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

Abstract

The present invention discloses a high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy and a preparation method thereof, relating to the technical field of magnesium alloys. The 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. The alloy is melted in an atmosphere-protected crucible resistance furnace, and a magnesium alloy ingot is obtained by casting. Then, it is prepared by means of double-stage solution treatment, forward extrusion pre-deformation treatment, severe plastic deformation treatment, and stress aging treatment. The magnesium alloy of the present invention has high strength and excellent corrosion resistance, and can achieve the matching of strength and corrosion resistance to simultaneously meet the strength requirements and corrosion resistance requirements.

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 alloys 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 alloys is low, which can reduce the medical cost of patients. For the above reasons, magnesium alloys show great potential in being applied to clinical medicine as biomedical alloys, and are currently regarded as new degradable biomedical materials and are 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 alloys are 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. It is difficult to match the strength and corrosion resistance after alloying, and it is impossible to meet both the strength requirements and the 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:

[0007] In the first aspect, a high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy is provided, which includes the following components by weight percentage:

[0008] 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.

[0009] 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:

[0010] Zn: 1.0%, Nd: 0.7%, Ca: 0.5%, Sn: 0.2%, Zr: 0.3%, with the balance being Mg and inevitable impurity elements.

[0011] 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:

[0012] 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, melted at 700~750°C, and a mixed gas of CO2 and SF6 is used as the protective gas during melting. 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;

[0013] 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×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 spiral torsion extrusion, the extrusion temperature is 300~350°C, the torsion angle is 180°, the extrusion rate is 5~10mm / min, and the number of extrusion passes is two passes. In the stress aging treatment, the stress type is tensile stress, the stress value is 75MPa, the aging temperature is 150°C, and the aging time is 1~2h.

[0014] In some alternative embodiments, the purity of pure Mg is above 99.99wt.%, and the purity of pure Zn is above 99.99wt.%.

[0015] In a second aspect, there is also provided a preparation method of the above-mentioned high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy. The preparation method at least comprises the following steps:

[0016] According to the composition and weight percentage of the high-strength, corrosion-resistant, low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy, put the raw materials into a crucible resistance furnace, melt them at 700-750 °C, and use a mixed gas of CO2 and SF6 as the protective gas during melting. 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;

[0017] 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 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 number of extrusion passes 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.

[0018] In some optional embodiments, the step of putting the raw materials into a crucible resistance furnace according to the composition and weight percentage of the high-strength, corrosion-resistant, low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy, melting them at 700-750 °C, and using a mixed gas of CO2 and SF6 as the protective gas during melting, and then pouring the melt to obtain a magnesium alloy ingot includes:

[0019] Step 1.1, 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 according to the composition and weight percentage of the high-strength, corrosion-resistant, low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy;

[0020] Step 1.2, preheat the crucible, stirring rod, and slag skimmer to 200-250 °C, take them out and brush on the pre-prepared coating. The coating is a mixed solution of zinc oxide and water glass;

[0021] Step 1.3: Put pure Mg and pure Zn into a crucible, heat it up to 700 °C and keep it warm. During this period, introduce a mixed gas of CO2 and SF6. After pure Mg and pure Zn are completely melted, heat it up to 730 °C, then add Mg-Sn master alloy and keep it warm for 15 min. After melting, heat it up to 750 °C, then add Mg-Nd master alloy and keep it warm for 15 min. After melting, cool it 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 it warm for 15 min. After melting, add Mg-Ca master alloy. After all the metals are melted, skim off the surface dross, add a refining agent for impurity removal, stir rapidly for 1 min, and then let it stand for 20 min;

[0022] Step 1.4: Skim off the dross above the melt, pour the melt uniformly into a mold preheated to 200 - 250 °C to complete casting. After cooling to room temperature, demold to take out the magnesium alloy ingot.

[0023] 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.%.

[0024] 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 the magnesium alloy finished product, including:

[0025] 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. The cooling method for both is water cooling at 25 °C;

[0026] Step 2.2: Cut the magnesium alloy ingot after double-stage solution treatment into round bars with a diameter of a specified size;

[0027] 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 half of the specified size;

[0028] Step 2.4: Cut the round bars after forward extrusion pre-deformation treatment into cuboids with a cross-section of the required size, put them 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 number of extrusion passes is two passes. After each extrusion pass, perform water quenching. After water quenching, put it into the screw torsion extrusion die, heat it up to the extrusion temperature and keep it warm for 10 min before the next extrusion pass;

[0029] 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 the finished magnesium alloy product.

[0030] In some alternative embodiments, the specified dimension is 30 mm.

[0031] In some alternative embodiments, the required dimension is 10 mm × 10 mm.

[0032] The main advantages of the technical solution of the present invention are as follows:

[0033] 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 precipitate 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 rate of more than 20% can be obtained, and the content of alloying elements in the magnesium alloy is low, which can further reduce the raw material cost. Description of the Drawings

[0034] 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 to the present invention. In the drawings:

[0035] Figure 1 It is the metallographic micrograph of the magnesium alloy obtained in Example 2 of the present invention;

[0036] Figure 2 It is the micrograph of the magnesium alloy obtained in Example 2 of the present invention under a scanning electron microscope;

[0037] Figure 3 It is the stress-strain curve of the magnesium alloy obtained in Example 2 of the present invention;

[0038] Figure 4 It is the morphology of the magnesium alloy obtained in Example 2 of the present invention after soaking for 300 hours and removing corrosion products;

[0039] Figure 5The hydrogen evolution curve of the magnesium alloy obtained in Example 2 of the present invention;

[0040] Figure 6 The average corrosion rate diagram of the magnesium alloys obtained in Examples 1-3 of the present invention. Detailed implementation manners

[0041] 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 the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0042] The technical solutions provided by the embodiments of the present invention are described in detail below.

[0043] 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, and the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy comprises the following components by weight percentage:

[0044] 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.

[0045] 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 alloy elements of Zn, Nd, Ca, Sn and Zr to the magnesium alloy and controlling the content of each alloy element within the above range is 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:

[0046] 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, lower the corrosion rate. At the same time, Zn has good solid solution aging strengthening effect, and 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 solid 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%.

[0047] As one of the light rare earth elements, microalloying with 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. Nd element has a good precipitation strengthening effect in the low-alloy system and can precipitate uniform and fine precipitate phases during subsequent aging, hindering dislocation slip and improving the alloy strength. At the same time, the fine and uniform distribution of the 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 protective 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 boundaries will become potential crack sources, 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 the precipitate phase 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%.

[0048] Ca element has excellent biocompatibility and can improve the composition of the corrosion product layer. The Ca-containing corrosion products 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 Mg2Ca will be formed, 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%.

[0049] Sn element has a relatively fast diffusion rate and will segregate at the grain boundaries. With the extension of the immersion time, Sn atoms will dissolve at the grain boundaries and then form SnO2 oxide attached to the corrosion product layer, thus increasing the denseness 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 Mg2Sn 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 corresponding SnO2 oxide formed by the Sn element segregated at the grain boundaries will decrease, reducing the protection of the corrosion product layer, and the corrosion resistance of the alloy will decline. Therefore, the Sn content is controlled at 0.1 - 0.4%.

[0050] The Zr element does not form a phase with Mg. Adding Zr element in combination can become heterogeneous nucleation sites during the solidification process of the alloy, promoting the nucleation rate, 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 discrete α-Zr particles will become potential crack sources, deteriorating the alloy strength, aggravating 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 grain refinement is not obvious. Therefore, the content of the Zr element is controlled at 0.3 - 0.6%.

[0051] Since there will be strong galvanic corrosion in the magnesium alloy when the content of alloying elements in the magnesium alloy is high, which will have a negative impact on the corrosion resistance of the alloy, resulting in too fast corrosion rate of the magnesium alloy. Therefore, controlling the total amount of alloying elements Zn, Nd, Ca, Sn, Zr added in the magnesium alloy below 3% can further reduce the corrosion tendency and improve the corrosion resistance of the magnesium alloy.

[0052] More preferably, the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy provided by the embodiment of the present invention comprises the following components by weight percentage:

[0053] Zn: 1.0%, Nd: 0.7%, Ca: 0.5%, Sn: 0.2%, Zr: 0.3%, and the balance is Mg and inevitable impurity elements.

[0054] Furthermore, in the embodiment 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:

[0055] 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, melted at 700 - 750 °C, and a mixed gas of CO2 and SF6 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;

[0056] 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 × 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 screw twist extrusion (STE), the extrusion temperature is 300 - 350 °C, the twist 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 - 2 h.

[0057] In the embodiment 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, through the combination of 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 uniformly fine precipitate phases. Through the combination of 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.

[0058] Specifically, in the embodiment of the present invention, through the double-stage solution treatment of 450 °C × 2 h + 500 °C × 0.5 h, the Mg 12 Nd phase and Mg2Ca 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, the basal plane is 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 an increase in the nucleation rate of the second phase and an acceleration of the precipitation rate during the subsequent aging process. Traditional deformation methods such as extrusion and rolling result in a strong basal texture in the alloy after deformation, leading to 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 using spiral torsion extrusion can perform multi-pass extrusion on the alloy. While accumulating deformation strain, it causes the C-axis of the alloy grains to continuously deflect along the torsion axis, thus significantly refining the grains and simultaneously weakening the basal texture, achieving a synergistic improvement in the strength and plasticity of the magnesium alloy. After extrusion, the grain size 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 precipitation phases can be precipitated, obtaining a microstructure with fine grains and finely and uniformly distributed precipitate phases.

[0059] Further preferably, the purity of pure Mg is above 99.99 wt.%, and the purity of pure Zn is above 99.99 wt.%.

[0060] In a second aspect, the embodiments of the present invention also provide 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:

[0061] 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 a mixed gas of CO2 and SF6 as the protective gas during melting. 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;

[0062] 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 pretreatment is 300 - 350 °C, and the extrusion ratio is 4:1. The severe plastic deformation treatment uses 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.

[0063] 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 a mixed gas of CO2 and SF6 is used as the protective gas during melting. Then, the melt is poured to obtain a magnesium alloy ingot, which further includes the following steps:

[0064] Step 1.1, 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 according to the composition and weight percentage of the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy;

[0065] Step 1.2, preheat the crucible, stirring rod, and slag skimming spoon to 200-250 °C, take them out and brush with a pre-prepared coating, and the coating is a mixed solution of zinc oxide (ZnO) and water glass (Na2O•nSiO2);

[0066] Step 1.3, put pure Mg and pure Zn into the crucible, heat up to 700 °C and keep warm, and introduce a mixed gas of CO2 and SF6 during this period. 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 rapidly for 1 min, and let it stand for 20 min;

[0067] 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.

[0068] In the embodiments of the present invention, in Step 1.3, introducing a mixed gas of CO2 and SF6 as the protective gas can prevent pure Mg from reacting violently with air and overburning during the melting process of the metal; using the 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, continuously stirring 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.

[0069] Preferably, the purity of pure Mg is above 99.99 wt.%, and the purity of pure Zn is above 99.99 wt.%.

[0070] 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:

[0071] 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 for both is water cooling at 25°C;

[0072] Step 2.2: Cut the magnesium alloy ingot after double-stage solution treatment into round bars with a diameter of 30 mm;

[0073] 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;

[0074] 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 spiral 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 number of extrusion passes is two passes, and water quenching is performed after each extrusion pass. After water quenching, it is placed in the spiral torsion extrusion die and heated to the extrusion temperature and held for 10 min before the next extrusion pass;

[0075] 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.

[0076] 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 fine grain 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 fine grain strengthening and precipitation strengthening, the problems of coarse grains in low-alloyed magnesium alloys, severe galvanic corrosion caused by the segregation of coarse second phases at grain boundaries, and poor strengthening effect due to insufficient driving force for second-phase precipitation and low alloy strength are improved. It can achieve the coordinated improvement of the strength and corrosion resistance of the magnesium alloy, and realize the matching of the strength and corrosion resistance of the magnesium alloy to simultaneously meet the strength requirements and corrosion resistance requirements.

[0077] In the embodiments of the present invention, the improvement in strength by fine grain strengthening lies in the hindering effect of high-density grain boundaries on dislocation slip, and the improvement in corrosion resistance by fine grain strengthening lies in the denser surface film formed in the fine grain region, which is beneficial to protecting the matrix. The Mg2Ca phase and Mg 12 Nd phases precipitated by stress aging treatment are small in size, large in number, and evenly distributed, which hinder dislocations and improve the strength of the alloy. At the same time, the uniform distribution of its fine second 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.

[0078] 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.

[0079] Example 1

[0080] 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.

[0081] The specific preparation process is as follows:

[0082] Preheat the crucible, stirring rod and slag skimmer to 200°C, take them out and brush on the coating, and the coating is a mixed solution of zinc oxide (ZnO) and water glass (Na2O•nSiO2);

[0083] 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 CO2 and SF6. 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, keep warm for 15 min. After melting, add Mg-Ca master alloy. After all the metals are melted, skim off the surface scum, add a refining agent for impurity removal, quickly stir 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 constant speed, cool to room temperature and then remove the mold to take out the magnesium alloy ingot, and obtain a Mg-Zn-Nd-Ca-Sn-Zr magnesium alloy ingot;

[0084] Perform double-stage solution treatment on the obtained Mg-Zn-Nd-Ca-Sn-Zr magnesium alloy ingot. The conditions for double-stage solution treatment are: 450°C × 2 h + 500°C × 0.5 h, and the cooling method is water cooling at 25°C;

[0085] 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 330 °C to obtain round bars with a diameter of 15 mm.

[0086] The round bars after forward extrusion pre-deformation treatment were cut into cuboids 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.

[0087] 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.

[0088] After testing, 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 simulated body fluid (SBF) at 37 ± 0.5 °C was 0.176 mm / year.

[0089] Example 2

[0090] 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 unavoidable impurity elements.

[0091] The specific preparation process was as follows:

[0092] The crucible, stirring rod and slag skimmer were preheated to 200 °C, and after taking them out, they were brushed with a coating, and the coating was a mixed solution of zinc oxide (ZnO) and water glass (Na2O•nSiO2).

[0093] Put pure Mg and pure Zn into a crucible, heat it up to 700 °C and keep it warm. During this period, introduce a mixed gas of CO2 and SF6. After pure Mg and pure Zn are completely melted, heat it up to 730 °C, then add Mg-Sn master alloy and keep it warm for 15 min. After melting, heat it up to 750 °C, then add Mg-Nd master alloy and keep it warm for 15 min. After melting, cool it down to 740 °C, then add Mg-Zr master alloy and stir for 1 min, keep it warm for 15 min. After melting, add 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 evenly into a mold preheated to 200 °C, cool it to room temperature and then demold to take out the magnesium alloy ingot, obtaining a Mg-Zn-Nd-Ca-Sn-Zr magnesium alloy ingot;

[0094] 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;

[0095] 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 300 °C, obtaining round bars with a diameter of 15 mm;

[0096] Cut the round bars after forward extrusion pre-deformation treatment into 10×10×60 mm cuboids for spiral torsion extrusion. The spiral torsion extrusion process is: the extrusion temperature is 300 °C, the torsion angle is 180°, the extrusion rate is 5 mm / min, and the number of extrusion passes is two passes;

[0097] Perform stress aging treatment on the extruded magnesium alloy. 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 2 h, and the cooling method is water cooling at 25 °C, obtaining the final magnesium alloy product.

[0098] Through tests, the average grain size of the magnesium alloy prepared in this Example 2 is 10 μm, the tensile strength is 339 MPa, the elongation is 22%, and according to the ASTM G31-72 immersion standard, the average corrosion rate of the magnesium alloy in 37 ± 0.5 °C simulated body fluid (SBF) is 0.197 mm / year.

[0099] Example 3

[0100] In this Example 3, the raw material composition is as follows: Zn: 1.2%, Nd: 0.7%, Ca: 0.5%, Sn: 0.2%, Zr: 0.4%, and the balance is Mg and unavoidable impurity elements.

[0101] The specific preparation process is as follows:

[0102] Preheat the crucible, stirring rod and slag skimming spoon to 200 °C. After taking them out, brush on the coating, and the coating is a mixed solution of zinc oxide (ZnO) and water glass (Na2O•nSiO2);

[0103] 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 CO2 and SF6. After all the pure Mg and pure Zn are 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, keep warm for 15 min. After melting, add Mg-Ca master alloy. After all the metal is melted, skim off the surface scum, add a refining agent for impurity removal, quickly stir for 1 min, let it stand for 20 min, skim off the impurity removal 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, and obtain a Mg-Zn-Nd-Ca-Sn-Zr magnesium alloy ingot;

[0104] Conduct double-stage solution treatment on the obtained Mg-Zn-Nd-Ca-Sn-Zr magnesium alloy ingot. The conditions for double-stage solution treatment are: 450 °C × 2 h + 500 °C × 0.5 h, and the cooling method is water cooling at 25 °C;

[0105] Cut the solution-treated magnesium alloy into round bars with a diameter of 30 mm, and then conduct 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;

[0106] Cut the round bars after forward extrusion pre-deformation treatment into cuboids of 10×10×60 mm for spiral torsion extrusion. The process of spiral torsion extrusion 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;

[0107] Conduct stress aging treatment on the extruded magnesium alloy. The conditions for stress aging treatment 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.

[0108] Through tests, 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.

[0109] 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 5 is the hydrogen evolution curve diagram of the magnesium alloy obtained in Example 2 of the present invention;Figure 6 It is the average corrosion rate diagram of the magnesium alloys obtained in Embodiments 1-3 of the present invention.

[0110] 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, the tendency of local pitting corrosion on the surface of the magnesium alloy is reduced, the synergistic improvement of the strength, plasticity, and corrosion resistance of the alloy is achieved, the matching of the strength and corrosion resistance of the magnesium alloy is realized to simultaneously meet the strength requirements and corrosion resistance requirements, and 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.

[0111] 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.

[0112] 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 described 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 and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy, characterized in that, Comprising 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; 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 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 a mixed gas of CO2 and SF6 as the protective gas during melting. 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, 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 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; The strength of the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy is greater than 320 MPa, the average corrosion rate is 0.1 - 0.2 mm / year, and the elongation is more than 20%.

2. The high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy according to claim 1, characterized in that, Comprising 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.

3. The high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy according to claim 1, characterized in that, The purity of pure Mg is above 99.99 wt.%, and the purity of pure Zn is above 99.99 wt.%.

4. A preparation method of a high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy as described in any one of claims 1-3, characterized in that, The 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 a mixed gas of CO2 and SF6 as the protective gas during melting. 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; 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 number of extrusion passes 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.

5. The preparation method of the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy according to claim 4, characterized in that, According to the composition and weight percentage of the high-strength, corrosion-resistant and 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 a mixed gas of CO2 and SF6 is used as the protective gas during melting. 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, corrosion-resistant and 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 on the 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 up to 700 °C and keep warm, and introduce a mixed gas of CO2 and SF6 during this period. After pure Mg and pure Zn are all 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 rapidly for 1 min, and let 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.

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

7. The preparation method of the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy according to claim 4, characterized in that, 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, 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. The cooling method for both is water quenching at 25°C; Step 2.2, cut the magnesium alloy ingot after double-stage solution treatment into round bars with a diameter of the specified size; 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 half of the specified size; Step 2.4, cut the round bars after forward extrusion pre-deformation treatment into cuboids with a cross-section of the required size, and place them in a spiral 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 number of extrusion passes is two passes. After each pass of extrusion, water quenching is carried out. After water quenching, it is placed in the spiral torsion extrusion die and heated to the extrusion temperature and held for 10 min before the next pass of extrusion; 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 the finished magnesium alloy product.

8. The preparation method of the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy according to claim 7, characterized in that, The specified size is 30 mm.

9. The preparation method of the high-strength and corrosion-resistant low-alloyed Mg-Zn-Nd-Ca-Sn-Zr alloy according to claim 8, characterized in that, The required size is 10 mm × 10 mm.

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