A magnesium alloy with high strain rate superplasticity and a short process for preparing the same

Abstract

The present invention provides a high strain rate superplastic magnesium alloy and a short process for preparing the same. The composition of the magnesium alloy is as follows by mass percentage: 8.5-9.2% of aluminum, 0.8-1.2% of zinc, 0.4-0.7% of tin, and the balance is magnesium and additive elements, and the additive element is 0.05-0.1% of manganese. The preparation method of the alloy includes casting, solution treatment, extrusion, rolling and annealing treatment. The present invention can achieve large-scale non-uniform dynamic recrystallization, further expand the microstructural non-uniformity, and obtain a coarse / fine grain micro-layer with significantly different sizes, namely a non-uniform lamellar structure, inside the magnesium alloy structure; at high temperature and high strain rate, the superplasticity of the magnesium alloy is >600%, and the alloy can be rapidly formed at high temperature; the alloy has low cost, simple preparation process, few rolling passes and short annealing time, breaks through the technical constraints of the poor superplastic forming ability of the original commercial magnesium alloy, and can be used for industrial rapid forming of complex magnesium alloy components.

Description

Technical Field

[0001] The present invention relates to the field of metal materials, and particularly to a magnesium alloy with high strain rate superplasticity and a short process preparation method thereof. Background Art

[0002] Magnesium and its alloys have high specific strength, damping properties and specific stiffness. At the same time, they also have good elastic modulus, thermal conductivity, welding performance and fatigue resistance, and have good industrial value and prospects in many industries such as national defense, military, automotive, medical, and electronics. Magnesium alloy sheets are considered industrial products with great application potential in the deep processing field. However, magnesium has a close-packed hexagonal structure and few independent slip systems at room temperature, resulting in poor processing performance and difficulty in room temperature forming. Therefore, the preparation of complex magnesium alloy components strongly depends on the high temperature superplasticity ability, that is, showing extremely high elongation without necking at high temperature, and the superplasticity is ~300%. According to the existing technology reports: the lower the strain rate, the finer the alloy grain size, and the easier it is to obtain high superplasticity.

[0003] In the prior art, in order to improve the superplastic deformation ability of magnesium alloys, large deformation means are usually used to achieve substantial grain refinement, such as equal channel angular pressing, differential speed rolling, and high pressure torsion. However, large deformation technologies are usually expensive, have complex processes, low efficiency, and small sizes, which limit large-scale applications. Commercial conventional rolling and extrusion, as important means for forming magnesium alloy sheets, have a wide range of applications, but the obtained magnesium alloy sheets have large grain sizes and are difficult to meet the requirements of superplasticity ability for forming complex components. In addition, limited by the atomic diffusion rate, the newly generated dislocations during the deformation process are difficult to recover and annihilate in time, and the superplasticity will be greatly reduced as the strain rate increases. That is to say, if an alloy with high superplasticity is to be obtained, it is necessary to be under a lower strain rate condition. However, in actual industrial production, considering energy consumption and cost, it is urgent to obtain superplastic magnesium alloys at high strain rates. In addition, other ways to obtain superplastic magnesium alloys also include adding rare earth elements to magnesium alloys to form thermally stable phases, and suppressing grain growth during the hot deformation process of superplastic magnesium alloys by forming uniform fine-grained / ultrafine-grained structures. However, due to the high price of rare earth elements, it is not conducive to large-scale production applications. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a magnesium alloy with high strain rate superplasticity. The composition of the alloy is calculated by mass percentage: aluminum 8.5 - 9.2%, zinc 0.8 - 1.2%, and tin 0.4 - 0.7%, and the rest is magnesium and additive elements. The additive element is manganese: 0.05 - 0.1%. Its preparation method includes the following steps:

[0005] (1) Casting: Under a protective gas, pure magnesium is melted at 690 - 710 °C; after the magnesium ingot melts, the temperature is lowered to 675 - 685 °C, slag is removed to eliminate impurities and the oxide layer on the melt surface, followed by degassing and refining processes, and then pure aluminum, pure zinc, and pure tin are added; it is kept warm at 690 - 710 °C for 10 - 20 min, then magnesium-manganese master alloy is added, and after complete melting, argon is blown in for refining, surface impurities and the oxide layer are removed, it is allowed to stand, and after being kept warm for 5 - 15 min, a magnesium alloy casting blank is obtained through iron mold casting. The protective gas is a mixed gas of CO2 and SF6, and the volume ratio of CO2 to SF6 is 90 - 99:10 - 1;

[0006] (2) Solution treatment + Extrusion: The magnesium alloy casting blank obtained in step (1) is subjected to multi-stage solution treatment; subsequently, extrusion deformation treatment is carried out. It is kept warm at 370 - 390 °C for 20 - 30 min, and the extrusion die is preheated at ~370 - 390 °C. The extrusion temperature is ~370 - 390 °C, the extrusion rate is ~60 - 70 mm / min, and the extrusion ratio is ~16:1 - 35:1. After extrusion deformation treatment, it is air-cooled to room temperature to obtain a magnesium alloy extruded sheet;

[0007] (3) Rolling + Annealing: A cemented carbide liner is added to the upper and lower surfaces of the magnesium alloy extruded sheet obtained in step (2). The liner is kept warm together with the magnesium alloy for synchronous single-pass large reduction rolling. The roll speed is 10 - 15 m / min, the roll temperature is 100 - 150 °C. The rolling temperature is 280 - 350 °C, the holding time is 5 - 50 min, and the reduction is 70 - 90%; after rolling, it is air-cooled to obtain a magnesium alloy rolled sheet, and then short-time annealing treatment is carried out. The annealing temperature is 280 - 350 °C, the annealing time is 200 - 360 s, and then it is air-cooled to obtain a magnesium alloy;

[0008] The multi-stage solution treatment described in step (2) is as follows: It is kept warm at 310 - 315 °C for 0.5 - 1 h, then at 410 - 420 °C for 10 - 15 h, and then at 435 - 445 °C for ~1.5 - 2.5 h;

[0009] The magnesium alloy obtained in step (3) has a completely recrystallized non-uniform lamellar structure, with coarse / fine grain micro-layers that are tightly intertwined and have significant size differences inside;

[0010] Furthermore, the rolling temperature described in step (3) is 290 - 330 °C, the holding time is 10 - 15 min; the annealing temperature is 290 - 320 °C, and the annealing time is 270 - 330 s.

[0011] Compared with the prior art, the advantages of the present invention are:

[0012] Through the synergistic effects of alloy element ratio, interaction, and process, the present invention promotes the non-uniform dynamic recrystallization refinement during rolling and the dynamic precipitation of a high density of second phases in the coupling matrix, providing non-uniform nucleation sites for the precipitation of phases such as Mg 17 Al 12 etc. A large number of Mg 17 Al 12 phases are introduced into the fine grain region, obtaining a magnesium alloy rolled sheet with non-uniform dynamic recrystallization and non-uniform dynamic precipitation; by using the process in combination with the solid solution of Sn element in the matrix and the non-uniform precipitation of Mg 17 Al 12 phases, the microstructural non-uniformity in the rolled sheet is expanded; it can promote static recrystallization and growth. The non-uniformly distributed dynamic precipitation phases provide a non-uniform pinning effect on static recrystallization and growth during annealing, while suppressing the growth of fine grains, obtaining a non-uniform lamellar structure with closely spaced coarse / fine grain micro-layers. The structure contains both coarse grain layers of 5 - 15 microns and ultra-fine / fine grain layers of ≤3 microns, as well as non-uniform precipitation of sub-micron Mg 17 Al 12 etc. phases. Therefore, during the high-temperature superplastic deformation process of the alloy obtained by the present invention at high strain rates, through the interlayer interaction, the structure "self-refines", stabilizes the grain structure, and obtains excellent superplasticity at high strain rates. The alloy obtained by the present invention has a superplasticity >600% at high temperature (≥300°C) and high strain rate (≥5×10 -3 s -1 ). BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Fig. is a SEM micrograph of a magnesium alloy with a non-uniform lamellar structure having closely spaced coarse and fine grain layers obtained in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0014] Example 1

[0015] Taking the Mg-8.5Al-1.2Zn-0.4Sn-0.05Mn alloy as an example, the ingredients are prepared according to the above mass percentages:

[0016] (1) Introduce protective gas into the melting furnace. The protective gas is a mixed gas of CO₂ and SF₆ with a volume ratio of 90:10. Put pure magnesium ingots into the crucible and heat them to melt at a temperature of 710 °C. After the magnesium ingots are melted, cool the temperature to 685 °C, skim the impurities and oxide layer on the surface of the melt to obtain pure magnesium melt. After degassing and refining the above-mentioned pure magnesium melt, add pure aluminum, pure zinc and pure tin to the pure magnesium melt. After the above-mentioned magnesium alloy melt is held at 710 °C for 10 minutes, continue to add magnesium-manganese master alloy. After complete melting, fully stir the melt, blow argon gas from the bottom of the melt for refining, and remove the surface impurities and oxide layer to obtain magnesium alloy melt. After the above-mentioned magnesium alloy melt is statically held and insulated for 15 minutes, cast the magnesium alloy melt through an iron mold to obtain a magnesium alloy casting blank.

[0017] (2) Perform three-stage step solution treatment on the magnesium alloy casting blank obtained in step (1) at ~310 °C / ~0.5 h + ~410 °C / ~15 h + 445 °C / 2 h.

[0018] (3) Preheat the obtained magnesium alloy solution ingot at ~370 °C for 20 min, and preheat the extrusion die at ~370 °C. The extrusion temperature is ~370 °C, the extrusion rate is ~60 mm / min, and the extrusion ratio is ~35:1. After extrusion deformation treatment, air-cool to room temperature to obtain magnesium alloy extrusion sheets.

[0019] (4) Add a cemented carbide liner to the upper and lower surfaces of the obtained magnesium alloy extrusion sheets. The liner is held with the magnesium alloy for synchronous rolling. The holding and rolling temperature is ~290 °C, the holding time is ~15 min, the reduction is ~70%, the roll speed is 10 m / min, the roll temperature is 150 °C, and air-cool after rolling to obtain magnesium alloy rolled sheets.

[0020] (5) Perform short-time annealing treatment on the obtained magnesium alloy rolled sheets. The annealing temperature is 290 °C and the annealing time is 330 s, and then air-cool to finally obtain a fully recrystallized non-uniform lamellar structure magnesium alloy.

[0021] The obtained magnesium alloy has a superplasticity of up to ~610% at a high strain rate (1×10 -2 s -1 ) at 300 °C.

[0022] Example 2

[0023] Taking the Mg-9Al-0.82Zn-0.5Sn-0.08Mn alloy as an example, charge materials according to the above mass percentages:

[0024] (1) Introduce protective gas into the melting furnace. The protective gas is a mixed gas of CO₂ and SF₆ with a volume ratio of 93:7. Place the pure magnesium ingot in the crucible and heat it to melt at a temperature of 710 °C. After the magnesium ingot melts, cool it down to 685 °C, skim the impurities and oxide layer on the surface of the melt to obtain pure magnesium melt. After degassing and refining the above pure magnesium melt, add pure aluminum, pure zinc and pure tin to the pure magnesium melt. After holding the above magnesium alloy melt at 700 °C for 15 minutes, continue to add magnesium-manganese master alloy. After it is completely melted, fully stir the melt, blow argon from the bottom of the melt for refining, and remove the surface impurities and oxide layer to obtain magnesium alloy melt. After standing and holding the above magnesium alloy melt for 10 minutes, pour the magnesium alloy melt through an iron mold to obtain a magnesium alloy ingot blank;

[0025] (2) Carry out three-stage stepped solution treatment of ~315 °C / ~1 h + ~415 °C / ~12 h + 440 °C / 2 h on the magnesium alloy ingot blank obtained in step (1);

[0026] (3) Preheat the obtained magnesium alloy solution ingot at ~380 °C for 25 min, and preheat the extrusion die at ~370 °C. The extrusion temperature is ~380 °C, the extrusion rate is ~70 mm / min, the extrusion ratio is ~16:1. After extrusion deformation treatment, air-cool to room temperature to obtain magnesium alloy extruded sheet;

[0027] (4) Add a cemented carbide liner on the upper and lower surfaces of the obtained magnesium alloy extruded sheet. The liner is held with the magnesium alloy for synchronous rolling. The holding and rolling temperature is ~305 °C, the holding time is ~15 min, the reduction is ~85%, the roll speed is 10 m / min, the roll temperature is 125 °C, and after rolling, air-cool to obtain magnesium alloy rolled sheet;

[0028] (5) Carry out short-time annealing treatment on the obtained magnesium alloy rolled sheet. The annealing temperature is 305 °C, the annealing time is 275 s, and then air-cool to finally obtain a fully recrystallized non-uniform lamellar structure magnesium alloy.

[0029] The obtained magnesium alloy has superplasticity of ~710% at a high strain rate (1.5×10 -2 s -1 ) at 300 °C.

[0030] Example 3

[0031] Taking the Mg-9.5Al-0.8Zn-0.7Sn-0.05Mn alloy as an example, charge according to the above mass percentages:

[0032] (1) Introduce protective gas into the melting furnace. The protective gas is a mixed gas of CO₂ and SF₆ with a volume ratio of 93:5. Put pure magnesium ingots into the crucible and heat and melt them at a temperature of 700 °C. After the magnesium ingots are melted, cool down to 680 °C, skim the slag to remove impurities and oxide layers on the melt surface to obtain pure magnesium melt. After degassing and refining the above pure magnesium melt, add pure aluminum, pure zinc, and pure tin to the pure magnesium melt. After the above magnesium alloy melt is held at 690 °C for 15 minutes, continue to add magnesium-manganese master alloy. After complete melting, fully stir the melt, blow argon from the bottom of the melt for refining, and remove surface impurities and oxide layers to obtain magnesium alloy melt. Let the above magnesium alloy melt stand and be held at a certain temperature, and then pour the magnesium alloy melt through an iron mold to obtain a magnesium alloy casting blank;

[0033] (2) Carry out three-stage step solution treatment of ~315 °C / ~0.5 h + ~420 °C / ~10 h + 440 °C / 2 h on the magnesium alloy casting blank obtained in step (1);

[0034] (3) Preheat the obtained magnesium alloy solution ingot at ~390 °C for 20 min, and preheat the extrusion die at ~390 °C. The extrusion temperature is ~390 °C, the extrusion rate is ~70 mm / min, the extrusion ratio is ~35:1. After extrusion deformation treatment, air-cool to room temperature to obtain magnesium alloy extruded sheets;

[0035] (4) Add a cemented carbide liner to the upper and lower surfaces of the obtained magnesium alloy extruded sheets. The liner is held at the same temperature as the magnesium alloy and undergoes synchronous rolling. The holding and rolling temperature is ~305 °C, the holding time is ~15 min, the reduction is ~85%, the roll speed is 15 m / min, the roll temperature is 100 °C, and after rolling, air-cool to obtain magnesium alloy rolled sheets;

[0036] (5) Carry out short-time annealing treatment on the obtained magnesium alloy rolled sheets. The annealing temperature is 300 °C, the annealing time is 300 s, and then air-cool to finally obtain a fully recrystallized non-uniform lamellar structure magnesium alloy. The obtained magnesium alloy has a superplasticity of ~680% at a high strain rate of 1×10 -2 s -1 ) at 300 °C.

[0037] Example 4

[0038] Taking the Mg-8.7Al-0.9Zn-0.6Sn-0.09Mn alloy as an example, charge materials according to the above mass percentages:

[0039] (1) Introduce protective gas into the melting furnace. The protective gas is a mixed gas of CO₂ and SF₆ with a volume ratio of 93:5. Put pure magnesium ingots into the crucible and heat and melt them at a temperature of 700 °C. After the magnesium ingots are melted, lower the temperature to 680 °C, skim the slag to remove impurities and oxide layers on the surface of the melt to obtain pure magnesium melt. After degassing and refining the above pure magnesium melt, add pure aluminum, pure zinc and pure tin to the pure magnesium melt. After the above magnesium alloy melt is held at 700 °C for 20 minutes, continue to add magnesium-manganese master alloy. After complete melting, fully stir the melt, blow argon from the bottom of the melt for refining, and remove surface impurities and oxide layers to obtain magnesium alloy melt. Let the above magnesium alloy melt stand and heat-insulate, and then cast the magnesium alloy melt through an iron mold to obtain a magnesium alloy ingot blank;

[0040] (2) Perform three-stage step solution treatment of ~310 °C / ~1 h + ~410 °C / ~15 h + 435 °C / 2.5 h on the magnesium alloy ingot blank obtained in step (1);

[0041] (3) Preheat the obtained magnesium alloy solution ingot at ~380 °C for 30 min, and preheat the extrusion die at ~380 °C. The extrusion temperature is ~380 °C, the extrusion rate is ~65 mm / min, the extrusion ratio is ~16:1. After extrusion deformation treatment, air-cool to room temperature to obtain magnesium alloy extruded sheets;

[0042] (4) Add a cemented carbide lining plate to the upper and lower surfaces of the obtained magnesium alloy extruded sheets. The lining plate is heat-insulated together with the magnesium alloy and subjected to synchronous rolling. Among them, the heat-insulation and rolling temperature is ~300 °C, the heat-insulation time is ~10 min, the reduction is ~85%, the roll speed is 10 m / min, the roll temperature is 100 - 150 °C, and air-cool after rolling to obtain magnesium alloy rolled sheets;

[0043] (5) Perform short-time annealing treatment on the obtained magnesium alloy rolled sheets. The annealing temperature is 300 °C and the annealing time is 270 s, and then air-cool to finally obtain a fully recrystallized non-uniform lamellar structure magnesium alloy.

[0044] The obtained magnesium alloy has superplasticity of ~650% at a high strain rate (5×10 [[ID=1:16]] -3 s -1 ) at 300 °C.

[0045] Comparative Example 1

[0046] T.J. Lee and W.J. Kim (T.J. Lee, W.J. Kim, Successful transition from low-temperature superplasticity to high-strain-rate superplasticity withincreasing temperature in an ultrafine-grained Mg–Y–Zn–Zr alloy, Journal ofAlloys and Compounds, Volume 817, 2020, 153298) disclosed the preparation of an Mg-9.48Zn-1.71Y-0.44Zr-0.02Mn-rare earth (Y) magnesium alloy by high-proportion differential speed rolling with severe plastic deformation technology. The obtained alloy has an ultrafine / grain-refined structure with an average grain size of about ~1 μm. At 300 °C, the superplasticity is 160% at a strain rate of 10 -2 s -1 and the superplasticity is up to ~310% at a strain rate of 10 -3 s -1 The obtained alloy does not have a non-uniform lamellar structure.

[0047] The superplasticity of the alloy obtained in Example 1 of the present invention is the lowest among all examples. Compared with Comparative Example 1, the addition of rare earth elements and noble metal Zr is omitted in Example 1 of the present invention, which saves costs, and the total alloy addition content is lower than that of the alloy disclosed in Comparative Example 1. The alloy obtained in Example 1 of the present invention has a non-uniform lamellar structure with fine-grained layers (average grain size ~1.4 μm) / coarse-grained layers (average grain size ~7.8 μm) closely spaced. The difference in the two grain sizes is significant. Compared with the single ultrafine / grain-refined structure in Comparative Example 1, the alloy obtained in Example 1 of the present invention has two types of structures, thick and thin. The superplasticity of the alloy disclosed in Comparative Example 1 is 160% at a strain rate of 10 -2 s -1 and the superplasticity is up to ~310% at a strain rate of 10 -3 s -1 It can be seen that the slower the strain rate disclosed in Comparative Example 1, the better the superplasticity. At the same temperature of 300 °C and the fastest strain rate of ~10 -2 s -1Under the conditions, the superplasticity of the alloy obtained in Example 1 of the present invention (~610%) is much higher than the highest superplasticity of the alloy obtained in Comparative Example 1. Moreover, even under high strain rate conditions, the present invention can still obtain alloy superplasticity exceeding that obtained at low strain rates in the prior art, achieving unexpected technical effects compared with the prior art. In addition, their structures are different: the alloy obtained in Example 1 of the present invention has a non-uniform lamellar structure, while no non-uniform lamellar structure is found in the alloy obtained in Comparative Example 1.

[0048] Comparative Example 2

[0049] Taking the Mg-8.5Al-1.2Zn-0.4Sn-0.05Mn alloy (with the same alloy components and contents as in Example 1) as an example, the preparation method is as follows:

[0050] (1) Introduce the protective gas into the melting furnace. The protective gas is a mixed gas of CO2 and SF6 with a volume ratio of 90:10. Put the pure magnesium ingot into the crucible and heat it to melt at a temperature of 710°C. After the magnesium ingot melts, cool it down to 685°C, skim the impurities and oxide layer on the melt surface to obtain pure magnesium melt. After degassing and refining the above pure magnesium melt, add pure aluminum, pure zinc and pure tin to the pure magnesium melt. After the above magnesium alloy melt is held at 710°C for 10 minutes, continue to add magnesium-manganese master alloy. After complete melting, fully stir the melt, blow argon from the bottom of the melt for refining, and remove the surface impurities and oxide layer to obtain magnesium alloy melt. After the above magnesium alloy melt is statically held and insulated for 15 minutes, the magnesium alloy melt is cast into a magnesium alloy ingot through a iron mold;

[0051] (2) Subject the magnesium alloy ingot obtained in step (1) to solution treatment at ~430°C for ~3h;

[0052] (3) Preheat the obtained magnesium alloy solution ingot at ~410°C for 20 min, and preheat the extrusion die at ~410°C. The extrusion temperature is ~410°C, the extrusion rate is ~55 mm / min, the extrusion ratio is ~37:1. After extrusion deformation treatment, air-cool it to room temperature to obtain a magnesium alloy extruded sheet; [[ID=·16]]

[0053] ( ) Roll the obtained magnesium alloy extruded sheet for 3 passes. The rolling temperature is ~360°C, the holding time is ~15 min, the reduction per pass is 50%, the total reduction is ~87.5%, the roll speed is 15 m / min, the roll temperature is 100°C, and air-cool it after rolling to obtain a magnesium alloy rolled sheet;

[0054] (5) Subject the obtained magnesium alloy rolled sheet to short-time annealing treatment. The annealing temperature is 355°C, the annealing time is 500 s, and then air-cool it.

[0055] The obtained magnesium alloy has a high strain rate (5×10-3 s -1 ) The superplasticity is up to 150%.

[0056] Compared with Example 1 of the present invention, although the components of the two are the same, the solution treatment process, extrusion, rolling and annealing processes adopted in Comparative Example 2 are different from those in Example 1. The superplasticity of the alloy obtained in Comparative Example 2 is ~150%, which is much lower than the superplasticity of the alloy obtained in Example 1 (~610%). This shows that the excellent superplasticity of the alloy obtained in the present invention is achieved by the synergistic effect of the alloy components, ratio and process.

[0057] In addition, it can be seen from all the examples of the present invention that the superplasticity of the alloy obtained in Example 2 is the most excellent. The components in the alloy of this example are not the ones with the highest alloy addition content, and it is under the condition of the highest strain rate. According to the technical inspiration given by the prior art, the higher the alloy content and the lower the strain rate, the better the superplasticity of the alloy can be. However, in Example 2 of the present invention, the most excellent superplasticity is obtained without the highest alloy content and the slowest strain rate. From this, it can be seen that the most excellent performance of the alloy obtained in the present invention is achieved by the synergistic effect of the alloy component ratio, interaction and process, which optimizes the alloy performance.

Claims

1. A magnesium alloy with high strain rate superplasticity, characterized in that The alloy composition is by mass percentage: 8.5 - 9.2% aluminum, 0.8 - 1.2% zinc, and 0.4 - 0.7% tin, with the rest being magnesium and additive elements. The additive element is 0.05 - 0.1% manganese; its preparation method includes the following steps: (1) Casting: Under a protective gas, pure magnesium is melted at 690 - 710 °C; after the magnesium ingot melts, the temperature is lowered to 675 - 685 °C, slag is removed to remove impurities and oxide layers on the melt surface, and then degassing and refining treatments are carried out. Then, pure aluminum, pure zinc, and pure tin are added; It is held at 690 - 710 °C for 10 - 20 min, then magnesium - manganese master alloy is added. After complete melting, argon is blown in for refining, surface impurities and oxide layers are removed, it is allowed to stand, and after holding for 5 - 15 min, a magnesium alloy ingot blank is obtained by casting in an iron mold. The protective gas is a mixed gas of CO2 and SF6, and the volume ratio of CO2 to SF6 is 90 - 99:10 - 1; (2) Solution + extrusion: The magnesium alloy ingot blank obtained in step (1) is subjected to multi - stage solution treatment; then extrusion deformation treatment is carried out: it is held at 370 - 390 °C for 20 - 30 min, and the extrusion die is pre - heated at ~370 - 390 °C. The extrusion temperature is ~370 - 390 °C, the extrusion rate is ~60 - 70 mm / min, and the extrusion ratio is ~16:1 - 35:

1. After extrusion deformation treatment, it is air - cooled to room temperature to obtain a magnesium alloy extruded sheet; (3) Rolling + annealing: A hard alloy backing plate is added to the upper and lower surfaces of the magnesium alloy extruded sheet obtained in step (2). The backing plate is held with the magnesium alloy for heat preservation, and synchronous single - pass heavy reduction rolling is carried out: the roll speed is 10 - 15 m / min, the roll temperature is 100 - 150 °C. The rolling temperature is 280 - 350 °C, the heat preservation time is 5 - 50 min, and the reduction is 70 - 90%; after rolling, it is air - cooled to obtain a magnesium alloy rolled sheet, and then short - time annealing treatment is carried out. The annealing temperature is 280 - 350 °C, the annealing time is 200 - 360 s, and then it is air - cooled to obtain the magnesium alloy; The multi - stage solution treatment described in step (2) is: it is held at 310 - 315 °C for 0.5 - 1 h, then at 410 - 420 °C for 10 - 15 h, and then at 435 - 445 °C for ~1.5 - 2.5 h; The magnesium alloy obtained in step (3) has a fully recrystallized non - uniform lamellar structure, with coarse / fine crystal micro - layers that are tightly intertwined and have significant size differences inside.

2. The superplastic magnesium alloy with high strain rate according to claim 1, characterized in that, The rolling temperature described in step (3) is 290 - 330 °C, the heat preservation time is 10 - 15 min; the annealing temperature is 290 - 320 °C, and the annealing time is 270 - 330 s.

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