An ultra-light magnesium-lithium alloy and a preparation and processing method thereof

Abstract

The application discloses an ultralight magnesium-lithium alloy and a preparation and processing method thereof. The magnesium-lithium alloy is composed of Li 8.0-10.0wt%, Al 6.0-7.5wt%, Gd 2.0-3.5wt%, Zn 2.0-3.5wt%, Mn 0.3-0.8wt%, Ca 0.4-0.7wt%, Sc 0.1-0.3wt%, and the balance of Mg and inevitable impurities. The preparation and processing method of the magnesium-lithium alloy comprises the following steps: (1) raw material pretreatment; (2) vacuum vibration smelting; (3) pouring; (4) mold homogenization treatment; (5) steel sleeve water cooling and demolding; (6) reheating and continuous forging; (7) direct extrusion; (8) multi-pass composite rolling; and (9) structure and performance stabilization treatment. The magnesium-lithium alloy has ultralow density and high specific strength, and the preparation and processing method can further improve the performance stability of the magnesium-lithium alloy product.

Description

Technical Field

[0001] This invention relates to the field of ultralight metal materials technology, specifically to an ultralight magnesium-lithium alloy and its preparation and processing method. Background Technology

[0002] Magnesium-lithium alloys are among the lowest density structural metal alloys currently used in engineering applications. With their ultra-lightweight density, excellent specific stiffness, good damping performance, and processability, they have become a core candidate material for lightweight upgrades in aerospace, high-end equipment, and precision instruments. Compared to conventional magnesium and aluminum alloys, magnesium-lithium alloys have significant weight reduction potential, effectively reducing equipment weight, improving load efficiency and energy utilization, and possessing irreplaceable application value in the development of high-end lightweight structural components. However, from the perspective of intrinsic material properties and practical applications, magnesium-lithium alloys face a core contradiction: the difficulty in synergistically optimizing density and strength. This is the biggest technical bottleneck restricting their large-scale application, manifested as a typical "seesaw" effect: pursuing low density sacrifices strength, while increasing strength leads to a rebound in density, making it impossible to achieve a balance between "ultra-light density + high-strength mechanical properties."

[0003] From the perspective of alloy composition and microstructure control, lithium, as the core alloying element of magnesium-lithium alloys, directly determines the alloy density and matrix phase structure. When the lithium content is in the range of 1% to 15%, as the lithium content increases, the alloy matrix transforms from single-phase α-Mg to α+β dual-phase and single-phase β-Li, and the alloy density continues to decrease, making the ultra-lightweight characteristics more and more significant. However, at the same time, the lattice stability and load-bearing capacity of the alloy matrix decrease significantly, leading to a sharp decline in mechanical properties such as yield strength and tensile strength. Pure ultra-light magnesium-lithium alloys may even be unable to meet the mechanical load-bearing requirements of basic structural components. If the alloy strength is improved by adding strengthening elements such as Al, Mn, Ce, Si, and Sn, the mechanical shortcomings can be compensated by precipitating strengthening phases and refining grains. However, the introduction of strengthening elements will directly increase the overall density of the alloy, weakening the core ultra-lightweight advantage of magnesium-lithium alloys, and even causing the alloy to lose its lightweight competitiveness.

[0004] In addition, existing magnesium-lithium alloys have derivative shortcomings in terms of performance and preparation, which further amplify the contradiction between density and strength: on the one hand, the performance synergy is poor, and modification methods to improve strength often reduce plasticity, heat resistance and corrosion resistance. Optimizing a single performance will break the overall performance balance; on the other hand, composition design and process control rely on traditional trial and error methods, which can only adjust the element ratio and process parameters such as melting, extrusion and heat treatment through extensive orthogonal experiments. It is difficult to accurately control the phase composition, precipitated phase morphology and grain size, and it is impossible to establish an intrinsic relationship between density control and strength improvement. This not only results in long R&D cycles and high costs, but also leads to poor product performance stability. Even if density and strength are barely balanced, it is still impossible to meet the stringent use standards of high-end equipment.

[0005] Currently, the industry has failed to overcome the technical challenge of the trade-off between density and strength in magnesium-lithium alloys. Existing alloy systems either prioritize ultra-lightweight properties at the expense of sufficient mechanical strength, or prioritize high-strength performance at the expense of excessive density, completely deviating from the core requirement of lightweight structural materials: "weight reduction without load reduction." In conclusion, breaking the inherent trade-off between density and strength, and developing magnesium-lithium alloys that combine ultra-low density and high specific strength, to resolve the core contradiction between lightweight and high load-bearing capacity, is of crucial practical significance for broadening the application scenarios of magnesium-lithium alloys in high-end fields and filling related technological gaps. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of this invention is to provide an ultra-light magnesium-lithium alloy that has both ultra-low density and high specific strength.

[0007] Another objective of this invention is to provide a method for preparing and processing the ultralight magnesium-lithium alloy, thereby improving the performance stability of magnesium-lithium alloy products.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: An ultralight magnesium-lithium alloy has the following composition: Li 8.0~10.0wt%, Al 6.0~7.5wt%, Gd 2.0~3.5wt%, Zn 2.0~3.5wt%, Mn 0.3~0.8wt%, Ca 0.4~0.7wt%, Sc 0.1~0.3wt%, with the balance being Mg and unavoidable impurities.

[0009] Furthermore, in the ultralight magnesium-lithium alloy, the total impurity content is ≤0.3%, of which the total content of Fe and Ni is ≤0.05%.

[0010] Furthermore, the density of the ultralight magnesium-lithium alloy is ≤1.55 g / cm³. 3 Tensile strength ≥ 310 MPa.

[0011] A method for preparing and processing the ultralight magnesium-lithium alloy includes the following steps: (1) Raw material pretreatment: Prepare raw materials according to the composition ratio and pretreat the raw materials; (2) Vacuum vibration melting: Add the pretreated raw materials into the graphite crucible of the vacuum induction furnace, evacuate the vacuum, and then fill with argon as a protective gas. Heat the furnace to 750~780℃, turn on the furnace body vibration device, adjust the vibration frequency to 50~80Hz and the amplitude to 0.5~1.0mm, and maintain the vibration state for melting for 30~40min; after melting, the alloy melt is filtered through a ceramic filter plate. (3) Casting: Slowly cast the filtered alloy melt into a steel mold preheated to 200~220℃, and let it cool naturally to below 300℃ to complete the initial solidification of the alloy; (4) Homogenization treatment with mold: without demolding, the steel sleeve mold with ingot is directly transferred into the argon-protected heat treatment furnace, the heating rate is set to 5~8℃ / min, the temperature is raised to 280~320℃, and the temperature is held for 4~6h. (5) Water spraying and demolding of steel sleeve: After the homogenization treatment is completed, water spraying is immediately applied to the outer surface of the steel sleeve to cool it. The cooling rate is controlled at 15~20℃ / min. After rapid cooling to room temperature, the mold is demolded to obtain the alloy ingot and the surface is machined. (6) Reheating and continuous forging: The turned ingot is heated to 280~320℃ and held for 2~3 hours; then, continuous forging is carried out using a high-speed forging machine; (7) Direct extrusion: After forging, the material is directly extruded at 260~300℃ without cooling to obtain extruded sheet; (8) Multi-pass composite rolling: The first hot rolling, liquid nitrogen-cooled cold rolling, second hot rolling, and room temperature cold rolling are performed in sequence; (9) Stabilization treatment of microstructure and properties: The rolled sheet is placed in a heat treatment furnace and heated to 120°C and held for 5-10 minutes. The sheet is then immediately removed and immersed in liquid nitrogen and rapidly cooled to -50°C and held for 5-10 minutes. The sheet is then placed back into a heating furnace at 120°C and held for 5-10 minutes. The above cycle of "holding at 120°C → cooling at -50°C liquid nitrogen → holding at 120°C" is repeated 3-5 times. After the last 120°C holding is completed, the sheet is removed and placed in the air environment to cool naturally to room temperature.

[0012] Further, in step (1), the raw materials are: Mg blocks with a purity ≥ 99.95%, Al blocks with a purity ≥ 99.97%, Li particles wrapped in aluminum foil with a purity ≥ 99.9%, Mg-30Gd master alloy, Mg-20Sc master alloy, Zn blocks with a purity ≥ 99.95%, Al-20Mn master alloy, and Mg-20Ca master alloy; all raw materials except Li particles are surface-polished to remove oxide scale, ultrasonically cleaned with anhydrous ethanol, and then vacuum-dried for later use; Li particles are ultrasonically degreased with acetone and then vacuum-sealed for storage.

[0013] Further, in step (2), the vacuum system is started to evacuate to ≤10Pa, and then argon gas is introduced to 0.08~0.12Mpa; the pore size of the ceramic filter plate is 5~10μm.

[0014] Furthermore, in step (5), an alloy ingot with a diameter of φ120~400mm is obtained.

[0015] Furthermore, in step (6), the total deformation amount of continuous forging is controlled to be 60-75%, and the reduction amount per pass is 10-15%.

[0016] Further, in step (7), the extrusion ratio is 20:1 to 30:1, the extrusion speed is 1.5 to 3 m / min, and an extruded sheet with a thickness of 8 to 12 mm is obtained.

[0017] Furthermore, in step (8), the specific operation of the multi-pass composite rolling is as follows: ① First hot rolling: The extruded sheet is placed in a heating furnace, heated to 280~310℃, and held for 1 hour. Each pass uses a reduction of 12~18%, and the total reduction is controlled at 40~50%. After rolling, the sheet thickness is reduced to 4~6mm. ② Liquid nitrogen cooling cold rolling: During the rolling process, liquid nitrogen is continuously sprayed onto the surface of the rolls, and the roll temperature is strictly controlled to be ≤-10℃. A reduction of 5~8% is adopted per pass, and the total reduction is controlled to be 30~40%. After rolling, the thickness of the plate is reduced to 2.5~4.0mm. ③ Second hot rolling: Repeat the temperature, holding time and reduction parameters of the first hot rolling, keep the total reduction at 40~50%, and reduce the thickness of the plate to 1.5~2.5mm after rolling; ④ Room temperature cold rolling: At a room temperature of 25~35℃, a reduction of 3~5% is adopted for each pass, and the total reduction is controlled at 50~70% to finally obtain an alloy sheet with a thickness of 0.5~5mm, ensuring the dimensional accuracy and performance stability of the sheet.

[0018] The beneficial effects of this invention are: (1) The magnesium-lithium alloy of the present invention adopts a composite rare earth system of Gd (2.0~3.5wt%) and Sc (0.1~0.3wt%), which synergistically improves heat resistance and mechanical property stability by forming Al3Gd and Al3Sc dual thermally stable phases; the ratio of Mn (0.3~0.8wt%) and Ca (0.4~0.7wt%) is optimized to improve the alloy strengthening effect; and the density is strictly controlled to be ≤1.55g / cm³. 3 The synergistic goal of achieving a tensile strength of ≥310MPa has resulted in a better balance between "ultra-lightweight and high specific strength".

[0019] (2) The preparation and processing method of the present invention, through multi-stage improvement and innovation, synergistically enhances the performance stability of magnesium-lithium alloy products, specifically in the following aspects: Melting and Casting: A new vibration + filtration combination enhances melt purity. A pioneering "vacuum vibration melting" process (vibration frequency 50~80Hz, amplitude 0.5~1.0mm) distinguishes it from all existing static melting processes. Vibration breaks up bubbles and inclusions in the melt, and combined with ceramic filter plates (pore size 5~10μm), it significantly reduces internal alloy defects, resolving performance fluctuations caused by insufficient melt purity. The mold preheating temperature is optimized to 200~220℃ to avoid compositional segregation caused by low-temperature casting.

[0020] Homogenization treatment: A homogenization scheme of "no demolding + argon protection" was proposed, which solved the surface oxidation problem of large-sized ingots (φ120~400mm) and avoided alloy contamination caused by residual covering agent. The homogenization regime (280~320℃×4~6h) ensured compositional uniformity. The subsequent addition of a steel sleeve for water spray cooling (cooling rate 15~20℃ / min) solved the problem of coarse microstructure caused by natural cooling.

[0021] Forging and Extrusion: Continuous, non-cooling-based process to ensure microstructure continuity. Employing a continuous forging-extrusion process without cooling avoids secondary oxide layers and structural stresses formed during cooling, ensuring a continuous and uniform internal alloy microstructure and improving subsequent rolling performance. Total forging deformation is controlled at 60-75%, and the extrusion ratio is optimized to 20:1-30:1 to meet the deformation requirements of large-size ingots.

[0022] Rolling and Stabilization Treatment: Composite Rolling + Cyclic Thermal Shock, Breaking Through Performance Bottlenecks. An innovative composite rolling process of "hot rolling → liquid nitrogen-cooled cold rolling → hot rolling → room temperature cold rolling" is designed: For the first time, "liquid nitrogen-cooled cold rolling" (roll temperature ≤ -10℃) is used to suppress grain growth, refine the microstructure, and introduce high-density dislocations through low temperature; the subsequent combination of secondary hot rolling and room temperature cold rolling balances strength and plasticity, avoiding the plasticity reduction problem caused by single cold rolling, and also constructing a twinned microstructure through low-temperature cold rolling. The total reduction in the first hot rolling is 40-50%, and the total reduction in the cold rolling is 30-40%, achieving precise shape and property control during the rolling process. A new cyclic thermal shock stabilization treatment of "120℃ holding → -50℃ liquid nitrogen cooling → 120℃ holding" is added, eliminating residual internal stress from rolling through hot and cold cycles and uniformly distributing the second phase. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below with reference to specific embodiments. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0024] The following embodiments further illustrate the content of the present invention, but should not be construed as limiting the present invention. Any modifications or substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and essence of the invention are within the scope of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0025] The ultralight, high-strength magnesium-lithium alloy of this invention has the following composition range by mass percentage: Li: 8.0~10.0wt%; Al: 6.0~7.5wt%; Gd: 2.0~3.5wt%; Zn: 2.0~3.5wt%; Mn: 0.3~0.8wt%; Ca: 0.4~0.7wt%; Sc: 0.1~0.3wt%; the remainder is Mg and unavoidable impurities, wherein the total impurity content is ≤0.3%, and the total content of harmful impurities such as Fe and Ni is ≤0.05%.

[0026] The preparation and processing methods include, in sequence: raw material pretreatment → vacuum vibration melting → filtration → casting → mold homogenization treatment → steel sleeve water spray cooling → demolding → turning → reheating → continuous forging → direct extrusion → multi-pass composite rolling → microstructure and property stabilization treatment, finally obtaining alloy plates with a thickness of 0.5~5mm.

[0027] Raw material pretreatment: Prepare pure Mg blocks (purity ≥99.95%), pure Al blocks (purity ≥99.97%), pure Li granules wrapped in aluminum foil (purity ≥99.9%), Mg-30Gd master alloy, Mg-20Sc master alloy, pure Zn blocks (purity ≥99.95%), Al-20Mn master alloy, and Mg-20Ca master alloy according to the above component ratios. For all raw materials except pure Li granules, perform surface grinding to remove oxide scale, ultrasonic cleaning with anhydrous ethanol, and vacuum drying for later use. Pure Li granules are ultrasonically degreased with acetone and then vacuum-sealed for storage to prevent oxidation and deterioration.

[0028] Vacuum vibration melting: Add all pretreated raw materials to the graphite crucible of the vacuum induction furnace, start the vacuum system to evacuate to ≤10Pa, and then purge with argon gas to 0.08~0.12MPa as a protective gas. Start the heating system and raise the temperature to 750~780℃. Turn on the furnace vibration device, adjust the vibration frequency to 50~80Hz and the amplitude to 0.5~1.0mm, and maintain the vibration state for 30~40min to fully homogenize the alloy composition and effectively remove gaseous impurities from the melt. After melting, filter the alloy melt through a ceramic filter plate with a pore size of 5~10μm to remove non-metallic inclusions from the melt.

[0029] Casting: Slowly pour the filtered alloy melt into a steel mold preheated to 200~220℃, close the furnace door, and allow it to cool naturally to below 300℃ to complete the initial solidification of the alloy and avoid compositional segregation caused by low-temperature casting.

[0030] Homogenization treatment with mold: Without demolding, the steel mold containing the ingot is directly transferred into an argon-protected heat treatment furnace. Through a dual protection method of "mold isolation from air + argon atmosphere," effective protection of the ingot surface is achieved. This protection method differs from existing technologies such as covering agent protection or single vacuum protection, and is suitable for the protection requirements of large-sized ingots. The heating rate is set at 5~8℃ / min, reaching 280~320℃, and held for 4~6 hours to achieve uniform alloy composition and stable microstructure.

[0031] Water spray cooling and demolding of steel sleeve: After homogenization treatment, the outer surface of the steel sleeve is immediately sprayed with water for cooling, and the cooling rate is controlled at 15~20℃ / min. After rapid cooling to room temperature, the mold is demolded to obtain an alloy ingot with a diameter of φ120~400mm. The surface of the ingot is turned to a bright finish using a CNC lathe to remove the oxide scale and defect layer, ensuring the dimensional accuracy and surface quality of subsequent processing.

[0032] Reheating and continuous forging: The machined ingot is placed in a resistance furnace, and argon gas is injected into the furnace for protection. The temperature is raised to 280~320℃ and held for 2~3 hours until the ingot is fully heated. After the ingot is fully heated, it is continuously forged using a high-speed forging machine. The total deformation is controlled at 60~75%, and the reduction per pass is 10~15%. After forging, a forging billet with dimensions equivalent to the original ingot is obtained. By reasonably controlling the deformation, the grain size is refined and the mechanical properties of the alloy are improved.

[0033] Direct extrusion: After forging, the billet is quickly transferred to an extrusion press without cooling. Extrusion is carried out at an extrusion temperature of 260~300℃, an extrusion ratio of 20:1~30:1, and an extrusion speed of 1.5~3m / min to obtain extruded sheets with a thickness of 8~12mm. This continuous, uncooled extrusion process, unlike existing segmented processing techniques, avoids the secondary oxide layer and structural stress formed during cooling, ensuring a continuous and uniform internal structure of the alloy.

[0034] Multi-pass composite rolling: The composite rolling process of "hot rolling → liquid nitrogen-cooled cold rolling → hot rolling → room temperature cold rolling" is adopted, and the specific operation is as follows: (1) First hot rolling: The extruded sheet is placed in a heating furnace and heated to 280~310℃. It is held for 1 hour. The reduction is 12~18% per pass, and the total reduction is controlled at 40~50%. After rolling, the sheet thickness is reduced to 4~6mm. (2) First cold rolling: During the rolling process, liquid nitrogen is continuously sprayed onto the surface of the rolls, and the roll temperature is strictly controlled to be ≤-10℃. A reduction of 5~8% is adopted per pass, and the total reduction is controlled to be 30~40%. After rolling, the thickness of the plate is reduced to 2.5~4.0mm. (3) Second hot rolling: Repeat the temperature, holding time and reduction parameters of the first hot rolling, keep the total reduction at 40~50%, and reduce the thickness of the plate to 1.5~2.5mm after rolling; (4) Room temperature cold rolling: At room temperature of 25~35℃, a reduction of 3~5% is adopted for each pass, and the total reduction is controlled at 50~70% to finally obtain an alloy plate with a thickness of 0.5~5mm, ensuring the dimensional accuracy and performance stability of the plate.

[0035] Microstructure and property stabilization treatment: The rolled sheet is placed in a heat treatment furnace and heated to 120℃, held for 5-10 minutes to ensure uniform temperature. After holding, the sheet is immediately removed and immersed in liquid nitrogen for rapid cooling to -50℃, held for 5-10 minutes to effectively eliminate rolling stress using thermal expansion and contraction. After the low-temperature holding, the sheet is directly placed back into a 120℃ heating furnace and held for 5-10 minutes to balance the distribution of internal stress. The above cycle of "120℃ holding → -50℃ liquid nitrogen cooling → 120℃ holding" is repeated 3-5 times. After the final 120℃ holding, the sheet is removed and placed in air to cool naturally to room temperature, completing the microstructure and property stabilization treatment. This further refines the alloy microstructure, uniformizes the distribution of second-phase particles, and avoids performance fluctuations caused by microstructure evolution during subsequent service. Example 1

[0036] 1. Alloy composition (percentage by mass) Li: 8.0wt%; Al: 6.0wt%; Gd: 2.0wt%; Zn: 2.0wt%; Mn: 0.3wt%; Ca: 0.4wt%; Sc: 0.1wt%; the remainder is Mg and unavoidable impurities (total impurity content ≤0.25%, Fe+Ni ≤0.03%).

[0037] 2. Preparation and processing technology Raw material pretreatment: Prepare pure Mg blocks (99.96%), pure Al blocks (99.97%), pure Li granules wrapped in aluminum foil (99.9%), Mg-30Gd master alloy, Mg-20Sc master alloy, pure Zn blocks (99.95%), Al-20Mn master alloy, and Mg-20Ca master alloy according to the above proportions. Except for the Li granules, all are polished, ultrasonically cleaned, and vacuum dried. The Li granules are degreased with acetone and then vacuum sealed.

[0038] Vacuum vibration melting: The raw material is added to a graphite crucible, vacuumed to 8 Pa, purged with argon to 0.08 MPa, heated to 750℃, and the vibration device (50 Hz, 0.5 mm) is started. The material is melted for 30 min and then filtered through a 5 μm ceramic filter plate.

[0039] Casting: The steel sleeve mold preheated to 200℃ is poured and then allowed to cool naturally to 280℃.

[0040] Homogenization of the mold: Transfer to an argon-protected furnace, heat to 280℃ at 5℃ / min, hold for 4 hours, cool with water spray on the steel sleeve (15℃ / min) to room temperature, and after demolding, machine the surface to a bright finish (φ120mm ingot).

[0041] Reheating and forging: The ingot is placed in a resistance furnace, filled with argon gas and heated to 280°C, held for 2 hours, and continuously forged (total deformation 60%, 10% per pass).

[0042] Direct extrusion: 260℃, extrusion ratio 20:1, speed 1.5m / min, to obtain 8mm thick extruded sheet.

[0043] Composite rolling: ① First hot rolling: Hold at 280℃ for 1 hour, 12% reduction per pass, total reduction 40%, to 4.8mm; ② First cold rolling: Spray liquid nitrogen on rolls (≤-10℃), 5% reduction per pass, total reduction 30%, to 3.36mm; ③ Second hot rolling: Repeat the parameters of the first hot rolling, total reduction 40%, to 2.02mm; ④ Room temperature cold rolling (25℃): 3% reduction per pass, total reduction 50%, to 1.01mm.

[0044] Stabilization treatment: Hold at 120℃ for 5 min → Cool to -50℃ with liquid nitrogen and hold for 5 min → Hold at 120℃ for 5 min, repeat 3 times, and finally cool to room temperature with air. Example 2

[0045] 1. Alloy composition (percentage by mass) Li: 8.5wt%; Al: 6.5wt%; Gd: 2.5wt%; Zn: 2.5wt%; Mn: 0.4wt%; Ca: 0.5wt%; Sc: 0.15wt%; the remainder is Mg and unavoidable impurities (total impurity content ≤0.28%, Fe+Ni ≤0.04%).

[0046] 2. Preparation and processing technology Raw material pretreatment: Prepare pure Mg blocks (99.96%), pure Al blocks (99.97%), pure Li granules wrapped in aluminum foil (99.9%), Mg-30Gd master alloy, Mg-20Sc master alloy, pure Zn blocks (99.95%), Al-20Mn master alloy, and Mg-20Ca master alloy according to the above proportions. Except for the Li granules, all are polished, ultrasonically cleaned, and vacuum dried. The Li granules are degreased with acetone and then vacuum sealed.

[0047] Vacuum vibration melting: Evacuate to 7Pa, fill with argon to 0.09MPa, heat to 760℃, vibrate the device (60Hz, 0.7mm), melt for 33min, and filter through an 8μm ceramic filter plate.

[0048] Casting: The steel sleeve mold, preheated to 210℃, is poured and allowed to cool naturally to 290℃.

[0049] Homogenization of the mold: Heat to 290℃ at 6℃ / min, hold for 4.5h, and then cool with water sprayed onto the steel sleeve (16℃ / min).

[0050] Reheating and forging: Hold at 290℃ for 2.5h, then forge continuously (total deformation 65%, 12% per pass).

[0051] Direct extrusion: 270℃, extrusion ratio 22:1, speed 2.0m / min, to obtain 9mm thick extruded sheet.

[0052] Composite rolling: ① First hot rolling: Hold at 290℃ for 1 hour, 14% reduction per pass, total reduction 45%, to 4.95mm; ② First cold rolling: Spray liquid nitrogen onto the rolls, 6% reduction per pass, total reduction 35%, to 3.22mm; ③ Second hot rolling: Repeat the parameters of the first hot rolling, total reduction 45%, to 1.77mm; ④ Room temperature cold rolling (28℃): 4% reduction per pass, total reduction 55%, to 0.79mm.

[0053] Stabilization treatment: hold at 120℃ for 7 min → cool to -50℃ with liquid nitrogen and hold for 7 min → hold at 120℃ for 7 min, repeat 4 times. Example 3

[0054] 1. Alloy composition (percentage by mass) Li: 9.0wt%; Al: 7.0wt%; Gd: 3.0wt%; Zn: 3.0wt%; Mn: 0.5wt%; Ca: 0.6wt%; Sc: 0.2wt%; the remainder is Mg and unavoidable impurities (total impurity content ≤0.27%, Fe+Ni ≤0.04%).

[0055] 2. Preparation and processing technology Raw material pretreatment: Prepare pure Mg blocks (99.96%), pure Al blocks (99.97%), pure Li granules wrapped in aluminum foil (99.9%), Mg-30Gd master alloy, Mg-20Sc master alloy, pure Zn blocks (99.95%), Al-20Mn master alloy, and Mg-20Ca master alloy according to the above proportions. Except for the Li granules, all are polished, ultrasonically cleaned, and vacuum dried. The Li granules are degreased with acetone and then vacuum sealed.

[0056] Vacuum vibration melting: Evacuate to 6Pa, fill with argon to 0.10MPa, heat to 770℃, vibrate the device (70Hz, 0.8mm), melt for 35min, and filter through a 10μm ceramic filter plate.

[0057] Casting: The steel sleeve mold, preheated to 215℃, is poured and then allowed to cool naturally to 295℃.

[0058] Homogenization of the mold: Heat to 300℃ at 7℃ / min, hold for 5 hours, and then cool with water sprayed onto the steel sleeve (18℃ / min).

[0059] Reheating and forging: Hold at 300℃ for 2.5h, then forge continuously (total deformation 70%, 14% per pass).

[0060] Direct extrusion: 280℃, extrusion ratio 25:1, speed 2.5m / min, to obtain 10mm thick extruded sheet.

[0061] Composite rolling: ① First hot rolling: Hold at 300℃ for 1 hour, 16% reduction per pass, total reduction 48%, to 5.2mm; ② First cold rolling: Spray liquid nitrogen onto the rolls, 7% reduction per pass, total reduction 38%, to 3.22mm; ③ Second hot rolling: Repeat the parameters of the first hot rolling, total reduction 48%, to 1.67mm; ④ Room temperature cold rolling (30℃): 4% reduction per pass, total reduction 60%, to 0.67mm.

[0062] Stabilization treatment: hold at 120℃ for 8 min → cool to -50℃ with liquid nitrogen and hold for 8 min → hold at 120℃ for 8 min, repeat 4 times. Example 4

[0063] 1. Alloy composition (percentage by mass) Li: 10.0wt%; Al: 7.5wt%; Gd: 3.5wt%; Zn: 3.5wt%; Mn: 0.8wt%; Ca: 0.7wt%; Sc: 0.3wt%; the remainder is Mg and unavoidable impurities (total impurity content ≤0.30%, Fe+Ni ≤0.05%).

[0064] 2. Preparation and processing technology Raw material pretreatment: Prepare pure Mg blocks (99.96%), pure Al blocks (99.97%), pure Li granules wrapped in aluminum foil (99.9%), Mg-30Gd master alloy, Mg-20Sc master alloy, pure Zn blocks (99.95%), Al-20Mn master alloy, and Mg-20Ca master alloy according to the above proportions. Except for the Li granules, all are polished, ultrasonically cleaned, and vacuum dried. The Li granules are degreased with acetone and then vacuum sealed.

[0065] Vacuum vibration melting: Evacuate to 5Pa, fill with argon to 0.12MPa, heat to 780℃, vibrate the device (80Hz, 1.0mm), melt for 40min, and filter through a 10μm ceramic filter plate.

[0066] Casting: The steel sleeve mold, preheated to 220°C, is poured and then allowed to cool naturally to 298°C.

[0067] Homogenization of the mold: Heat to 320℃ at 8℃ / min, hold for 6 hours, and then cool with water sprayed onto the steel sleeve (20℃ / min).

[0068] Reheating and forging: Hold at 320℃ for 3 hours, then forge continuously (total deformation 75%, 15% per pass).

[0069] Direct extrusion: 300℃, extrusion ratio 30:1, speed 3.0m / min, to obtain 12mm thick extruded sheet.

[0070] Composite rolling: ① First hot rolling: Hold at 310℃ for 1 hour, 18% reduction per pass, total reduction 50%, to 6.0mm; ② First cold rolling: Spray liquid nitrogen onto the rolls, 8% reduction per pass, total reduction 40%, to 3.6mm; ③ Second hot rolling: Repeat the parameters of the first hot rolling, total reduction 50%, to 1.8mm; ④ Room temperature cold rolling (35℃): 5% reduction per pass, total reduction 70%, to 0.54mm.

[0071] Stabilization treatment: hold at 120℃ for 10 min → cool to -50℃ with liquid nitrogen and hold for 10 min → hold at 120℃ for 10 min, repeat 5 times. Examples 5-10

[0072] The composition and process parameters of Examples 5-10 are adjusted in a gradient based on the above examples. The specific parameters form a complete gradient covering the scope of the claims of this invention with those of Examples 1-4. The differences in the core parameters of each example are as follows: Example 5: Li=8.2wt%, Al=6.2wt%, Gd=2.2wt%, Zn=2.2wt%, Mn=0.4wt%, Ca=0.45wt%, Sc=0.12wt%; melting temperature 755℃, homogenization temperature 285℃, forging deformation 62%, extrusion ratio 21:1, final thickness 2.00mm.

[0073] Example 6: Li=8.8wt%, Al=6.8wt%, Gd=2.8wt%, Zn=2.8wt%, Mn=0.6wt%, Ca=0.55wt%, Sc=0.22wt%; melting temperature 765℃, homogenization temperature 305℃, forging deformation 68%, extrusion ratio 26:1, final thickness 3.50mm.

[0074] Example 7: Li=9.2wt%, Al=7.2wt%, Gd=3.2wt%, Zn=3.2wt%, Mn=0.7wt%, Ca=0.65wt%, Sc=0.25wt%; melting temperature 775℃, homogenization temperature 310℃, forging deformation 72%, extrusion ratio 28:1, final thickness 4.00mm.

[0075] Example 8: Li=9.5wt%, Al=6.7wt%, Gd=2.6wt%, Zn=2.6wt%, Mn=0.5wt%, Ca=0.52wt%, Sc=0.18wt%; melting temperature 768℃, homogenization temperature 295℃, forging deformation 66%, extrusion ratio 24:1, final thickness 1.50mm.

[0076] Example 9: Li=8.6wt%, Al=7.3wt%, Gd=3.3wt%, Zn=3.3wt%, Mn=0.6wt%, Ca=0.68wt%, Sc=0.28wt%; melting temperature 772℃, homogenization temperature 315℃, forging deformation 73%, extrusion ratio 29:1, final thickness 4.80mm.

[0077] Example 10: Li=9.8wt%, Al=6.4wt%, Gd=2.4wt%, Zn=2.4wt%, Mn=0.35wt%, Ca=0.48wt%, Sc=0.16wt%; melting temperature 778℃, homogenization temperature 300℃, forging deformation 64%, extrusion ratio 23:1, final thickness 0.50mm.

[0078] The thickness, density, yield strength, tensile strength, elongation and other properties of the magnesium-lithium alloy plates obtained in Examples 1 to 10 were determined. The mechanical property tests were performed in accordance with GB / T 228.1-2021, and the results are shown in Table 1.

[0079] Table 1 Performance test results of Examples 1-10 As can be seen from Table 1, the magnesium-lithium alloy of the present invention has both ultra-low density (density ≤ 1.55 g / cm³) and... 3 With high specific strength and mechanical properties (tensile strength ≥310MPa, of which specific strength ≥200), it achieves a better balance of "ultra-light + high specific strength".

Claims

1. An ultralight magnesium-lithium alloy, characterized in that, The composition of the magnesium-lithium alloy is as follows: Li 8.0~10.0wt%, Al 6.0~7.5wt%, Gd 2.0~3.5wt%, Zn 2.0~3.5wt%, Mn 0.3~0.8wt%, Ca 0.4~0.7wt%, Sc 0.1~0.3wt%, with the balance being Mg and unavoidable impurities.

2. The ultralight magnesium-lithium alloy according to claim 1, characterized in that, The total impurity content is ≤0.3%, of which the total content of Fe and Ni is ≤0.05%.

3. The ultralight magnesium-lithium alloy according to claim 1, characterized in that, The density of the ultralight magnesium-lithium alloy is ≤1.55 g / cm³. 3 Tensile strength ≥ 310 MPa.

4. A method for preparing and processing an ultralight magnesium-lithium alloy according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Raw material pretreatment: Prepare raw materials according to the composition ratio and pretreat the raw materials; (2) Vacuum vibration melting: Add the pretreated raw materials into the graphite crucible of the vacuum induction furnace, evacuate the vacuum, and then fill with argon as a protective gas. Heat the furnace to 750~780℃, turn on the furnace body vibration device, adjust the vibration frequency to 50~80Hz and the amplitude to 0.5~1.0mm, and maintain the vibration state for melting for 30~40min; after melting, the alloy melt is filtered through a ceramic filter plate. (3) Casting: Slowly cast the filtered alloy melt into a steel mold preheated to 200~220℃, and let it cool naturally to below 300℃ to complete the initial solidification of the alloy; (4) Homogenization treatment with mold: without demolding, the steel sleeve mold with ingot is directly transferred into the argon-protected heat treatment furnace, the heating rate is set to 5~8℃ / min, the temperature is raised to 280~320℃, and the temperature is held for 4~6h. (5) Water spraying and demolding of steel sleeve: After the homogenization treatment is completed, water spraying is immediately applied to the outer surface of the steel sleeve to cool it. The cooling rate is controlled at 15~20℃ / min. After rapid cooling to room temperature, the mold is demolded to obtain the alloy ingot and the surface is machined. (6) Reheating and continuous forging: The turned ingot is heated to 280~320℃ and held for 2~3 hours; then, continuous forging is carried out using a high-speed forging machine; (7) Direct extrusion: After forging, the material is directly extruded at 260~300℃ without cooling to obtain extruded sheet; (8) Multi-pass composite rolling: The first hot rolling, liquid nitrogen-cooled cold rolling, second hot rolling, and room temperature cold rolling are performed in sequence; (9) Tissue property stabilization treatment: Place the rolled sheet into a heat treatment furnace and heat it to 120°C. Hold it for 5-10 minutes. Immediately remove the sheet and immerse it in liquid nitrogen. Cool it down rapidly to -50°C and hold it for 5-10 minutes. Place the sheet back into the 120°C heating furnace and hold it for 5-10 minutes. Repeat the above cycle of "holding at 120°C → cooling at -50°C liquid nitrogen → holding at 120°C" 3-5 times. After the last 120°C holding is completed, remove the sheet and place it in the air environment to cool down naturally to room temperature.

5. The method for preparing and processing ultralight magnesium-lithium alloy according to claim 4, characterized in that, In step (1), the raw materials are: Mg blocks with a purity ≥ 99.95%, Al blocks with a purity ≥ 99.97%, Li particles wrapped in aluminum foil with a purity ≥ 99.9%, Mg-30Gd master alloy, Mg-20Sc master alloy, Zn blocks with a purity ≥ 99.95%, Al-20Mn master alloy, and Mg-20Ca master alloy; all raw materials except Li particles are surface-polished to remove oxide scale, ultrasonically cleaned with anhydrous ethanol, and then vacuum-dried for later use; Li particles are ultrasonically degreased with acetone and then vacuum-sealed for storage.

6. The method for preparing and processing ultralight magnesium-lithium alloy according to claim 4, characterized in that, In step (2), the vacuum system is started to evacuate to ≤10Pa, and then argon gas is introduced to 0.08~0.12Mpa; the pore size of the ceramic filter plate is 5~10μm.

7. The method for preparing and processing ultralight magnesium-lithium alloy according to claim 4, characterized in that, In step (5), an alloy ingot with a diameter of φ120~400mm is obtained.

8. The method for preparing and processing ultralight magnesium-lithium alloy according to claim 4, characterized in that, In step (6), the total deformation is controlled to be 60-75% during continuous forging, and the reduction per pass is 10-15%.

9. The method for preparing and processing ultralight magnesium-lithium alloy according to claim 4, characterized in that, In step (7), the extrusion ratio is 20:1 to 30:1, the extrusion speed is 1.5 to 3 m / min, and an extruded sheet with a thickness of 8 to 12 mm is obtained.

10. The method for preparing and processing the ultralight magnesium-lithium alloy according to claim 4, characterized in that, In step (8), the specific operation of the multi-pass composite rolling is as follows: ① First hot rolling: The extruded sheet is placed in a heating furnace, heated to 280~310℃, and held for 1 hour. Each pass uses a reduction of 12~18%, and the total reduction is controlled at 40~50%. After rolling, the sheet thickness is reduced to 4~6mm. ② Liquid nitrogen cooling cold rolling: During the rolling process, liquid nitrogen is continuously sprayed onto the surface of the rolls, and the roll temperature is strictly controlled to be ≤-10℃. A reduction of 5~8% is adopted per pass, and the total reduction is controlled to be 30~40%. After rolling, the thickness of the plate is reduced to 2.5~4.0mm. ③ Second hot rolling: Repeat the temperature, holding time and reduction parameters of the first hot rolling, keep the total reduction at 40~50%, and reduce the thickness of the plate to 1.5~2.5mm after rolling; ④ Room temperature cold rolling: At a room temperature of 25~35℃, a reduction of 3~5% is adopted for each pass, and the total reduction is controlled at 50~70%, finally obtaining an alloy sheet with a thickness of 0.5~5mm.

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