Short-time annealing high strength plastic Mg-Zn-Nd-Zr alloy and preparation method thereof

Abstract

The application provides a short-time annealing high-strength plastic Mg-Zn-Nd-Zr alloy and a preparation method thereof, and belongs to the technical field of magnesium alloys; the alloy contains Zn 1.1-2.1%, Nd 0.2-0.5%, Zr 0.1-0.4%, unavoidable impurities ≤0.05% and the balance of Mg according to percentage by mass; the preparation method of the magnesium alloy comprises the following steps: casting, homogenization treatment, hot extrusion, multi-pass rotary hot rolling and annealing treatment; the total alloy content of the application is ≤2.5 wt.%, the average grain size is ≤3 μm, a short-time annealing forms a small-angle grain boundary network which is uniformly distributed and the length ratio is 40-50%; the high-strength plastic magnesium alloy with low alloy content, fine grains and high small-angle grain boundary ratio is prepared, wherein the yield strength is ≥260.1 MPa and the elongation is ≥26.0%; the application effectively avoids the rolling edge crack while shortening the process flow and reducing the process energy consumption, significantly improves the organization regulation efficiency, and provides a new method for the economic production of magnesium alloy plates.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy material processing technology, specifically relating to a short-time annealed high-strength and high-ductility Mg-Zn-Nd-Zr alloy and its preparation method. Background Technology

[0002] Close-packed hexagonal magnesium alloys have limited independent slip systems at room temperature, resulting in poor plastic deformation capacity and low strength. The difficulty in achieving a balance between strength and plasticity further limits their industrial applications. Traditional low-alloy magnesium alloys, due to their low solute atomic content, struggle to form effective precipitation strengthening, leading to limited strengthening effects. While hot deformation can effectively refine grains and improve strength, it easily creates a strong basal texture, resulting in a significant decrease in plasticity. Conversely, improving plasticity by weakening the texture is difficult to maintain strength.

[0003] Currently, the development of high-strength ductile magnesium alloys mainly relies on complex processes such as high alloy content (≥10 wt.%) or large plastic deformation. However, these technical routes often sacrifice plasticity for increased strength. For example, while the LPSO phase formed in high rare earth alloy systems can significantly strengthen the alloy, its improvement on plasticity is limited, and excessively high rare earth additions (≥6 wt.%) can significantly increase raw material costs. While large deformation methods such as multi-directional, multi-pass forging can obtain fine-grained structures to improve strength, the complex deformation path and numerous passes easily introduce microcracks and reduce plasticity. Furthermore, long-term aging treatment after deformation to precipitate high-density nano-β' phases can contribute to precipitation strengthening, but it prolongs the process cycle and increases energy consumption. Overall, existing technologies result in high raw material and manufacturing costs due to high alloy content, complex processing steps, and long heat treatment times. Therefore, how to achieve a synergistic improvement in the strength and plasticity of magnesium alloys while reducing alloy additions, simplifying processes, reducing energy consumption, and avoiding alloy cracking defects has become a key technical challenge that urgently needs to be solved in the research field of low-alloy magnesium alloys. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a short-time annealed high-strength and high-ductility Mg-Zn-Nd-Zr alloy, wherein the alloy is composed of the following components by mass percentage: Zn 1.1-2.1%, Nd 0.2-0.5%, Zr 0.1-0.4%, total alloy content ≤2.5 wt.%, unavoidable impurities ≤0.05%, and the balance being Mg; the preparation method of the magnesium alloy includes the following steps: (1) Casting: Remove the oxide layer on the surface of pure Mg, pure Zn, Mg-Nd master alloy, and Mg-Zr master alloy. Under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 95:5-99:1, hold pure magnesium at 250-400 ℃ for 60-100 min, and then heat it to 680-720 ℃ to melt it. Add pure Zn, Mg-Nd, and Mg-Zr master alloys that have been preheated at 100-250 ℃ for 30-80 min in sequence. After they are fully melted, stir at 690-720 ℃ for 2-10 min and let stand for 2-8 min. Then, pass high-purity argon gas to refine and remove slag. Cast the alloy into a mold that has been preheated at 200-300 ℃ and air-cool it to room temperature to obtain a magnesium alloy ingot. (2) Homogenization treatment: The magnesium alloy ingot obtained in step (1) is subjected to multi-level gradient homogenization treatment, and then quenched in warm water to obtain a homogeneous magnesium alloy ingot; the multi-level gradient homogenization treatment is: held at 300-500 ℃ for 5-15 h, and then held at 450-550 ℃ for 2-5 h. (3) Extrusion: The homogeneous magnesium alloy ingot obtained in step (2) is kept at 350-450 ℃ for 20-50 min, and then hot extrusion is performed to obtain alloy extruded sheet; the hot extrusion is performed at an extrusion temperature of 350-450 ℃, an extrusion speed of 0.1-0.5 mm / s, and an extrusion ratio of 10:1-18:1. (4) Rotary hot rolling: The alloy extruded sheet obtained in step (3) is held at 300-380 ℃ for 5-15 min, and then subjected to multiple passes of rotary hot rolling to obtain an alloy rolled sheet; the multiple passes of rotary hot rolling: the upper and lower rolls are heated to 70-130 ℃, the rolling temperature is 300-380 ℃, a total of 2-7 passes, and the total reduction is 60-90%; the reduction per pass is 25-40%; after the sheet is held at 300-380 ℃ for 5-15 min between adjacent passes, the next pass of rolling is rotated 80-100° clockwise relative to the previous pass along the normal ND of the sheet, wherein the rolling direction of odd-numbered passes is basically parallel to the extrusion direction ED of the extruded sheet, and the rolling direction of even-numbered passes is basically parallel to the transverse direction TD of the extruded sheet; (5) Annealing treatment: The alloy rolled plate obtained in step (4) is kept at 250-350 ℃ for 10-30 min, and then water quenched to obtain a short-time annealed high-strength and ductile Mg-Zn-Nd-Zr alloy; the short-time annealed high-strength and ductile Mg-Zn-Nd-Zr alloy has a uniformly distributed small-angle grain boundary length ratio of 40-50%, an average grain size ≤3 μm, a yield strength ≥260.1MPa, and an elongation ≥26.0%.

[0005] Further, the multi-level gradient homogenization treatment described in step (2) involves holding the temperature at 350-450 ℃ for 7-13 h, and then holding it at 470-530 ℃ for 2.5-4.5 h.

[0006] Further, the homogeneous magnesium alloy ingot described in step (3) is kept at 375-425 ℃ for 30-45 min and then hot extruded to obtain alloy extruded sheet; the hot extrusion is carried out at an extrusion temperature of 375-425 ℃, an extrusion speed of 0.15-0.35 mm / s, and an extrusion ratio of 12:1-16:1.

[0007] Furthermore, the extruded sheet material described in step (4) is kept at 325-365 ℃ for 8-12 min.

[0008] Furthermore, the total reduction in step (4) is 65-85%, and the reduction per pass is 25-35%.

[0009] Furthermore, in step (4), after the sheet material is kept at 325-365 ℃ for 7-13 min between adjacent passes, the next rolling pass is rotated 85-95° clockwise relative to the previous pass along the normal ND direction of the sheet material.

[0010] Further, the rolled magnesium alloy sheet described in step (5) is annealed at 275-325 ℃ for 15-25 min.

[0011] Furthermore, the uniformly distributed small-angle grain boundary length ratio in step (5) is 42-48%, and the average grain size is 0.8-2.5 μm.

[0012] Furthermore, the yield strength in step (5) is 266.0-300.0 MPa, and the elongation is 27.0-30.0%.

[0013] Compared with the prior art, the present invention has the following beneficial effects: Compared with existing technologies, this invention reduces alloy costs (total alloy content ≤ 2.5 wt.%, rare earth content ≤ 0.5 wt.%) and shortens the annealing time after deformation without relying on high-density precipitates or reinforcing phases. Through the synergistic control of component interactions, proportions, processes, and process parameters, it utilizes the segregation of low-content solute atoms to stabilize the interface and effectively suppress grain growth, resulting in finer grains compared to alloys with high-content solute systems, with an average grain size ≤ 3 μm. Simultaneously, this invention forms uniformly distributed high-density small-angle grain boundaries, with a length ratio of 40-50%, preserving the high dislocation storage capacity of the deformed structure. Furthermore, the small-angle grain boundaries effectively accommodate strain during deformation, serving as a key carrier for dislocation storage and movement, hindering dislocations while promoting uniform deformation, achieving a yield strength ≥ 260.1 MPa and an elongation ≥ 26.0%. Based on low alloy content, fine grains, and a high proportion of small-angle grain boundaries, this invention avoids cracking defects, reduces raw material addition costs, simplifies the process, and achieves short-process manufacturing, resulting in an alloy with synergistically improved strength and plasticity, suitable for industrial production. Detailed Implementation Example 1

[0014] A short-time annealed high-strength and ductile Mg-Zn-Nd-Zr alloy 1, the composition by mass percentage is: Zn 1.67%, Nd 0.42%, Zr 0.39%, unavoidable impurities ≤0.05%, and the balance being Mg. The preparation method of the magnesium alloy includes the following steps: (1) Casting: Remove the oxide layer on the surface of pure Mg, pure Zn, Mg-Nd master alloy and Mg-Zr master alloy. Under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 97:3, hold pure magnesium at 360 ℃ for 60 min and then heat it to 700 ℃ to melt it. Add pure Zn, Mg-Nd and Mg-Zr master alloys that have been preheated at 200 ℃ for 50 min in sequence. After they are fully melted, stir at 700 ℃ for 3 min and let stand for 5 min. Then, pass high-purity argon gas to refine and remove slag. Cast the mixture into a mold that has been preheated at 250 ℃ and air-cool it to room temperature to obtain magnesium alloy ingots. (2) Homogenization treatment: The magnesium alloy ingot obtained in step (1) is subjected to multi-level gradient homogenization treatment, and then quenched in warm water to obtain a homogeneous magnesium alloy ingot; the multi-level gradient homogenization treatment is: held at 400 ℃ for 10 h, and then held at 500 ℃ for 3 h. (3) Extrusion: The homogeneous magnesium alloy ingot obtained in step (2) is held at 380 ℃ for 38 min, and then hot extruded to obtain an alloy extruded sheet. The hot extrusion is as follows: the extrusion temperature is 380 ℃, the extrusion speed is 0.15 mm / s, and the extrusion ratio is 12.5:1; (4) Rotary hot rolling: After holding the alloy extruded sheet obtained in step (3) at 370 ℃ for 8 min, it is subjected to multiple passes of rotary hot rolling to obtain an alloy rolled sheet; the multiple passes of rotary hot rolling: the upper and lower rolls are heated to 85 ℃, the rolling temperature is 370 ℃, a total of 7 passes, and the total reduction is 89%; the reduction of each pass is 26%; after the sheet is held at 370 ℃ for 7 min between adjacent passes, the next pass of rolling is rotated 85° clockwise relative to the previous pass along the normal ND of the sheet, wherein the rolling direction of odd-numbered passes is basically parallel to the extrusion direction ED of the extruded sheet, and the rolling direction of even-numbered passes is basically parallel to the transverse direction TD of the extruded sheet; (5) Annealing treatment: The alloy rolled plate obtained in step (4) is kept at 300 ℃ for 20 min and then water quenched to obtain a short-time annealed high-strength and ductile Mg-Zn-Nd-Zr alloy; the short-time annealed high-strength and ductile Mg-Zn-Nd-Zr alloy has a uniformly distributed small-angle grain boundary length of 47%, an average grain size of 3.0 μm, a yield strength of 265.5 MPa, and an elongation of 26.2%. Example 2

[0015] A short-time annealed high-strength and ductile Mg-Zn-Nd-Zr alloy 2, the composition by mass percentage is: Zn 1.78%, Nd 0.40%, Zr 0.31%, unavoidable impurities ≤0.05%, and the balance being Mg. The preparation method of the magnesium alloy includes the following steps: (1) Casting: Remove the oxide layer on the surface of pure Mg, pure Zn, Mg-Nd master alloy and Mg-Zr master alloy. Under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 98:2, pure magnesium is held at 320 ℃ for 75 min and then heated to 690 ℃ to melt it. Pure Zn, Mg-Nd and Mg-Zr master alloys that have been preheated at 230 ℃ for 45 min are added in sequence. After they are fully melted, they are stirred at 690 ℃ for 6 min and let stand for 6 min. Then, high-purity argon is introduced for refining and slag removal. The mixture is then cast into a mold preheated at 240 ℃ and air-cooled to room temperature to obtain magnesium alloy ingots. (2) Homogenization treatment: The magnesium alloy ingot obtained in step (1) is subjected to multi-level gradient homogenization treatment, and then quenched in warm water to obtain a homogeneous magnesium alloy ingot; the multi-level gradient homogenization treatment is: held at 410 ℃ for 11 h, and then held at 490 ℃ for 4 h. (3) Extrusion: The homogeneous magnesium alloy ingot obtained in step (2) is held at 390 ℃ for 30 min, and then hot extruded to obtain an alloy extruded sheet. The hot extrusion is as follows: the extrusion temperature is 390 ℃, the extrusion speed is 0.18 mm / s, and the extrusion ratio is 14:1; (4) Rotary hot rolling: After holding the alloy extruded sheet obtained in step (3) at 320 ℃ for 10 min, it is subjected to multiple passes of rotary hot rolling to obtain alloy rolled sheet; the multiple passes of rotary hot rolling: the upper and lower rolls are heated to 90 ℃, the rolling temperature is 320 ℃, a total of 4 passes, and the total reduction is 87%; the reduction of each pass is 37%; after the sheet is held at 320 ℃ for 10 min between adjacent passes, the next pass of rolling is rotated 90° clockwise relative to the previous pass along the normal ND of the sheet, wherein the rolling direction of odd-numbered passes is basically parallel to the extrusion direction ED of the extruded sheet, and the rolling direction of even-numbered passes is basically parallel to the transverse direction TD of the extruded sheet; (5) Annealing treatment: The alloy rolled plate obtained in step (4) is held at 298 ℃ for 21 min and then water quenched to obtain a short-time annealed high-strength and ductile Mg-Zn-Nd-Zr alloy; the short-time annealed high-strength and ductile Mg-Zn-Nd-Zr alloy has a uniformly distributed small-angle grain boundary length of 45%, an average grain size of 2.8 μm, a yield strength of 263.5 MPa, and an elongation of 26.5%. Example 3

[0016] A short-time annealed high-strength and ductile Mg-Zn-Nd-Zr alloy 3, the composition by mass percentage is: Zn 1.56%, Nd 0.46%, Zr 0.37%, unavoidable impurities ≤0.05%, and the balance being Mg. The preparation method of the magnesium alloy includes the following steps: (1) Casting: Remove the oxide layer on the surface of pure Mg, pure Zn, Mg-Nd master alloy and Mg-Zr master alloy. Under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 98:1, pure magnesium is held at 310 ℃ for 87 min and then heated to 710 ℃ to melt it. Pure Zn, Mg-Nd and Mg-Zr master alloys that have been preheated at 250 ℃ for 48 min are added in sequence. After they are fully melted, they are stirred at 708 ℃ for 5 min and let stand for 7 min. Then, high-purity argon is introduced for refining and slag removal. The mixture is then cast into a mold preheated at 275 ℃ and air-cooled to room temperature to obtain magnesium alloy ingots. (2) Homogenization treatment: The magnesium alloy ingot obtained in step (1) is subjected to multi-level gradient homogenization treatment, and then quenched in warm water to obtain a homogeneous magnesium alloy ingot; the multi-level gradient homogenization treatment is: held at 370 ℃ for 12 h, and then held at 495 ℃ for 2.5 h. (3) Extrusion: The homogeneous magnesium alloy ingot obtained in step (2) is held at 396 ℃ for 35 min, and then hot extruded to obtain an alloy extruded sheet. The hot extrusion is as follows: the extrusion temperature is 396 ℃, the extrusion speed is 0.2 mm / s, and the extrusion ratio is 14.2:1; (4) Rotary hot rolling: After holding the alloy extruded sheet obtained in step (3) at 332 ℃ for 11 min, it is subjected to multiple passes of rotary hot rolling to obtain an alloy rolled sheet; the multiple passes of rotary hot rolling: the upper and lower rolls are heated to 100 ℃, the rolling temperature is 332 ℃, a total of 6 passes, and the total reduction is 84%; the reduction of each pass is 27%; after the sheet is held at 332 ℃ for 12 min between adjacent passes, the next pass of rolling is rotated 92° clockwise relative to the previous pass along the normal ND of the sheet, wherein the rolling direction of odd-numbered passes is basically parallel to the extrusion direction ED of the extruded sheet, and the rolling direction of even-numbered passes is basically parallel to the transverse direction TD of the extruded sheet; (5) Annealing treatment: The alloy rolled plate obtained in step (4) is held at 306 ℃ for 17 min and then water quenched to obtain a short-time annealed high-strength and ductile Mg-Zn-Nd-Zr alloy; the short-time annealed high-strength and ductile Mg-Zn-Nd-Zr alloy has a uniformly distributed small-angle grain boundary length of 43%, an average grain size of 2.5 μm, a yield strength of 262.7 MPa, and an elongation of 26.3%. Example 4

[0017] A short-time annealed high-strength and ductile Mg-Zn-Nd-Zr alloy 4, the composition by mass percentage is: Zn 1.91%, Nd 0.29%, Zr 0.28%, unavoidable impurities ≤0.05%, and the balance being Mg. The preparation method of the magnesium alloy includes the following steps: (1) Casting: Remove the oxide layer on the surface of pure Mg, pure Zn, Mg-Nd master alloy and Mg-Zr master alloy. Under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 96:1, pure magnesium is held at 277 ℃ for 89 min and then heated to 712 ℃ to melt it. Pure Zn, Mg-Nd and Mg-Zr master alloys that have been preheated at 180 ℃ for 70 min are added in sequence. After they are fully melted, they are stirred at 710 ℃ for 4 min and let stand for 8 min. Then, high-purity argon is introduced for refining and slag removal. The mixture is then cast into a mold preheated at 260 ℃ and air-cooled to room temperature to obtain magnesium alloy ingots. (2) Homogenization treatment: The magnesium alloy ingot obtained in step (1) is subjected to multi-level gradient homogenization treatment, and then quenched in warm water to obtain a homogeneous magnesium alloy ingot; the multi-level gradient homogenization treatment is: held at 470 ℃ for 8 h, and then held at 520 ℃ for 3.2 h. (3) Extrusion: The homogeneous magnesium alloy ingot obtained in step (2) is held at 402 ℃ for 40 min, and then hot extruded to obtain alloy extruded sheet. The hot extrusion is as follows: the extrusion temperature is 402 ℃, the extrusion speed is 0.3 mm / s, and the extrusion ratio is 15:1; (4) Rotary hot rolling: After holding the alloy extruded sheet obtained in step (3) at 350 ℃ for 13 min, it is subjected to multiple passes of rotary hot rolling to obtain an alloy rolled sheet; the multiple passes of rotary hot rolling: the upper and lower rolls are heated to 110 ℃, the rolling temperature is 350 ℃, a total of 5 passes, and the total reduction is 76%; the reduction of each pass is 25%; after the sheet is held at 350 ℃ for 9 min between adjacent passes, the next pass of rolling is rotated 95° clockwise relative to the previous pass along the normal ND of the sheet, wherein the rolling direction of odd-numbered passes is basically parallel to the extrusion direction ED of the extruded sheet, and the rolling direction of even-numbered passes is basically parallel to the transverse TD of the extruded sheet; (5) Annealing treatment: The alloy rolled plate obtained in step (4) is held at 302 ℃ for 23 min and then water quenched to obtain a short-time annealed high-strength and ductile Mg-Zn-Nd-Zr alloy; the short-time annealed high-strength and ductile Mg-Zn-Nd-Zr alloy has a uniformly distributed small-angle grain boundary length of 42%, an average grain size of 2.2 μm, a yield strength of 260.7 MPa, and an elongation of 26.6%. Comparative Example 1

[0018] A rotary-rolled annealed Mg-Zn-Nd-Zr alloy, the composition of which, by mass percentage, is: Zn 2.25%, Nd 0.82%, Zr 0.77%, with the balance being Mg and unavoidable impurities (≤0.05%). The preparation method of the magnesium alloy includes the following steps: (1) Casting: Remove the oxide layer on the surface of pure Mg, pure Zn, Mg-Nd master alloy and Mg-Zr master alloy. Under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 93:7, hold pure magnesium at 220 ℃ for 50 min and then heat it to 725 ℃ to melt it. Add pure Zn, Mg-Nd and Mg-Zr master alloys that have been preheated at 255 ℃ for 20 min in sequence. After they are fully melted, stir at 725 ℃ for 1 min and let stand for 10 min. Then, pass high-purity argon gas to refine and remove slag. Cast the mixture into a mold that has been preheated at 310 ℃ and air-cool it to room temperature to obtain magnesium alloy ingots. (2) Homogenization treatment: The magnesium alloy ingot obtained in step (1) is subjected to multi-level gradient homogenization treatment, and then quenched in warm water to obtain a homogeneous magnesium alloy ingot; the multi-level gradient homogenization treatment is: held at 290 ℃ for 18 h, and then held at 430 ℃ for 8 h. (3) Extrusion: The homogeneous magnesium alloy ingot obtained in step (2) is held at 460 ℃ for 55 min, and then hot extruded to obtain alloy extruded sheet. The hot extrusion is as follows: the extrusion temperature is 460 ℃, the extrusion speed is 0.6 mm / s, and the extrusion ratio is 9.7:1; (4) Rotary hot rolling: After holding the alloy extruded sheet obtained in step (3) at 400 ℃ for 25 min, it is subjected to multiple passes of rotary hot rolling to obtain alloy rolled sheet; the multiple passes of rotary hot rolling: the upper and lower rolls are heated to 140 ℃, the rolling temperature is 400 ℃, a total of 12 passes, and the total reduction is 58%; the reduction per pass is 7%; after the sheet is held at 400 ℃ for 15 min between adjacent passes, the next pass of rolling is rotated 75° clockwise relative to the previous pass along the normal ND of the sheet, wherein the rolling direction of odd-numbered passes is basically parallel to the extrusion direction ED of the extruded sheet, and the rolling direction of even-numbered passes is basically parallel to the transverse direction TD of the extruded sheet; (5) Annealing treatment: The alloy rolled plate obtained in step (4) is kept at 360 ℃ for 5 min and then water quenched to obtain Mg-Zn-Nd-Zr alloy; the Mg-Zn-Nd-Zr alloy has a uniformly distributed small-angle grain boundary length of 25%, an average grain size of 7.0 μm, a yield strength of 200.3 MPa, and an elongation of 16.8%. Comparative Example 2

[0019] The paper "Dislocation-induced β' precipitation behavior and strength-ductility synergistic enhancement in Mg-Gd-Y-Zr-Ag alloy" published by Yingjie Huang et al. in the Journal of Alloys and Compounds, 2023, Vol. 944, No. 25, p. 169187, reports the following alloy preparation method: by mass percentage, Gd 8.9%, Y 1.8%, Zr 0.5%, Ag 0.2%, with the balance being Mg. Ingots were obtained by semi-continuous casting according to the above mass ratio; the obtained ingots were solution treated at 525 ℃ for 12 h and then water quenched to room temperature; and preheated at 575 ℃ for 2 hours. After h, multi-directional forging is performed, which is carried out in the x, y, z directions in sequence, with a true strain of 0.15 per pass, for a total of 15 passes, and the final forging temperature of the alloy surface is 427 ℃; the obtained forged alloy is aged at 225 ℃ for 72 h, and the final alloy yield strength is 241 MPa and the elongation is 18.5%.

[0020] Compared with the alloys processed in Comparative Examples 1 and 2, the alloy obtained by the present invention has lower minimum strength and higher plasticity than the alloy obtained in the comparative examples. Although Comparative Example 1 uses similar components and processes as the present invention, its alloy composition ratio and process parameters are not within the scope of protection of the claims of the present invention, and its strength and plasticity are lower than the minimum performance of the alloy obtained by the present invention. Comparative Example 2 uses a Mg-Gd-Y-Zr-Ag alloy with a total alloy content (>11 wt.%) and a high rare earth content (>10 wt.%), which is subjected to high-temperature (575 ℃) multi-directional multi-pass forging to introduce accumulated large strain, followed by a long-term (72 h) aging treatment. The total alloy content and rare earth content disclosed in Comparative Example 2 are higher than the maximum total alloy content and the maximum rare earth content added by the present invention, and it uses complex processes such as high-temperature homogenization, high-temperature large plastic deformation, and long-term aging treatment, which further increases the cost of raw materials and deformation processes, and does not achieve a superior strength-plasticity match. Furthermore, the component ratios and process parameters differ in each embodiment of this invention, resulting in different mechanical properties and microstructures of the final alloys. This demonstrates that the optimal effect obtained by this invention is not determined by a specific component ratio, process, or process parameter, but rather achieved through the interaction of components, the synergistic regulation of component ratios, processes, and process parameters. Moreover, the optimal technical effect can only be achieved within the scope of protection of the claims of this invention. In summary, this invention significantly reduces raw material costs through the combined addition of low alloy content and low rare earth content (total alloy content ≤ 2.5 wt.%, rare earth content ≤ 0.5 wt.%). The short-time annealing process effectively preserves a high proportion of deformed microstructure, achieves significant grain refinement, avoids rolling edge cracks, and simplifies the preparation process. The obtained alloy exhibits a room temperature yield strength ≥ 260.1 MPa and an elongation ≥ 26.0%, achieving a simultaneous improvement in strength and plasticity compared to existing technologies.

[0021] Table 1 Comparison of room temperature mechanical properties of alloys in Examples 1-4 and Comparative Examples 1 and 2

Claims

1. A short-time annealed high-strength and high-ductility Mg-Zn-Nd-Zr alloy, characterized in that, The alloy, by mass percentage, comprises the following components: Zn 1.1-2.1%, Nd 0.2-0.5%, Zr 0.1-0.4%, total alloy content ≤2.5 wt.%, unavoidable impurities ≤0.05%, and the balance being Mg; the preparation method of the magnesium alloy includes the following steps: (1) Casting: Remove the oxide layer on the surface of pure Mg, pure Zn, Mg-Nd master alloy, and Mg-Zr master alloy. Under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 95:5-99:1, hold pure magnesium at 250-400 ℃ for 60-100 min, and then heat it to 680-720 ℃ to melt it. Add pure Zn, Mg-Nd, and Mg-Zr master alloys that have been preheated at 100-250 ℃ for 30-80 min in sequence. After they are fully melted, stir at 690-720 ℃ for 2-10 min and let stand for 2-8 min. Then, pass high-purity argon gas to refine and remove slag. Cast the alloy into a mold that has been preheated at 200-300 ℃ and air-cool it to room temperature to obtain a magnesium alloy ingot. (2) Homogenization treatment: The magnesium alloy ingot obtained in step (1) is subjected to multi-level gradient homogenization treatment, and then quenched in warm water to obtain a homogeneous magnesium alloy ingot; the multi-level gradient homogenization treatment is: held at 300-500 ℃ for 5-15 h, and then held at 450-550 ℃ for 2-5 h. (3) Extrusion: The homogeneous magnesium alloy ingot obtained in step (2) is kept at 350-450 ℃ for 20-50 min, and then hot extrusion is performed to obtain alloy extruded sheet; the hot extrusion is performed at an extrusion temperature of 350-450 ℃, an extrusion speed of 0.1-0.5 mm / s, and an extrusion ratio of 10:1-18:

1. (4) Rotary hot rolling: The alloy extruded sheet obtained in step (3) is held at 300-380 ℃ for 5-15 min, and then subjected to multiple passes of rotary hot rolling to obtain an alloy rolled sheet; the multiple passes of rotary hot rolling: the upper and lower rolls are heated to 70-130 ℃, the rolling temperature is 300-380 ℃, a total of 2-7 passes, and the total reduction is 60-90%; the reduction per pass is 25-40%; after the sheet is held at 300-380 ℃ for 5-15 min between adjacent passes, the next pass of rolling rotates 80-100° clockwise relative to the previous pass along the normal ND of the sheet, wherein the rolling direction of odd-numbered passes is basically parallel to the extrusion direction ED of the extruded sheet, and the rolling direction of even-numbered passes is basically parallel to the transverse TD of the extruded sheet; (5) Annealing treatment: The alloy rolled plate obtained in step (4) is kept at 250-350 ℃ for 10-30 min, and then water quenched to obtain a short-time annealed high-strength and ductile Mg-Zn-Nd-Zr alloy; the short-time annealed high-strength and ductile Mg-Zn-Nd-Zr alloy has a uniformly distributed small-angle grain boundary length ratio of 40-50%, an average grain size ≤3 μm, a yield strength ≥260.1 MPa, and an elongation ≥26.0%.

2. The short-time annealed high-strength and high-ductility Mg-Zn-Nd-Zr alloy according to claim 1, characterized in that: The multi-level gradient homogenization process described in step (2) involves holding the temperature at 350-450 ℃ for 7-13 h, and then holding it at 470-530 ℃ for 2.5-4.5 h.

3. The short-time annealed high-strength and high-ductility Mg-Zn-Nd-Zr alloy according to claim 1, characterized in that: The homogeneous magnesium alloy ingot described in step (3) is kept at 375-425 ℃ for 30-45 min, and then hot extruded to obtain alloy extruded sheet; the hot extrusion is carried out at an extrusion temperature of 375-425 ℃, an extrusion speed of 0.15-0.35 mm / s, and an extrusion ratio of 12:1-16:

1.

4. The short-time annealed high-strength and high-ductility Mg-Zn-Nd-Zr alloy according to claim 1, characterized in that: The extruded sheet material described in step (4) is kept at 325-365 ℃ for 8-12 min.

5. A short-time annealed high-strength and high-ductility Mg-Zn-Nd-Zr alloy according to claim 1, characterized in that: The total reduction in step (4) is 65-85%, and the reduction per pass is 25-35%.

6. The short-time annealed high-strength and high-ductility Mg-Zn-Nd-Zr alloy according to claim 1, characterized in that: In step (4), after the sheet material is kept at 325-365 ℃ for 7-13 min between adjacent passes, the next rolling pass rotates 85-95° clockwise relative to the previous pass along the normal ND direction of the sheet material.

7. A short-time annealed high-strength and high-ductility Mg-Zn-Nd-Zr alloy according to claim 1, characterized in that: The rolled magnesium alloy sheet described in step (5) is annealed at 275-325 ℃ for 15-25 min.

8. A short-time annealed high-strength and high-ductility Mg-Zn-Nd-Zr alloy according to claim 1, characterized in that: The uniformly distributed small-angle grain boundary length ratio in step (5) is 42-48%, and the average grain size is 0.8-2.5 μm.

9. A short-time annealed high-strength and high-ductility Mg-Zn-Nd-Zr alloy according to claim 1, characterized in that: The yield strength described in step (5) is 266.0-300.0 MPa, and the elongation is 27.0-30.0%.

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