A high-toughness (alpha+beta) dual-phase magnesium-lithium alloy rod and a method of making the same

Abstract

The application provides a high-toughness (alpha+beta) dual-phase magnesium-lithium alloy rod and a preparation method thereof, and contains, in percentage by mass, Li: 8-11%, Al: 2-6%, Sn: 1-5%, rare earth elements (RE): 0.5-4%, Ca: 0-1%, Mn: 0-1%, Ag: 0-0.5%, and the balance of magnesium and inevitable impurities, wherein the total amount of the impurities in the magnesium-lithium alloy material is less than 0.1 wt.%. The processing procedure comprises vacuum melting to prepare an ingot, homogenization annealing, upsetting-extruding pre-deformation, blank straightening and cutting, multi-pass upsetting-drawing forming, low-temperature aging treatment, and mechanical processing of the rod. The application adopts a method combining multiple plastic deformations for the (alpha+beta) dual-phase magnesium-lithium alloy, promotes grain organization refinement and uniform distribution of strengthening phases, significantly improves the organization uniformity and mechanical properties, and finally prepares the high-toughness (alpha+beta) dual-phase magnesium-lithium alloy rod, with a rod diameter of greater than or equal to 200 mm, a room-temperature tensile strength of greater than or equal to 330 Mpa, and an elongation of greater than or equal to 10%.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal materials technology, and specifically relates to a high-strength and tough (α+β) dual-phase magnesium-lithium alloy rod and its preparation method. Background Technology

[0002] The density of magnesium-lithium alloys is generally 0.9–1.6 g / cm³. 3 It is one-fifth the weight of steel, one-half the weight of aluminum alloy, and one-quarter to one-third lighter than ordinary magnesium alloy, hence the name ultralight alloy. Simultaneously, it possesses characteristics such as high specific strength, high specific stiffness, compressive strength, ductility, low impact toughness, low notch sensitivity, damping performance, and good electromagnetic shielding performance, making it one of the next generation of lightweight structural materials in the aerospace field with broad application prospects. However, currently available alloys such as LA141, LA103, and LAZ931 suffer from low strength, poor performance stability, and small product size, failing to meet the demands of aerospace development for high-strength and high-toughness magnesium-lithium alloy materials.

[0003] According to the magnesium-lithium binary phase diagram, when the lithium content is below 5.7 wt%, the alloy exhibits a close-packed hexagonal α-Mg single-phase structure. As the lithium content continues to increase, a body-centered cubic β-Li phase begins to appear, and the alloy exhibits a typical α+β dual-phase structure. When the lithium content exceeds 10.3 wt%, the alloy exhibits a β-Li single-phase structure. Alloys with an α-phase matrix have higher strength but poorer plasticity. Compared to the α phase, the β phase is a relatively "softening phase" with a body-centered cubic crystal structure and more slip systems. Therefore, high-Li content alloys with a β-phase matrix generally have better plastic deformation processing performance. When magnesium-lithium alloys are in a dual-phase structure, they possess high hardness, yield strength, and tensile strength. Simultaneously, as the Li content increases, the alloy's hardness and strength begin to decline, while its plasticity gradually improves. Traditional plastic deformation (such as extrusion, forging, and rolling) has a lower strengthening effect on α+β dual-phase binary magnesium-lithium alloys than on α single-phase alloys, resulting in generally lower alloy strength. Alloying is one of the important means to improve the mechanical properties of magnesium-lithium alloys. Current research mainly focuses on adding alloying elements to high-Li-content magnesium-lithium alloys to introduce high-temperature stable phases to inhibit aging softening, or combining solid solution aging heat treatment and other methods to obtain dispersed precipitates to strengthen the alloy. The addition of these high alloying elements generally leads to a decrease in the plasticity of magnesium-lithium alloys and has a significant impact on the microstructure changes during hot working. This makes it more difficult to control the microstructure and significantly improve the alloy properties by using traditional extrusion deformation to prepare bars. At the same time, problems such as easy cracking, uneven microstructure, and low performance exist, which bring difficulties to the subsequent processing and preparation of materials and affect the application of the final product performance.

[0004] Therefore, a forging method for high-strength and high-toughness (α+β) dual-phase magnesium-lithium alloy bars is needed to meet the urgent demand for large-size high-strength and high-toughness magnesium-lithium alloy bars in the aerospace field. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the inventors have conducted intensive research and developed a high-strength and high-toughness (α+β) dual-phase magnesium-lithium alloy rod and its preparation method. By rationally controlling the Li content in the magnesium-lithium alloy, the alloy is placed in the (α+β) dual-phase region, resulting in a cast magnesium-lithium alloy with high comprehensive performance. Adding Al, Sn, and rare earth elements (RE) to the magnesium-lithium alloy achieves the combined effects of grain refinement strengthening, solid solution strengthening, and precipitation strengthening, improving the alloy's strength and toughness while effectively suppressing over-aging softening. Introducing trace amounts of alloying elements Ca, Mn, and Ag into the magnesium-lithium alloy further enhances its thermal stability. Based on optimized alloy element composition, this invention employs a combination of multiple reshaping deformation methods to promote grain refinement and uniform distribution of strengthening phases, significantly improving the material's microstructure uniformity and mechanical properties, ultimately producing a high-strength and high-toughness (α+β) dual-phase magnesium-lithium alloy rod.

[0006] The technical solution provided by this invention is as follows:

[0007] In the first aspect, a high-strength and tough (α+β) dual-phase magnesium-lithium alloy rod contains, by mass percentage: Li: 8%–11%, Al: 2%–6%, Sn: 1%–5%, rare earth elements (RE): 0.5%–4%, Ca: 0–1%, Mn: 0–1%, Ag: 0–0.5%, with the balance being magnesium and unavoidable impurities, wherein the total amount of impurities accounts for less than 0.1 wt.% of the magnesium-lithium alloy material.

[0008] Secondly, a method for preparing a high-strength and high-toughness (α+β) dual-phase magnesium-lithium alloy rod includes:

[0009] Vacuum melting and casting are carried out under an inert atmosphere to obtain alloy ingot blanks with a diameter of not less than 400 mm and a length of not less than 800 mm.

[0010] The alloy ingot blank is homogenized under vacuum or inert atmosphere protection.

[0011] The billet is upset on a hydraulic press, and after upset, the billet is placed into a preheated extrusion cylinder for extrusion deformation.

[0012] The extruded billet is straightened and cut;

[0013] The billet is formed by multiple slow upsetting and fast drawing, and then annealed.

[0014] The billet is subjected to low-temperature aging treatment and then machined into finished bar products.

[0015] The high-strength and high-toughness (α+β) dual-phase magnesium-lithium alloy rod and its preparation method provided by the present invention have the following beneficial effects:

[0016] (1) This invention provides a high-strength and tough (α+β) dual-phase magnesium-lithium alloy rod and its preparation method. The alloy composition has a high Li content, and the alloy matrix is ​​an α+β phase structure. At the same time, the introduction of Al, Sn, and RE elements and the control of their contents can not only produce solid solution strengthening effect, but also form high-temperature stable strengthening phases such as MgLi2Sn, Al2RE, and Al3RE, reduce the formation of AlLi phase, improve the strength and toughness of the alloy and improve its thermal stability;

[0017] (2) The present invention provides a high strength and toughness (α+β) dual-phase magnesium-lithium alloy rod and its preparation method. The upsetting and pre-deformation method is used for billet preparation. This method can not only obtain a pre-deformed billet with the original billet structure and size, but also eliminate casting defects, improve the overall deformation uniformity of the billet, refine the microstructure of the billet, improve the forging performance of the material, and provide a good billet foundation for subsequent forging deformation.

[0018] (3) The present invention provides a high-strength and tough (α+β) dual-phase magnesium-lithium alloy rod and its preparation method, which adopts multi-pass slow upsetting and fast drawing forming, that is, combining single axial large deformation slow compression deformation and multiple multi-directional small deformation rapid compression deformation, to obtain cumulative plastic deformation to refine the grains while introducing a large number of twins and dislocation structures, effectively improving the mechanical properties of the rod.

[0019] (4) The present invention provides a high-strength and tough (α+β) dual-phase magnesium-lithium alloy rod and its preparation method. The multi-pass slow upsetting and fast drawing forming can reduce the billet temperature loss, reduce the number of annealing times, effectively reduce the risk of rod forming cracking caused by the temperature sensitivity of (α+β) dual-phase magnesium-lithium alloy and the over-aging softening phenomenon of magnesium-lithium alloy, and improve the quality of the final rod.

[0020] (5) The present invention provides a high-strength and tough (α+β) dual-phase magnesium-lithium alloy rod and its preparation method, which promotes grain refinement and uniform distribution of strengthening phases through a combination of multiple reshaping deformation methods, significantly improving the uniformity of the microstructure and mechanical properties; the density of the α+β phase high-strength and tough magnesium-lithium alloy material involved is not higher than 1.60 g / cm³. 3 (Preferred value: 1.5–1.6 g / cm³) 3 The yield strength at room temperature is not less than 210 MPa (preferably 210-250 MPa); the tensile strength is not less than 330 MPa (preferably 330-360 MPa); and the elongation is not less than 10% (preferably 10%-13%).

[0021] (6) The present invention provides a high-strength and tough (α+β) dual-phase magnesium-lithium alloy rod and its preparation method. The process is simple, the cost is low, and the rods are large in size and have a wide range of applications. Attached Figure Description

[0022] Figure 1 The casting process for high-strength and high-toughness (α+β) dual-phase magnesium-lithium alloy rods. Detailed Implementation

[0023] The features and advantages of the present invention will become clearer and more apparent from the following detailed description.

[0024] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0025] This invention provides a high-strength and high-toughness (α+β) dual-phase magnesium-lithium alloy rod, comprising, by mass percentage: Li: 8%–11%, Al: 2%–6%, Sn: 1%–5%, rare earth elements (RE): 0.5%–4%, Ca: 0–1%, Mn: 0–1%, Ag: 0–0.5%, with the balance being magnesium and unavoidable impurities, wherein the total amount of impurities accounts for less than 0.1 wt.% of the magnesium-lithium alloy material.

[0026] Preferably, the high-strength and tough (α+β) dual-phase magnesium-lithium alloy rod contains, by mass percentage: Li: 8%–11%, Al: 4%–6%, Sn: 2.5%–5%, rare earth elements (RE): 0.5%–2.5%, Ca: 0.5%–1%, Mn: 0.5%–1%, Ag: 0%–0.5%, with the balance being magnesium and unavoidable impurities, wherein the total amount of impurities in the magnesium-lithium alloy material is less than 0.1 wt.%.

[0027] The magnesium-lithium alloy mentioned in this invention contains 8-11% wt.% Li, which ensures a low alloy density, improves its plasticity, and avoids the adverse effects of excessive Li content on the alloy's strength, thermal stability, and corrosion resistance. This invention adds Al to the magnesium-lithium alloy. Al has a high solid solubility in Mg, resulting in significant solid solution strengthening. However, too low an Al content fails to achieve the desired strengthening effect, while too high an Al content significantly reduces alloy plasticity and forms an AlLi softening phase, leading to over-aging. Furthermore, Al has a low density and has a relatively small impact on the alloy's density. This invention adds Sn and RE elements to the magnesium-lithium alloy along with Al. By controlling their content and mass ratio, while maintaining a low alloy density, it not only achieves solid solution strengthening but also forms high-temperature stable strengthening phases such as MgLi₂Sn, Al₂RE, and Al₃RE. This reduces the formation of the soft AlLi phase and suppresses the over-aging softening phenomenon caused by the metastable MgLi₂Al transforming into the AlLi phase, thereby improving the alloy's strength and the thermal stability of its mechanical properties. Meanwhile, the addition of Sn and RE elements can effectively refine the alloy microstructure, further improve the strength and toughness of the alloy, and achieve the combined effects of fine grain strengthening, solid solution strengthening and precipitation strengthening. While improving the overall performance of the alloy, it can effectively suppress the occurrence of over-aging softening.

[0028] This invention introduces trace alloying elements Ca, Sr, and Mn into magnesium-lithium alloys. Ca and Sr act as grain refiners during the smelting process, further refining the grain structure of the as-cast alloy and effectively improving its strength and toughness. Additionally, Ca acts as a flame retardant during smelting. The introduction of Mn not only improves the plasticity of the magnesium-lithium alloy but also enhances its resistance to over-aging softening and improves its thermal stability. If the content of the introduced alloying elements Ca, Sr, and Mn is too low, the desired strengthening effect cannot be achieved; if the content is too high, it will form a large number of large-size intermetallic compounds with Al, reducing the Al content and negatively impacting the overall performance of the alloy.

[0029] Preferably, the rare earth element is either a single rare earth element Y or a Y-rich mixed rare earth; wherein, the Y-rich mixed rare earth is a mixed rare earth in which Y accounts for more than 85 wt.% of the total rare earth.

[0030] The main reason for choosing Y is that its addition can refine and spheroidize the α phase, while simultaneously forming a high-temperature stable strengthening phase with Al, acting as a second-phase strengthening agent and improving the alloy's thermal stability. Furthermore, the addition of Y is beneficial for improving the alloy's plasticity, resulting in excellent overall mechanical properties. Choosing Y-rich mixed rare earth elements can be seen as a way to incorporate Y into alloys, as the cost of mixed rare earth elements is relatively lower than that of pure rare earth elements. Under the condition of achieving the same strengthening effect through alloying, alloys prepared using mixed rare earth elements are more valuable for application.

[0031] This invention also provides a method for processing high-strength and high-toughness (α+β) dual-phase magnesium-lithium alloy rods, such as... Figure 1 As shown, it includes:

[0032] Step 1: Vacuum melting and casting are carried out under an inert atmosphere to obtain alloy ingot blanks with a diameter of not less than 400 mm and a length of not less than 800 mm.

[0033] Step 2, homogenization annealing: The alloy ingot billet is homogenized under vacuum or inert atmosphere protection. The homogenization temperature is 300-400℃ and the holding time is 4-10h.

[0034] Step 3, upsetting and pre-deformation: First, the billet is upset and deformed on a hydraulic press. After upsetting, the billet is placed into a preheated extrusion cylinder for extrusion deformation.

[0035] In this step, the upsetting deformation parameters include: upsetting deformation amount of 35% to 45%, upper and lower anvil temperatures of 275℃ to 300℃, and upsetting pressing rate of 2 to 5 mm / s.

[0036] In this step, the extrusion deformation parameters include: extrusion deformation temperature controlled at 275℃~300℃, extrusion ratio of 2~5, and extrusion speed of 0.5~1.5m / min.

[0037] Step 4: Straighten and cut the extruded billet, with a height-to-diameter ratio of 1.4 to 2:1;

[0038] Step 5: Perform multiple slow upsetting and fast drawing on the billet. The temperature of the upper and lower anvils is 275℃~300℃. The down pressing rate of the anvil in the upsetting pass is 2~5mm / s, and the deformation amount per pass is 30~50%. The down pressing rate of the anvil in the drawing pass is ≥10mm / s, and the deformation amount per pass is 10~15%. The upsetting and drawing passes are cycled once, and the total number of deformation passes is counted as one. When the total number of deformation passes reaches more than 2 or the surface temperature of the billet is lower than 200℃, the billet is annealed at a temperature of 300~350℃ for a holding time of 1~2h. The billet is then formed into a round bar with a diameter ≥200mm through multiple deformation passes.

[0039] The addition of high-alloying elements reduces the plasticity of magnesium-lithium alloys and significantly affects the microstructure changes during hot working. This makes it more difficult to control the microstructure and significantly improve alloy properties using traditional extrusion deformation methods to prepare bars, resulting in problems such as easy cracking, uneven microstructure, and lower performance. This invention employs multi-pass slow upsetting and rapid drawing. During upsetting, the billet undergoes a large deformation to refine the microstructure and improve performance, while avoiding the risk of cracking due to excessively rapid deformation. During drawing, the billet is rapidly deformed to the predetermined size to avoid the risk of cracking due to excessively rapid cooling, and a large number of twins and dislocations are effectively introduced, significantly improving the billet's performance.

[0040] Step 6: Perform low-temperature aging treatment on the billet at an aging temperature of 125-150℃ for 15-30 hours.

[0041] Step 7: Machining to produce finished bar stock.

[0042] Example

[0043] Example 1

[0044] A high-strength and high-toughness (α+β) dual-phase magnesium-lithium alloy rod comprises, by mass percentage: Li: 8.5%, Al: 4.5%, Sn: 4.5%, rare earth elements (RE): 1%, Ca: 0.8%, Mn: 0.5%, Ag: 0.3%, with the balance being magnesium and unavoidable impurities, wherein the total amount of impurities in the magnesium-lithium alloy material is less than 0.1 wt.%. The rare earth element (RE) is Y.

[0045] The preparation method of this high-strength and high-toughness (α+β) dual-phase magnesium-lithium alloy rod includes the following steps:

[0046] Step 1: Vacuum melting and casting are carried out under an inert atmosphere to obtain an alloy ingot billet with a diameter of 400 mm and a length of 800 mm.

[0047] Step 2, homogenization annealing, homogenization treatment is carried out under vacuum or inert atmosphere protection conditions. The homogenization treatment temperature is 350℃ and the holding time is 6h. After the homogenization treatment is completed, proceed directly to the subsequent steps.

[0048] Step 3, upsetting and pre-deformation: First, the billet is upset and deformed on a hydraulic press. The upsetting deformation amount is 40%, the upper and lower anvil temperatures are 285℃, and the upsetting pressing rate is 3mm / s. After upsetting, the billet is placed into a preheated extrusion cylinder for extrusion deformation. The extrusion deformation temperature is controlled at 280℃, the extrusion ratio is 2.5, and the extrusion rate is 1m / min.

[0049] Step 4: Straighten and cut the extruded billet, with a height-to-diameter ratio of 2:1;

[0050] Step 5: Perform multiple slow upsetting and fast drawing on the billet. The temperature of the upper and lower anvils is 285℃. The down pressing rate of the anvil in the upsetting pass is 2mm / s, and the deformation amount per pass is 46%. The down pressing rate of the anvil in the drawing pass is 10mm / s, and the deformation amount per pass is 13%. When the total number of deformation passes reaches 2, the billet is annealed at 300℃ for 1 hour. The billet is then transformed into a round bar with a diameter of 200mm through multiple deformation passes.

[0051] Step 6: Perform low-temperature aging treatment on the billet at an aging temperature of 125℃ for 25 hours.

[0052] Step 7: Machining to produce the finished bar stock with a density of 1.59 g / cm³. 3 The yield strength at room temperature is 228 MPa, the tensile strength is 335 MPa, and the elongation is 12.5%.

[0053] Example 2

[0054] A high-strength and high-toughness (α+β) dual-phase magnesium-lithium alloy rod comprises, by mass percentage: Li: 10%, Al: 6%, Sn: 3%, rare earth elements (RE): 2%, Ca: 1%, Mn: 0.5%, Ag: 0.3%, with the balance being magnesium and unavoidable impurities. The total amount of impurities in the magnesium-lithium alloy material is less than 0.1 wt.%. The rare earth elements (RE) are Y-rich (85 wt.%) mixed rare earths, with the remainder being La, Ce, Nd, and Pr.

[0055] The preparation method of this high-strength and high-toughness (α+β) dual-phase magnesium-lithium alloy rod includes the following steps:

[0056] Step 1: Vacuum melting and casting are carried out under an inert atmosphere to obtain an alloy ingot billet with a diameter of 480 mm and a length of 800 mm.

[0057] Step 2, homogenization annealing, homogenization treatment is carried out under vacuum or inert atmosphere protection conditions. The homogenization treatment temperature is 335℃ and the holding time is 6h. After the homogenization treatment is completed, proceed directly to the subsequent steps.

[0058] Step 3, upsetting and pre-deformation: First, the billet is upset and deformed on a hydraulic press. The upsetting deformation amount is 40%, the upper and lower anvil temperatures are 290℃, and the upsetting pressing rate is 4mm / s. After upsetting, the billet is placed into a preheated extrusion cylinder for extrusion deformation. The extrusion deformation temperature is controlled at 280℃, the extrusion ratio is 4, and the extrusion rate is 1m / min.

[0059] Step 4: Straighten and cut the extruded billet, with a height-to-diameter ratio of 1.8:1;

[0060] Step 5: Perform multiple slow upsetting and fast drawing on the billet. The temperature of the upper and lower anvils is 290℃. The down pressing rate of the anvil in the upsetting pass is 4mm / s, and the deformation amount per pass is 40%. The down pressing rate of the anvil in the drawing pass is 15mm / s, and the deformation amount per pass is 10%. When the total number of deformation passes reaches 2, the billet is annealed at 300℃ for 1 hour. The billet is then transformed into a round bar with a diameter of 220mm through multiple deformation passes.

[0061] Step 6: Perform low-temperature aging treatment on the billet at an aging temperature of 135℃ for 16 hours.

[0062] Step 7: Machining to produce the finished bar stock with a density of 1.55 g / cm³. 3 The yield strength at room temperature is 230 MPa, the tensile strength is 339 MPa, and the elongation is 12%.

[0063] Examples 3-4, Comparative Examples 1-2

[0064] Examples 3-4 and Comparative Examples 1-2 are the same as Example 1, except that the pressing rate of the anvil in the upsetting pass is different in the slow upsetting and fast drawing forming step. The parameters and effect data are shown in Table 1.

[0065] Table 1 Parameters and Effect Data

[0066] Examples / Comparative Examples Example 1 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Downward pressure rate mm / s 2 3 5 1 7 Room temperature yield strength (MPa) 228 232 240 212 242 room temperature tensile strength (MPa) 335 346 351 307 326 Room temperature elongation % 12.5 11 10 10.5 8.5

[0067] Example 5, Comparative Example 3

[0068] Example 5 and Comparative Example 3 are the same as Example 1, except that the pressing rate of the anvil is different in the lengthening process. The parameters and effect data are shown in Table 2.

[0069] Table 2 Parameters and Effect Data

[0070] Examples / Comparative Examples Example 1 Example 5 Comparative Example 3 Downward pressure rate mm / s 10 12 6 Room temperature yield strength (MPa) 228 224 208 room temperature tensile strength (MPa) 335 341 312 Room temperature elongation % 12.5 10.5 10

[0071] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0072] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for preparing high-strength and high-toughness α+β dual-phase magnesium-lithium alloy rods, characterized in that, The rods contain, by weight percentage: Li: 8%~11%, Al: 2%~6%, Sn: 1%~5%, rare earth elements (RE): 0.5%~4%, Ca: 0~1%, Mn: 0~1%, Ag: 0~0.5%, with the balance being magnesium and unavoidable impurities, wherein the total amount of impurities in the magnesium-lithium alloy material is less than 0.1 wt.%. The preparation method includes: Vacuum melting and casting are carried out under an inert atmosphere to obtain alloy ingot blanks with a diameter of not less than 400 mm and a length of not less than 800 mm. The alloy ingot blank is homogenized under vacuum or inert atmosphere protection. The billet is upset on a hydraulic press, and after upset, the billet is placed into a preheated extrusion cylinder for extrusion deformation. The extruded billet is straightened and cut; The billet is formed by multiple slow upsetting and fast drawing, and then annealed. The billet is subjected to low-temperature aging treatment and then machined into finished bar stock. In the step of forming the billet by multiple slow upsetting and fast drawing, the temperature of the upper and lower anvils is 275℃~300℃, the pressing rate of the anvils in the upsetting pass is 2~5mm / s, the deformation amount per pass is 30~50%, and the pressing rate of the anvils in the drawing pass is ≥10mm / s, the deformation amount per pass is 10~15%.

2. The method for preparing high-strength and high-toughness α+β dual-phase magnesium-lithium alloy rods according to claim 1, characterized in that, The rare earth element is either a single rare earth element Y or a Y-rich mixed rare earth; wherein, the Y-rich mixed rare earth is a mixed rare earth in which Y accounts for more than 85 wt.% of the total rare earth.

3. The method for preparing high-strength and high-toughness α+β dual-phase magnesium-lithium alloy rods according to claim 1, characterized in that, In the step of homogenizing the alloy ingot billet under vacuum or inert atmosphere protection, the homogenization temperature is 300-400℃ and the holding time is 4-10h.

4. The method for preparing high-strength and high-toughness α+β dual-phase magnesium-lithium alloy rods according to claim 1, characterized in that, In the step of upsetting the billet on a hydraulic press and then placing the billet into a preheated extrusion cylinder for extrusion deformation, the upsetting deformation amount is 35%~45%, the temperature of the upper and lower anvils is 275℃~300℃, and the upsetting pressing rate is 2~5mm / s.

5. The method for preparing high-strength and high-toughness α+β dual-phase magnesium-lithium alloy rods according to claim 1, characterized in that, In the step of upsetting the billet on a hydraulic press and then placing the billet into a preheated extrusion cylinder for extrusion deformation, the extrusion deformation temperature is controlled at 275℃~300℃, the extrusion ratio is 2~5, and the extrusion rate is 0.5~1.5m / min.

6. The method for preparing high-strength and high-toughness α+β dual-phase magnesium-lithium alloy rods according to claim 1, characterized in that, In the step of straightening and cutting the extruded billet, the height-to-diameter ratio of the straightened and cut billet is 1.4~2:

1.

7. The method for preparing high-strength and high-toughness α+β dual-phase magnesium-lithium alloy rods according to claim 1, characterized in that, In the step of annealing the billet, the upsetting pass and the drawing pass are cycled once, and the total deformation pass is counted once. When the total deformation pass reaches more than 2 passes or the surface temperature of the billet is lower than 200°C, the billet is annealed at a temperature of 300~350°C and a holding time of 1~2 hours. The billet is then transformed into a round bar with a diameter ≥200mm through multiple passes.

8. The method for preparing high-strength and high-toughness α+β dual-phase magnesium-lithium alloy rods according to claim 1, characterized in that, In the step of performing low-temperature aging treatment on the billet, the aging temperature is 125~150℃ and the aging time is 15~30h.

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