Magnesium alloy with high strength, plasticity, corrosion resistance, double-peak structure and low alloy content and preparation method

Abstract

The invention belongs to the technical field of metal materials, and provides a high-strength plastic corrosion-resistant bimodal structure low-alloy-content magnesium alloy and a preparation method thereof. The magnesium alloy comprises the following components in percentage by mass: 2.2-2.5% of zinc, 0.1-0.2% of cerium, less than or equal to 0.02% of inevitable impurities and the balance of magnesium. The high-strength and high-plasticity corrosion-resistant magnesium alloy with the double-peak structure and the low alloy content is obtained through smelting, hot extrusion and 2-8-pass temperature-controlled equal-channel angular pressing (hereinafter referred to as ECAP). The magnesium alloy obtained through the method has high strength and plasticity and corrosion resistance, the corrosion rate of the magnesium alloy is smaller than or equal to 8 mm / y, the tensile strength is larger than or equal to 304 MPa, and the ductility is larger than or equal to 19%.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal materials, and in particular relates to a high-strength, plastic, and corrosion-resistant double-peak structure low-alloy content magnesium alloy and a preparation method thereof. Background Art

[0002] Magnesium alloys have shown important application potential in aerospace, new energy vehicles, biomedicine and other fields due to their high specific strength, lightweight and good biocompatibility. However, magnesium alloys still face two key bottlenecks in practical applications: First, magnesium alloys have a hexagonal close-packed (hcp) structure with few independent slip systems, making it difficult to activate non-basal slip at room temperature and resulting in poor plastic deformation ability. At the same time, magnesium alloys have low absolute strength compared to commonly used alloys such as aluminum alloys and titanium alloys. Traditional strengthening mechanisms usually increase strength while reducing plasticity, making it difficult for magnesium alloys to achieve both strength and plasticity. Second, since most of the strengthening phases in magnesium alloys have a higher corrosion potential than the magnesium matrix, the magnesium matrix usually acts as an anode area and suffers from severe microgalvanic corrosion. In addition, the product film generated on the surface of the magnesium alloy is loose and porous, and has poor protection for the matrix.

[0003] Compared with high-alloy magnesium alloys, low-alloy magnesium alloys have the advantages of low cost and easy deformation. However, due to the lack of effective strengthening mechanism and difficulty in forming a strong protective passivation film, the problems of low strength, poor plasticity and poor corrosion resistance are particularly prominent, making it difficult to meet the needs of industrial production. Since the paths leading to the difficulty in simultaneously improving the strength and plasticity of magnesium alloys or poor corrosion resistance are different, the existing methods for improving the strength, plasticity and corrosion resistance of magnesium alloys are also different, including: (1) The technical path to solve the difficulty in simultaneously improving the strength and plasticity of alloys mainly includes complex processes such as large-scale reduction, multi-pass high-temperature rolling (prone to cracking), and long-term high-temperature aging treatment to introduce precipitation phases; (2) The technical path to improve the corrosion resistance of alloys includes adding a large amount of precious alloy elements to change the second phase composition, thereby reducing micro-galvanic corrosion and forming a dense passivation film layer to improve corrosion resistance. However, adding a large amount of precious metal elements will lead to increased production costs. Large-scale reduction, multi-pass high-temperature rolling (prone to cracking) and high-temperature and long-term heat treatment will lead to complex processes, which are not conducive to industrial production. Since the alloy composition, process, process parameters and microstructure have different mechanisms of action on the strength, plasticity and corrosion resistance of the alloy, it is still unknown which factor plays a major role in improving the comprehensive performance of the alloy. Therefore, how to simultaneously improve the strength, plasticity and corrosion resistance of magnesium alloys and achieve stable industrial production while reducing the amount of element addition and simplifying the process is a technical problem that needs to be solved urgently. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a high-strength, high-ductility and corrosion-resistant magnesium alloy with a bimodal structure and low alloy content. By mass percentage, the components of the magnesium alloy include zinc: 2.2 - 2.5%, cerium: 0.1 - 0.2%, inevitable impurities ≤ 0.02%, and the balance is magnesium. Its preparation method includes the following steps:

[0005] (1) By mass percentage, weigh pure magnesium, pure zinc and Mg-25Ce master alloy. Under the protection of a mixed gas of SF6 and CO2 with a volume ratio of 1 - 10:90 - 99, heat the pure magnesium to melt it into a melt at 640 - 660°C; then add the preheated pure zinc and Mg-25Ce master alloy at 450 - 470°C, keep it warm for 20 - 30 min, then stir, blow air and skim the slag, and after standing and keeping warm for 25 - 35 min, pour it into an iron mold to obtain a magnesium alloy ingot;

[0006] (2) Homogenize and hot-extrude the magnesium alloy ingot obtained in step (1) to obtain a magnesium alloy extrusion rod. The homogenization treatment is as follows: keep it warm at 300 - 325°C for 6.5 - 7.5 h, keep it warm at 385 - 400°C for 2.2 - 2.8 h, and then keep it warm at 415 - 430°C for 1.9 - 2.5 h; the hot extrusion treatment is as follows: the extrusion temperature is 345 - 360°C, the extrusion ratio is 15:1 - 17:1, and the extrusion speed is 4 - 10 min / m;

[0007] (3) Perform 2 - 8 passes of temperature-controlled ECAP treatment on the magnesium alloy extrusion rod obtained in step (2) to obtain a high-strength, high-ductility and corrosion-resistant magnesium alloy with a bimodal structure and low alloy content. The 2 - 8 passes of temperature-controlled ECAP treatment are as follows: the temperature, time and extrusion speed of each pass of ECAP treatment are different. Starting from the second pass of ECAP treatment, the extrusion plate needs to be rotated clockwise by 90° before each pass of ECAP treatment for the next pass of ECAP treatment. Each pass of ECAP treatment is as follows: keep the magnesium alloy extrusion rod warm at 150 - 240°C for 20 - 40 min, and then perform ECAP treatment at an extrusion speed of 4 - 8 min / m;

[0008] For the high-strength, high-ductility and corrosion-resistant magnesium alloy with a bimodal structure and low alloy content, the corrosion rate ≤ 8 mm / y, the tensile strength ≥ 304 MPa, and the elongation ≥ 19%;

[0009] The internal structure of the high-strength, high-ductility and corrosion-resistant magnesium alloy with a bimodal structure and low alloy content is a bimodal structure, which is composed of deformed coarse grains with a strong basal texture and an average grain size of ~9 - 12 μm and recrystallized fine grains with a weak texture and an average grain size of ~1 - 2.5 μm, where the volume fraction of the recrystallized fine grains with a weak texture accounts for ~55 - 70%.

[0010] Furthermore, the extrusion speed in step (2) is 5 - 6 min / m.

[0011] Furthermore, after subjecting the magnesium alloy extrusion rod to 4 - 6 passes of temperature - controlled ECAP treatment in step (3), a high - strength, high - plasticity, corrosion - resistant dual - peak - structure magnesium alloy with low alloy content is obtained.

[0012] Beneficial effects

[0013] Compared with the prior art, through the synergistic regulation of the interaction, ratio, process, and process parameters among components, the present invention achieves the following excellent effects:

[0014] Compared with the prior art, only two alloying elements are added in the magnesium alloy system obtained by the present invention, and the total alloy addition content is controlled within 2.7%. While reducing the types and content of alloy additions, an alloy system with low addition types and low content is formed. The present invention omits the long-time high-temperature heat treatment and multi-pass high-temperature rolling with large reduction in the prior art and improves the extrusion speed, breaking through the problems faced by the prior art. The prior art mainly realizes the strength and plasticity and corrosion resistance of the alloy by adjusting the following structures respectively: First, in terms of improving the strength and plasticity of the alloy: mainly by introducing precipitation phases, enhancing the activity of non-basal slip and restricting dynamic recrystallization, etc.; Second, in terms of improving the corrosion resistance of the alloy: improving the corrosion resistance of the alloy by changing the second-phase composition. From the above analysis, it can be seen that it is difficult to solve all the strength and plasticity and corrosion resistance of the magnesium alloy through one path. Therefore, the paths to improve the strength and plasticity and corrosion resistance of the alloy are different. Even when the strength and plasticity are improved, it is difficult to improve the corrosion resistance, and vice versa. In addition, the above problems are more difficult to solve for magnesium alloys with low alloy content, especially for solving the three problems simultaneously. The present invention breaks through the bottleneck of the prior art and simultaneously solves three problems such as the simultaneous improvement of the strength and plasticity and corrosion resistance faced by magnesium alloys with low alloy content, specifically including: The present invention simultaneously solves three problems faced by magnesium alloys by coordinately regulating factors such as the size and proportion of coarse grains and fine grains inside the alloy. Especially for magnesium alloys with low alloy content, the purpose of cost reduction and efficiency increase is achieved. Specifically: The internal microstructure of the low-alloy-content magnesium alloy obtained by the present invention is a bimodal structure, where the bimodal structure is composed of deformed coarse grains with strong basal texture and an average grain size of ~9 - 12 μm and recrystallized fine grains with weak texture and an average grain size of ~1 - 2.5 μm. Among them, the recrystallized fine grains with weak texture effectively overcome the difficulty of achieving a high proportion of fine-grained structure in low-alloy-content magnesium alloys due to the lack of second-phase pinning. The volume fraction of the recrystallized fine grains with weak texture obtained by the present invention accounts for ~55 - 70%, achieving a high proportion of fine-grained structure, and the above two types of grains do not aggregate but form a uniform distribution; the microstructure obtained by the present invention can achieve strong grain boundary strengthening, high-energy high-density grain boundaries, and is more likely to form nucleation sites for oxidation products (which will help increase the density and protection of the product film), the deformed coarse grains with strong basal texture form a discontinuous embedded distribution in the fine-grained area (which is beneficial for storing dislocations, forming a discontinuous substructure, and hindering the continuous corrosion process along the grain boundary), the unique staggered arrangement of fine grains and coarse grains makes the product more dense, while slowing down and dissipating the stress concentration on the corrosion product (enhancing the protection of the film), significantly enhancing the protection ability of the film, and finally effectively coordinating plastic deformation, improving the work-hardening ability of the alloy, forming hetero-deformation-induced strengthening, and accumulating more dislocations in the coarse grains, simultaneously improving the strength and plasticity and corrosion resistance of the alloy.In addition, during the research process of the present invention, it was found that if the sizes and proportions of coarse grains and fine grains are not within the scope protected by the claims of the present invention, the simultaneous improvement of the properties such as high strength and plasticity and corrosion resistance of the magnesium alloy cannot be achieved. Therefore, the composition, size and proportion of coarse grains and fine grains in the bimodal structure are crucial for the simultaneous improvement of the strength, plasticity and corrosion resistance of the alloy. The corrosion rate of the obtained alloy is ≤8 mm / y, the tensile strength is ≥304 MPa, and the elongation is ≥19%. The above properties are significantly superior to those of existing alloys with high alloy content or high precious metal addition content, and alloys subjected to multi-pass rolling with large reduction and high-temperature heat treatment. Therefore, parameters such as the bimodal structure composition, structure, size and proportion of the alloy obtained by the present invention are crucial for the improvement of the comprehensive properties of the alloy. The synergistic regulation of the above variables finally realizes the simultaneous improvement of the comprehensive properties of the alloy. Detailed implementation manners

[0015] The present invention will be described in detail below in conjunction with specific embodiments. The corrosion resistance tests of all alloys were carried out in a NaCl solution (by mass percentage, the solution concentration is 3.5%).

[0016] Example 1

[0017] Mg-2.2Zn-0.1Ce alloy (by mass percentage, the alloy components include zinc: 2.2 wt%, cerium: 0.1 wt%, unavoidable impurities ≤0.02%, and the balance is magnesium), and its preparation method is as follows:

[0018] (1) According to the above alloy percentages, pure magnesium, pure zinc and Mg-25Ce master alloy were weighed and polished. Under the protection of a mixed gas of SF6 and CO2 with a volume ratio of 1:99, pure magnesium was heated and melted into a melt at 650 °C; then preheated pure zinc and Mg-25Ce master alloy at 460 °C were added. After holding for 30 min, stirring, gas blowing and slag removal were carried out, and after standing and holding for 25 min, it was cast into a cast iron mold to obtain a magnesium alloy ingot;

[0019] (2) The magnesium alloy ingot obtained in step (1) was subjected to homogenization treatment. The homogenization treatment was: holding at 300 °C for 7 h, then holding at 390 °C for 2 h, and finally holding at 420 °C for 2 h to obtain a homogenized magnesium alloy ingot. The homogenized magnesium alloy ingot was subjected to hot extrusion. The extrusion temperature was 350 °C, the extrusion ratio was 16:1, and the extrusion speed was 5 min / m to obtain a magnesium alloy extrusion rod;

[0020] (3) The magnesium alloy extrusion bar obtained in step (2) is subjected to ECAP treatment. The ECAP treatment is as follows: The extrusion bar obtained in step (2) is kept at a temperature of 200 °C for 25 min, and then undergoes one pass of ECAP processing to obtain a one-pass magnesium alloy extrusion bar, where the extrusion rate is 4 min / m. Then, the one-pass extrusion bar is kept at a temperature of 190 °C for 30 min, rotated clockwise by 90°, and then undergoes a second pass of ECAP processing to obtain a Mg-2.2Zn-0.1Ce alloy, and the ECAP extrusion rate is 6 min / m. The Mg-2.2Zn-0.1Ce alloy has a bimodal microstructure, with a strong basal texture deformed coarse grain size of ~11.2 μm, a weak texture recrystallized fine grain size of ~2.4 μm, a fine grain proportion of ~56%, a corrosion rate of 7.9 mm / y (hydrogen evolution rate), a tensile strength of 304 MPa, and an elongation of 19%.

[0021] Example 2

[0022] Mg-2.3Zn-0.15Ce alloy (by mass percentage, the alloy components include zinc: 2.3 wt%, cerium: 0.15 wt%, unavoidable impurities ≤ 0.02%, and the balance is magnesium), and its preparation method is as follows:

[0023] (1) According to the above alloy percentages, pure magnesium, pure zinc, and Mg-25Ce master alloy are weighed and polished. Under the protection of a mixed gas of SF6 and CO2 with a volume ratio of 1:99, pure magnesium is heated to melt into a melt at 660 °C; then, preheated pure zinc and Mg-25Ce master alloy at 450 °C are added. After keeping warm for 25 min, stirring, gas blowing, and slag skimming are carried out, and after standing and keeping warm for 27 min, it is cast into a cast iron mold to obtain a magnesium alloy ingot;

[0024] (2) The magnesium alloy ingot obtained in step (1) is subjected to homogenization treatment. The homogenization treatment is as follows: It is kept at 320 °C for 7 h, then at 400 °C for 2 h, and finally at 430 °C for 2.5 h to obtain a homogenized magnesium alloy ingot. The homogenized magnesium alloy ingot is subjected to hot extrusion. The extrusion temperature is 345 °C, the extrusion ratio is 17:1, and the extrusion speed is 5.4 min / m to obtain a magnesium alloy extrusion bar;

[0025] (3) Perform ECAP treatment on the magnesium alloy extrusion rod obtained in step (2). The ECAP treatment is as follows: Keep the extrusion rod obtained in step (2) at a temperature of 215 °C for 25 min, and then perform one-pass ECAP processing to obtain a one-pass magnesium alloy extrusion rod. The extrusion rate is 4.5 min / m. Subsequently, keep the one-pass magnesium alloy extrusion rod at a temperature of 200 °C for 30 min, rotate it clockwise by 90°, and then perform ECAP processing to obtain a two-pass magnesium alloy extrusion rod. The extrusion rate is 5.6 min / m. Then, keep the two-pass magnesium alloy extrusion rod at a temperature of 185 °C for 30 min, rotate it clockwise by 90°, and then perform ECAP processing to obtain a three-pass magnesium alloy extrusion rod. The extrusion rate is 5.2 min / m. Then, keep the three-pass magnesium alloy extrusion rod at a temperature of 185 °C for 30 min, rotate it clockwise by 90°, and then perform ECAP processing to obtain a Mg-2.3Zn-0.15Ce alloy. The ECAP extrusion rate is 5 min / m. The Mg-2.3Zn-0.15Ce alloy has a bimodal microstructure, with the deformed coarse grain size of the strong basal texture being ~10.8 μm, the recrystallized fine grain size of the weak texture being ~2.3 μm, the proportion of fine grains being ~60%, the corrosion rate being 8.0 mm / y (hydrogen evolution rate), the tensile strength being 305 MPa, and the elongation being 23%.

[0026] Example 3

[0027] Mg-2.4Zn-0.2Ce alloy (by mass percentage, the alloy components include zinc: 2.4 wt%, cerium: 0.2 wt%, unavoidable impurities ≤ 0.02%, and the balance is magnesium), and its preparation method is as follows:

[0028] (1) Weigh pure magnesium, pure zinc, and Mg-25Ce master alloy according to the above alloy percentages and polish them. Under the protection of a mixed gas of SF6 and CO2 with a volume ratio of 1:99, heat the pure magnesium to melt it into a melt at 655 °C; then add the pure zinc and Mg-25Ce master alloy preheated at 465 °C, keep it warm for 20 min, then stir, blow air, and skim the slag, and finally pour it into a cast iron mold after standing and keeping warm for 30 min to obtain a magnesium alloy ingot.

[0029] (2) Perform homogenization treatment on the magnesium alloy ingot obtained in step (1). The homogenization treatment is as follows: Keep it at 310 °C for 7.5 h, then at 395 °C for 2.2 h, and finally at 425 °C for 2.3 h to obtain a homogenized magnesium alloy ingot. The homogenized magnesium alloy ingot is subjected to hot extrusion at an extrusion temperature of 360 °C, an extrusion ratio of 15:1, and an extrusion speed of 4.8 min / m to obtain a magnesium alloy extrusion rod;

[0030] (3) Perform ECAP treatment on the magnesium alloy extrusion rod obtained in step (2). The ECAP treatment is as follows: Insulate the extrusion rod obtained in step (2) at a temperature of 210 °C for 27 min, and then perform one-pass ECAP processing to obtain a one-pass magnesium alloy extrusion rod. The extrusion rate is 4.2 min / m. Subsequently, insulate the one-pass magnesium alloy extrusion rod at a temperature of 215 °C for 32 min, rotate it 90° clockwise and then perform ECAP processing to obtain a two-pass magnesium alloy extrusion rod. The extrusion rate is 4.6 min / m. Then, insulate the two-pass magnesium alloy extrusion rod at a temperature of 175 °C for 40 min, rotate it 90° clockwise and then perform ECAP processing to obtain a three-pass magnesium alloy extrusion rod. The extrusion rate is 5.4 min / m. Then, insulate the three-pass magnesium alloy extrusion rod at a temperature of 175 °C for 45 min, rotate it 90° clockwise and then perform ECAP processing to obtain a Mg-2.4Zn-0.2Ce alloy. The ECAP extrusion rate is 4.5 min / m. The Mg-2.4Zn-0.2Ce alloy has a bimodal microstructure, with the deformed coarse grain size of the strong basal texture being ~10.5 μm, the recrystallized fine grain size of the weak texture being ~2.2 μm, the proportion of fine grains being ~64%, the corrosion rate being 6.6 mm / y (hydrogen evolution rate), the tensile strength being 308 MPa, and the elongation being 21%.

[0031] Example 4

[0032] Mg-2.5Zn-0.2Ce alloy (by mass percentage, the alloy components include zinc: 2.5 wt%, cerium: 0.2 wt%, unavoidable impurities ≤ 0.02%, and the balance is magnesium), and its preparation method is as follows:

[0033] (1) Weigh pure magnesium, pure zinc, and Mg-25Ce master alloy according to the above alloy percentages and polish them. Under the protection of a mixed gas of SF6 and CO2 with a volume ratio of 1:99, heat pure magnesium to melt it into a melt at 640 °C; then add preheated pure zinc and Mg-25Ce master alloy at 470 °C, keep it warm for 27 min, then stir, blow air, and skim the slag, and pour it into a cast iron mold after standing and keeping warm for 35 min to obtain a magnesium alloy ingot;

[0034] (2) Perform homogenization treatment on the magnesium alloy ingot obtained in step (1). The homogenization treatment is as follows: Keep it warm at 325 °C for 6.5 h, then at 385 °C for 2.8 h, and finally at 415 °C for 1.9 h to obtain a homogenized magnesium alloy ingot. The homogenized magnesium alloy ingot is subjected to hot extrusion. The extrusion temperature is 355 °C, the extrusion ratio is 16:1, and the extrusion speed is 5.2 min / m to obtain a magnesium alloy extrusion rod;

[0035] (3) The magnesium alloy extrusion bar obtained in step (2) is subjected to ECAP treatment. The ECAP treatment is as follows: the extrusion bar obtained in step (2) is kept at a temperature of 225 °C for 23 min, and then subjected to one pass of ECAP processing to obtain a one-pass magnesium alloy extrusion bar. The extrusion rate is 6 min / m. Subsequently, the one-pass magnesium alloy extrusion bar is kept at a temperature of 205 °C for 40 min, rotated clockwise by 90°, and then subjected to ECAP processing to obtain a two-pass magnesium alloy extrusion bar. The extrusion rate is 6.1 min / m. Then, the two-pass magnesium alloy extrusion bar is kept at a temperature of 150 °C for 45 min, rotated clockwise by 90°, and then subjected to ECAP processing to obtain a three-pass magnesium alloy extrusion bar. The extrusion rate is 5.8 min / m. Then, the three-pass magnesium alloy extrusion bar is kept at a temperature of 150 °C for 40 min, rotated clockwise by 90°, and then subjected to ECAP processing to obtain a Mg-2.5Zn-0.2Ce alloy. The ECAP extrusion rate is 4 min / m. The Mg-2.5Zn-0.2Ce alloy has a bimodal microstructure. The deformed coarse grain size of the strong basal texture is about 9.8 μm, the recrystallized fine grain size of the weak texture is about 1.9 μm, the proportion of fine grains is about 70%, the corrosion rate is 4.9 mm / y (hydrogen evolution rate), the tensile strength is 314 MPa, and the elongation is 19%.

[0036] Comparative Example 1

[0037] Literature Name: Static Recrystallization and Mechanical Properties of 823K Asymmetrical Rolling Mg-4Y-3RE Magnesium Alloy Sheets, Materials Science and Engineering A, 538 (2012) 281–287, WOS: 000301901200037, Authors: Xinsheng Huang, Kazutaka Suzuki, Yasumasa Chino, etc. Example on Page 2: The Mg-4.2Y-3.4Nd magnesium alloy ingot is extruded into a 5-mm-thick sheet at an extrusion ratio of 6:1 at 450 °C, and then homogenized in flowing argon at 500 °C for 24 h, and then water quenched to obtain a Mg-4.2Y-3.4Nd magnesium alloy extrusion sheet. The extrusion sheet is kept at 550 °C and then subjected to asymmetrical rolling. The roll speed ratio is 1.36, and the deformation amount is about 80%. Subsequently, it is annealed at 450 °C for 1 h to finally obtain a Mg-4.2Y-3.4Nd magnesium alloy rolled sheet. The structure obtained for this alloy is a single grain structure, where the grain size is about 18 μm, the tensile strength is 304 MPa, and the elongation is 12.9% (the best performance in Figure 3 on Page 4).

[0038] Comparative Example 2

[0039] Document Name: High Corrosion Resistance and Weak Corrosion Anisotropy of Cross-Rolled Icosahedral Phase Reinforced Mg-8Li-6Zn-1Y Alloy, Corrosion Science, 245(2025)112666, WOS: 001412560200001, Authors: Dongliang Wang, Daokui Xu, Baojie Wang, etc. Example on Page 2: The as-cast Mg-8Li-6Zn-1Y magnesium alloy was subjected to four passes of cross-rolling at 250 °C, and the total thickness reduction rate was 80%, and finally a rolled plate of Mg-8Li-6Zn-1Y magnesium alloy was obtained. The literature refined the second phase and promoted the uniform distribution of the second phase through multi-pass cross-rolling. The obtained grain structure was a single grain structure with an average grain size of ~7 μm. The best corrosion rate of the Mg-8Li-6Zn-1Y magnesium alloy was 9.0 mm / y (the best performance in Figure 6 on Page 6).

[0040] When comparing with Comparative Examples 1-2 and the prior art, although the types and contents of alloying additions in the alloy of the present invention are lower than those of the comparative examples and the prior art, the post-deformation heat treatment process is also omitted. However, the strength, plasticity and corrosion resistance of the alloy are better than those of the alloys obtained in Comparative Examples 1 and 2. In addition, compared with Comparative Examples 1-2, the alloy structures obtained in Comparative Examples 1-2 are both single structures, that is, single grain structures. Compared with the present invention, the strength and plasticity of Comparative Example 1 are lower than those obtained in the present invention. It can be seen from this that Comparative Example 1 fails to achieve the simultaneous improvement of the strength and plasticity of the alloy; only the corrosion resistance is mentioned in Comparative Example 2, and the strength and plasticity are unknown. It can be seen from Comparative Examples 1 and 2 that it is difficult for the prior art to simultaneously achieve the improvement of strength and plasticity or strength, plasticity and corrosion resistance. At the same time, compared with the prior art, the present invention also omits multi-pass rolling with large reduction at high temperature, avoiding alloy cracking.

[0041] The alloy obtained in the present invention has a bimodal structure, which is composed of strongly textured deformed coarse grains with an average grain size of ~9 - 12 μm and weakly textured recrystallized fine grains with an average grain size of ~1 - 2.5 μm. The single grain structure sizes obtained in Comparative Examples 1 - 2 are not within the ranges of the coarse and fine grain sizes obtained in the present invention. In addition, the volume fraction of the weakly textured recrystallized fine grains obtained in the present invention is the highest, being ~55 - 70%, and such high volume fraction ratios have not been reported in the prior art. Moreover, the alloy obtained in the present invention can simultaneously maintain high corrosion resistance, strength, and plasticity, breaking through the technical bottleneck in the prior art that it is difficult to simultaneously improve strong plasticity and corrosion resistance. Therefore, compared with the prior art, the present invention saves the raw material addition cost and simplifies the process, while simultaneously improving the strength, plasticity, and corrosion resistance of the alloy. In addition, the components and process parameters of each embodiment of the present invention are different, and the finally obtained strength, plasticity, and corrosion resistance are also different. Thus, it can be said that the improvement of the comprehensive properties such as corrosion resistance and strong plasticity of the alloy obtained in the present invention is not determined by a certain component, ratio, process, or process parameter, but is achieved by the synergistic regulation of components, component ratios, processes, and process parameters. And only within the scope of protection of the claims of the present invention can the most excellent technical effects be achieved.

Claims

1. A high-strength, plastic-resistant and corrosion-resistant magnesium alloy with a bimodal structure and low alloy content, characterized in that: By mass percentage, the magnesium alloy components include zinc: 2.2 - 2.5%, cerium: 0.1 - 0.2%, inevitable impurities ≤ 0.02%, and the balance is magnesium; its preparation method includes the following steps: (1) By mass percentage, weigh pure magnesium, pure zinc, and Mg-25Ce master alloy. Under the protection of a mixed gas of SF6 and CO2 with a volume ratio of 1 - 10:90 - 99, heat the pure magnesium to melt it into a melt at 640 - 660 °C; then add the preheated pure zinc and Mg-25Ce master alloy at 450 - 470 °C, keep warm for 20 - 30 min, then stir, blow air, and skim the slag, and keep warm and stand for 25 - 35 min before casting into an iron mold to obtain a magnesium alloy ingot; (2) Homogenize and hot-extrude the magnesium alloy ingot obtained in step (1) to obtain a magnesium alloy extrusion rod. The homogenization treatment is: keep warm at 300 - 325 °C for 6.5 - 7.5 h, keep warm at 385 - 400 °C for 2.2 - 2.8 h, and then keep warm at 415 - 430 °C for 1.9 - 2.5 h; the hot extrusion treatment is: the extrusion temperature is 345 - 360 °C, the extrusion ratio is 15:1 - 17:1, and the extrusion speed is 4 - 10 min / m; (3) Perform 2 - 8 passes of temperature-controlled ECAP treatment on the magnesium alloy extrusion rod obtained in step (2) to obtain a high-strength, high-ductility, corrosion-resistant magnesium alloy with a bimodal structure and low alloy content. The 2 - 8 passes of temperature-controlled ECAP treatment are: the temperature, time, and extrusion speed of each pass of ECAP treatment are different. Starting from the second pass of ECAP treatment, the extrusion rod needs to be rotated clockwise by 90° before each pass of ECAP treatment for the next pass. Each pass of ECAP treatment is: keep the magnesium alloy extrusion rod warm at 150 - 240 °C for 20 - 40 min, and then perform ECAP treatment at an extrusion speed of 4 - 8 min / m; The corrosion rate of the high-strength, high-ductility, corrosion-resistant magnesium alloy with a bimodal structure and low alloy content is ≤ 8 mm / y, the tensile strength is ≥ 304 MPa, and the elongation is ≥ 19%; The internal structure of the high-strength, high-ductility, corrosion-resistant magnesium alloy with a bimodal structure and low alloy content is a bimodal structure, which is composed of strongly basal-textured deformed coarse grains with an average grain size of ~9 - 12 μm and weakly textured recrystallized fine grains with an average grain size of ~1 - 2.5 μm, where the volume fraction of the weakly textured recrystallized fine grains accounts for ~55 - 70%.

2. The high-strength, plastic and corrosion-resistant bimodal structure low-alloy magnesium alloy according to claim 1, characterized in that: The extrusion speed described in step (2) is 5 - 6 min / m.

3. A high-strength, plastic and corrosion-resistant bimodal structure magnesium alloy with low alloy content according to claim 1, characterized in that: The magnesium alloy extrusion rod described in step (3) is subjected to 4 - 6 passes of temperature-controlled ECAP treatment to obtain a high-strength, high-ductility, corrosion-resistant magnesium alloy with a bimodal structure and low alloy content.