloy, the corrosion resistance of the magnesium alloy is simultaneously improved, realizing the coordinated improvement of the strength and corrosion resistance of the magnesium alloy.

[0030] Specifically, in the embodiments of the present invention, through the double-stage solution treatment of 450°C × 2h + 500°C × 0.5h, the Mg 12 Nd phase and Mg 2 Ca phase in the as-cast magnesium alloy can be fully dissolved into the matrix to obtain a supersaturated solid solution; solute atoms are generally distributed at the grain boundaries. Through the forward extrusion pre-deformation treatment, basal planes are introduced Dislocations can provide "channels" for the diffusion of solute atoms into the crystal. The solute atoms diffusing into the crystal can pin the dislocations. Dislocations can also serve as heterogeneous nucleation sites for the precipitation phase, promoting the increase in the nucleation rate of the second phase and the acceleration of the precipitation rate during the subsequent aging process. Traditional deformation methods such as extrusion and rolling can generate a strong basal texture in the alloy after deformation, resulting in poor plasticity and processing performance, which is not conducive to subsequent processing. Different from the single deformation path in traditional deformation, the severe plastic deformation treatment by spiral torsion extrusion can perform multi-pass extrusion on the alloy. While accumulating the deformation strain, it makes the C-axis of the alloy grains continuously deflect along the torsion axis, thus significantly refining the grains and weakening the basal texture at the same time, achieving the synergistic improvement of the strength and plasticity of the magnesium alloy. The grain size after extrusion can be significantly refined from 150 - 200 μm to 1 - 10 μm, and the microstructure changes from coarse dendritic crystals to uniformly refined equiaxed crystals. By performing tensile stress aging treatment after the severe plastic deformation treatment, a large number of uniformly fine precipitates can be precipitated, obtaining a microstructure with fine grains and fine and uniformly distributed precipitate phases.

[0031] Further preferably, the purity of pure Mg is above 99.99 wt.%, and the purity of pure Zn is above 99.99 wt.%.

[0032] In a second aspect, an embodiment of the present invention further provides a preparation method for the above-mentioned high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy. The preparation method at least includes the following steps: According to the composition and weight percentage of the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy, put the raw materials into a crucible resistance furnace, melt at 700 - 750 °C, and use CO 2 and SF 6 mixed gas as the protective gas during melting, and then pour the melt to obtain a magnesium alloy ingot. The raw materials include: pure Mg, pure Zn, Mg-Nd master alloy, Mg-Ca master alloy, Mg-Sn master alloy, and Mg-Zr master alloy; Perform double-stage solution treatment, cutting treatment, forward extrusion pre-deformation treatment, severe plastic deformation treatment, and stress aging treatment on the magnesium alloy ingot in sequence to obtain the magnesium alloy finished product. The double-stage solution treatment adopts a double-stage solution treatment of 450 °C × 2 h + 500 °C × 0.5 h. The cutting treatment is used to cut the magnesium alloy ingot into round bars of specified dimensions. The extrusion temperature of the forward extrusion pre-treatment is 300 - 350 °C, and the extrusion ratio is 4:1. The severe plastic deformation treatment adopts spiral torsion extrusion, the extrusion temperature is 300 - 350 °C, the torsion angle is 180°, the extrusion rate is 5 - 10 mm / min, and the extrusion pass is two passes. In the stress aging treatment, the stress type is tensile stress, the stress value is 75 MPa, the aging temperature is 150 °C, and the aging time is 1 - 2 h.

[0033] Further, in the embodiments of the present invention, according to the composition and weight percentage of the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy, the raw materials are put into a crucible resistance furnace, melted at 700~750 °C, and CO 2 and SF 6 mixed gas is used as the protective gas during melting, and then the melt is poured to obtain a magnesium alloy ingot, which further includes the following steps: Step 1.1, according to the composition and weight percentage of the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy, determine the dosages of pure Mg, pure Zn, Mg-Nd master alloy, Mg-Ca master alloy, Mg-Sn master alloy and Mg-Zr master alloy; Step 1.2, preheat the crucible, stirring rod and slag skimming spoon to 200~250 °C, take them out and brush with the pre-prepared coating, and the coating is a mixed solution of zinc oxide (ZnO) and water glass (Na 2 O•nSiO 2 ); Step 1.3, put pure Mg and pure Zn into the crucible, heat up to 700 °C and keep warm, during which CO 2 and SF 6 mixed gas is introduced. After pure Mg and pure Zn are completely melted, heat up to 730 °C, then add Mg-Sn master alloy and keep warm for 15 min. After melting, heat up to 750 °C, then add Mg-Nd master alloy and keep warm for 15 min. After melting, cool down to 740 °C, then add Mg-Zr master alloy and stir for 1 min to prevent the Mg-Zr master alloy from depositing at the bottom of the melt, keep warm for 15 min. After melting, add Mg-Ca master alloy. After all the metals are melted, skim the surface scum, add a refining agent for impurity removal, stir quickly for 1 min, and let it stand for 20 min; Step 1.4, skim the scum above the melt, pour the melt into a mold preheated to 200~250 °C at a uniform speed to complete pouring, and demold and take out the magnesium alloy ingot after cooling to room temperature.

[0034] In the embodiments of the present invention, in Step 1.3, introducing CO 2 and SF 6 mixed gas as the protective gas can prevent pure Mg from reacting violently with air and overburning during the metal melting process; using Mg-Ca master alloy as the last added master alloy can form an oxide layer on the surface of the melt, isolate the oxidation reaction between the melt and air, and play a role in protecting the melt; after adding the refining agent for impurity removal, continuing to stir up and down with the stirring rod for 1 min can prevent the uneven structure of the ingot caused by Mg-Ca floating on the surface of the melt and the Mg-Zr master alloy sinking to the bottom.

[0035] Preferably, the purity of pure Mg is above 99.99 wt.%, and the purity of pure Zn is above 99.99 wt.%.

[0036] Furthermore, in the embodiments of the present invention, the magnesium alloy ingot is successively subjected to double-stage solution treatment, cutting treatment, forward extrusion pre-deformation treatment, severe plastic deformation treatment, and stress aging treatment to obtain the finished magnesium alloy, which further includes the following steps: Step 2.1: Perform double-stage solution treatment on the magnesium alloy ingot. The temperature of the first-stage solution treatment is 450 °C and the time is 2 h, and the temperature of the second-stage solution treatment is 500 °C and the time is 0.5 h. The cooling method is water cooling at 25 °C for both stages; Step 2.2: Cut the magnesium alloy ingot after double-stage solution treatment into round bars with a diameter of 30 mm; Step 2.3: Perform forward extrusion pre-deformation treatment on the round bars. The extrusion temperature is 300 - 350 °C and the extrusion ratio is 4:1 to obtain round bars with a diameter of 15 mm; Step 2.4: Cut the round bars after forward extrusion pre-deformation treatment into cuboids with a cross-section of 10 mm × 10 mm, and place them in a screw torsion extrusion die for severe plastic deformation extrusion. The extrusion temperature is 300 - 350 °C, the torsion angle is 180°, the extrusion rate is 5 - 10 mm / min, and the number of extrusion passes is two. After each extrusion pass, water quenching is carried out. After water quenching, it is placed in the screw torsion extrusion die and heated to the extrusion temperature and held for 10 min before the next extrusion pass; Step 2.5: Perform stress aging treatment on the specimen obtained after severe plastic deformation extrusion. The stress type is tensile stress, the stress value is 75 MPa, the aging temperature is 150 °C, and the aging time is 1 - 2 h to obtain the finished magnesium alloy.

[0037] In the embodiments of the present invention, by using the above-defined double-stage solution treatment, forward extrusion pre-deformation treatment, severe plastic deformation treatment, and stress aging treatment, the grain refinement strengthening and precipitation strengthening of the magnesium alloy are realized. By using a low-alloy (the content of alloying elements is below 3 wt.%) as the alloy design system and combining grain refinement strengthening and precipitation strengthening, the problems of coarse grains in the low-alloyed magnesium alloy, severe galvanic corrosion caused by the segregation of coarse second phases at grain boundaries, and poor strengthening effect due to insufficient precipitation driving force of the second phase resulting in low alloy strength are improved. It can realize the coordinated improvement of the strength and corrosion resistance of the magnesium alloy, and achieve the matching of the strength and corrosion resistance of the magnesium alloy to simultaneously meet the strength requirements and corrosion resistance requirements.

[0038] In the embodiments of the present invention, the improvement of strength by grain refinement strengthening lies in the hindering effect of high-density grain boundaries on dislocation slip, and the improvement of corrosion resistance by grain refinement strengthening lies in the denser surface film formed in the fine grain region, which is beneficial to protecting the matrix. The Mg 2 Ca phase and Mg 12 The Nd phase has a small size, a large number, and is evenly distributed, which hinders the generation of dislocations, improves the strength of the alloy. At the same time, the uniform distribution of its fine secondary phase improves the uniformity of the structure, helps to form smaller cathode-anode galvanic couples, reduces local micro-galvanic corrosion, transforms severe local corrosion into uniform corrosion, and improves the corrosion resistance of the alloy.

[0039] To make the above technical solutions of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0040] Example 1

[0041] In this Example 1, the raw material composition is as follows: Zn: 1.1%, Nd: 0.7%, Ca: 0.4%, Sn: 0.3%, Zr: 0.3%, and the balance is Mg and unavoidable impurity elements.

[0042] The specific preparation process is as follows: Preheat the crucible, stirring rod and slag skimmer to 200 °C, take them out and brush on the coating. The coating is a mixed solution of zinc oxide (ZnO) and water glass (Na 2 O•nSiO 2 ); Put pure Mg and pure Zn into the crucible, heat up to 700 °C and keep warm. During this period, introduce a mixed gas of CO 2 and SF 6 . After all the pure Mg and pure Zn are melted, heat up to 730 °C, then add the Mg-Sn master alloy and keep warm for 15 min. After melting, heat up to 750 °C, then add the Mg-Nd master alloy and keep warm for 15 min. After melting, cool down to 740 °C, then add the Mg-Zr master alloy and stir for 1 min, keep warm for 15 min. After melting, add the Mg-Ca master alloy. After all the metals are melted, skim the surface scum, add a refining agent for impurity removal, quickly stir for 1 min, let it stand for 20 min, skim the impurity scum above the melt, pour the melt into a mold preheated to 200 °C at a uniform speed, cool to room temperature and then remove the mold to obtain a Mg-Zn-Nd-Ca-Sn-Zr magnesium alloy ingot; Perform double-stage solution treatment on the obtained Mg-Zn-Nd-Ca-Sn-Zr magnesium alloy ingot. The double-stage solution treatment conditions are: 450 °C × 2 h + 500 °C × 0.5 h, and the cooling method is water cooling at 25 °C; Cut the solution-treated magnesium alloy into round bars with a diameter of 30 mm, and then perform forward extrusion pre-deformation treatment. The extrusion ratio is 4:1, and the extrusion temperature is 330 °C to obtain round bars with a diameter of 15 mm; The round bar after forward extrusion pre-deformation treatment was cut into a cuboid of 10×10×60 mm for spiral torsion extrusion. The spiral torsion extrusion process was as follows: the extrusion temperature was 330 °C, the torsion angle was 180°, the extrusion rate was 10 mm / min, and the number of extrusion passes was two passes; The extruded magnesium alloy was subjected to stress aging treatment. The stress aging treatment conditions were as follows: the stress type was tensile stress, the stress value was 75 MPa, the aging temperature was 150 °C, the aging time was 1.5 h, and the cooling method was water cooling at 25 °C to obtain the final magnesium alloy product.

[0043] Through experiments, the average grain size of the magnesium alloy prepared in Example 1 was 8 μm, the tensile strength was 331 MPa, the elongation was 20%, and according to the ASTM G31-72 immersion standard, the average corrosion rate of the magnesium alloy in a simulated body fluid (SBF) at 37 ± 0.5 °C was 0.176 mm / year.

[0044] Example 2

[0045] In this Example 2, the raw material composition was as follows: Zn: 1.0%, Nd: 0.7%, Ca: 0.5%, Sn: 0.2%, Zr: 0.3%, and the balance was Mg and inevitable impurity elements.

[0046] The specific preparation process was as follows: Preheat the crucible, stirring rod and slag skimmer to 200 °C, take them out and brush on the coating. The coating was a mixed solution of zinc oxide (ZnO) and water glass (Na 2 O•nSiO 2 ) Put pure Mg and pure Zn into the crucible, heat up to 700 °C and hold for heat preservation. During this period, introduce a mixed gas of CO 2 and SF 6 . After all the pure Mg and pure Zn are melted, heat up to 730 °C, then add the Mg-Sn master alloy and hold for 15 min. After melting, heat up to 750 °C, then add the Mg-Nd master alloy and hold for 15 min. After melting, cool down to 740 °C, then add the Mg-Zr master alloy and stir for 1 min, hold for 15 min. After melting, add the Mg-Ca master alloy. After all the metals are melted, skim off the surface scum, add a refining agent for impurity removal, stir rapidly for 1 min, let it stand for 20 min, skim off the impurity scum above the melt, pour the melt into a mold preheated to 200 °C at a uniform speed, cool to room temperature and then demold to take out the magnesium alloy ingot to obtain the Mg-Zn-Nd-Ca-Sn-Zr magnesium alloy ingot; The obtained Mg-Zn-Nd-Ca-Sn-Zr magnesium alloy ingot was subjected to a two-stage solution treatment. The conditions of the two-stage solution treatment were: 450 °C × 2 h + 500 °C × 0.5 h, and the cooling method was water cooling at 25 °C; The solution-treated magnesium alloy was cut into round bars with a diameter of 30 mm, and then subjected to forward extrusion pre-deformation treatment. The extrusion ratio was 4:1, and the extrusion temperature was 300 °C to obtain round bars with a diameter of 15 mm; The round bars after the forward extrusion pre-deformation treatment were cut into cuboids of 10×10×60 mm for spiral torsion extrusion. The spiral torsion extrusion process was: the extrusion temperature was 300 °C, the torsion angle was 180°, the extrusion rate was 5 mm / min, and the number of extrusion passes was two passes; The extruded magnesium alloy was subjected to stress aging treatment. The conditions of the stress aging treatment were: the stress type was tensile stress, the stress value was 75 MPa, the aging temperature was 150 °C, the aging time was 2 h, and the cooling method was water cooling at 25 °C to obtain the final magnesium alloy product.

[0047] Through tests, the average grain size of the magnesium alloy prepared in Example 2 was 10 μm, the tensile strength was 339 MPa, the elongation was 22%, and according to the ASTM G31-72 immersion standard, the average corrosion rate of the magnesium alloy in a simulated body fluid (SBF) at 37 ± 0.5 °C was 0.197 mm / year.

[0048] Example 3

[0049] In this Example 3, the raw material composition was as follows: Zn: 1.2%, Nd: 0.7%, Ca: 0.5%, Sn: 0.2%, Zr: 0.4%, and the balance was Mg and unavoidable impurity elements.

[0050] The specific preparation process was as follows: Preheat the crucible, stirring rod and slag skimmer to 200 °C, take them out and brush on the coating. The coating was a mixed solution of zinc oxide (ZnO) and water glass (Na 2 O•nSiO 2 ) Put pure Mg and pure Zn into the crucible, heat up to 700 °C and keep warm, and during this period, introduce CO 2 and SF 6 A mixed gas. After all the pure Mg and pure Zn are melted, the temperature is raised to 730 °C. Subsequently, a Mg-Sn master alloy is added and held for 15 min. After melting, the temperature is raised to 750 °C. Then, a Mg-Nd master alloy is added and held for 15 min. After melting, the temperature is lowered to 740 °C. Subsequently, a Mg-Zr master alloy is added and stirred for 1 min, and held for 15 min. After melting, a Mg-Ca master alloy is added. After all the metals are melted, the surface scum is skimmed off. A refining agent is added for impurity removal, and stirred rapidly for 1 min, then left standing for 20 min. The impurity removal scum above the melt is skimmed off. The melt is poured uniformly into a mold preheated to 200 °C. After cooling to room temperature, the mold is removed to obtain a Mg-Zn-Nd-Ca-Sn-Zr magnesium alloy ingot; The obtained Mg-Zn-Nd-Ca-Sn-Zr magnesium alloy ingot is subjected to a two-stage solution treatment. The two-stage solution treatment conditions are: 450 °C × 2 h + 500 °C × 0.5 h, and the cooling method is water cooling at 25 °C; The solution-treated magnesium alloy is cut into round bars with a diameter of 30 mm, and then subjected to forward extrusion pre-deformation treatment. The extrusion ratio is 4:1, and the extrusion temperature is 350 °C to obtain round bars with a diameter of 15 mm; The round bars after the forward extrusion pre-deformation treatment are cut into 10×10×60 mm cuboids for screw torsion extrusion. The screw torsion extrusion process is: the extrusion temperature is 350 °C, the torsion angle is 180°, the extrusion rate is 10 mm / min, and the number of extrusion passes is two passes; The extruded magnesium alloy is subjected to stress aging treatment. The stress aging treatment conditions are: the stress type is tensile stress, the stress value is 75 MPa, the aging temperature is 150 °C, the aging time is 1 h, and the cooling method is water cooling at 25 °C to obtain the final magnesium alloy product.

[0051] After testing, the average grain size of the magnesium alloy prepared in Example 3 of this embodiment is 10 μm, the tensile strength is 324 MPa, the elongation is 25%, and according to the ASTM G31-72 immersion standard, the average corrosion rate of the magnesium alloy in a simulated body fluid (SBF) at 37 ± 0.5 °C is 0.142 mm / year.

[0052] Reference Figure 1-6 , Figure 1 is the metallographic microstructure diagram of the magnesium alloy obtained in Example 2 of the present invention; Figure 2 is the microscopic structure diagram of the magnesium alloy obtained in Example 2 of the present invention under a scanning electron microscope; Figure 3 is the stress-strain curve diagram of the magnesium alloy obtained in Example 2 of the present invention; Figure 4 is the morphology diagram of the magnesium alloy obtained in Example 2 of the present invention after soaking for 300 hours and removing corrosion products; Figure 5The hydrogen evolution curve of the magnesium alloy obtained in Example 2 of the present invention; Figure 6 The average corrosion rate diagram of the magnesium alloys obtained in Examples 1-3 of the present invention.

[0053] It can be seen that the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy and its preparation method provided by the embodiments of the present invention regulate a fine-grained structure with a uniform and fine precipitate phase distribution through microalloying, two-stage solution treatment, severe plastic deformation treatment, and stress aging treatment. By using grain refinement strengthening, precipitation strengthening, and weakening the basal texture, the strength and plasticity of the alloy are improved. At the same time, the compactness of the surface film of the magnesium alloy is improved by using the characteristics of fine grains and uniform distribution of fine second phases, the corrosion mode of the magnesium alloy is changed, and the tendency of local pitting corrosion on the surface of the magnesium alloy is reduced, achieving a synergistic improvement in the strength, plasticity, and corrosion resistance of the alloy, realizing the matching of the strength and corrosion resistance of the magnesium alloy to simultaneously meet the strength requirements and corrosion resistance requirements. A high-strength and corrosion-resistant low-alloyed magnesium alloy with a strength greater than 320 MPa, an average corrosion rate of 0.1-0.2 mm / year, and an elongation of more than 20% can be obtained. Moreover, the content of alloying elements in the magnesium alloy is low, which can further reduce the raw material cost.

[0054] It should be noted that in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. And these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-strength, corrosion-resistant, low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy, characterized in that: The composition comprises the following components by weight percentage: Zn: 0.7~1.2%, Nd: 0.4~0.7%, Ca: 0.1~0.6%, Sn: 0.1~0.4%, Zr: 0.3~0.6%, and Zn+Nd+Ca+Sn+Zr≤3%, the balance is Mg and unavoidable impurity elements.

2. The high-strength, corrosion-resistant, low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy according to claim 1, characterized in that: The composition comprises the following components by weight percentage: Zn: 1.0%, Nd: 0.7%, Ca: 0.5%, Sn: 0.2%, Zr: 0.3%, and the balance is Mg and inevitable impurity elements.

3. The high-strength, corrosion-resistant, low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy according to claim 1 or 2, characterized in that: The high-strength, corrosion-resistant, low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy is prepared by at least the following steps: According to the composition and weight percentage of the high-strength, corrosion-resistant, low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy, raw materials are placed in a crucible resistance furnace, smelted at 700-750° C., and a mixed gas of CO2 and SF6 is used as a protective gas during smelting, and then the melt is poured to obtain a magnesium alloy ingot, wherein the raw materials include: pure Mg, pure Zn, Mg-Nd master alloy, Mg-Ca master alloy, Mg-Sn master alloy and Mg-Zr master alloy; The magnesium alloy ingot is subjected to a two-stage solution treatment, a cutting treatment, a forward extrusion pre-deformation treatment, a large plastic deformation treatment and a stress aging treatment in sequence to obtain a magnesium alloy finished product, wherein the two-stage solution treatment adopts a two-stage solution treatment of 450°C×2h+500°C×0.5h, the cutting treatment is used to cut the magnesium alloy ingot into round bars of a specified size, the extrusion temperature of the forward extrusion pre-deformation treatment is 300-350°C, and the extrusion ratio is 4:1, the large plastic deformation treatment adopts spiral torsion extrusion, the extrusion temperature is 300-350°C, the torsion angle is 180°, the extrusion rate is 5-10mm / min, and the extrusion pass is two passes, and the stress type in the stress aging treatment is tensile stress, the stress value is 75MPa, the aging temperature is 150°C, and the aging time is 1-2h.

4. The high-strength, corrosion-resistant, low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy according to claim 3, characterized in that: The purity of pure Mg is 99.99 wt.% or more, and the purity of pure Zn is 99.99 wt.% or more.

5. A method for preparing a high-strength, corrosion-resistant, low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy as claimed in any one of claims 1 to 4, characterized in that: The method comprises at least the following steps: According to the composition and weight percentage of the high-strength, corrosion-resistant, low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy, raw materials are placed in a crucible resistance furnace, smelted at 700-750° C., and a mixed gas of CO2 and SF6 is used as a protective gas during smelting, and then the melt is poured to obtain a magnesium alloy ingot, wherein the raw materials include: pure Mg, pure Zn, Mg-Nd master alloy, Mg-Ca master alloy, Mg-Sn master alloy and Mg-Zr master alloy; The magnesium alloy ingot is subjected to a two-stage solution treatment, a cutting treatment, a forward extrusion pre-deformation treatment, a large plastic deformation treatment and a stress aging treatment in sequence to obtain a magnesium alloy finished product, wherein the two-stage solution treatment adopts a two-stage solution treatment of 450°C×2h+500°C×0.5h, the cutting treatment is used to cut the magnesium alloy ingot into round bars of a specified size, the extrusion temperature of the forward extrusion pre-treatment is 300-350°C, and the extrusion ratio is 4:1, the large plastic deformation treatment adopts spiral torsion extrusion, the extrusion temperature is 300-350°C, the torsion angle is 180°, the extrusion rate is 5-10mm / min, and the extrusion pass is two passes, and the stress type in the stress aging treatment is tensile stress, the stress value is 75MPa, the aging temperature is 150°C, and the aging time is 1-2h.

6. The method for preparing the high-strength, corrosion-resistant, low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy according to claim 5, characterized in that: According to the composition and weight percentage of the high-strength, corrosion-resistant, low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy, the raw materials are placed in a crucible resistance furnace, smelted at 700-750° C., and a mixed gas of CO2 and SF6 is used as a protective gas during smelting, and then the melt is poured to obtain a magnesium alloy ingot, comprising: Step 1.1, determining the amount of pure Mg, pure Zn, Mg-Nd master alloy, Mg-Ca master alloy, Mg-Sn master alloy and Mg-Zr master alloy according to the composition and weight percentage of the high-strength corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy; Step 1.2, preheating the crucible, stirring rod and slag scoop to 200-250° C., taking them out and brushing them with pre-made coating, wherein the coating is a mixed solution of zinc oxide and water glass; Step 1.3, put pure Mg and pure Zn into a crucible and heat it to 700°C and keep it warm, during which a mixed gas of CO2 and SF6 is introduced, after pure Mg and pure Zn are completely melted, heat it to 730°C, then add Mg-Sn master alloy and keep it warm for 15 minutes, heat it to 750°C after melting, then add Mg-Nd master alloy and keep it warm for 15 minutes, cool it to 740°C after melting, then add Mg-Zr master alloy and stir it for 1 minute to prevent Mg-Zr master alloy from depositing at the bottom of the melt, keep it warm for 15 minutes, add Mg-Ca master alloy after melting, skim off the surface scum after the metal is completely melted, add refining agent to remove impurities, stir rapidly for 1 minute, and let it stand for 20 minutes; Step 1.4, scrape off the scum on the top of the melt, pour the melt into the mold preheated to 200~250℃ at a uniform speed, complete the pouring, cool to room temperature, remove the mold and take out the magnesium alloy ingot.

7. The method for preparing the high-strength, corrosion-resistant, low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy according to claim 5, characterized in that: The purity of pure Mg is 99.99 wt.% or more, and the purity of pure Zn is 99.99 wt.% or more.

8. The method for preparing the high-strength, corrosion-resistant, low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy according to claim 5, characterized in that: The magnesium alloy ingot is subjected to a two-stage solution treatment, a cutting treatment, a positive extrusion pre-deformation treatment, a large plastic deformation treatment and a stress aging treatment in sequence to obtain a magnesium alloy finished product, including: Step 2.1, performing a two-stage solution treatment on the magnesium alloy ingot, the temperature of the first stage solution treatment is 450°C, the time is 2h, the temperature of the second stage solution treatment is 500°C, the time is 0.5h, and the cooling method is 25°C water cooling; Step 2.2, cutting the magnesium alloy ingot after the double-stage solid solution treatment into round bars with a specified diameter; Step 2.3, performing a positive extrusion pre-deformation treatment on the round rod, with an extrusion temperature of 300-350°C and an extrusion ratio of 4:1, to obtain a round rod with a diameter of half the specified size; Step 2.4, cutting the round rod after the positive extrusion pre-deformation treatment into a rectangular parallelepiped with a required cross-section size, placing it in a spiral twisting extrusion die for large plastic deformation extrusion, the extrusion temperature is 300-350°C, the twisting angle is 180°, the extrusion rate is 5-10 mm / min, the extrusion pass is two passes, and water quenching is performed after each extrusion pass. After water quenching, the rod is placed in a spiral twisting extrusion die and heated to the extrusion temperature and kept warm for 10 minutes before the next extrusion pass; Step 2.5, subjecting the sample obtained after large plastic deformation extrusion to stress aging treatment with a stress type of tensile stress, a stress value of 75 MPa, an aging temperature of 150° C., and an aging time of 1 to 2 h to obtain a magnesium alloy product.

9. The method for preparing the high-strength, corrosion-resistant, low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy according to claim 8, characterized in that: The specified dimension is 30 mm.

10. The method for preparing the high-strength, corrosion-resistant, low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy according to claim 9, characterized in that: The required size is 10 mm×10 mm.

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