A method for improving the plasticity of magnesium alloys by secondary regulation of twin orientation using torsional deformation

Abstract

The present invention discloses a method for improving the plasticity of a magnesium alloy by secondary manipulation of twin orientation through torsional deformation. The method comprises the following steps: applying compressive stress to a pretreated magnesium alloy bar for pre-deformation, wherein the compressive stress is applied perpendicular to the c-axis of the grains within the magnesium alloy bar, and the deformation amount of the pre-deformation is 0.5% to 8%; subjecting the pre-deformed magnesium alloy bar to one to eight torsional deformation passes at a temperature of 150°C to 250°C and a torsion angle of 10° to 180°, followed by annealing to obtain a high-plasticity magnesium alloy. The method of the present invention can achieve the purpose of secondary manipulation of twin orientation, thereby significantly improving the plasticity of the magnesium alloy bar. It has the advantages of simple process, convenient operation, and low equipment cost, and can be applied to large-sized magnesium alloy billets.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnesium alloy processing, and in particular relates to a method for improving the plasticity of magnesium alloy by secondary regulating twin orientation through torsional deformation. Background Art

[0002] In the social context of energy conservation and environmental protection, lightweighting has received widespread attention as an effective way. As we all know, magnesium alloys have the characteristics of low density, high specific strength, and high specific modulus. Therefore, they have excellent application prospects in the fields of aerospace, transportation, electronic products, etc. However, for magnesium alloy materials, their poor plasticity seriously restricts the widespread application of magnesium alloys. As a close-packed hexagonal crystal structure metal, the basal slip critical shear stress of magnesium alloy at room temperature is much smaller than the non-basal slip critical shear stress, which makes the basal orientation of the grains of magnesium alloy materials converge during the forming process, thereby forming a very strong basal texture. Since the basal slip is difficult to start, the strain cannot be further effectively coordinated, resulting in poor plasticity of magnesium alloy materials and difficulty in deformation. In order to improve the plasticity of magnesium alloys, severe plastic deformation processes such as equal channel angular extrusion and high-pressure torsion are usually used. However, these technologies have their limitations. Not only do they require the use of large equipment, but their processes are also relatively complicated. The sample size obtained is small, and it is difficult to perform secondary processing and forming later. Therefore, it is urgent to invent a method for improving the plasticity of plastic magnesium alloys with simple process and convenient operation. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for improving the plasticity of magnesium alloys by secondary regulation of twin orientation by torsional extrusion deformation, which can be applied to large-sized magnesium alloy billets.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions.

[0005] A method for improving the plasticity of a magnesium alloy by secondary regulation of twin orientation through torsional deformation comprises the following steps:

[0006] S1. performing homogenization annealing on the magnesium alloy rod, grinding, and cleaning to obtain a pretreated magnesium alloy rod;

[0007] S2. applying compressive stress to the pretreated magnesium alloy rod for pre-deformation; wherein the direction of applying the compressive stress is perpendicular to the c-axis of the grain inside the magnesium alloy rod, and the deformation amount of the pre-deformation is 0.5% to 8%;

[0008] S3, performing 1 to 8 torsional deformation on the pre-deformed magnesium alloy bar; the temperature of the torsional deformation is 150° C. to 250° C., and the torsion angle of the torsional deformation is 10° to 180°;

[0009] S4. Annealing the magnesium alloy rod after torsional deformation to obtain a high-plasticity magnesium alloy.

[0010] In the above method, preferably, in step S3, the extrusion rate of the torsional deformation is 0.01 mm / min to 100 mm / min, the torsional deformation is carried out under lubrication conditions, and the lubricant used for lubrication is at least one of graphite oil solution, MoS2 oil solution, graphite powder and grease.

[0011] In the above method, preferably, in step S2, the method of applying compressive stress is at least one of rolling and compression, the pre-deformation temperature is 25°C to 150°C, and the pre-deformation rate is 0.01mm / min to 100mm / min.

[0012] In the above method, preferably, in step S4, the specific process of annealing is: keeping warm at 150°C to 250°C for 6h to 48h, or keeping warm at 300°C to 500°C for 1h to 48h.

[0013] In the above method, preferably, in step S1, the temperature of the homogenization annealing is 300° C. to 500° C., and the time of the homogenization annealing is 6 h to 48 h.

[0014] In the above method, preferably, in step S4, the following treatment is further performed after annealing: the surface of the annealed magnesium alloy rod is polished using 600-1200 mesh sandpaper, then ultrasonically cleaned for 30-90 minutes, then cleaned with anhydrous ethanol, and dried.

[0015] In the above method, preferably, in step S1, the specific process of the polishing is: the surface of the magnesium alloy rod is polished with 600 mesh sandpaper to remove oil stains, and then polished with 1000 mesh, 1200 mesh, and 2500 mesh sandpaper in sequence to make the surface of the magnesium alloy rod clean and smooth; the specific process of the cleaning is: placing the polished magnesium alloy rod in a mixture of acetone and anhydrous ethanol for ultrasonic cleaning, then cleaning with anhydrous ethanol, and drying; the volume ratio of acetone to anhydrous ethanol in the mixture of acetone and anhydrous ethanol is 3:2.

[0016] Compared with the prior art, the advantages of the present invention are:

[0017] (1) The present invention provides a method for improving the plasticity of magnesium alloys by secondary regulation of twin orientation through torsional deformation, wherein the magnesium alloy rod is subjected to homogenization annealing, pre-deformation, torsional deformation, and annealing in sequence to obtain a high-plasticity magnesium alloy. In the method of the present invention, the magnesium alloy rod is subjected to pre-deformation with a deformation amount of 0.5% to 8% to fully promote the initial twin nucleation, so that tensile twins are introduced into the magnesium alloy rod, and the twin orientation is deviated from the basal plane and turned to 86.3°, thereby achieving the first regulation change of the twin orientation. For magnesium alloy materials with strong basal texture, this twin orientation change can weaken the basal texture and enhance the basal slip; then, the magnesium alloy rod with the tensile twins introduced is subjected to 1 to 8 torsional deformation, wherein the torsional deformation temperature is 150° to 250° and the torsion angle is 10° to 180°. The initial twin orientation is secondary regulated. The torsional deformation can form a spiral torsional shear stress to force the grains to deflect toward the torsion axis, further regulating the twin orientation. Specifically, for general grain orientation, the torsional deformation only slightly regulates the twin orientation. However, for deflected twins, the torsional shear stress can be used to secondary regulate the twin orientation inside the magnesium alloy bar, improving its twin orientation and satisfying the Schmidt law to maximize the basal slip Schmidt factor, so that the twin orientation is turned to the direction where basal slip is more easily activated, thereby promoting a large-scale activation of basal slip and ultimately significantly improving the plasticity of the magnesium alloy. The method of the present invention can achieve the purpose of secondary regulation of twin orientation, thereby significantly improving the plasticity of the magnesium alloy bar. It has the advantages of simple process, convenient operation, low equipment cost, etc., and can be applied to large-sized magnesium alloy billets.

[0018] (2) The method of the present invention further optimizes the annealing process of the magnesium alloy, performs stress relief annealing for 6h to 48h under low temperature conditions (150℃ to 250℃), removes stress while retaining the twin structure, refines the grains, and further improves the plasticity of the magnesium alloy; or performs recrystallization annealing for 1h to 48h under high temperature conditions (300℃ to 500℃), promotes twin-induced static recrystallization, eliminates the twin lamellae while retaining the orientation inherited by the twins, and further improves the plasticity of the magnesium alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the spiral extrusion die when the rotation angle of the extrusion deformation is 90° in Example 1 of the present invention.

[0020] Figure 2 Schematic diagram of the rotational evolution of twin orientation of the magnesium alloy rod in Example 1 of the present invention.

[0021] Figure 3 This is the basal plane pole figure of the high plasticity magnesium alloy (PT3E) in Example 1 of the present invention.

[0022] Figure 4This is a comparison diagram of the true stress-strain curves of the AZ31 magnesium alloy square bar billet (AS) and the high plasticity magnesium alloy (PT3E) in Example 1 of the present invention.

[0023] Figure 5 Schematic diagram of the spiral extrusion die when the rotation angle of the extrusion deformation is 180° in Example 2 of the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but the scope of protection of the present invention is not limited thereby. The materials and instruments used in the following examples are all commercially available.

[0025] Example 1:

[0026] A method of improving the plasticity of a magnesium alloy by secondary regulation of twin orientation by torsional deformation according to the present invention comprises the following steps:

[0027] S1. Select an AZ31 magnesium alloy rod with a diameter of 10 mm as the material and perform homogenization annealing on the magnesium alloy rod, that is, annealing at 350° C. for 12 hours. The AZ31 magnesium alloy rod is denoted as AS.

[0028] S2. After annealing, the outer surface of the magnesium alloy rod is polished with 600-mesh sandpaper to remove oil stains, and then polished with 1000-mesh, 1200-mesh and 2500-mesh sandpaper in sequence to make the surface of the magnesium alloy rod clean and smooth; then, acetone and anhydrous ethanol are mixed to prepare an ultrasonic cleaning solution according to a volume ratio of acetone to anhydrous ethanol of 3:2, and the polished magnesium alloy square rod is placed in the ultrasonic cleaning solution for ultrasonic cleaning for 30 minutes; finally, the magnesium alloy rod is taken out, cleaned with anhydrous ethanol, and then dried with cold air from a hair dryer to obtain a pretreated magnesium alloy rod.

[0029] S3. The pretreated magnesium alloy bar was fixed and, at room temperature (i.e., 25°C), a compressive deformation force parallel to the extrusion direction (ED) was applied. This compression deformation direction was perpendicular to the c-axis of the grains within the magnesium alloy bar. The compression rate was 1 mm / min and the deformation was 3%. This uniformly pre-compressed the magnesium alloy bar along the ED direction. Because the compressive deformation force was perpendicular to the c-axis of the grains within the AZ31 magnesium alloy bar, tensile twins were easily introduced into the bar. At this point, the volume fraction of tensile twins was 18%, and the twin orientation deviated by approximately 86.3° from the basal plane, achieving the first controlled change in twin orientation.

[0030] S4. The pre-compressed magnesium alloy rod is subjected to torsional deformation using a spiral torsional extrusion die, that is, one pass of torsional deformation with a rotation angle of 90° is performed under the conditions of a temperature of 150°C, an extrusion rate of 0.1 mm / min, and a graphite oil solution as a lubricant, thereby introducing torsional shear deformation. The shear stress acts on the twins so that the twin orientation rotates toward the torsion axis, thereby obtaining a magnesium alloy with a larger basal slip Schmidt factor, and its basal slip Schmidt factor is 0.368.

[0031] S5. The magnesium alloy rod after torsional deformation is subjected to stress relief annealing, that is, it is kept at 200°C for 6 hours to retain the twin lamellar structure and realize secondary control of the twin orientation of the magnesium alloy rod; the outer surface of the annealed magnesium alloy rod is polished with 600-1200 mesh sandpaper, and then placed in an ultrasonic cleaning solution for ultrasonic cleaning for 60 minutes. Finally, the magnesium alloy rod is cleaned with anhydrous ethanol and then dried with cold air from a hair dryer to obtain a high-plasticity magnesium alloy, which is recorded as PT3E.

[0032] Uniaxial tensile tests were performed on the original AZ31 magnesium alloy bar and the high-plasticity magnesium alloy prepared in Example 1 to test their elongation at break. The elongation at break of the original AZ31 magnesium alloy bar was 13.8%, and the elongation at break of the high-plasticity magnesium alloy was 33.2%, indicating that its plasticity was increased by 2.4 times.

[0033] Figure 2 Schematic diagram of the evolution of twin orientation rotation in a magnesium alloy bar in Example 1 of the present invention. The initial billet exhibits a typical basal texture, with grains oriented perpendicular to the extrusion direction. However, after pre-twinning, the crystal orientation shifts parallel to the extrusion direction. After torsional deformation, the twin orientation is reoriented toward the torsional plane, further facilitating basal slip initiation.

[0034] Figure 3 : This is the basal plane pole figure of the high plasticity magnesium alloy (PT3E) in Example 1 of the present invention. It can be seen that the grains are mainly distributed in the 45° direction position in the (0001) pole figure.

[0035] Figure 4 This is a comparison diagram of the true stress-strain curves of the AZ31 magnesium alloy bar (AS) and the high plasticity magnesium alloy (PT3E) in Example 1 of the present invention. The elongation of the high plasticity magnesium alloy in Example 1 can be increased by up to 2.4 times.

[0036] Example 2:

[0037] A method of improving the plasticity of a magnesium alloy by secondary regulation of twin orientation by torsional deformation according to the present invention comprises the following steps:

[0038] S1. Select AZ31 magnesium alloy square bars with a size of 10 (width) × 10 (thickness) × 100 (length) mm as the material, and perform homogenization annealing on the magnesium alloy bars, i.e., annealing at 450° C. for 6 h.

[0039] S2. After annealing, the outer surface of the magnesium alloy rod is polished with 600-mesh sandpaper to remove oil stains, and then polished with 1000-mesh, 1200-mesh and 2500-mesh sandpaper in sequence to make the surface of the magnesium alloy rod clean and smooth; then, acetone and anhydrous ethanol are mixed to prepare an ultrasonic cleaning solution according to a volume ratio of acetone to anhydrous ethanol of 3:2, and the polished magnesium alloy square rod is placed in the ultrasonic cleaning solution for ultrasonic cleaning for 60 minutes; finally, the magnesium alloy rod is taken out, cleaned with anhydrous ethanol, and then dried with cold air from a hair dryer to obtain a pretreated magnesium alloy rod.

[0040] S3. The pretreated magnesium alloy bar was rolled in a single pass in the transverse direction (TD) at room temperature, perpendicular to the c-axis of the grains within the bar. The rolling rate was 1 mm / min and the reduction (i.e., deformation) was 5%. Because the external force was perpendicular to the c-axis of the grains within the AZ31 magnesium alloy bar, tensile twins were easily introduced into the bar. At this point, the twin volume fraction was 38%, and the twin orientation shifted to approximately 86.3° in the TD, achieving the first controlled change in twin orientation.

[0041] S4. The rolled magnesium alloy bar is subjected to torsional deformation using a spiral torsional extrusion die, that is, the torsional deformation is performed for two passes with a rotation angle of 180° per pass under the conditions of a temperature of 200°C, an extrusion rate of 10 mm / min, and a molybdenum disulfide solution as a lubricant, thereby introducing torsional shear deformation. The shear stress acts on the twins so that the twin orientation rotates toward the torsion axis, thereby obtaining a magnesium alloy with a larger basal slip Schmidt factor, and its basal slip Schmidt factor is 0.423.

[0042] S5. The magnesium alloy rod after torsional deformation is subjected to twin-induced recrystallization annealing, that is, it is kept at 350°C for 5 hours to eliminate the twin lamellar structure while retaining the twin orientation, so that the magnesium alloy rod can achieve secondary control of the twin orientation; the outer surface of the annealed magnesium alloy rod is polished with sandpaper, and then placed in an ultrasonic cleaning solution for ultrasonic cleaning for 60 minutes. Finally, the magnesium alloy rod is cleaned with anhydrous ethanol and then blown dry with cold air from a hair dryer to obtain a high-plasticity magnesium alloy.

[0043] Uniaxial tensile tests were performed on the original AZ31 magnesium alloy bar and the high-plasticity magnesium alloy prepared in Example 2 to test their elongation at fracture. The elongation at fracture of the original AZ31 magnesium alloy bar was 13.8%, and the elongation at fracture of the high-plasticity magnesium alloy was 42%. The elongation at fracture was increased by 3.04 times, which means that the plasticity of the high-plasticity magnesium alloy prepared in this example was greatly improved.

[0044] Comparative Example 1:

[0045] A method for improving the plasticity of a magnesium alloy comprises the following steps:

[0046] S1. Select AZ31 magnesium alloy square bars with a size of 10 (width) × 10 (thickness) × 100 (length) mm as the material, and perform homogenization annealing on the magnesium alloy bars, i.e., annealing at 450° C. for 6 h.

[0047] S2. After annealing, the outer surface of the magnesium alloy rod is polished with 600-mesh sandpaper to remove oil stains, and then polished with 1000-mesh, 1200-mesh and 2500-mesh sandpaper in sequence to make the surface of the magnesium alloy rod clean and smooth; then, acetone and anhydrous ethanol are mixed to prepare an ultrasonic cleaning solution according to a volume ratio of acetone to anhydrous ethanol of 3:2, and the polished magnesium alloy square rod is placed in the ultrasonic cleaning solution for ultrasonic cleaning for 60 minutes; finally, the magnesium alloy rod is taken out, cleaned with anhydrous ethanol, and then dried with cold air from a hair dryer to obtain a pretreated magnesium alloy rod.

[0048] S3. The pretreated magnesium alloy bar was fixed and, at room temperature, a compressive deformation force was applied parallel to the extrusion direction (ED), perpendicular to the c-axis of the grains within the magnesium alloy bar. This compression deformation was performed at a rate of 1 mm / min and a deformation of 5%, resulting in uniform pre-compression of the magnesium alloy bar along the ED. At this point, the volume fraction of tensile twins was 36%, and the twin orientation deviated by approximately 86.3° from the basal plane, achieving the first controlled change in twin orientation.

[0049] S4: The pre-compressed magnesium alloy rod was subjected to torsional deformation using a spiral torsional extrusion die. This deformation was performed at a temperature of 300°C, an extrusion rate of 0.1 mm / min, and a graphite oil solution as a lubricant, with a single pass and a rotation angle of 180°. However, due to the excessively high temperature during the torsional deformation, recrystallized grains appeared at the twin locations, the twins disappeared, and the basal slip Schmidt factor was 0.312.

[0050] S5. The magnesium alloy rod after torsional deformation is subjected to stress relief annealing, that is, the rod is kept at 200°C for 6 hours; the outer surface of the annealed magnesium alloy rod is polished with paper, and then placed in an ultrasonic cleaning solution for ultrasonic cleaning for 60 minutes. Finally, the magnesium alloy rod is cleaned with anhydrous ethanol and then blown dry with cold air from a hair dryer to obtain a magnesium alloy billet.

[0051] Uniaxial tensile tests were performed on the original AZ31 magnesium alloy bar and the magnesium alloy billet prepared in Comparative Example 1 to test their elongation at break. The original AZ31 magnesium alloy bar had an elongation at break of 13.8%, while the magnesium alloy billet had an elongation at break of 15.6%. Their plasticity was only slightly improved, and the improvement was not significant. This is because: when the temperature of the torsional deformation is too high, dynamic recrystallization occurs during the torsional deformation process, causing the twins to disappear and the twin orientation to disappear as well. The twin orientation cannot be retained, and thus secondary control of the twin orientation cannot be achieved. Therefore, the torsional deformation in the method of the present invention needs to be carried out within the temperature range of 150°C to 250°C. Otherwise, the twin orientation cannot be secondary controlled, and the twins will disappear instead, thus failing to effectively improve the plasticity of the magnesium alloy.

[0052] Comparative Example 2:

[0053] A method for improving the plasticity of a magnesium alloy comprises the following steps:

[0054] S1. Select AZ31 magnesium alloy square bars with a size of 10 (width) × 10 (thickness) × 100 (length) mm as the material, and perform homogenization annealing on the magnesium alloy bars, i.e., annealing at 450° C. for 6 h.

[0055] S2. After annealing, the outer surface of the magnesium alloy rod is polished with 600-mesh sandpaper to remove oil stains, and then polished with 1000-mesh, 1200-mesh and 2500-mesh sandpaper in sequence to make the surface of the magnesium alloy rod clean and smooth; then, acetone and anhydrous ethanol are mixed to prepare an ultrasonic cleaning solution according to a volume ratio of acetone to anhydrous ethanol of 3:2, and the polished magnesium alloy square rod is placed in the ultrasonic cleaning solution for ultrasonic cleaning for 60 minutes; finally, the magnesium alloy rod is taken out, cleaned with anhydrous ethanol, and then dried with cold air from a hair dryer to obtain a pretreated magnesium alloy rod.

[0056] S3. The pretreated magnesium alloy bar was fixed and, at room temperature, a compressive deformation force was applied parallel to the extrusion direction (ED), perpendicular to the c-axis of the grains within the magnesium alloy bar. This compression deformation was performed at a rate of 1 mm / min and a deformation of 10%, resulting in uniform pre-compression of the magnesium alloy bar along the ED. At this point, the volume fraction of tensile twins reached 32%, and the twin orientation deviated by approximately 86.3° from the basal plane, achieving the first controlled change in twin orientation.

[0057] S4. The pre-compressed magnesium alloy rod was subjected to torsional deformation using a spiral torsional extrusion die. Specifically, the torsional deformation was performed at a temperature of 200°C, an extrusion rate of 0.1 mm / min, and a graphite oil solution as a lubricant, with a rotation angle of 180° in one pass. At this point, the basal slip Schmidt factor of the magnesium alloy rod was 0.376.

[0058] S5. The magnesium alloy rod after torsional deformation is subjected to stress relief annealing, that is, the rod is kept at 200°C for 6 hours; the outer surface of the annealed magnesium alloy rod is polished with paper, and then placed in an ultrasonic cleaning solution for ultrasonic cleaning for 60 minutes. Finally, the magnesium alloy rod is cleaned with anhydrous ethanol and then blown dry with cold air from a hair dryer to obtain a magnesium alloy billet.

[0059] Uniaxial tensile tests were conducted on the original AZ31 magnesium alloy bar and the magnesium alloy billet prepared in Comparative Example 2 to test their elongation at break. The original AZ31 magnesium alloy bar had an elongation at break of 13.8%, while the magnesium alloy billet had an elongation at break of 28.6%. This indicates that the plasticity improvement is not ideal. This is because when the pre-deformation deformation is too large, twin growth dominates, the nucleation effect is weakened, and the improvement in the magnesium alloy's plasticity is reduced. Therefore, the pre-deformation deformation in the method of the present invention must be controlled within the range of 0.5% to 8%. Otherwise, the improvement in the magnesium alloy's plasticity is reduced.

[0060] The method of the present invention pre-deforms a magnesium alloy bar by applying compressive stress (the pre-deformation amount is 0.5% to 8%) to pre-twin it, and then performs a subsequent spiral extrusion deformation (the extrusion deformation temperature is 150° to 250°C and the torsion angle is 10° to 180°). This significantly improves the elongation at break. Furthermore, if the pre-deformation amount is too large or too small, or the extrusion deformation temperature is too high or too low, the elongation at break will not be significantly improved. The method of the present invention, whether pre-twinning or spiral extrusion, is a simple deformation method that can be easily repeated multiple times. The deformation amount of both deformations is easily controlled, resulting in a simple process and convenient operation.

[0061] To address the poor plasticity of magnesium alloy bars, the present invention applies torsional deformation to secondary control twin orientation, thereby significantly softening the twin orientation and greatly improving the basal slip Schmidt factor. A suitable annealing process is also determined: stress relief annealing at low temperatures (150°C to 250°C) for 6 to 48 hours removes stress while preserving the twin structure and refining the grains; alternatively, recrystallization annealing at high temperatures (300°C to 500°C) for 1 to 48 hours promotes twin-induced recrystallization, eliminates twin lamellae, and retains the twin-inherited orientation, further improving the plasticity of the magnesium alloy. The pre-deformation amount and torsional deformation parameters designed in the present invention can be precisely controlled and varied, the deformation process is simple, the equipment cost is low, and it can be repeatedly introduced on a large scale. This has important theoretical and practical significance for the preparation and promotion of high-performance magnesium alloys.

[0062] The above description is only a preferred embodiment of the present invention and does not constitute any formal limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the spirit and technical solution of the present invention, use the methods and technical contents disclosed above to make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention, still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for improving the plasticity of magnesium alloy by secondary regulation of twin orientation through torsional deformation, characterized in that: The following steps are involved: S1. performing homogenization annealing on the magnesium alloy rod, and then grinding and cleaning to obtain a pretreated magnesium alloy rod; S2. applying compressive stress to the pretreated magnesium alloy rod for pre-deformation; the direction of applying the compressive stress is perpendicular to the c-axis of the grain inside the magnesium alloy rod, and the deformation amount of the pre-deformation is 0.5% to 8%; S3, performing 1 to 8 torsional deformation on the pre-deformed magnesium alloy bar; the temperature of the torsional deformation is 150°C to 250°C, and the torsion angle of the torsional deformation is 10° to 180°; S4. Annealing the magnesium alloy bar after torsional deformation to obtain a high-plasticity magnesium alloy; the specific process of the annealing is: keeping it at 150°C to 250°C for 6h to 48h, or keeping it at 300°C to 500°C for 1h to 48h.

2. The method for improving the plasticity of magnesium alloy by secondary regulation of twin orientation by torsional deformation according to claim 1, characterized in that: In step S3, the extrusion rate of the torsional deformation is 0.01 mm / min to 100 mm / min, and the torsional deformation is performed under lubrication conditions. The lubricant used for the lubrication is at least one of graphite oil solution, MoS2 oil solution, graphite powder and grease.

3. The method for improving the plasticity of magnesium alloy by secondary regulation of twin orientation by torsional deformation according to claim 1, characterized in that: In step S2, the compressive stress is applied by at least one of rolling and compression, the pre-deformation temperature is 25°C to 150°C, and the pre-deformation rate is 0.01 mm / min to 100 mm / min.

4. The method for improving the plasticity of magnesium alloy by secondary regulation of twin orientation by torsional deformation according to any one of claims 1 to 3, characterized in that: In step S1, the temperature of the homogenization annealing is 300° C. to 500° C., and the time of the homogenization annealing is 6 hours to 48 hours.

5. The method for improving the plasticity of magnesium alloy by secondary regulation of twin orientation by torsional deformation according to any one of claims 1 to 3, characterized in that: In step S4, the following treatment is further performed after annealing: the surface of the annealed magnesium alloy rod is polished with 600-1200 mesh sandpaper, then ultrasonically cleaned for 30-90 minutes, then cleaned with anhydrous ethanol, and dried.

6. The method for improving the plasticity of magnesium alloy by secondary regulation of twin orientation by torsional deformation according to any one of claims 1 to 3, characterized in that: In step S1, the specific process of the polishing is: the surface of the magnesium alloy rod is polished with 600 mesh sandpaper to remove oil stains, and then polished with 1000 mesh, 1200 mesh, and 2500 mesh sandpaper in sequence to make the surface of the magnesium alloy rod clean and smooth; the specific process of the cleaning is: placing the polished magnesium alloy rod in a mixture of acetone and anhydrous ethanol for ultrasonic cleaning, then cleaning with anhydrous ethanol, and drying; the volume ratio of acetone to anhydrous ethanol in the mixture of acetone and anhydrous ethanol is 3:2.

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