High-plasticity magnesium-lithium alloy and preparation method thereof

Abstract

The invention discloses a high-plasticity magnesium-lithium alloy and a preparation method thereof, and the magnesium-lithium alloy comprises the following components in percentage by mass: 6.0 to 8.0 percent of Li, 4.5 to 6.9 percent of Al, 1.5 to 2.5 percent of Ca, 0.01 to 0.8 percent of Mn and the balance of Mg. The alloy is a double-phase magnesium-lithium alloy, the density is smaller than or equal to 1.58 g / cm < 3 >, two-phase structures are evenly distributed, the grain size is smaller than or equal to 8 microns, the initial phase structure is relatively large but soft and tough, and the eutectic phase is fine and high in strength. The alloy has the good tensile mechanical property at the room temperature, the yield strength, the ultimate tensile strength and the total elongation of the alloy are larger than or equal to 190 MPa, larger than or equal to 250 MPa and larger than or equal to 15% respectively, and the strength and plasticity matching is good. And the alloy has good plasticity at 150-400 DEG C, and the total elongation is greater than or equal to 110%.

Description

Technical Field

[0001] The present application relates to the technical field of metal materials, and in particular to a high-plasticity magnesium-lithium alloy and a preparation method thereof. Background Art

[0002] With the development of the times, environmental issues have intensified, and the issue of industrial lightweighting has attracted more and more attention. Mg-Li alloy is widely considered to be the lightest metal material at present, with a density of only 1.35g / cm 3 Up to 1.65g / cm 3 , ideally suited for lightweight structural applications. Mg-Li alloys, in particular, are increasingly popular in aerospace, automotive engineering, advanced electronics, medical devices, and defense technology due to their excellent specific strength, stiffness, and machinability. However, the application of Mg-Li alloys is limited by their insufficient mechanical properties and structural instability at ambient temperatures.

[0003] Studies have shown that the simultaneous addition of multiple alloying elements to magnesium alloys for multi-element alloying treatment can effectively improve the strength, plasticity and comprehensive properties of magnesium alloys, but the co-addition of multiple alloying elements can easily have a significant impact on the subsequent forming of magnesium alloys. This is because magnesium alloys are prone to produce strong basal textures during deformation processing, which is not conducive to improving the plasticity of magnesium alloys, and the performance of deformed magnesium alloys is often better than that of cast magnesium alloys. This requires that the alloying elements added to the deformed magnesium alloys can weaken the basal texture or form non-basal textures, which is conducive to the dynamic recrystallization of magnesium alloys. The dynamic precipitation phases produced during the deformation process can inhibit the growth of recrystallized grains. This type of element is mainly RE elements. This type of element can weaken the basal texture or form a new texture different from the basal texture. This is due to the segregation effect of these elements at the grain boundaries. However, the cost of RE is relatively high.

[0004] Therefore, providing a magnesium-lithium alloy with excellent strength and ductility at room temperature and good plasticity at high temperature has become a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0005] In order to solve the problems of the prior art, the present invention provides a high-plasticity magnesium-lithium alloy and a preparation method thereof. The technical solution is as follows:

[0006] In a first aspect, a high-plasticity magnesium-lithium alloy is provided, comprising, by mass percentage, 6.0-8.0% Li, 4.5-6.9% Al, 1.5-2.5% Ca, 0.01-0.8% Mn, and the remainder Mg.

[0007] Furthermore, in terms of mass percentage, it includes: Li 6.8-7.2%, Al 5.7-6.2%, Ca 1.8-2.2%, Mn 0.01-0.8%, and the rest is Mg.

[0008] Furthermore, in terms of mass percentage, the composition includes: Li 7.0%, Al 6.0%, Ca 2.0%, Mn 0.4%, and the remainder is Mg.

[0009] Furthermore, the density of the magnesium-lithium alloy is ≤1.58 g / cm 3 .

[0010] Furthermore, the grain size of the magnesium-lithium alloy is ≤8 μm.

[0011] In a second aspect, a method for preparing a high plasticity magnesium-lithium alloy is provided, comprising the following steps:

[0012] According to the mass percentage of each element in the magnesium-lithium alloy, magnesium, lithium, aluminum, Mg-10Mn alloy and Mg-30Ca alloy were weighed respectively;

[0013] The magnesium, lithium, aluminum, Mg-10Mn alloy and Mg-30Ca alloy are melted and stirred uniformly under argon protection;

[0014] A magnesium-lithium alloy ingot is obtained by casting under vacuum conditions;

[0015] cutting the magnesium-lithium alloy ingot into magnesium-lithium alloy cylinders, removing the oxide scale or contamination layer, and then performing heat treatment;

[0016] The heat-treated magnesium-lithium alloy cylinder is extruded to obtain a magnesium-lithium alloy rod.

[0017] Furthermore, the specific process of melting the magnesium, lithium, aluminum, Mg-10Mn alloy and Mg-30Ca alloy under argon protection is as follows:

[0018] The magnesium, lithium, aluminum, Mg-10Mn alloy and Mg-30Ca alloy were placed in a vacuum furnace, evacuated, and then a mixed gas of SF and Ar was introduced to a pressure of 0.013MPa-0.015MPa. When the temperature was raised to 450-455°C, the paraffin attached to the surface of the lithium was volatilized. After volatilization for 10-11 minutes, the heating was stopped and the temperature was maintained. The vacuum was again evacuated to 1.0×10 -2 Pa, when the furnace is clearly visible, raise the temperature to 780℃-790℃ and wait until the alloy is completely melted.

[0019] Furthermore, the specific process of stirring uniformly is as follows:

[0020] Stir at a speed of 250rpm-300rpm for 20min-25min, stop stirring, continue to heat up to 800℃-820℃ and remove the slag on the surface of the alloy solution. After the slag removal is completed, adjust the temperature back to 780℃-790℃ and keep it warm for 10-12min.

[0021] Furthermore, the specific method of the heat treatment is: keeping warm at 150°C-300°C for 6min-90min.

[0022] Furthermore, it is preferred to keep the temperature at 200°C-210°C for 20min-25min.

[0023] Furthermore, the specific method for extruding the magnesium-lithium alloy rod is as follows: the extrusion temperature is 150°C-300°C, the extrusion ratio is 4-7:1, the extrusion speed is 0.5-5mm / s, and the rod is air-cooled to room temperature after extrusion molding.

[0024] Furthermore, the preferred extrusion temperature is 200° C., the extrusion ratio is 5.7:1, and the extrusion speed is 2.8-3.2 mm / s.

[0025] Furthermore, the magnesium-lithium alloy comprises, by mass percentage, 6.8-7.2% Li, 5.7-6.2% Al, 1.8-2.2% Ca, 0.01-0.8% Mn, and the remainder Mg.

[0026] The beneficial effects of the technical solution provided in the embodiment of the present application are as follows: the high plasticity magnesium-lithium alloy of the present application comprises, by mass percentage, 6.0-8.0% Li, 4.5-6.9% Al, 1.5-2.5% Ca, 0.01-0.8% Mn, and the remainder Mg. The alloy of the present application is a dual-phase magnesium-lithium alloy with a density of ≤1.58g / cm 3, the two-phase structure is evenly distributed, the grain size is ≤8μm, the primary phase structure is relatively large but soft and tough, the eutectic phase is fine and has high strength. The alloy has good tensile mechanical properties at room temperature, and the yield strength, ultimate tensile strength and total elongation of the alloy are ≥190MPa, ≥250MPa and ≥15% respectively, and the strength and plasticity are well matched. It has good plasticity between 150℃-400℃, and the total elongation is ≥110%. On the basis of the Mg-Li-Al-Ca system, the present application further adds the Mn element, and through extrusion molding at a lower temperature, it can effectively prevent the abnormal growth of recrystallized grains, thereby promoting the formation of fine-grained structure in the finished alloy material. Larger plastic deformation is carried out at a lower temperature, and the microstructure of the deformed profile formed is finer and more uniform, with better plasticity, and the prepared magnesium-lithium alloy has high plasticity. At the same time, low-temperature and high-speed deformation is conducive to saving energy, improving production efficiency and reducing production costs. The magnesium, aluminum, calcium, and manganese raw materials used in this application are all common, inexpensive elements. The preparation process is simple, efficient, and energy-efficient. Large blocks of material can be easily produced without solution treatment and can be used directly. The alloy's properties are suitable for applications such as 3C product casings, load-bearing structures for leisure products, and aerospace components, demonstrating promising industrial prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0028] Figure 1 : is a tensile engineering stress-strain curve of the magnesium-lithium alloy prepared in the embodiment of the present application at room temperature;

[0029] Figure 2 is a scanning electron microscope photograph of an extruded magnesium-lithium alloy prepared in an embodiment of the present application;

[0030] Figure 3 is a scanning electron microscope photograph of the cast magnesium-lithium alloy prepared in the examples of the present application;

[0031] Figure 4 This is an EDS surface scan photograph of the extruded magnesium-lithium alloy prepared in the examples of the present application;

[0032] Figure 5 This is a scanning electron microscope photograph of the magnesium-lithium alloy after high-temperature stretching prepared in the examples of the present application;

[0033] Figure 6The tensile engineering stress-strain curves are: the cast magnesium-lithium alloy prepared in the examples of the present application; the magnesium-lithium alloy extruded at room temperature; and the magnesium-lithium alloy at high temperature after extrusion. DETAILED DESCRIPTION

[0034] In order to make the objectives, technical solutions and advantages of this application clearer, the implementation methods of this application will be further described in detail below with reference to the accompanying drawings.

[0035] Example 1

[0036] (1) Raw material preparation

[0037] Prepare the raw materials according to the following mass percentages of each element: Li: 6.8wt.%, Al: 5.7wt.%, Ca: 1.8wt.%, Mn: 0.01wt.%, and the rest is Mg. The raw materials can be magnesium blocks (purity 99.5wt.%), aluminum blocks (purity 99.9wt.%), lithium particles (purity 99.9wt.%), Mg-10Mn alloy (purity 99.5wt.%), and Mg-30Ca alloy (purity 99.5wt.%). Mg-10Mn and Mg-30Ca alloys can be prepared by vacuum induction melting. The magnesium blocks, aluminum blocks, and Mg-10Mn and Mg-30Ca alloys are polished to remove the surface oxide layer.

[0038] (2) Melting alloy ingots

[0039] The prepared raw materials were placed in a vacuum furnace, vacuumed, and then a mixture of SF (sulfur hexafluoride) and Ar was introduced to a pressure of 0.013 MPa, and the temperature was raised to 450°C. The paraffin attached to the surface of the lithium will evaporate and emit white smoke. After 10 minutes of evaporation, the heating was stopped and the temperature was maintained. The vacuum was then pumped to 1.0×10 -2Pa, when the furnace is clearly visible, fill it with argon as a protective gas. After the protective atmosphere is stable and fills the furnace, restart the heating, raise the temperature to 780-790℃ and then fill it with argon as a protective gas, and continue heating until the vacuum furnace is completely under the atmosphere of protective gas. Raise the temperature to 780℃, and after the alloy is completely melted, lower the stirring paddle below the alloy liquid level and stir at a speed of 250rpm for 25min. Then stop stirring, continue to raise the temperature to 800℃ and remove the slag on the surface of the alloy solution. After the slag removal is completed, adjust the temperature back to 780℃ and keep it warm for 12min, raise the stirring paddle above the liquid level, cast the alloy liquid into the mold below, and cool it to room temperature with the furnace to obtain an alloy ingot of 320mm×110mm×65mm. This application adopts a vacuum induction melting and then pouring process, and the mold is also placed in a vacuum furnace to protect the solidification process with inert gas, thereby reducing metal oxidation during the melting, pouring and solidification processes. The ingot is designed in a prism shape to optimize the solidification process to promote directional solidification and accelerate cooling, thereby minimizing the compositional inhomogeneity caused by solidification segregation.

[0040] (3) Extrusion molding

[0041] The obtained alloy ingot was cut into Φ40 mm × 50 mm cylinders using an electric spark wire cutting machine, and then the surface was polished with coarse sandpaper to remove the oxide scale or contamination layer. The treated alloy rod was then directly kept in a muffle furnace at 200 °C for 25 min.

[0042] The heat-treated alloy rod was placed on an extruder, and the extrusion temperature was set to 200°C, the extrusion ratio was 5.7:1, and the extrusion speed was 2.8 mm / s. The alloy rod was extruded and cooled to room temperature by a fan to obtain a magnesium-lithium alloy extruded rod with a diameter of 7 mm.

[0043] Example 2

[0044] (1) Raw material preparation

[0045] Prepare the raw materials according to the following mass percentages of each element: Li: 7.2wt.%, Al: 6.2wt.%, Ca: 2.2wt.%, Mn: 0.8wt.%, and the rest is Mg. The raw materials can be magnesium blocks (purity 99.5wt.%), aluminum blocks (purity 99.9wt.%), lithium particles (purity 99.9wt.%), Mg-10Mn alloy (purity 99.5wt.%), and Mg-30Ca alloy (purity 99.5wt.%). Mg-10Mn and Mg-30Ca alloys can be prepared by vacuum induction melting. The magnesium blocks, aluminum blocks, and Mg-10Mn and Mg-30Ca alloys are polished to remove the surface oxide layer.

[0046] (2) Melting alloy ingots

[0047] The prepared raw materials were placed in a vacuum furnace, vacuumed, and then a mixture of SF (sulfur hexafluoride) and Ar was introduced to a pressure of 0.015 MPa and the temperature was raised to 455°C. The paraffin attached to the surface of the lithium will evaporate and emit white smoke. After 11 minutes of evaporation, the heating was stopped and the temperature was maintained. The vacuum was then pumped to 1.0×10 -2 Pa, when the furnace is clearly visible, argon is filled as a protective gas until the vacuum furnace is completely heated under the atmosphere of protective gas, the temperature is raised to 790 ° C, and after the alloy is completely melted, the stirring paddle is lowered below the alloy liquid level, and stirred at a speed of 300 rpm for 20 minutes. Then stop stirring, continue to heat to 820 ° C and remove the slag on the surface of the alloy solution. After the slag removal is completed, the temperature is adjusted back to 790 ° C and kept warm for 10 minutes, the stirring paddle is raised above the liquid level, and the alloy liquid is cast into the mold below, and cooled to room temperature with the furnace to obtain an alloy ingot of 320 mm × 110 mm × 65 mm. This application adopts a vacuum induction melting and pouring process, and the mold is also set in a vacuum furnace to protect the solidification process through inert gas, thereby reducing metal oxidation during melting, pouring and solidification. The ingot is designed in a prism shape to optimize the solidification process to promote directional solidification and accelerate cooling, thereby minimizing the composition inhomogeneity caused by solidification segregation.

[0048] (3) Extrusion molding

[0049] The obtained alloy ingot was cut into Φ40 mm × 50 mm cylinders using an electric spark wire cutting machine, and then the surface was polished with coarse sandpaper to remove the oxide scale or contamination layer. The treated alloy rod was then directly kept at 210 °C in a muffle furnace for 20 min.

[0050] The heat-treated alloy rod was placed on an extruder, and the extrusion temperature was set to 200°C, the extrusion ratio was set to 5.7:1, and the extrusion speed was set to 3.2 mm / s. The alloy rod was extruded and cooled to room temperature by a fan to obtain a magnesium-lithium alloy extruded rod with a diameter of 7 mm.

[0051] Example 3

[0052] (1) Raw material preparation

[0053] Prepare the raw materials according to the following mass percentages of each element: Li: 6.0wt.%, Al: 4.5wt.%, Ca: 1.5wt.%, Mn: 0.1wt.%, and the rest is Mg. The raw materials can be magnesium blocks (purity 99.5wt.%), aluminum blocks (purity 99.9wt.%), lithium particles (purity 99.9wt.%), Mg-10Mn alloy (purity 99.5wt.%), and Mg-30Ca alloy (purity 99.5wt.%). Mg-10Mn and Mg-30Ca alloys can be prepared by vacuum induction melting. The magnesium blocks, aluminum blocks, and Mg-10Mn and Mg-30Ca alloys are polished to remove the surface oxide layer.

[0054] (2) Melting alloy ingots

[0055] Place the prepared raw materials in a vacuum furnace, evacuate, and then introduce a mixture of SF (sulfur hexafluoride) and Ar to a pressure of 0.014 MPa, and heat to 455°C. The paraffin attached to the surface of the lithium will evaporate and emit white smoke. After evaporation for 10 minutes, stop heating and maintain the temperature, and start evacuating to 1.0×10 -2 Pa, when the furnace is clearly visible, argon is filled as a protective gas until the vacuum furnace is completely heated under the atmosphere of protective gas, and the temperature is raised to 785 ° C. After the alloy is completely melted, the stirring paddle is lowered below the alloy liquid surface and stirred at a speed of 280 rpm for 22 minutes. Then stop stirring, continue to heat to 810 ° C and remove the slag on the surface of the alloy solution. After the slag removal is completed, the temperature is adjusted back to 785 ° C and kept warm for 11 minutes, the stirring paddle is raised above the liquid surface, and the alloy liquid is cast into the mold below, and cooled to room temperature with the furnace to obtain an alloy ingot of 320 mm × 110 mm × 65 mm. This application adopts a vacuum induction melting and pouring process, and the mold is also set in a vacuum furnace to protect the solidification process through inert gas, thereby reducing metal oxidation during melting, pouring and solidification. The ingot is designed in a prism shape to optimize the solidification process to promote directional solidification and accelerate cooling, thereby minimizing the composition inhomogeneity caused by solidification segregation.

[0056] (3) Extrusion molding

[0057] The obtained alloy ingot was cut into Φ40 mm × 50 mm cylinders using an electric spark wire cutting machine, and then the surface was polished with coarse sandpaper to remove the oxide scale or contamination layer. The treated alloy rod was then directly kept in a muffle furnace at 150 °C for 90 min.

[0058] The heat-treated alloy rod was placed on an extruder, and the extrusion temperature was set to 150°C, the extrusion ratio was 7:1, and the extrusion speed was 0.5 mm / s. The alloy rod was extruded and cooled to room temperature by a fan to obtain a magnesium-lithium alloy extruded rod with a diameter of 7 mm.

[0059] Example 4

[0060] (1) Raw material preparation

[0061] Prepare the raw materials according to the following mass percentages of each element: Li: 8.0wt.%, Al: 6.9wt.%, Ca: 2.5wt.%, Mn: 0.05wt.%, and the rest is Mg. The raw materials can be magnesium blocks (purity 99.5wt.%), aluminum blocks (purity 99.9wt.%), lithium particles (purity 99.9wt.%), Mg-10Mn alloy (purity 99.5wt.%), and Mg-30Ca alloy (purity 99.5wt.%). Mg-10Mn and Mg-30Ca alloys can be prepared by vacuum induction melting. The magnesium blocks, aluminum blocks, and Mg-10Mn and Mg-30Ca alloys are polished to remove the surface oxide layer.

[0062] (2) Melting alloy ingots

[0063] Place the prepared raw materials in a vacuum furnace, evacuate, and then introduce a mixture of SF (sulfur hexafluoride) and Ar to a pressure of 0.013MPa-0.015MPa, and heat to 450℃-455℃. The paraffin attached to the surface of the lithium will evaporate and emit white smoke. After evaporation for 10min-11min, stop heating and maintain the temperature, and start evacuating to 1.0×10 -2 Pa, and then fill with argon as a protective gas when the furnace is clearly visible. Continue heating until the vacuum furnace is completely under the protective gas atmosphere, raise the temperature to 780℃-790℃, and after the alloy is completely melted, lower the stirring paddle below the alloy liquid surface and stir at a speed of 250rpm-300rpm for 20min-25min. Then stop stirring, continue to raise the temperature to 800℃-820℃ and remove the slag on the surface of the alloy solution. After the slag removal is completed, adjust the temperature back to 780℃-790℃ and keep it warm for 10min-12min. Raise the stirring paddle above the liquid surface and cast the alloy liquid into the mold below. Cool it to room temperature with the furnace to obtain an alloy ingot of 320mm×110mm×65mm. This application adopts a vacuum induction melting and then pouring process, and the mold is also placed in a vacuum furnace to protect the solidification process with inert gas, thereby reducing metal oxidation during the melting, pouring and solidification processes. The ingot is designed in a prism shape to optimize the solidification process to promote directional solidification and accelerate cooling, thereby minimizing the compositional inhomogeneity caused by solidification segregation.

[0064] (3) Extrusion molding

[0065] The obtained alloy ingot was cut into Φ40 mm × 50 mm cylinders using an electric spark wire cutting machine, and then the surface was polished with coarse sandpaper to remove the oxide scale or contamination layer. The treated alloy rod was then directly kept at 300 °C in a muffle furnace for 6 min.

[0066] The heat-treated alloy rod was placed on an extruder, and the extrusion temperature was set to 300°C, the extrusion ratio was 4:1, and the extrusion speed was 5.0 mm / s. The alloy rod was extruded and cooled to room temperature by a fan to obtain a magnesium-lithium alloy extruded rod with a diameter of 7 mm.

[0067] Example 5

[0068] (1) Raw material preparation

[0069] Prepare the raw materials according to the following mass percentages of each element: Li: 6.8wt.%, Al: 5.2wt.%, Ca: 2.5wt.%, Mn: 0.6wt.%, and the rest is Mg. The raw materials can be magnesium blocks (purity 99.5wt.%), aluminum blocks (purity 99.9wt.%), lithium particles (purity 99.9wt.%), Mg-10Mn alloy (purity 99.5wt.%), and Mg-30Ca alloy (purity 99.5wt.%). Mg-10Mn and Mg-30Ca alloys can be prepared by vacuum induction melting. The magnesium blocks, aluminum blocks, and Mg-10Mn and Mg-30Ca alloys are polished to remove the surface oxide layer.

[0070] (2) Melting alloy ingots

[0071] Place the prepared raw materials in a vacuum furnace, evacuate, and then introduce a mixture of SF (sulfur hexafluoride) and Ar to a pressure of 0.013MPa-0.015MPa, and heat to 450℃-455℃. The paraffin attached to the surface of the lithium will evaporate and emit white smoke. After evaporation for 10min-11min, stop heating and maintain the temperature, and start evacuating to 1.0×10 -2 Pa, and then fill with argon as a protective gas when the furnace is clearly visible. Continue heating until the vacuum furnace is completely under the protective gas atmosphere, raise the temperature to 780℃-790℃, and after the alloy is completely melted, lower the stirring paddle below the alloy liquid surface and stir at a speed of 250rpm-300rpm for 20min-25min. Then stop stirring, continue to raise the temperature to 800℃-820℃ and remove the slag on the surface of the alloy solution. After the slag removal is completed, adjust the temperature back to 780℃-790℃ and keep it warm for 10min-12min. Raise the stirring paddle above the liquid surface and cast the alloy liquid into the mold below. Cool it to room temperature with the furnace to obtain an alloy ingot of 320mm×110mm×65mm. This application adopts a vacuum induction melting and then pouring process, and the mold is also placed in a vacuum furnace to protect the solidification process with inert gas, thereby reducing metal oxidation during the melting, pouring and solidification processes. The ingot is designed in a prism shape to optimize the solidification process to promote directional solidification and accelerate cooling, thereby minimizing the compositional inhomogeneity caused by solidification segregation.

[0072] (3) Extrusion molding

[0073] The obtained alloy ingot was cut into Φ40 mm × 50 mm cylinders using an electric spark wire cutting machine, and then the surface was polished with coarse sandpaper to remove the oxide scale or contamination layer. The treated alloy rod was then directly kept at 260 °C in a muffle furnace for 50 min.

[0074] The heat-treated alloy rod was placed on an extruder, and the extrusion temperature was set to 260°C, the extrusion ratio was set to 6.3:1, and the extrusion speed was set to 4.5 mm / s. The alloy rod was extruded and cooled to room temperature by a fan to obtain a magnesium-lithium alloy extruded rod with a diameter of 7 mm.

[0075] Example 6

[0076] (1) Raw material preparation

[0077] Prepare the raw materials according to the following mass percentages of each element: Li: 7.0wt.%, Al: 6.0wt.%, Ca: 2.0wt.%, Mn: 0.4wt.%, and the rest is Mg. The raw materials can be magnesium blocks (purity 99.5wt.%), aluminum blocks (purity 99.9wt.%), lithium particles (purity 99.9wt.%), Mg-10Mn alloy (purity 99.5wt.%), and Mg-30Ca alloy (purity 99.5wt.%). Mg-10Mn and Mg-30Ca alloys can be prepared by vacuum induction melting. The magnesium blocks, aluminum blocks, and Mg-10Mn and Mg-30Ca alloys are polished to remove the surface oxide layer.

[0078] (2) Melting alloy ingots

[0079] Place the prepared raw materials in a vacuum furnace, evacuate, and then introduce a mixture of SF (sulfur hexafluoride) and Ar to a pressure of 0.013MPa-0.015MPa, and heat to 450℃-455℃. The paraffin attached to the surface of the lithium will evaporate and emit white smoke. After evaporation for 10min-11min, stop heating and maintain the temperature, and start evacuating to 1.0×10 -2Pa, and then fill with argon as a protective gas when the furnace is clearly visible. Continue heating until the vacuum furnace is completely under the protective gas atmosphere, raise the temperature to 780℃-790℃, and after the alloy is completely melted, lower the stirring paddle below the alloy liquid surface and stir at a speed of 250rpm-300rpm for 20min-25min. Then stop stirring, continue to raise the temperature to 800℃-820℃ and remove the slag on the surface of the alloy solution. After the slag removal is completed, adjust the temperature back to 780℃-790℃ and keep it warm for 10min-12min. Raise the stirring paddle above the liquid surface and cast the alloy liquid into the mold below. Cool it to room temperature with the furnace to obtain an alloy ingot of 320mm×110mm×65mm. This application adopts a vacuum induction melting and then pouring process, and the mold is also placed in a vacuum furnace to protect the solidification process with inert gas, thereby reducing metal oxidation during the melting, pouring and solidification processes. The ingot is designed in a prism shape to optimize the solidification process to promote directional solidification and accelerate cooling, thereby minimizing the compositional inhomogeneity caused by solidification segregation.

[0080] (3) Extrusion molding

[0081] The obtained alloy ingot was cut into Φ40 mm × 50 mm cylinders using an electric spark wire cutting machine, and then the surface was polished with coarse sandpaper to remove the oxide scale or contamination layer. The treated alloy rod was then directly kept at 280 °C in a muffle furnace for 75 min.

[0082] The heat-treated alloy rod was placed on an extruder, and the extrusion temperature was set to 280°C, the extrusion ratio was set to 4.6:1, and the extrusion speed was set to 1.7 mm / s. The alloy rod was extruded and cooled to room temperature by a fan to obtain a magnesium-lithium alloy extruded rod with a diameter of 7 mm.

[0083] Example 7

[0084] The performance test of the magnesium-lithium alloy extruded rod prepared in Example 1 was carried out at a strain rate of 10 -3 s -1 , room temperature results are as follows Figure 1 As shown: yield strength is 198MPa, tensile strength is 260MPa, elongation is 16%, density is 1.575g / cm3. The results at 350℃ are as follows Figure 6 Shown: Elongation is 112%.

[0085] The magnesium-lithium alloy prepared in Example 1 was subjected to microstructural observation and mechanical property testing. The SEM of the cast magnesium-lithium alloy is as follows: Figure 3 The SEM of magnesium-lithium alloy extruded at 200℃ is shown in Figure 2 As shown in the figure, (a) is a low-magnification image in the extrusion direction, (b) is a high-magnification image in the extrusion direction, (c) is a low-magnification image in the axial direction, and (d) is a high-magnification image in the axial direction. Figure 4As shown (corresponding to Figure 2 (a) EDS spectrum analysis of low-magnification SEM position of extruded state). This result confirms the strengthening phase formation ability of Al and Mn elements and the grain refining effect of Ca element, providing a composition basis for improving the mechanical properties of extruded alloy. Figure 5 As shown in the figure, this is a SEM image of the microstructure of the magnesium-lithium alloy taken from the sample away from the fracture area after the high-temperature tensile test at 350℃. Figure (a) is a low-magnification image and Figure (b) is a high-magnification image. Both clearly show that the uniform distribution of the second phase particles can maintain the pinning effect. The stress-strain curve from cast to extruded state to high-temperature tensile is shown in Figure 1. Figure 6 shown.

[0086] from Figure 3 It can be seen that the cast alloy presents a typical two-phase structure and a network structure, which is mainly composed of α-Mg phase, β-Li phase and the second phase. The distribution of the second phase mainly has three forms: strips connected by thin lines, network eutectic structure and irregular small particles. The coarse second phase corresponds to the lower mechanical properties. Figure 6 The yield strength and tensile strength of the cast alloy are 67MPa and 71MPa respectively, and it has no plasticity. The microstructure of the alloy after hot extrusion deformation is as follows: Figure 2 As shown in the figure, significant changes have occurred. The dual-phase matrix and the black second phase have been elongated along the extrusion direction. The original coarse dendritic and discontinuous network eutectic structure has been crushed, turning into many fibrous second phases along the extrusion direction and small particles distributed along the phase boundaries. Many fine equiaxed grains have appeared in the β-Li phase. The refinement of the second phase, substructure, and equiaxed grains has greatly improved the strength and plasticity of the extruded alloy compared to the cast state. Mechanical properties such as Figure 6 As shown in the figure, its yield strength and tensile strength at room temperature reach 199 MPa and 261 MPa respectively, its elongation reaches 16%, and its density is 1.575 g / cm 3 . Then at 350℃, its elongation reaches 112%.

[0087] From the above examples and their data, it can be seen that the magnesium-lithium alloy material prepared in this application has high comprehensive performance at room temperature; after adding the Li element to the magnesium alloy, the c / a ratio of the α-Mg matrix can be changed, which promotes the initiation of non-basal slip systems and increases the material's coordination ability during deformation, further improving the material's plasticity. A reasonable plastic deformation process ensures that the Mg-7Li-6Al-2Ca-0.5Mn alloy grains are further refined after plastic deformation. The micromorphology of the alloy after high-temperature stretching shows a relatively complex texture structure. It can be seen that there are some layered or banded textures on the surface of the material, with many small white particles, which are second-phase particles. In the dual-phase magnesium-lithium alloy, these particles are unevenly distributed in the matrix and vary in size. Some particles are large and irregular in shape, while others are smaller and more rounded. Secondary α-Mg phase may precipitate in the β-Li phase matrix. This evolution enhances the grain boundary sliding ability, thereby improving superplasticity.

[0088] The alloy of this application is a dual-phase magnesium-lithium alloy with a density of ≤1.58g / cm 3 , the two-phase structure is evenly distributed, the grain size is ≤8μm, the primary phase structure is relatively large but soft and tough, the eutectic phase is fine and has high strength. The alloy has good tensile mechanical properties at room temperature, and the yield strength, ultimate tensile strength and total elongation of the alloy are ≥190MPa, ≥250MPa and ≥15% respectively, and the strength and plasticity are well matched. It has good plasticity between 150℃-400℃, and the total elongation is ≥110%. On the basis of the Mg-Li-Al-Ca system, the present application further adds the Mn element, and through extrusion molding at a lower temperature, it can effectively prevent the abnormal growth of recrystallized grains, thereby promoting the formation of fine-grained structure in the finished alloy material. Larger plastic deformation is carried out at a lower temperature, and the microstructure of the deformed profile formed is finer and more uniform, with better plasticity, and the prepared magnesium-lithium alloy has high plasticity. At the same time, low-temperature and high-speed deformation is conducive to saving energy, improving production efficiency and reducing production costs. The magnesium, aluminum, calcium, and manganese raw materials used in this application are all common, inexpensive elements. The preparation process is simple, efficient, and energy-efficient. Large blocks of material can be easily produced without solution treatment and can be used directly. The alloy's properties are suitable for applications such as 3C product casings, load-bearing structures for leisure products, and aerospace components, demonstrating promising industrial prospects.

[0089] The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A high plasticity magnesium-lithium alloy, characterized in that: Calculated by mass percentage, it includes: Li 6.0-8.0%, Al 4.5-6.9%, Ca 1.5-2.5%, Mn 0.01-0.8%, and the rest is Mg.

2. The high plasticity magnesium-lithium alloy according to claim 1, characterized in that: Calculated by mass percentage, it includes: Li 6.8-7.2%, Al 5.7-6.2%, Ca 1.8-2.2%, Mn 0.01-0.8%, and the rest is Mg.

3. The high plasticity magnesium-lithium alloy according to claim 1, characterized in that: Calculated by mass percentage, it includes: Li 7.0%, Al 6.0%, Ca 2.0%, Mn 0.4%, and the rest is Mg.

4. The high plasticity magnesium-lithium alloy according to claim 1, characterized in that The magnesium-lithium alloy density is ≤1.58g / cm 3 , the grain size of the magnesium-lithium alloy is ≤8μm.

5. A method for preparing a high plasticity magnesium-lithium alloy, characterized in that: The following steps are involved: According to the mass percentage of each element in the magnesium-lithium alloy, magnesium, lithium, aluminum, Mg-10Mn alloy and Mg-30Ca alloy were weighed respectively; The magnesium, lithium, aluminum, Mg-10Mn alloy and Mg-30Ca alloy are melted and stirred uniformly under argon protection; A magnesium-lithium alloy ingot is obtained by casting under vacuum conditions; cutting the magnesium-lithium alloy ingot into magnesium-lithium alloy cylinders, removing the oxide scale or contamination layer, and then performing heat treatment; The heat-treated magnesium-lithium alloy cylinder is extruded to obtain a magnesium-lithium alloy rod.

6. The method according to claim 5, characterized in that The specific process of melting the magnesium, lithium, aluminum, Mg-10Mn alloy and Mg-30Ca alloy under argon protection is as follows: The magnesium, lithium, aluminum, Mg-10Mn alloy and Mg-30Ca alloy were placed in a vacuum furnace, evacuated, and then a mixed gas of SF and Ar was introduced to a pressure of 0.013MPa-0.015MPa. When the temperature was raised to 450-455°C, the paraffin attached to the surface of the lithium was volatilized. After volatilization for 10-11 minutes, the heating was stopped and the temperature was maintained. The vacuum was again evacuated to 1.0×10 -2 Pa, when the furnace is clearly visible, raise the temperature to 780℃-790℃ and wait until the alloy is completely melted.

7. The method according to claim 5, characterized in that The specific process of the stirring is as follows: Stir at a speed of 250rpm-300rpm for 20min-25min, stop stirring, continue to heat up to 800℃-820℃ and remove the slag on the surface of the alloy solution. After the slag removal is completed, adjust the temperature back to 780℃-790℃ and keep it warm for 10-12min.

8. The method according to claim 5, characterized in that The specific method of the heat treatment is: keeping the temperature at 150° C.-300° C. for 6 min-90 min; preferably keeping the temperature at 200° C.-210° C. for 20 min-25 min.

9. The method according to claim 5, characterized in that The specific method for extruding the magnesium-lithium alloy rod is as follows: the extrusion temperature is 150°C-300°C, the extrusion ratio is 4-7:1, the extrusion speed is 0.5-5mm / s, and the extrusion is followed by air cooling to room temperature after extrusion molding; preferably, the extrusion temperature is 200°C, the extrusion ratio is 5.7:1, and the extrusion speed is 2.8-3.2mm / s.

10. The method according to claim 9, characterized in that The magnesium-lithium alloy comprises, by mass percentage, 6.8-7.2% Li, 5.7-6.2% Al, 1.8-2.2% Ca, 0.01-0.8% Mn, and the remainder Mg.

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