Preparation method of high-toughness magnesium alloy based on low-temperature multidirectional high-speed impact

Abstract

The invention belongs to the technical field of alloy materials, and provides a preparation method of a high-toughness magnesium alloy based on low-temperature multidirectional high-speed impact. The twin network structure is introduced into a fine-grain magnesium alloy matrix, the technical problems that in the prior art, strength and plasticity of magnesium alloy are difficult to synergistically improve, and fine-grain or high-rare-earth-content alloy is difficult to form the twin network structure are solved, and the beneficial effects that strength and plasticity are synchronously enhanced, and the application range of the magnesium alloy is widened are achieved. In addition, according to the preparation method of the high-toughness magnesium alloy based on low-temperature multidirectional high-speed impact, the technological process is short in time consumption, liquid nitrogen can be recycled, the preparation method has the characteristics of high efficiency, low carbon and environmental protection, and a feasible scheme is provided for large-scale industrial application of the high-toughness magnesium alloy.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy materials, and particularly to a method for preparing a high-strength and high-toughness magnesium alloy based on low-temperature multi-directional high-speed impact. Background Art

[0002] Magnesium alloy is the lightest metal structural material in practical applications, with advantages such as high specific strength and specific stiffness, easy processing and forming, and recyclability. It is one of the most ideal structural materials for lightweighting in fields such as transportation, aerospace, and weaponry.

[0003] It is a technical problem urgently to be solved in the prior art that the strength and plasticity of magnesium alloy are difficult to be synergistically improved. Although methods such as severe plastic deformation processing (such as rotary forging process) to refine grains and introducing rare earth elements for solid solution or second-phase strengthening will greatly improve the strength, they will significantly reduce the plasticity. Currently, through multi-directional hot working processes such as hot rolling and hot forging, a twin network structure can be introduced in non-rare earth or low-rare earth content (Re≤5wt.%) magnesium alloys with grain size generally greater than 50μm. However, it is very difficult to introduce a twin network structure in fine grains after hot working or in magnesium alloys with grain refinement agents in the solidification process, especially in high-rare earth (Re≥5wt.%) content magnesium alloys (grain size generally less than 50μm), because the decrease in grain size and the increase in rare earth content have an inhibitory effect on twin formation.

[0004] The method for preparing a high-strength and high-toughness magnesium alloy based on low-temperature multi-directional high-speed impact provided in this article, based on the characteristic that twins are easily excited at high strain rates, introduces a twin network structure in fine grains through low-temperature high-speed multi-directional impact. Among them, high-speed multi-directional impact is to excite multiple twin variants inside a grain to form a twin network to divide the grain. The internal of the high-speed impact material is an adiabatic temperature rise process, and low temperature is to inhibit the dynamic recovery of dislocations and further introduce a high density of dislocations, solving the technical problems in the prior art that it is difficult to synergistically improve the strength and plasticity of magnesium alloy and it is difficult to form a twin network structure in fine-grained or high-rare earth content alloys. Summary of the Invention

[0005] The present invention provides a method for preparing a high-strength and high-toughness magnesium alloy based on low-temperature multi-directional high-speed impact, so as to solve the technical problems in the prior art that it is difficult to synergistically improve the strength and plasticity of magnesium alloy and it is difficult to form a twin network structure in fine-grained or high-rare earth content alloys.

[0006] The present invention provides a method for preparing a high-strength and high-toughness magnesium alloy based on low-temperature multi-directional high-speed impact, including the following steps: (1) Weigh pure magnesium, Mg-Y alloy or pure aluminum according to the element composition of the high-strength and high-toughness magnesium alloy based on low-temperature multi-directional high-speed impact, and perform preheating treatment; (2) Under the protection of a mixed gas, melt pure magnesium to obtain molten magnesium, raise the furnace temperature to a preset temperature, add Mg-Y alloy or pure aluminum and perform heat preservation treatment; (3) Under the protection of the mixed gas, raise the furnace temperature, carry out refining under stirring conditions, and perform heat preservation treatment to obtain a magnesium alloy melt; (4) Lower the furnace temperature, pour the magnesium alloy melt into a mold to obtain a magnesium alloy ingot; (5) Carry out solution treatment and hot extrusion treatment on the magnesium alloy ingot in sequence to obtain a fine-grained magnesium alloy matrix with an average grain size of less than 30 μm; (6) Place the fine-grained magnesium alloy matrix in liquid nitrogen for cryogenic pretreatment; (7) Carry out multi-directional high-speed impact on the cryogenically pretreated fine-grained magnesium alloy matrix to obtain a high-strength and tough magnesium alloy based on cryogenic multi-directional high-speed impact; The elemental composition of the high-strength and tough magnesium alloy based on cryogenic multi-directional high-speed impact is 0-6 at% yttrium, 0-6 at% aluminum, the balance being magnesium and unavoidable impurities, or 0-6 at% aluminum, the balance being magnesium and unavoidable impurities; The multi-directional high-speed impact is a cyclic impact carried out sequentially in the X, Y, and Z directions. Each impact cycle includes at least 3 commutation impacts. Before each impact, the fine-grained magnesium alloy matrix is placed in liquid nitrogen for cryogenic pretreatment.

[0007] According to a method for preparing a high-strength and tough magnesium alloy based on cryogenic multi-directional high-speed impact provided by the present invention, in the step (1), the temperature of the preheating treatment is 190-210 °C.

[0008] According to a method for preparing a high-strength and tough magnesium alloy based on cryogenic multi-directional high-speed impact provided by the present invention, in the step (2), the furnace temperature is 680-700 °C, and the heat preservation treatment time is 20-30 min.

[0009] According to a method for preparing a high-strength and tough magnesium alloy based on cryogenic multi-directional high-speed impact provided by the present invention, in the step (3), the furnace temperature is 730-740 °C, the stirring time is 5-8 min, and the heat preservation treatment time is 30-40 min.

[0010] According to a method for preparing a high-strength and tough magnesium alloy based on cryogenic multi-directional high-speed impact provided by the present invention, in the step (4), the furnace temperature is 720 °C, and the mold is preheated to 190-210 °C.

[0011] According to a method for preparing a high-strength and tough magnesium alloy based on cryogenic multi-directional high-speed impact provided by the present invention, in the step (5), the solution treatment temperature is 300-550 °C, the solution treatment time is 8-48 h, the hot extrusion treatment temperature is 300-430 °C, the extrusion ratio of the hot extrusion treatment is 10-50:1, and the extrusion speed of the hot extrusion treatment is 40-200 mm / min.

[0012] According to a preparation method of a high-strength and high-toughness magnesium alloy based on low-temperature multi-directional high-speed impact provided by the present invention, in the step (6), the time for low-temperature pretreatment is 5 to 20 minutes.

[0013] According to a preparation method of a high-strength and high-toughness magnesium alloy based on low-temperature multi-directional high-speed impact provided by the present invention, in the step (7), the equipment for multi-directional high-speed impact is a Hopkinson bar, and the impact strain rate ≥ 1000 s -1 , and the deformation amount of each impact is 2 to 15%.

[0014] According to a preparation method of a high-strength and high-toughness magnesium alloy based on low-temperature multi-directional high-speed impact provided by the present invention, the mixed gas is a mixed gas of SF 6 and CO 2 .

[0015] The preparation method of the high-strength and high-toughness magnesium alloy based on low-temperature multi-directional high-speed impact provided by the present invention solves the technical problems in the prior art that it is difficult to synergistically improve the strength and plasticity of magnesium alloys, and it is difficult to form a twin network structure in fine-grained or high-rare-earth-content alloys by introducing a twin network structure into the fine-grained magnesium alloy matrix, achieving the beneficial effects of simultaneously enhancing strength and plasticity and broadening the application range of magnesium alloys. Moreover, the preparation method of the high-strength and high-toughness magnesium alloy based on low-temperature multi-directional high-speed impact provided by the present invention has a short process time and can recycle liquid nitrogen, combining high efficiency and low-carbon environmental protection characteristics, providing a feasible solution for the large-scale industrial application of high-strength and high-toughness magnesium alloys. In addition, the preparation method of the high-strength and high-toughness magnesium alloy based on low-temperature multi-directional high-speed impact provided by the present invention has a wide applicability and can be realized in both rare-earth and non-rare-earth magnesium alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0017] Figure 1 It is a comparison diagram of the microstructure and properties of the Mg-3at.% Y alloy before and after low-temperature multi-directional high-speed impact provided in Embodiment 1 of the present invention; Figure 2 It is a comparison diagram of the microstructure and properties of the Mg-3at.% Al alloy before and after low-temperature multi-directional high-speed impact provided in Embodiment 2 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions in the present invention in conjunction with the accompanying drawings in the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts belong to the scope of protection of the present invention.

[0019] The following will describe the method for preparing a high-strength and tough magnesium alloy based on low-temperature multi-directional high-speed impact of the present invention in conjunction with Figures 1 - 2 the description of the present invention.

[0020] Figure 1 It is a comparison diagram of the microstructural properties of the Mg-3at.% Y alloy before and after low-temperature multi-directional high-speed impact provided in Embodiment 1 of the present invention.

[0021] As Figure 1 shown, it is a comparison diagram of the microstructural properties of the Mg-3at.% Y alloy before and after low-temperature multi-directional high-speed impact provided in Embodiment 1 of the present invention, where Figure 1 (a) is the phase diagram of the Mg-3at.% Y alloy after hot extrusion treatment before low-temperature multi-directional high-speed impact, Figure 1 (b) is the phase diagram of the Mg-3at.% Y alloy after low-temperature multi-directional high-speed impact, Figure 1(c) shows the stress-strain curves of the Mg-3at.% Y alloy before and after low-temperature multi-directional high-speed impact. It can be seen that the average grain size of the Mg-3at.% Y alloy is 13.1 μm without low-temperature multi-directional high-speed impact. After low-temperature high-speed multi-directional impact, the matrix grain size remains unchanged, but a large number of fine and dense twins appear inside the grains, and the twin width is between 0.2 and 1.2 μm. The yield strength of the Mg-3at.% Y alloy after hot extrusion treatment is 233.1 Mpa, the tensile strength is 295.4 MPa, and the elongation is 3.6%; the yield strength of the Mg-3at.% Y alloy after low-temperature multi-directional high-speed impact is 296.6 Mpa, the tensile strength is 373.4 MPa, and the elongation is 8.3%; compared with the Mg-3at.% Y alloy without low-temperature multi-directional high-speed impact, the yield is increased by 27%, the tensile is increased by 26%, and the elongation is increased by 128%. Generally, it is difficult to introduce a similar twin state in fine-grained magnesium alloys with high rare earth content because the addition of rare earth elements will significantly increase the critical resolved shear stress of twins, and fine grains also have a strong inhibitory effect on the activation of twins. Thus, it can be seen that the preparation method of high-strength and tough magnesium alloys based on low-temperature multi-directional high-speed impact provided by the present invention utilizes the characteristics of different mechanical responses of dislocations and twins at high strain rates, that is, under high strain rate conditions, the movement of dislocations is limited by a short time scale and cannot fully expand and cross-slip, that is, it cannot fully relieve local stress, so it is easier to induce twin nucleation to quickly release local stress, and successfully introduces a twin network structure in the Mg-3at.% Y fine grains, obtaining a good strengthening and toughening effect.

[0022] Figure 2 It is a comparison diagram of the microstructure and properties of the Mg-3at.% Al alloy before and after low-temperature multi-directional high-speed impact provided in Example 2 of the present invention.

[0023] As Figure 2 shown, it is a comparison diagram of the microstructure and properties of the Mg-3at.% Al alloy before and after low-temperature multi-directional high-speed impact provided in Example 2 of the present invention, where Figure 2 (a) is the phase diagram of the Mg-3at.% Al alloy after hot extrusion treatment before low-temperature multi-directional high-speed impact, Figure 2 (b) is the phase diagram of the Mg-3at.% Al alloy after low-temperature multi-directional high-speed impact, Figure 2(c) are the stress-strain curves of Mg-3at.% Al alloy before and after low-temperature multi-directional high-speed impact. It can be seen that the average grain size of Mg-3at.% Al alloy is 10.8 μm without low-temperature multi-directional high-speed impact. After low-temperature high-speed multi-directional impact, the matrix grain size remains unchanged, while a large number of fine and dense twins appear inside the grains, and the twin width is between 0.4 and 1.4 μm. The yield strength of Mg-3at.% Al alloy after hot extrusion treatment is 97.2 MPa, the tensile strength is 244.6 MPa, and the elongation is 28.8%; the yield strength of Mg-3at.% Al alloy after low-temperature multi-directional high-speed impact is 295.9 Mpa, the tensile strength is 312.4 MPa, and the elongation is 23.6%; compared with Mg-3at.% Al alloy without low-temperature multi-directional high-speed impact, the yield strength is increased by 204%, the tensile strength is increased by 28%, and the elongation only decreases by 17%. Although both are extruded fine grains, the width of twins in Mg-3at.% Al alloy is larger than that in Mg-3at.% Y, and the cross situation is more significant, which is because the inhibitory effect of non-rare earth elements on twins is worse than that of rare earth elements. Thus, it can be seen that the preparation method of high-strength and tough magnesium alloy based on low-temperature multi-directional high-speed impact provided by the present invention can make the alloy yield 295.9 Mpa after constructing a twin network structure in Mg-3at.% Al alloy, which can be comparable to rare earth magnesium alloy and still maintain high plasticity. Considering the cost advantage of non-rare earth magnesium alloy, the low-temperature multi-directional high-speed impact process has greater application potential in the field of non-rare earth magnesium alloy.

[0024] In summary, the preparation method of high-strength and tough magnesium alloy based on low-temperature multi-directional high-speed impact provided by the present invention successfully constructs a twin network structure in rare earth and non-rare earth magnesium alloys after hot extrusion treatment, and further strengthens and toughens the magnesium alloy after hot extrusion treatment. The low-temperature multi-directional high-speed impact process is efficient and simple, and has the value of large-scale industrial application. The present invention is also applicable to coarse-grained samples, but the advantage of introducing a twin network structure in fine grains is more significant. Moreover, the fine-grained samples adopted by the present invention are not limited to those obtained by plastic processing, and magnesium alloys with grain refinement by adding grain refiners or controlling the cooling rate during solidification are also applicable to the present invention.

[0025] In the present invention, a preparation method of high-strength and tough magnesium alloy based on low-temperature multi-directional high-speed impact includes the following steps: (1) Weigh pure magnesium, Mg-Y alloy or pure aluminum according to the element composition of high-strength and tough magnesium alloy based on low-temperature multi-directional high-speed impact, and carry out preheating treatment; (2) Under the protection of mixed gas, melt pure magnesium to obtain molten magnesium, raise the furnace temperature to a preset temperature, add Mg-Y alloy or pure aluminum and carry out heat preservation treatment; (3) Under the protection of mixed gas, raise the furnace temperature, carry out refining under stirring conditions, and carry out heat preservation treatment to obtain a magnesium alloy melt; (4) Lower the furnace temperature, pour the magnesium alloy melt into a mold to obtain a magnesium alloy ingot; (5) Subject the magnesium alloy ingot to solution treatment and hot extrusion treatment in sequence to obtain a fine-grained magnesium alloy matrix with an average grain size less than 30 μm; (6) Place the fine-grained magnesium alloy matrix in liquid nitrogen for cryogenic pretreatment; (7) Subject the cryogenically pretreated fine-grained magnesium alloy matrix to multi-directional high-speed impact to obtain a high-strength and tough magnesium alloy based on cryogenic multi-directional high-speed impact; The elemental composition of the high-strength and tough magnesium alloy based on cryogenic multi-directional high-speed impact is: yttrium 0 - 6 at%, aluminum 0 - 6 at%, the balance being magnesium and inevitable impurities, or aluminum 0 - 6 at%, the balance being magnesium and inevitable impurities; The multi-directional high-speed impact is a cyclic impact carried out sequentially along the X, Y, and Z directions. Each impact cycle includes at least 3 commutation impacts. Before each impact, the fine-grained magnesium alloy matrix is placed in liquid nitrogen for cryogenic pretreatment.

[0026] In the present invention, in step (1), the temperature of the preheating treatment is 190 - 210 °C, preferably 195 - 205 °C.

[0027] In the present invention, in step (2), the furnace temperature is 680 - 700 °C, preferably 685 - 695 °C; the holding time of the heat preservation treatment is 20 - 30 min, preferably 22 - 28 min, more preferably 24 - 26 min.

[0028] In the present invention, in step (3), the furnace temperature is 730 - 740 °C, the stirring time is 5 - 8 min, preferably 6 - 7 min; the holding time of the heat preservation treatment is 30 - 40 min, preferably 32 - 38 min, more preferably 34 - 36 min.

[0029] In the present invention, in step (4), the furnace temperature is 720 °C, and the mold is preheated to 190 - 210 °C.

[0030] In the present invention, in step (5), the temperature of the solution treatment is 300 - 550 °C, preferably 400 - 550 °C, more preferably 430 - 550 °C; the time of the solution treatment is 8 - 48 h, preferably 10 - 36 h, more preferably 12 - 24 h; the temperature of the hot extrusion treatment is 300 - 430 °C, preferably 300 - 400 °C; the extrusion ratio of the hot extrusion treatment is 10 - 50:1, preferably 15 - 40:1, more preferably 16 - 20:1; the extrusion speed of the hot extrusion treatment is 40 - 200 mm / min, preferably 80 - 160 mm / min, more preferably 100 - 140 mm / min.

[0031] In the present invention, in the step (6), the time for low-temperature pretreatment is 5 to 20 min, preferably 8 to 18 min, and more preferably 14 to 16 min.

[0032] In the present invention, in the step (7), the device for multi-directional high-speed impact is a Hopkinson bar, and the impact strain rate is ≥1000 s -1 , and the deformation amount per impact is 2 to 15%, preferably 5 to 12%, and more preferably 7 to 10%.

[0033] In the present invention, the mixed gas is a mixed gas of SF 6 and CO 2 .

[0034] Example 1 According to the proportion of Mg-3Y (at.%) alloy, pure magnesium and Mg-Y master alloy were weighed according to the elemental composition, and preheated at 200 °C for 60 min; Under the protection of a mixed gas of SF 6 and CO 2 , pure magnesium was melted at 680 °C, then the furnace temperature was raised to 700 °C, the Mg-Y master alloy was added, and after holding for 25 minutes, the slag on the melt surface was removed; Under the protection of a mixed gas of SF 6 and CO 2 , the furnace temperature was raised to 735 °C, and refined under vigorous stirring for 7 min, and held for 35 min to obtain a magnesium alloy melt; Subsequently, the furnace temperature was lowered to 720 °C, and the magnesium alloy melt was cast into a mold preheated to 200 °C to obtain a magnesium alloy ingot; The magnesium alloy ingot was solution-treated at 550 °C for 12 h, and then hot-extruded at 400 °C with an extrusion ratio of 16:1 and an extrusion speed of 120 mm / min to obtain a fine-grained magnesium alloy matrix with an average grain size of less than 30 μm; The fine-grained magnesium alloy matrix was immersed in liquid nitrogen for 15 min for low-temperature pretreatment; A Hopkinson bar with a penetration rod diameter of 14 mm was used to impact the fine-grained magnesium alloy matrix cut into 10*10*10 mm along the X, Y, and Z directions at a pressure of 0.7 Mpa once each, so that the strain rate of the fine-grained magnesium alloy matrix reached 1000 s -1 or more, and the deformation amount per time was 9%. Moreover, before each impact, the fine-grained magnesium alloy matrix was immersed in liquid nitrogen for 15 min for low-temperature pretreatment to obtain a high-strength and tough magnesium alloy based on low-temperature multi-directional high-speed impact.

[0035] After testing, for the high-strength and tough magnesium alloy obtained in this embodiment based on low-temperature multi-directional high-speed impact, compared with the Mg-3Y (at.%) alloy without low-temperature multi-directional high-speed impact, the matrix grain size remains unchanged, but a large number of fine and dense twins appear inside the grains, and the twin width is between 0.2 and 1.2 μm. The yield strength of the high-strength and tough magnesium alloy obtained in this embodiment based on low-temperature multi-directional high-speed impact is 296.6 Mpa, the tensile strength is 373.4 MPa, and the elongation is 8.3%. Compared with the Mg-3 at.% Y alloy without low-temperature multi-directional high-speed impact, the yield strength is increased by 27%, the tensile strength is increased by 26%, and the elongation is increased by 128%.

[0036] Example 2 According to the proportion of the Mg-3Al (at.%) alloy, pure magnesium and Mg-Al master alloy were weighed according to the elemental composition, and preheated at 200 °C for 60 min; In SF 6 and CO 2 Under the protection of the mixed gas, pure magnesium was melted at 680 °C, then the furnace temperature was raised to 700 °C, pure Al was added, and after holding for 25 minutes, the molten slag on the surface of the melt was removed; In SF 6 and CO 2 Under the protection of the mixed gas, the furnace temperature was raised to 735 °C, and refined for 7 min under the condition of vigorous stirring, and held for 35 min to obtain a magnesium alloy melt; Subsequently, the furnace temperature was lowered to 720 °C, and the magnesium alloy melt was cast into a mold preheated to 200 °C to obtain a magnesium alloy ingot; The magnesium alloy ingot was first solution-treated at 430 °C for 12 h, and then hot-extruded at 300 °C with an extrusion ratio of 16:1 and an extrusion speed of 120 mm / min to obtain a fine-grained magnesium alloy matrix with an average grain size of less than 30 μm; The fine-grained magnesium alloy matrix was immersed in liquid nitrogen for 15 min for low-temperature pretreatment; Using a Hopkinson bar with a penetrator diameter of 14 mm, the fine-grained magnesium alloy matrix cut into 10*10*10 mm was impacted once in the X, Y, and Z directions with a pressure of 0.5 Mpa, so that the strain rate of the fine-grained magnesium alloy matrix reached 1000 s -1 Above, the deformation amount per time is 9%. And before each impact, the fine-grained magnesium alloy matrix was immersed in liquid nitrogen for 15 min for low-temperature pretreatment to obtain a high-strength and tough magnesium alloy based on low-temperature multi-directional high-speed impact.

[0037] After testing, for the high-strength and high-toughness magnesium alloy obtained in this embodiment based on low-temperature multi-directional high-speed impact, compared with the Mg-3Al (at.%) alloy without low-temperature multi-directional high-speed impact, the matrix grain size remains unchanged, but a large number of fine and dense twins appear inside the grains, and the twin width is between 0.4 and 1.4 μm. The yield strength of the high-strength and high-toughness magnesium alloy obtained in this embodiment based on low-temperature multi-directional high-speed impact is 295.9 Mpa, the tensile strength is 312.4 MPa, and the elongation is 23.6%. Compared with the Mg-3at.% Y alloy without low-temperature multi-directional high-speed impact, the yield strength is increased by 204%, the tensile strength is increased by 28%, and the elongation only decreases by 17%.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a high-strength and tough magnesium alloy based on low-temperature multi-directional high-speed impact, characterized in that: The following steps are involved: (1) Weigh pure magnesium, Mg-Y alloy or pure aluminum according to the elemental composition of high-strength and toughness magnesium alloy based on low-temperature multi-directional high-speed impact, and perform preheating treatment; (2) Under the protection of the mixed gas, pure magnesium is melted to obtain molten magnesium, the furnace temperature is increased to a preset temperature, Mg-Y alloy or pure aluminum is added, and heat preservation treatment is performed; (3) Under the protection of the mixed gas, the furnace temperature is increased, and refining and heat preservation treatment are performed under stirring conditions to obtain a magnesium alloy melt; (4) lowering the furnace temperature and casting the magnesium alloy melt into a mold to obtain a magnesium alloy ingot; (5) subjecting the magnesium alloy ingot to solution treatment and hot extrusion treatment in sequence to obtain a fine-grained magnesium alloy matrix having an average grain size of less than 30 μm; (6) placing the fine-grained magnesium alloy substrate in liquid nitrogen for low-temperature pretreatment; (7) subjecting the fine-grained magnesium alloy matrix after low-temperature pretreatment to multi-directional high-speed impact to obtain a high-strength and toughness magnesium alloy based on low-temperature multi-directional high-speed impact; The element composition of the high-strength and toughness magnesium alloy based on low-temperature multi-directional high-speed impact is 0-6 at% yttrium, the balance is magnesium and inevitable impurities, or 0-6 at% aluminum, the balance is magnesium and inevitable impurities; The multi-directional high-speed impact is a cyclic impact performed in sequence along the three directions of X, Y and Z. Each impact cycle includes at least three reversing impacts. Before each impact, the fine-grained magnesium alloy substrate is placed in liquid nitrogen for low-temperature pretreatment.

2. The method for preparing a high-strength and tough magnesium alloy based on low-temperature multi-directional high-speed impact according to claim 1, characterized in that: In the step (1), the temperature of the preheating treatment is 190-210°C.

3. The method for preparing a high-strength and tough magnesium alloy based on low-temperature multi-directional high-speed impact according to claim 1, characterized in that: In the step (2), the furnace temperature is 680-700° C., and the insulation treatment time is 20-30 minutes.

4. The method for preparing a high-strength and tough magnesium alloy based on low-temperature multi-directional high-speed impact according to claim 1, characterized in that: In the step (3), the furnace temperature is 730-740° C., the stirring time is 5-8 min, and the heat preservation time is 30-40 min.

5. The method for preparing a high-strength and tough magnesium alloy based on low-temperature multi-directional high-speed impact according to claim 1, characterized in that: In the step (4), the furnace temperature is 720°C and the mold is preheated to 190-210°C.

6. The method for preparing a high-strength and tough magnesium alloy based on low-temperature multi-directional high-speed impact according to claim 1, characterized in that: In the step (5), the temperature of the solution treatment is 300-550° C., the time of the solution treatment is 8-48 h, the temperature of the hot extrusion treatment is 300-430° C., the extrusion ratio of the hot extrusion treatment is 10-50:1, and the extrusion speed of the hot extrusion treatment is 40-200 mm / min.

7. The method for preparing a high-strength and tough magnesium alloy based on low-temperature multi-directional high-speed impact according to claim 1, characterized in that: In the step (6), the low temperature pretreatment time is 5 to 20 minutes.

8. The method for preparing a high-strength and tough magnesium alloy based on low-temperature multi-directional high-speed impact according to claim 1, characterized in that: In step (7), the multi-directional high-speed impact device is a Hopkinson bar, and the impact strain rate is ≥1000s -1 The deformation of each impact is 2~15%.

9. The method for preparing a high-strength and tough magnesium alloy based on low-temperature multi-directional high-speed impact according to claim 1, characterized in that: The mixed gas is a mixed gas of SF6 and CO2.

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