High-strength plastic magnesium alloy based on isothermal annealing under constant stress and preparation method

Abstract

The invention belongs to the field of metal materials, and provides a high-strength plastic magnesium alloy based on isothermal annealing under constant stress and a preparation method. The magnesium alloy is prepared from the following components in percentage by mass: 1.2 to 1.5 percent of Al, 0.2 to 0.4 percent of Ca, 0.5 to 0.8 percent of Gd, less than or equal to 0.05 percent of inevitable impurities and the balance of magnesium. The preparation method of the high-strength plastic magnesium alloy comprises the steps of casting, stepped homogenization treatment, hot extrusion, high-temperature solid solution treatment, rolling and isothermal annealing treatment under constant stress. Rapid recrystallization and texture weakening are achieved under the low-temperature and short-time conditions, a large number of high-thermal-stability nano Al-Gd and Al-Ca phases exist in the alloy, the strength is improved, meanwhile, the defects of uneven tissue, abnormal grain growth and the like caused by traditional high-temperature heat treatment are overcome, and the heat treatment cost is remarkably reduced. The finally obtained alloy has a weak texture which deflects in the rolling direction RD and the transverse direction TD, and the peak strength is smaller than or equal to 6.8 mrd. The recrystallization area fraction is larger than or equal to 63.8%, the average grain size is smaller than or equal to 7.7 micrometers, the tensile strength is larger than or equal to 234.6 MPa, the ductility is larger than or equal to 17.9%, and excellent strength and plasticity matching is achieved.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing, specifically relating to a high-strength ductile magnesium alloy based on isothermal annealing under constant stress and its preparation method. Background Technology

[0002] Magnesium alloys, with their advantages of low density (1.74 g / cm³), high specific strength, good shock absorption, and recyclability, are gradually becoming key structural materials under the carbon neutrality strategy. Their lightweight advantage meets the weight reduction and energy consumption requirements of automobiles and spacecraft, and also satisfies the demand for thinner and lighter 3C electronic products. However, due to their low absolute strength, magnesium alloys cannot meet the application requirements of load-bearing structural components. In traditional technical approaches, strength is often improved by increasing the content of alloying elements (>6 wt.%) and using mechanisms such as second-phase strengthening, but this often leads to high manufacturing costs and reduced plasticity. During solidification, highly alloyed magnesium alloys are prone to severe segregation of alloying elements at grain boundaries, forming coarse and brittle eutectic phases, which easily become crack initiators under external forces, leading to material failure. This microstructure inhomogeneity can be eliminated by reducing casting superheat and increasing cooling rate. However, low superheat casting can easily lead to casting problems such as gate blockage, while excessive cooling rate may induce new thermal stress or crack defects. Electromagnetic stirring can homogenize the composition of the melt, but it requires significant investment in equipment and is complex to control; excessive stirring can also exacerbate segregation. Furthermore, as-cast alloys often have low strength, necessitating aging to precipitate strengthening phases to improve strength. However, low-temperature aging is inefficient and time-consuming, while high-temperature aging tends to coarsen the precipitated phases, resulting in limited strength gains and impaired plasticity. Therefore, reducing alloy additive amounts, simplifying processes, achieving shorter processing times, simultaneously improving alloy strength and plasticity, and realizing industrial-scale production are key challenges that urgently need to be overcome in the development of magnesium alloys. Summary of the Invention

[0003] To address the aforementioned challenges, this invention provides a high-strength ductile-magnesium alloy based on isothermal annealing under constant stress. The alloy composition, by mass percentage, comprises: Al 1.2~1.5%, Ca 0.2~0.4%, Gd 0.5~0.8%, with a total alloy content ≤2.7%, unavoidable impurities ≤0.05%, and the balance being Mg. The preparation method of the magnesium alloy includes the following steps: (1) Commercial pure Mg, pure Al, Mg-20wt.%Ca, and Mg-20wt.%Gd master alloys are selected as raw materials. The materials are proportioned according to the mass percentage of the alloy components. After grinding to remove the surface oxides and dirt, the pure Mg, pure Al, Mg-20wt.%Ca, and Mg-20wt.%Gd master alloys are kept at 400-450℃ for 2-3 hours. Under the protection of CO2 and SF6 mixed gas, the volume ratio of CO2 and SF6 is 90-99:1-10. The pure Mg is heated and melted at 690-720℃ and then pure Al, Mg-20wt.%Ca, and Mg-20wt.%Gd master alloys are added. After melting for 20-30 minutes, the mixture is stirred and slag is removed. After standing for 10-60 minutes, high-purity Ar gas is introduced. After standing for another 25-30 minutes, the mixture is poured into a steel mold preheated at 200-300℃. After cooling to room temperature, magnesium alloy ingots are obtained. (2) The magnesium alloy ingot obtained in step (1) is subjected to step homogenization treatment, hot extrusion, high temperature solution treatment, rolling, and isothermal annealing under constant stress to obtain a high-strength ductile magnesium alloy based on isothermal annealing under constant stress. The stepped homogenization process is as follows: heat treatment at 310-330℃ for 1-2 hours, then heat treatment at 415-430℃ for 3-4 hours, and then heat treatment at 470-490℃ for 1-2 hours. The hot extrusion is carried out after holding at 400-420℃ for 40-60 minutes. The extrusion temperature is 400-420℃, the extrusion speed is 12-16mm / s, and the extrusion ratio is 19:1-21:1. The high-temperature solution treatment involves holding the solution at 490-510℃ for 0.5-4 hours. The rolling process is described as follows: 3-8 passes of unidirectional rolling at a rolling temperature of 280-400℃, with a holding time of 5-15 minutes between passes, and a total reduction of 70-80%. The isothermal annealing treatment under constant stress is carried out by applying uniaxial tensile constant stress during isothermal annealing. The annealing temperature is 210-270℃, and a uniaxial tensile constant stress of 2-20MPa along the rolling direction is applied at the same time. The annealing holding time is 20-70min. The high-strength PVC-Mg alloy texture based on isothermal annealing under constant stress has a peak strength ≤6.8mrd, recrystallization area fraction ≥63.8%, average grain size ≤7.7μm, tensile strength ≥234.6MPa, and elongation ≥17.9%.

[0004] Further, the isothermal annealing under constant stress described in step (2) involves applying uniaxial tensile constant stress during isothermal annealing, with an annealing temperature of 225-250℃, and simultaneously applying uniaxial tensile constant stress of 5-15MPa along the rolling direction, and an annealing holding time of 25-60min.

[0005] Further, the high-temperature solution treatment in step (2) involves holding the solution at 495-505℃ for 1-2 hours.

[0006] Further, the rolling process described in step (2) is: 4-6 passes of unidirectional rolling, with a rolling temperature of 300-350℃, a holding time of 10-12 minutes between passes, and a total reduction of 72-78%.

[0007] Compared with the existing technology, the present invention has the following characteristics: Compared with existing technologies, this invention reduces the total alloy content, controlling the total amount of added elements to ≤2.7 wt.%, achieving low alloy addition; while existing technologies often require the addition of >6 wt.% of alloying elements to improve alloy strength. Simultaneously, this invention simplifies the process and achieves efficient and energy-saving short-process heat treatment. Through the synergistic control of component interactions, proportions, processes, and process parameters, the alloy recrystallizes at lower temperatures (<300℃), and the heat treatment time is significantly shortened from several hours (≤70 min), avoiding the complex process control and long-term high-temperature heat treatment of existing technologies. In existing technologies, after annealing at lower temperatures and for shorter times, the recrystallization area fraction is <50%, and the texture often exhibits a strong basal surface texture without any deflection, with the texture peak intensity typically >10 mrd. The alloy obtained by this invention has a recrystallization area fraction ≥63.8%, and simultaneously introduces grain boundary co-segregation to inhibit basal plane orientation grain growth, effectively changing the texture type (deflection) and weakening the texture intensity, transforming from a strong basal plane texture to a weak texture with simultaneous deflection along RD and TD, and the peak intensity of the recrystallization texture ≤6.8mrd. Furthermore, in existing technologies, abnormal grain growth easily occurs after long-term heat treatment at high temperatures (>400℃), resulting in a coarse microstructure in the obtained magnesium alloy, with an average grain size >40μm, tensile strength <220MPa, and plasticity <14%. This invention, through the coupling effect of stress and temperature fields, provides a higher driving force for recrystallization while promoting the precipitation of a large number of highly thermally stable nano-Al-Gd and Al-Ca phases, improving strength while effectively pinning grain boundaries to inhibit grain growth, resulting in an average grain size ≤7.7μm, significantly refining the grain size and ensuring microstructure uniformity. In summary, this invention achieves rapid recrystallization through the synergistic control of component interactions, proportions, processes, and process parameters. Simultaneously, it utilizes recrystallization to construct a microstructure beneficial to performance, obtaining a fine-grained structure with a weak texture along the rolling direction (RD) and transverse direction (TD), a peak strength ≤6.8 mrd, and an average grain size ≤7.7 μm. This achieves a good match between strength and plasticity, with a tensile strength ≥234.6 MPa and an elongation ≥17.9%. Attached Figure Description

[0008] Figure 1 This is a recrystallization area fraction diagram of the high-strength ductile-magnesium alloy 2 obtained in Example 2 based on isothermal annealing under constant stress;

[0009] Figure 2 The pole figure of the high-strength ductile-magnesium alloy 2 obtained in Example 2 based on isothermal annealing under constant stress;

[0010] Figure 3 The image shows the EBSD microstructure of the high-strength ductile-magnesium alloy 2 obtained in Example 2 based on isothermal annealing under constant stress. Detailed Implementation

[0011] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Example 1

[0012] The high-strength ductile-magnesium alloy 1, based on isothermal annealing under constant stress, comprises, by mass percentage: 1.2% Al, 0.3% Ca, 0.8% Gd, with unavoidable impurities ≤0.05%, and the balance being Mg. The preparation method of the magnesium alloy includes the following steps: (1) Commercial pure Mg, pure Al, Mg-20wt.%Ca, and Mg-20wt.%Gd master alloys were selected as raw materials. The materials were prepared according to the mass percentage of the alloy components. After grinding to remove the surface oxides and dirt, the pure Mg, pure Al, Mg-20wt.%Ca, and Mg-20wt.%Gd master alloys were kept at 450℃ for 2 hours. Under the protective atmosphere of CO2 and SF6, where the volume ratio of CO2 to SF6 was 95:5, the pure Mg was heated and melted at 710℃ and then the pure Al, Mg-20wt.%Ca, and Mg-20wt.%Gd master alloys were added. After melting for 25 minutes, the mixture was stirred and slag was removed. After standing for 30 minutes, high-purity Ar gas was introduced. After standing for another 25 minutes, the mixture was poured into a steel mold preheated at 250℃ and cooled to room temperature to obtain magnesium alloy ingots. (2) The magnesium alloy ingot obtained in step (1) is subjected to step homogenization treatment, hot extrusion, high temperature solution treatment, rolling, and isothermal annealing under constant stress to obtain a high-strength ductile magnesium alloy 1 based on isothermal annealing under constant stress. The stepped homogenization process is as follows: heat treatment at 320℃ for 2 hours, heat treatment at 420℃ for 3 hours, and finally heat treatment at 480℃ for 1 hour. The hot extrusion is carried out after holding at 410℃ for 40 minutes. The extrusion temperature is 410℃, the extrusion speed is 15mm / s, and the extrusion ratio is 20:1. The high-temperature solution treatment involves holding the solution at 500°C for 1 hour. The rolling process is as follows: the rolling temperature is 350℃, the temperature is held for 10 minutes between passes, 3 passes are rolled, then the temperature is reduced to 300℃ and rolled for another pass, with a total reduction of 76%; The isothermal annealing treatment under constant stress is carried out by applying uniaxial tensile constant stress during isothermal annealing. The annealing temperature is 250℃, and a uniaxial tensile constant stress of 12MPa along the rolling direction is applied simultaneously. The annealing holding time is 25min. Based on isothermal annealing under constant stress, the recrystallization area fraction of high-strength PVC-Mg alloy 1 can reach ~63.8%, the recrystallization texture strength is weakened to ~6.4 μm, the average grain size is ~6.8 μm, and its room temperature tensile properties are a tensile strength of 247.4 MPa and an elongation of 21.9%. Example 2

[0013] The high-strength ductile-magnesium alloy 2, based on isothermal annealing under constant stress, comprises, by mass percentage: 1.2% Al, 0.3% Ca, 0.6% Gd, with unavoidable impurities ≤0.05%, and the balance being Mg. The preparation method of the magnesium alloy includes the following steps: (1) Commercial pure Mg, pure Al, Mg-20wt.%Ca, and Mg-20wt.%Gd master alloys were selected as raw materials. The alloy components were weighed according to their mass percentage. After grinding to remove surface oxides and dirt, the pure Mg, pure Al, Mg-20wt.%Ca, and Mg-20wt.%Gd master alloys were kept at 420℃ for 3 hours. Under the protective atmosphere of CO2 and SF6, where the volume ratio of CO2 to SF6 was 95:5, the pure Mg was heated and melted at 710℃ and then the pure Al, Mg-20wt.%Ca, and Mg-20wt.%Gd master alloys were added. After melting for 25 minutes, the mixture was stirred and slag was removed. After standing for 30 minutes, high-purity Ar gas was introduced. After standing for another 25 minutes, the mixture was poured into a steel mold preheated at 250℃ and cooled to room temperature to obtain magnesium alloy ingots. (2) The magnesium alloy ingot obtained in step (1) is subjected to step homogenization treatment, hot extrusion, high temperature solution treatment, rolling, and isothermal annealing under constant stress to obtain a high-strength ductile magnesium alloy 2 based on isothermal annealing under constant stress. The stepped homogenization process is as follows: heat treatment at 320℃ for 2 hours, heat treatment at 420℃ for 3 hours, and finally heat treatment at 480℃ for 1 hour. The hot extrusion is carried out after holding at 410℃ for 40 minutes. The extrusion temperature is 410℃, the extrusion speed is 15mm / s, and the extrusion ratio is 20:1. The high-temperature solution treatment involves holding the solution at 500°C for 1 hour. The rolling process is as follows: the rolling temperature is 350℃, the temperature is held for 10 minutes between passes, 3 passes are rolled, then the temperature is reduced to 300℃ and rolled for 1 more pass, with a total reduction of 72%; The isothermal annealing treatment under constant stress is carried out by applying uniaxial tensile constant stress during isothermal annealing. The annealing temperature is 250℃, and a uniaxial tensile constant stress of 5MPa along the rolling direction is applied simultaneously. The annealing holding time is 60min. like Figure 1 As shown, the recrystallization area fraction of high-strength ductile-magnesium alloy 2, based on isothermal annealing under constant stress, reaches ~90.1%, essentially achieving complete recrystallization. Figure 2 As shown, its texture exhibits a weak texture with simultaneous deflection along RD and TD, and its intensity is only ~6.8mrd, as... Figure 3 The average grain size is ~7.7μm, and its room temperature tensile properties are a tensile strength of 239.5MPa and an elongation of 17.9%. Example 3

[0014] The high-strength ductile-magnesium alloy 3, based on isothermal annealing under constant stress, comprises, by mass percentage: 1.5% Al, 0.3% Ca, 0.5% Gd, with unavoidable impurities ≤0.05%, and the balance being Mg. The preparation method of the magnesium alloy includes the following steps: (1) Commercial pure Mg, pure Al, Mg-20wt.%Ca, and Mg-20wt.%Gd master alloys were selected as raw materials. The alloy components were weighed according to their mass percentage. After grinding to remove surface oxides and dirt, the pure Mg, pure Al, Mg-20wt.%Ca, and Mg-20wt.%Gd master alloys were kept at 430℃ for 3 hours. Under the protective atmosphere of CO2 and SF6, where the volume ratio of CO2 to SF6 was 95:5, the pure Mg was heated and melted at 710℃ and then the pure Al, Mg-20wt.%Ca, and Mg-20wt.%Gd master alloys were added. After melting for 25 minutes, the mixture was stirred and slag was removed. After standing for 30 minutes, high-purity Ar gas was introduced. After standing for another 25 minutes, the mixture was poured into a steel mold preheated at 250℃ and cooled to room temperature to obtain magnesium alloy ingots. (2) The magnesium alloy ingot obtained in step (1) is subjected to step homogenization treatment, hot extrusion, high temperature solution treatment, rolling, and isothermal annealing under constant stress to obtain a high-strength ductile magnesium alloy 3 based on isothermal annealing under constant stress. The stepped homogenization process is as follows: heat treatment at 320℃ for 2 hours, heat treatment at 420℃ for 3 hours, and finally heat treatment at 480℃ for 1 hour. The hot extrusion is carried out after holding at 410℃ for 40 minutes. The extrusion temperature is 410℃, the extrusion speed is 15mm / s, and the extrusion ratio is 20:1. The high-temperature solution treatment involves holding the solution at 500°C for 1 hour. The rolling process is as follows: the rolling temperature is 350℃, the temperature is held for 10 minutes between passes, 3 passes are rolled, then the temperature is reduced to 300℃ and rolled for 1 more pass, with a total reduction of 78%; The isothermal annealing treatment under constant stress is carried out by applying uniaxial tensile constant stress during isothermal annealing. The annealing temperature is 250℃, and a uniaxial tensile constant stress of 10MPa along the rolling direction is applied simultaneously. The annealing holding time is 50min. The high-strength PVC-Mg alloy 3, based on isothermal annealing under constant stress, exhibits a room temperature tensile strength of 234.6 MPa and an elongation of 19.0%.

[0015] Comparative Example 1 The paper "Influence of Aging Process on the Microstructure and Mechanical Properties of WE43 Magnesium Alloy," published in the journal "Heat Treatment of Metals, 2022, Vol. 47, No. 5, pp. 208-212," prepared a WE43 (Mg-3.04Y-2.70Nd-0.41Zr) alloy. The authors are Chen Lichao, Wang Changxi, Su Zhicheng, Wang Yuyu, Ren Jingtao, Li Jing, Deng Ting, and Zhao Liping. The preparation method involved heat-treating a conventionally cast WE43 alloy at 520℃ for 8 hours, followed by aging at 230℃ and 250℃ for 8, 12, 16, and 18 hours, respectively. The resulting alloy had an average grain size greater than 40 μm, a maximum tensile strength less than 220 MPa, and an elongation of only 5%.

[0016] Comparative Example 2 The paper "Microstructure and Mechanical Properties of Heat-Treated Mg-9Y-1Cu Alloy," published in the journal "Shanxi Metallurgy, 2020, Vol. 43, No. 4, pp. 10-13," describes the preparation of Mg-9Y-1Cu alloy. The authors are Wei Xiaojin, Feng Yabin, Sun Erdong, Liu Baosheng, Wang Zhengyi, and Zhang Fangping. The preparation method involves heat-treating a conventionally cast Mg-9Y-1Cu alloy at 400℃ for 10 hours and 430℃ for 24 hours, followed by aging at 200℃ for 12 hours. The aged alloy exhibits an average grain size of 44.8 μm, a tensile strength of 193 MPa, and an elongation of 14.5%.

[0017] Compared to existing technologies, this invention exhibits significant advantages in terms of alloy element content, process parameters, and manufacturing costs. In terms of alloy element design, the total alloy addition in this invention is ≤2.7 wt.%, with rare earth element addition ≤0.8 wt.%, far lower than the alloy content (>6 wt.%) and rare earth element addition (>2.7 wt.%) in existing technologies, thus reducing costs from the outset. Existing technologies often involve high heat treatment temperatures (>400℃), long treatment times (>3h), low recrystallization area fraction (<50%), and the resulting alloy texture often exhibits a strong basal plane texture with no texture deflection, and the texture peak intensity is typically >10 mrd. This invention achieves short-process processing through the synergistic adjustment of component interactions, proportions, processes, and process parameters. It enables recrystallization at lower temperatures (<300℃) and in shorter times (≤70min), significantly increasing the recrystallization area fraction (≥63.8%), substantially reducing the energy consumption and time of annealing heat treatment, improving production efficiency, and avoiding equipment damage caused by long-term high-temperature processing. Simultaneously, it weakens the basal texture of the alloy microstructure, resulting in a weak texture deflected along both RD and TD directions, with a peak recrystallization texture intensity ≤6.8mrd. In contrast, prior art heat treatment at higher temperatures (>400℃) results in magnesium alloys with coarse microstructures in Comparative Examples 1 and 2, with an average grain size >40μm, tensile strength <220MPa, and plasticity <14%. This invention, under low-energy-consumption and high-efficiency process conditions, introduces a large amount of highly thermally stable nano-Al-Gd and Al-Ca phases, which enhances strength while suppressing abnormal grain growth, achieving significant grain refinement with an average grain size ≤7.7μm. This results in a good balance of strength and plasticity in the alloy: tensile strength ≥234.6MPa and elongation ≥17.9%. Therefore, this invention achieves rapid recrystallization through the synergistic control of component interactions, proportions, processes, and process parameters, while simultaneously constructing a microstructure beneficial to performance. This effectively overcomes the bottleneck problems of existing technologies, such as coarse grains caused by long-term high-temperature heat treatment, making it difficult to simultaneously achieve both strength and plasticity.

[0018] Table 1. Comparison of room temperature mechanical properties of Examples 1-3 and Comparative Examples 1-2 Examples / Comparative Examples Tensile strength / MPa Elongation / % Example 1 247.4 21.9 Example 2 239.5 17.9 Example 3 234.9 19.0 Comparative Example 1 220 5 Comparative Example 2 193 14.5 Furthermore, the component ratios and process parameters differ in each embodiment of the present invention, resulting in different final properties and microstructures. This demonstrates that the superior effects obtained by the present invention are not determined by a specific component, ratio, or process parameter, but rather by the synergistic regulation of component interactions, ratios, processes, and process parameters. Moreover, the optimal effects can only be achieved within the scope of the claims of this invention. The high-strength ductile-magnesium alloy obtained by the present invention achieves rapid recrystallization at a lower temperature and in a shorter time, while simultaneously constructing a microstructure beneficial to performance through recrystallization. This microstructure possesses a weak texture with deflection along the rolling direction (RD) and transverse direction (TD), a peak strength ≤ 6.8 mrd, and an average grain size ≤ 7.7 μm, achieving a good balance between strength and plasticity, with a tensile strength ≥ 234.6 MPa and an elongation ≥ 17.9%.

Claims

1. A high-strength ductile-magnesium alloy based on isothermal annealing under constant stress, characterized in that: The alloy composition, by mass percentage, comprises: Al 1.2~1.5%, Ca 0.2~0.4%, Gd 0.5~0.8%, with a total alloy addition of ≤2.7%, unavoidable impurity content ≤0.05%, and the balance being Mg. The preparation method of the magnesium alloy includes the following steps: (1) Commercial pure Mg, pure Al, Mg-20wt.%Ca, and Mg-20wt.%Gd master alloys are selected as raw materials. The materials are proportioned according to the mass percentage of the alloy components. After grinding to remove the surface oxides and dirt, the pure Mg, pure Al, Mg-20wt.%Ca, and Mg-20wt.%Gd master alloys are kept at 400-450℃ for 2-3 hours. Under the protection of CO2 and SF6 mixed gas, the volume ratio of CO2 and SF6 is 90-99:1-10. The pure Mg is heated and melted at 690-720℃ and then pure Al, Mg-20wt.%Ca, and Mg-20wt.%Gd master alloys are added. After melting for 20-30 minutes, the mixture is stirred and slag is removed. After standing for 10-60 minutes, high-purity Ar gas is introduced. After standing for another 25-30 minutes, the mixture is poured into a steel mold preheated at 200-300℃. After cooling to room temperature, magnesium alloy ingots are obtained. (2) The magnesium alloy ingot obtained in step (1) is subjected to step homogenization treatment, hot extrusion, high temperature solution treatment, rolling, and isothermal annealing under constant stress to obtain a high-strength ductile magnesium alloy based on isothermal annealing under constant stress. The stepped homogenization process is as follows: heat treatment at 310-330℃ for 1-2 hours, then heat treatment at 415-430℃ for 3-4 hours, and then heat treatment at 470-490℃ for 1-2 hours. The hot extrusion is carried out after holding at 400-420℃ for 40-60 minutes. The extrusion temperature is 400-420℃, the extrusion speed is 12-16mm / s, and the extrusion ratio is 19:1-21:

1. The high-temperature solution treatment involves holding the solution at 490-510℃ for 0.5-4 hours. The rolling process is described as follows: 3-8 passes of unidirectional rolling at a rolling temperature of 280-400℃, with a holding time of 5-15 minutes between passes, and a total reduction of 70-80%. The isothermal annealing treatment under constant stress is carried out by applying uniaxial tensile constant stress during isothermal annealing. The annealing temperature is 210-270℃, and a uniaxial tensile constant stress of 2-20MPa along the rolling direction is applied at the same time. The annealing holding time is 20-70min. The high-strength PVC-Mg alloy texture based on isothermal annealing under constant stress has a peak strength ≤6.8mrd, recrystallization area fraction ≥63.8%, average grain size ≤7.7μm, tensile strength ≥234.6MPa, and elongation ≥17.9%.

2. The high-strength ductile-magnesium alloy based on isothermal annealing under constant stress as described in claim 1, characterized in that, The isothermal annealing treatment under constant stress described in step (2) involves applying uniaxial tensile constant stress during isothermal annealing, with an annealing temperature of 225-250℃ and an additional uniaxial tensile constant stress of 5-15MPa along the rolling direction. The annealing holding time is 25-60min.

3. The high-strength ductile-magnesium alloy based on isothermal annealing under constant stress as described in claim 1, characterized in that, The high-temperature solution treatment in step (2) involves holding the solution at 495-505℃ for 1-2 hours.

4. The high-strength ductile-magnesium alloy based on isothermal annealing under constant stress as described in claim 1, characterized in that, The rolling process described in step (2) is as follows: 4-6 passes of unidirectional rolling, with a rolling temperature of 300-350℃, a holding time of 10-12 minutes between passes, and a total reduction of 72-78%.

Images