Low-cost easy-to-process high-plasticity magnesium alloy and preparation method thereof

Abstract

The invention provides a low-cost, easy-to-process and high-plasticity magnesium alloy and a preparation method thereof, and belongs to the field of metal material processing, the magnesium alloy comprises the following components in percentage by mass: 0.35-0.65 wt.% of bismuth, 0.25-0.65 wt.% of manganese, 0.15-0.45 wt.% of zinc, 0.35-0.65 wt.% of cerium, 0.05-0.4 wt.% of calcium and the balance of magnesium and inevitable impurities, and the content of the inevitable impurities is less than or equal to 0.05 wt.%. The total content of alloying elements in the alloy system is less than or equal to 2.8 wt.%, and the alloy system belongs to a low-alloy system. The preparation method of the alloy mainly comprises the steps that the alloy is prepared according to the set mass percent, and the high-plasticity magnesium alloy easy to machine is obtained after casting, extrusion and other technological treatment. The raw material cost is saved, industrial production is facilitated, the prepared alloy presents a fine grain structure with the multi-scale characteristics of micron-submicron-nanometer-atomic cluster, the average grain size is smaller than 3 microns, multiple strengthening mechanisms are innovatively coupled, good matching of the strength and plasticity of the magnesium alloy is achieved, the yield strength is larger than or equal to 230 MPa, and the ductility is larger than or equal to 22%.

Description

Technical Field

[0001] The present invention belongs to the field of metal material processing, and in particular relates to a low-cost, easy-to-process, high-plasticity magnesium alloy and a preparation method thereof. Background Art

[0002] As the lightest metal structural material available, magnesium alloys, with their low density, high specific stiffness, and excellent biocompatibility, offer promising applications in a variety of fields, including automotive, aerospace, electronic communications, and biomedicine. my country boasts abundant magnesium resources, providing a strong resource base for the large-scale development and application of magnesium alloys. With the growing demand for lightweight, high-performance materials, magnesium alloys are attracting increasing attention as a lightweight material. However, due to bottlenecks such as their poor room-temperature ductility and low absolute strength, their practical application remains significantly limited. Compared to traditional steel and aluminum alloys, their widespread use in structural and load-bearing components has yet to be realized. Prior art approaches to improve the mechanical properties of magnesium alloys primarily utilize high-temperature deformation and multi-stage heat treatment processes, such as high-temperature extrusion (extrusion temperature > 450°C), severe plastic deformation (SPD), equal-channel angular extrusion (ECAP), high-pressure torsion (HPT), multidirectional forging (MDF), and high-temperature, multi-pass, high-reduction rolling. However, these processes are complex, energy-intensive, and prone to alloy cracking, making them unsuitable for industrial production. The second method is to increase the content of alloying elements (generally the total content is greater than 6wt.%), so that a large amount of intermetallic compounds are generated in the alloy, and then the strength of the alloy is improved by second phase strengthening and solid solution strengthening. However, the coarse second phase in the alloy is not conducive to the subsequent processing process, and it is easy to generate stress concentration during the plastic deformation process, inducing microcracks, which seriously affects the plasticity of the alloy; in addition, the addition of a large amount of alloying elements leads to a slow extrusion speed of the alloy and low production efficiency, which further increases the cost of the alloy and is not conducive to the engineering promotion and application of magnesium alloys. In summary: the existing process equipment has high requirements, complex process control and high alloy content leads to increased costs and alloy cracking, so it is difficult to achieve large-scale production; in addition, when the alloy shows good plasticity, its strength is usually low, that is, it is difficult to achieve simultaneous improvement of alloy strength and plasticity. In summary, how to reduce the content of alloying elements, simplify the process, increase the extrusion speed, reduce production costs and energy consumption, and reduce alloy cracking to achieve industrial production of high-strength and plastic magnesium alloys is a technical problem that needs to be solved urgently. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention provides a low-cost, easy-to-process, high-plasticity magnesium alloy. The alloy is composed of the following components, calculated by mass percentage: the magnesium alloy components are: bismuth: 0.35-0.65wt.%, manganese: 0.25-0.65wt.%, zinc: 0.15-0.45wt.%, cerium: 0.35-0.65wt.%, calcium: 0.05-0.4wt.%, unavoidable impurity content ≤ 0.05wt.%, and the balance is magnesium. The content of the alloy components is ≤ 2.8wt.%;

[0004] The preparation method of the magnesium alloy comprises the following steps:

[0005] (1) According to the proportion of alloy components, pure magnesium, pure bismuth, pure zinc, magnesium-manganese master alloy, magnesium-cerium master alloy and magnesium-calcium master alloy are selected, and under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 97-99:3-1, pure magnesium is kept at 500-510°C for 60-65 minutes, and then the temperature is raised to 690-700°C for melting, and then pure bismuth, pure zinc, magnesium-manganese master alloy, magnesium-cerium master alloy and magnesium-calcium master alloy preheated at 190-200°C are added, and then the alloy is kept at 690-700°C until it is completely melted and stirred for 1-5 minutes, and then argon is introduced for 1-3 minutes for refining to obtain an alloy melt, and the alloy melt is poured into a mold preheated to 190-200°C by gravity casting, and then cooled to room temperature to obtain a magnesium alloy ingot;

[0006] (2) subjecting the alloy ingot obtained in step (1) to hot extrusion treatment to obtain an extruded magnesium alloy, wherein the hot extrusion treatment comprises: keeping the magnesium alloy ingot and the extrusion die at 290-300° C. for 1-3 hours, and then extruding at 290-300° C. at an extrusion speed of 4-5 m / min and an extrusion ratio of 26-28:1; the extruded magnesium alloy has a multi-scale weak texture fine-grained structure of “micron-submicron-nanometer-atomic clusters”, an average grain size of less than 3 μm, a recrystallization ratio of more than 93%, and a texture strength of 1.9-5.7 mrd;

[0007] (3) The extruded magnesium alloy obtained in step (2) is subjected to a 3-4% tensile pre-deformation treatment and then kept at 150-175° C. for 18-20 hours to obtain a low-cost, easy-to-process, high-plasticity magnesium alloy, wherein the yield strength of the low-cost, easy-to-process, high-plasticity magnesium alloy is ≥230 MPa and the elongation is ≥22%.

[0008] Furthermore, the low-cost, easy-to-process, high-plasticity magnesium alloy is characterized by: in terms of mass percentage, the bismuth: 0.45-0.55wt.%, manganese: 0.4-0.6wt.%, zinc: 0.3-0.4wt.%, cerium: 0.45-0.55wt.%, and calcium: 0.15-0.35wt.%.

[0009] Compared with the prior art, the present invention has the following beneficial effects:

[0010] Compared with the prior art, the present invention achieves the following significant advantages through the coordinated optimization of alloy component interactions, proportions, processing technology and process parameters, and only within the scope of protection of the present invention claims:

[0011] (1) Low-cost alloying elements are used, and the alloy addition content is controlled within 2.8wt.%, forming a low-alloying system, thereby significantly reducing the raw material addition content and cost; at the same time, the process adopted by the present invention only includes melting, pouring, extrusion, pre-deformation and aging processes, and uses low-temperature, short-process processing and low-temperature high-speed extrusion to eliminate high-temperature and long-term solution treatment, simplifying the process, achieving cost reduction and efficiency improvement, and being suitable for industrial production; in addition, the present invention utilizes the interaction between alloying elements and the coordinated regulation with the process to achieve the following excellent effects: generating fine ternary phases and binary phases, promoting the elements to be fully dissolved in the matrix, weakening the texture, and reducing the critical shear stress for the non-basal slip of the alloy, which is beneficial to improving the plasticity of the alloy; by constructing crystallographic defects such as dislocations and twins in the matrix, providing channels for atomic diffusion, significantly promoting the precipitation of nano-second phases, and ultimately improving the plasticity of the alloy while also improving the strength, breaking the technical bottleneck of the existing magnesium alloy plasticity and strength being difficult to improve simultaneously, wherein the yield strength is ≥230MPa and the elongation is ≥22%.

[0012] (2) The internal structure of the alloy obtained by the present invention is uniform, forming a multi-scale fine-grained structure of "micron-submicron-nanometer-atomic clusters", wherein the average grain size of the alloy is less than 3μm, the recrystallization ratio is greater than 93%, the texture strength is ≤5.7mrd, and there is no residual dislocation, which is conducive to subsequent processing deformation. The alloys obtained by the prior art usually contain a large deformation structure with high density residual dislocations and an uneven recrystallization structure, which seriously hinders the subsequent deformation of the alloy, affects the machinability of the alloy, and reduces the plasticity of the alloy; in addition, through comparative experiments, it is found that only by adopting the components, proportions, processes and process parameter ranges of the present invention can the multi-scale fine-grained structure of the alloy with an average grain size of less than 3μm be achieved. The microstructure of the present invention cannot be achieved when the range is greater than or less than the protection scope of the claims of the present invention. This shows that the coordinated regulation of components, processes and process parameters is crucial. The excellent effect obtained by the present invention is not determined by a certain component, process or ratio range or process parameter range, but by the coordinated regulation between multiple factors, ratios, variables and process parameters, which is also an effect not disclosed in the prior art. Therefore, it is concluded that the best technical effect can be achieved only within the protection scope of the claims of the present invention. DETAILED DESCRIPTION

[0013] Example 1

[0014] Mg-0.45Bi-0.4Mn-0.35Zn-0.45Ce-0.15Ca alloy, the alloy is composed of the following components, calculated by mass percentage: Bi: 0.45wt.%, Mn: 0.4wt.%, Zn: 0.35wt.%, Ce: 0.45wt.%, Ca: 0.15wt.%, inevitable impurity content ≤ 0.05wt.%, and the balance is Mg; the preparation method thereof comprises the following steps:

[0015] (1) According to the proportion of alloy components, pure magnesium, pure bismuth, pure zinc, magnesium-manganese master alloy, magnesium-cerium master alloy and magnesium-calcium master alloy are selected, and under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 99:1, pure magnesium is kept at 500°C for 60 minutes, and then the temperature is raised to 700°C for melting, and then pure bismuth, pure zinc, magnesium-manganese master alloy, magnesium-cerium master alloy and magnesium-calcium master alloy that have been preheated and dried at 200°C are added, and then the alloy is kept at 700°C until it is completely melted and stirred for 1-10 minutes, and then argon gas is introduced for 1-20 minutes for refining to obtain an alloy melt, and the alloy melt is poured into a mold preheated to 190°C by gravity casting, and then cooled to room temperature to obtain a magnesium alloy ingot;

[0016] (2) subjecting the alloy ingot obtained in step (1) to hot extrusion treatment to obtain an extruded magnesium alloy 1, wherein the hot extrusion treatment comprises: keeping the magnesium alloy ingot and the extrusion die at 290° C. for 2 hours, and then extruding at 290° C. at an extrusion speed of 4 m / min and an extrusion ratio of 28:1; the extruded magnesium alloy 1 has a multi-scale fine-grained structure of “micron-submicron-nanometer-atomic clusters”, an average grain size of 2.87 μm, a recrystallization ratio of 93.1%, and a texture strength of 5.70 mrd;

[0017] (3) The extruded magnesium alloy 1 obtained in step (2) was subjected to a 3% tensile pre-deformation treatment and then kept at 150°C for 20 hours to obtain a Mg-0.45Bi-0.4Mn-0.35Zn-0.45Ce-0.15Ca alloy having a yield strength of 230 MPa and an elongation of 24.2%.

[0018] Example 2

[0019] Mg-0.55Bi-0.6Mn-0.45Zn-0.55Ce-0.35Ca alloy, the alloy is composed of the following components, calculated by mass percentage: Bi: 0.55wt.%, Mn: 0.6wt.%, Zn: 0.45wt.%, Ce: 0.55wt.%, Ca: 0.35wt.%, inevitable impurity content ≤ 0.05wt.%, and the balance is Mg; the preparation method thereof comprises the following steps:

[0020] (1) According to the proportion of alloy components, pure magnesium, pure bismuth, pure zinc, magnesium-manganese master alloy, magnesium-cerium master alloy and magnesium-calcium master alloy are selected. Under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 97:3, pure magnesium is kept at 510°C for 65 minutes, and then the temperature is raised to 690°C for melting. Subsequently, pure bismuth, pure zinc, magnesium-manganese master alloy, magnesium-cerium master alloy and magnesium-calcium master alloy that have been preheated and dried at 190°C are added. The alloy is kept at 690°C until it is completely melted, stirred for 2 minutes, and then argon gas is introduced for 1 minute for refining to obtain an alloy melt. The alloy melt is poured into a mold preheated to 200°C by gravity casting, and cooled to room temperature to obtain a magnesium alloy ingot;

[0021] (2) subjecting the alloy ingot obtained in step (1) to hot extrusion treatment to obtain an extruded magnesium alloy 2, wherein the hot extrusion treatment comprises: keeping the magnesium alloy ingot and the extrusion die at 300° C. for 1 hour, and then extruding at 300° C. at an extrusion speed of 5 m / min and an extrusion ratio of 26:1; the extruded magnesium alloy 2 has a multi-scale fine-grained structure of “micron-submicron-nanometer-atomic clusters”, an average grain size of 2.75 μm, a recrystallization ratio of 98.2%, and a texture strength of 1.94 mrd;

[0022] (3) The extruded magnesium alloy 2 obtained in step (2) was subjected to a 4% tensile pre-deformation treatment and then kept at 175°C for 18 hours to obtain a Mg-0.45Bi-0.4Mn-0.35Zn-0.45Ce-0.15Ca alloy having a yield strength of 237 MPa and an elongation of 24.2%.

[0023] Comparative Example 1

[0024] Publicly published journal article titled "Deformation mechanism orientation evolution and mechanical properties of annealed cross-rolled Mg-Zn-Zr-Y-Gd sheet during tension" (author: Xia Lin et al., published in Journal of Magnesium andAlloys, Journal Volume: Volume 11, Paper Publication Date: July 2023), mentioned in the experiment that the selected forged Mg-Zn-Zr-Y-Gd alloy material is calculated by mass percentage: Zn: 6.75wt.%, Zr: 0.57wt.%, Y: 0.4wt.%, Gd: 0.18wt.%, and the balance is Mg. The preparation method of the alloy is as follows: the forged Mg-Zn-Zr-Y-Gd alloy is preheated at 425℃ for 30min, and then cross-rolled for 12 times at the same temperature with a total reduction of 90%. The passes are kept at 425℃ for 15min. After each rolling pass, the sample is rotated 90° before the next rolling pass. After rolling, the alloy was annealed at 400°C for 1 hour and then water quenched to room temperature. The resulting Mg-Zn-Zr-Y-Gd alloy had a yield strength of 211 MPa, an elongation of 14.7%, and a grain size of 7 μm. Comparative Example 1 undergoes multiple passes of high-temperature rolling after forging, requiring high temperatures and rotary rolling during rolling, and a high-temperature annealing process after rolling. The present invention does not employ the multiple passes of high reduction and rotary rolling used in Comparative Example 1. Furthermore, the present invention does not perform high-temperature, multi-pass deformation and heat treatment processes after extrusion, reducing energy consumption and facilitating industrial production. Furthermore, the alloying element addition in Comparative Example 1 is 7.9 wt.%, which is higher than the maximum alloying element addition in the present invention (2.8 wt.%). Furthermore, the rare earth elements Gd and Y used therein are expensive, while the rare earth element Ce added in the present invention is much less expensive than Gd and Y. Furthermore, the total rare earth content in Comparative Example 1 is higher than that in the present invention. The results show that the grain size of the alloy in comparative example 1 is 7 μm, while the maximum grain size of the alloy in the present invention is 2.87 μm. The strength and plasticity of the alloy obtained in the present invention are higher than those of the alloy obtained in comparative example 1.

[0025] Comparative Example 2

[0026] Mg-0.9Bi-0.7Mn-0.6Zn-0.7Ce-0.8Ca alloy, the alloy is composed of the following components, calculated by mass percentage: Bi: 0.9wt.%, Mn: 0.7wt.%, Zn: 0.6wt.%, Ce: 0.7wt.%, Ca: 0.8wt.%, inevitable impurity content ≤ 0.05wt.%, and the balance is Mg; the preparation method thereof comprises the following steps:

[0027] (1) According to the proportion of alloy components, pure magnesium, pure bismuth, pure zinc, magnesium-manganese master alloy, magnesium-cerium master alloy and magnesium-calcium master alloy are selected. Under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 95:5, pure magnesium is kept at 530°C for 70 minutes, and then the temperature is raised to 720°C for melting. Subsequently, pure bismuth, pure zinc, magnesium-manganese master alloy, magnesium-cerium master alloy and magnesium-calcium master alloy that have been preheated and dried at 210°C are added. The alloy is kept at 690°C until it is completely melted, stirred for 5 minutes, and then argon is introduced for 4 minutes for refining to obtain an alloy melt. The alloy melt is poured into a mold preheated at 210°C by gravity casting, and cooled to room temperature to obtain a magnesium alloy ingot.

[0028] (2) subjecting the alloy ingot obtained in step (1) to hot extrusion treatment to obtain an extruded magnesium alloy 3, wherein the hot extrusion treatment comprises: keeping the magnesium alloy ingot and the extrusion die at 310° C. for 3 hours, and then extruding at 310° C. at an extrusion speed of 2 m / min and an extrusion ratio of 25:1; the extruded magnesium alloy 3 has a relatively coarse microstructure, an average grain size of 4.8 μm, a recrystallization ratio of 84.7%, and a texture strength of 8.10 mrd;

[0029] (3) The extruded magnesium alloy 3 obtained in step (2) was subjected to a 5% tensile pre-deformation treatment and then kept at 200°C for 22 hours to obtain a Mg-0.9Bi-0.7Mn-0.6Zn-0.7Ce-0.8Ca alloy having a yield strength of 217 MPa and an elongation of 18.7%. Although the component selection and process flow of Comparative Example 2 are similar to those of the present invention, its specific alloy ratio and process parameters do not fall within the scope of protection of the claims of the present invention. More importantly, the present invention has obvious differences and advantages over Comparative Example 2. First, the total content of alloying elements added in the present invention is ≤2.8wt.%, which is significantly lower than the alloying element content (3.7wt.%) in Comparative Example 2. The lower alloying element content can significantly reduce the cost of raw materials; in addition, the extrusion speed of the low-alloyed magnesium alloy developed by the present invention reaches 4-5m / min, which is more than twice the extrusion speed of the comparative example, significantly improving production efficiency. The results show that the performance of the alloy obtained by the present invention is significantly better than that of the alloy in Comparative Example 2. Specifically, the maximum grain size of the alloy obtained by the present invention is 2.87 μm, significantly smaller than the grain size of the alloy prepared in Comparative Example 2 (4.8 μm), indicating that the present invention has a superior microstructure refinement effect. Furthermore, the texture strength of the alloy obtained by the present invention is significantly lower than that of Comparative Example 2, while the degree of recrystallization is higher than that of Comparative Example 2. Furthermore, the minimum yield strength and plasticity of the alloy obtained by the present invention are both higher than those of Comparative Example 2, further demonstrating the effectiveness of the present invention in achieving excellent comprehensive mechanical properties.

[0030] This invention reduces the total amount of alloying additives and utilizes low-cost alloying elements to construct a low-cost, low-alloyed magnesium alloy system, significantly reducing raw material costs. This alloy system exhibits excellent process adaptability, meeting process requirements such as low-temperature, high-speed extrusion, and is suitable for large-scale industrial applications. Furthermore, the invention utilizes a thermal processing route that combines low-temperature extrusion with low-temperature aging, avoiding the reliance on high-temperature deformation and prolonged, high-temperature heat treatment required in existing technologies. This significantly reduces energy consumption and equipment requirements, simplifies the preparation process, and improves production efficiency. What is particularly important is that compared with the complex organizational control methods such as multiple passes, large reductions, rotary rolling, high-temperature homogenization treatment and large plastic deformation processes in the prior art, the present invention can obtain a "micron-submicron-nano-atomic cluster" multi-scale fine-grained magnesium alloy with a grain size of <3μm, a texture strength of ≤5.7mrd, and a recrystallization ratio of >93% by simply optimizing the alloy design and simple process control; subsequently, defects such as dislocations and twins are introduced to promote the precipitation of the second phase, and ultimately a low-cost, easy-to-process, high-plasticity magnesium alloy is obtained with an alloy elongation of ≥22% and a strength of ≥230MPa. Moreover, within the scope of protection of the claims of the present invention, and on the premise of simplifying the preparation process, the synergistic improvement of the strength and plasticity of the magnesium alloy is simultaneously achieved, solving the key technical bottleneck in the prior art where it is difficult to take both strength and plasticity into account.

Claims

1. A low-cost, easily machinable, high-plasticity magnesium alloy, characterized by: The alloy is composed of the following components in percentage by mass: the magnesium alloy components are: bismuth: 0.35-0.65wt.%, manganese: 0.25-0.65wt.%, zinc: 0.15-0.45wt.%, cerium: 0.35-0.65wt.%, calcium: 0.05-0.4wt.%, unavoidable impurities content ≤ 0.05wt.%, the balance is magnesium, and the alloy component content is ≤ 2.8wt.%; The preparation method of the magnesium alloy comprises the following steps: (1) According to the proportion of alloy components, pure magnesium, pure bismuth, pure zinc, magnesium-manganese master alloy, magnesium-cerium master alloy and magnesium-calcium master alloy are selected, and under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 97-99:3-1, pure magnesium is kept at 500-510°C for 60-65 minutes, and then the temperature is raised to 690-700°C for melting, and then pure bismuth, pure zinc, magnesium-manganese master alloy, magnesium-cerium master alloy and magnesium-calcium master alloy preheated at 190-200°C are added, and then the alloy is kept at 690-700°C until it is completely melted and stirred for 1-5 minutes, and then argon is introduced for 1-3 minutes for refining to obtain an alloy melt, and the alloy melt is poured into a mold preheated to 190-200°C by gravity casting, and then cooled to room temperature to obtain a magnesium alloy ingot; (2) subjecting the magnesium alloy ingot obtained in step (1) to hot extrusion treatment to obtain an extruded magnesium alloy, wherein the hot extrusion treatment comprises: keeping the magnesium alloy ingot and the extrusion die at 290-300° C. for 1-3 hours, and then extruding at 290-300° C. at an extrusion speed of 4-5 m / min and an extrusion ratio of 26-28:1; the extruded magnesium alloy has a multi-scale weak texture fine-grained structure of “micron-submicron-nanometer-atomic clusters”, an average grain size of less than 3 μm, a recrystallization ratio of more than 93%, and a texture strength of 1.9-5.7 mrd; (3) The extruded magnesium alloy obtained in step (2) is subjected to a 3-4% tensile pre-deformation treatment and then kept at 150-175° C. for 18-20 hours to obtain a low-cost, easy-to-process, high-plasticity magnesium alloy, wherein the yield strength of the low-cost, easy-to-process, high-plasticity magnesium alloy is ≥230 MPa and the elongation is ≥22%.

2. The low-cost, easy-to-process, high-plasticity magnesium alloy according to claim 1, characterized in that: Calculated by mass percentage, the bismuth is 0.45-0.55 wt.%, manganese is 0.4-0.6 wt.%, zinc is 0.3-0.4 wt.%, cerium is 0.45-0.55 wt.%, and calcium is 0.15-0.35 wt.%.