Preparation process for high-quality mg-li and al-li alloys with large melting capacity under atmospheric pressure

Abstract

The present application relates to the field of light metal alloy smelting. To meet market requirements for high-quality large ingots of magnesium-lithium (Mg-Li) and aluminum-lithium (Al-Li) alloys, the present application provides a preparation process for high-quality Mg-Li and Al-Li alloys with large melting capacity under atmospheric pressure. First, a Li-Mg binary alloy element is prepared by means of a reduction reaction between a lithium salt and oxides of Ca, Mg and Al, and the Li-Mg binary alloy element is melted with a magnesium ingot or an aluminum ingot under atmospheric pressure to obtain a corresponding Mg-Li or Al-Li alloy. According to the method of the present application, high-quality Mg-Li and Al-Li alloy large castings can be prepared under atmospheric pressure, and moreover, the yield of lithium is improved. Metal lithium produced by electrolysis is not used as a raw material for preparing the Mg-Li or Al-Li alloy, thereby avoiding the pollution caused by chlorine generated by conventional lithium electrolysis.

Description

A preparation process for high-yield, high-quality Mg-Li and Al-Li alloys under normal pressure Technical Field

[0001] This application belongs to the field of light metal alloy smelting, specifically relating to a preparation process for high-quality Mg-Li and Al-Li alloys with large melting capacity under normal pressure. Background Technology

[0002] Magnesium-lithium (MgL) and aluminum-lithium (ALT) alloys are the lightest among metallic structural materials. MgL alloys have a density of 1.3-1.6 g / cm³, while ALT alloys have a density of 2.45-2.80 g / cm³. They possess high specific strength, specific stiffness, and specific damping properties, good low-temperature plasticity and impact resistance, good corrosion resistance and fatigue resistance, and excellent heat dissipation. They are used in many industries and high-tech civilian fields, including aerospace, aviation, marine, ordnance, nuclear reactors, tank armor-piercing projectiles, torpedoes, automobiles, robotics, and electronics. This has attracted numerous scientists worldwide to research MgL and ALT alloys, leading to their rapid development.

[0003] Currently, the methods used domestically and internationally to produce magnesium-lithium and aluminum-lithium alloys involve alloying in a vacuum furnace using a doping method. This involves melting high-quality aluminum ingots conforming to GB / T 1196-2008 or high-quality magnesium ingots conforming to GB / T 3499-2023 into a liquid state at 750-780℃ in a crucible within a vacuum furnace. Metallic lithium is then added to the molten aluminum or magnesium using a bell jar method to obtain aluminum-lithium or magnesium-lithium alloys. However, the main problem with alloys prepared using this process is:

[0004] 1. Adding metallic lithium directly to molten magnesium or aluminum is problematic because metallic lithium is reactive and flammable, and it readily reacts with oxygen, nitrogen, water, etc. in the air, resulting in a decrease in lithium yield. The compounds generated by the reaction increase impurities in the alloy liquid, and the gaseous impurities generated by the reaction cause thermal cracking in the alloy, making it impossible to obtain high-quality magnesium-lithium and aluminum-lithium alloy large castings, which cannot meet the requirements of large smelting furnaces in specific fields such as aerospace.

[0005] 2. It has high requirements for reaction equipment. The alloy melting furnace used is a vacuum melting furnace, which is not completely domestically produced, resulting in large fixed asset investment.

[0006] 3. During alloying, due to insufficient stirring and the significant differences in melting point, density, and other properties between lithium metal and magnesium and aluminum metals, segregation is severe, resulting in low absolute strength, stiffness, and modulus of the alloy.

[0007] 4. Electrolytic lithium first requires a complex process to obtain pure lithium chloride. When lithium chloride is electrolyzed to produce metallic lithium, chlorine gas is released. This results in high manufacturing costs, large fixed asset investments, and difficult environmental protection issues. Summary of the Invention

[0008] To meet the market demand for high-quality magnesium-lithium and aluminum-lithium alloy large ingots, this application provides a preparation process for high-quality Mg-Li and Al-Li alloys with large melting capacity under normal pressure.

[0009] A process for preparing high-quality Mg-Li and Al-Li alloys with large melting capacity under normal pressure includes the following steps:

[0010] S1. Preparation of composite oxide containing lithium metal: Lithium salt and oxide are thoroughly mixed and pressed into cylinders, which are then calcined under vacuum at high temperature to obtain composite oxide containing lithium metal;

[0011] S2. Preparation of Li-Mg binary alloy: The composite oxide obtained in step S1 is fully mixed with reducing agent and flux and then pressed into pellets. The pellets are subjected to high-temperature vacuum thermal reduction reaction to generate lithium and magnesium metal mixture gas. The metal mixture gas is cooled in a cooling collector to form metastable Li-Mg binary alloy condensed phase with metallic bonds.

[0012] S3. Paraffin purification: The Li-Mg binary alloy condensed phase collected in step S2 is placed into the molten paraffin along with the collector, so that the Li-Mg binary alloy condensed phase is completely melted and floats on the surface of the paraffin, while the high melting point impurities sink to the bottom of the paraffin. The temperature of the paraffin is reduced, and the Li-Mg binary alloy liquid phase floating on the surface of the paraffin solidifies into a solid phase, which is then removed.

[0013] S4. Distillation purification and ingot casting: The solidified Li-Mg binary alloy condensate phase retrieved in step S3 is purified by distillation in an argon-protected distillation furnace. The purified Li-Mg binary alloy is then melted in a melting furnace with flux added, and cast into Li-Mg binary alloy ingots under argon protection. The ingots are packaged in aluminum foil and stored in argon-filled containers.

[0014] S5. Magnesium and aluminum alloying: The cleaned and dried magnesium or aluminum ingots are heated and melted in an electric furnace. The Li-Mg binary alloy ingots obtained in step S4 are placed into the molten magnesium or aluminum liquid for melting, so that the Li-Mg binary alloy ingots are melted quickly. The mixture is stirred, cooled, and then cast into the corresponding magnesium-lithium alloy ingots or aluminum-lithium alloy ingots.

[0015] Further, in step S1, the mass ratio of lithium salt to oxide is (35-45):(65-55); the lithium salt is one, two, or three of anhydrous lithium carbonate, lithium nitrate, and lithium hydroxide; the oxide is a mixture of calcium oxide and magnesium oxide, or a mixture of aluminum oxide and magnesium oxide; the particle size of the lithium salt is selected to be D50 of 75-90 μm, and the particle size of the oxide is selected to be D50 of 85-100 μm.

[0016] Furthermore, the vacuum high-temperature calcination mentioned in step S1 refers to calcination at a vacuum degree of 5-20 Pa and a temperature of 850-950℃ for 6-8 hours. The reaction mechanism of calcined lithium salts is the same, and the chemical reaction formulas are similar. Taking the reaction of lithium carbonate during calcination as an example, the reaction formulas of different oxides with lithium carbonate are as follows:

[0017] Li₂CO₃ + MgO = Li₂O·MgO + CO₂↑

[0018] Li₂CO₃ + CaO = Li₂O·CaO + CO₂ ↑

[0019] Li2CO3+Al2O3=Li2O·Al2O3+CO2 ↑.

[0020] Furthermore, in step S2, the mass ratio of the composite oxide, reducing agent, and flux is (80-83):(15-17):(2-4), and the particle size of the composite oxide, reducing agent, and flux is selected to be 80-90 μm with a D50.

[0021] Furthermore, the reducing agent in step S2 is any one of ferrosilicon, aluminum powder, or carbon powder, and the flux is fluorite.

[0022] Furthermore, the high-temperature vacuum thermal reduction reaction of the pellets in step S2 is carried out at a pressure of 5-10 Pa and a temperature of 1100-1200 °C for 8-10 hours. The reaction of the lithium-containing composite oxide obtained by calcination is as follows:

[0023] 2(Li2O·MgO)+Si=2MgO·SiO2+4Li↑

[0024] 2(Li₂O·GaO) + Si = 2CaO·SiO₂ + 4Li↑

[0025] 2(Li2O·Al2O3)+Si=2Al2O3·SiO2+4Li↑

[0026] 2(CaO·MgO)+Si=2CaO·SiO2+2Mg↑.

[0027] Furthermore, in step S3, the melting temperature of the Li-Mg binary alloy condensed phase in the paraffin wax in the cooling collector is controlled to be 7-10°C higher than the melting point of the Li-Mg binary alloy, and the melting time is 2-2.5 hours. After the Li-Mg binary alloy floats on the surface of the paraffin wax, the temperature of the paraffin wax is lowered to 5-7°C below the melting point of the Li-Mg binary alloy component, and the temperature is maintained for 1-1.5 hours. The solid is then removed using a slotted spoon.

[0028] Furthermore, in step S4, the Li-Mg binary alloy is purified by three-stage distillation in a distillation furnace. The distillation vessel in the furnace is made of stainless steel, and the temperatures of the three distillations are controlled to be 15°C, 30°C, and 45°C higher than the melting point of the Li-Mg alloy, respectively.

[0029] Furthermore, when the Li-Mg binary alloy is melted in step S4, and when the magnesium ingot or aluminum ingot is heated and melted in step S5, a flux is added and protected with argon gas. The flux is a mixture of three compounds: LiCl, MgCl2 and LiF, and the mass ratio of the three compounds is LiCl:MgCl2:LiF = (55-65):(4-21):(25-31).

[0030] Furthermore, the metastable metallic bonded Li-Mg binary alloy condensed phase is the compounds Mg2.49Li and Mg4.72Li. In step S5, after the Li-Mg binary alloy reaches its melting point and melts, at a temperature close to 600°C, the compounds Mg2.49Li and Mg4.72Li decompose into atomic Li and atomic Mg. By stirring, the atomic Li and atomic Mg are uniformly distributed in the corresponding magnesium or aluminum liquid.

[0031] Furthermore, the smelting process in step S5 is carried out under atmospheric pressure, and the smelting furnace is a domestically produced electric furnace such as a resistance furnace or induction furnace that can smelt under atmospheric pressure. These types of electric furnaces are inexpensive, and smelting under atmospheric pressure facilitates large-capacity smelting.

[0032] In summary, the technical method of this application includes at least one of the following beneficial technical effects:

[0033] 1. The technical method of this application is to further produce Mg-Li and Al-Li alloys from the intermediate product Li-Mg alloying element. This breaks through the traditional method of using electrolytic lithium metal to form alloys with magnesium / aluminum liquid. It solves the problems of severe segregation of lithium metal in the alloy, poor appearance quality, and substandard mechanical properties, and effectively improves product quality.

[0034] 2. The technical method of this application is not limited by production equipment. It can use domestic electric furnaces such as conventional resistance furnaces or induction furnaces, which reduces fixed asset investment. The equipment is completely domestic and can produce large alloy castings with large melting capacity, which can fill the current demand for large alloy castings in the aerospace and other fields.

[0035] 3. The intermediate product Li-Mg alloy element prepared by the technical method of this application has a lithium content of 85-95%, which has not been reported at home and abroad. The thin plate rolled by this alloy is expected to be used directly as the negative electrode of lithium battery.

[0036] 4. Magnesium and lithium mixed metal gas is obtained by direct vacuum thermal reduction of mixed oxides of calcium, magnesium and aluminum, and then condensed to obtain lithium-magnesium binary alloy, which effectively improves the lithium yield.

[0037] 4. It effectively avoids the problem of chlorine gas generation in traditional lithium electrolysis methods, thus solving the environmental pollution problem. Attached Figure Description

[0038] Figure 1 is a process flow diagram of the technical method of this application;

[0039] Figure 2 is a schematic diagram of the appearance of the LA141 magnesium-lithium alloy product prepared by the technical method of this application in an electric furnace with a melting capacity of 400 kg under atmospheric pressure.

[0040] Figure 3 is a schematic diagram of the appearance of the 2195 aluminum-lithium alloy product prepared by the technical method of this application in an electric furnace with a melting capacity of 400 kg under atmospheric pressure.

[0041] Figure 4 is a schematic diagram of the appearance of the LA141 magnesium-lithium alloy product prepared by the lithium metal doping method in a vacuum electric furnace with a melting capacity of 400 kg.

[0042] Figure 5 shows a schematic diagram of the appearance of the LA141 magnesium-lithium alloy product prepared by the lithium metal doping method in a vacuum electric furnace with a melting capacity of 400 kg.

[0043] Figure 6 is a schematic diagram of the appearance of the 2195 aluminum-lithium alloy product prepared by the lithium metal doping method using a 400kg smelting capacity vacuum electric furnace.

[0044] Figure 7 is a schematic diagram of the appearance of the 2195 aluminum-lithium alloy product prepared by the lithium metal doping method in a vacuum electric furnace with a melting capacity of 400 kg. Detailed Implementation

[0045] The specific embodiments of this application will be further described below with reference to the accompanying drawings.

[0046] As shown in the process flow diagram in Figure 1, the core of the technical method of this application lies in first preparing the intermediate product Li-Mg binary alloy ingot, which can also be called Li-Mg binary alloy element or lithium-magnesium alloy element, and then using the lithium-magnesium alloy element to melt with magnesium ingot / aluminum ingot to obtain the corresponding Mg-Li alloy ingot / Al-Li alloy ingot. Example 1

[0047] This embodiment is used to prepare LA141A magnesium-lithium alloy ingots. The specific preparation process is as follows:

[0048] S1. Lithium carbonate and calcium oxide were selected as raw materials. The calcium oxide contained a small amount of magnesium oxide. Both raw materials were powders with a D50 of 85 μm. The mass ratio of lithium carbonate to calcium oxide containing a small amount of magnesium oxide was 43:57. The lithium carbonate and calcium oxide powders were mixed and pressed into cylinders with a diameter of Φ20 mm * 25 mm using a briquetting machine at 45 MPa. The cylinders were then calcined in a calcining furnace at a vacuum of 15 Pa and a temperature of 910 °C for 8 hours to obtain the composite oxide calcium lithiumate.

[0049] The calcination reaction is as follows:

[0050] Li₂CO₃ + CaO = Li₂O·CaO + CO₂ ↑

[0051] Li₂CO₃ + MgO = Li₂O·MgO + CO₂↑

[0052] Meanwhile, because lithium carbonate can be prepared in various ways and the raw materials are abundant, when limestone is involved in its preparation, the dolomite in the limestone undergoes the following reaction during calcination:

[0053] CaC03·MgC03 = Mg0·Ca0+2C02 ↑

[0054] Therefore, if the presence of limestone in the raw materials will not affect the technical method of this application, the trace amount of magnesium oxide generated during the calcination process can be used as the reaction raw material for this step.

[0055] Similarly, if aluminum oxide and magnesium oxide are selected as the oxide raw materials, the reaction between aluminum oxide and lithium salt is as follows:

[0056] Li2CO3+Al2O3=Li2O·Al2O3+CO2 ↑.

[0057] S2. Calcium lithiumate, ferrosilicon No. 75, and fluorite are all ground into powder with a D50 of 80 mg. The mass ratios of calcium lithiumate, ferrosilicon, and calcium fluoride are mixed in the ratio of 82:16:2. The mixed powder is then pressed into 35 g / apricot-shaped pellets using a briquetting machine under a pressure of 45 MPa. Ferrosilicon is used as a reducing agent, and fluorite is used as a flux. The pellets are then reacted in a vacuum reactor at a vacuum of 10 Pa and a temperature of 1150 °C for 9.5 hours. The gas produced by the reaction enters a cooling collector, and the metal contained in the gas phase is condensed into a condensed phase and collected in the cooling collector, resulting in a metastable Li-Mg binary alloy condensed phase with metallic bonds.

[0058] The reduction reaction process is as follows:

[0059] 2(Li2O·MgO)+Si=2MgO·SiO2+4Li↑

[0060] 2(Li₂O·GaO) + Si = 2CaO·SiO₂ + 4Li ↑

[0061]

[0062] 2(CaO·MgO)+Si=2CaO·SiO₂+2Mg↑

[0063] Similarly, when aluminum oxide is used as a raw material, the reaction is as follows:

[0064] 2(Li2O·Al2O3)+Si=2Al2O3·SiO2+4Li↑

[0065] S3. The collector containing the Li-Mg binary alloy condensate phase is placed into the paraffin melt at 220°C. After maintaining the temperature at 220°C for 2 hours, the paraffin melt is cooled to 203°C and kept at that temperature for 1 hour. The Li-Mg binary alloy liquid phase solidifies into a solid phase. The solidified Li-Mg binary alloy condensate phase is scooped out with a slotted spoon, and the high-melting-point impurities sink to the bottom of the paraffin.

[0066] S4. The retrieved Li-Mg binary alloy solid is purified in a series of three-stage temperature-controlled stainless steel distillation kettles at 235℃, 250℃, and 265℃ respectively. The paraffin wax carried by the retrieved Li-Mg binary alloy solid is returned to the paraffin melting furnace. 86% of the K and Na are converted into gases or become another product with high K and Na content. 87% of the impurities in the Li-Mg binary alloy meet the GB / T4369-2015 standard. The alloy is then melted in an electric furnace at 280℃ under the combined protection of flux (LiCl:MgCl2:LiF = 63:6:31 by mass) and argon gas. The Li-Mg binary alloy liquid is cast into metal ingots in an argon-filled glove box and vacuum-packed with aluminum foil to obtain the purified Li-Mg binary alloy ingot. The lithium content of this Li-Mg binary alloy ingot is 95%, and the Li+Mg content is 99.5%. The obtained Li-Mg binary alloy ingots are used as alloying elements for the subsequent preparation of Mg-Li alloys (magnesium-lithium alloys) and Al-Li alloys (aluminum-lithium alloys), and are referred to below as Li-Mg binary alloying elements or lithium-magnesium alloying elements. The high-melting-point impurities are mainly high-melting-point oxides and fluorides, specifically CaO, MgO, Li₂O, 2CaOSiO₂, 2CaOLi₂O, FeO, Fe₂O₃, CaF₂, and trace amounts of Li₂O, ferrosilicon, etc.

[0067] S5. Place 200 kg of washed and dried magnesium ingots into a crucible in an atmospheric pressure electric furnace and heat to 750°C. After 45 minutes, the magnesium ingots are completely melted. Use 32.7 kg of Li-Mg binary alloying element obtained in step S4 to prepare LA141A magnesium-lithium alloy. Place the Li-Mg binary alloying element packaged in aluminum foil directly into the molten magnesium at a depth of 300 mm. After melting for 5 minutes, mechanically stir for 25 minutes, cool to 710°C, and cast into an ingot in a cylindrical mold to obtain a magnesium-lithium alloy ingot. The analysis results of the prepared magnesium-lithium alloy ingot show that the lithium metal yield reaches 94.35%, the lithium content at various points in the magnesium-lithium alloy ingot is 14±0.1%, no segregation occurs, the ingot surface is smooth and without cracks, and its elemental composition meets the high-quality standard of GB / T3499-2023. Example 2

[0068] This embodiment is used to prepare 2195 aluminum-lithium alloy ingots. The process of preparing lithium-magnesium alloy elements (steps S1-S4) is the same as in Example 1.

[0069] S5. Place 200 kg of cleaned and dried aluminum ingots into a crucible in an atmospheric pressure induction furnace and heat to 750℃. After 45 minutes, the aluminum is completely melted. Take out 2.49 kg of lithium-magnesium alloy element to prepare 2195 aluminum-lithium alloy. Place the lithium-magnesium alloy element containing 95% lithium, packaged in aluminum foil, into the molten aluminum at a depth of 300 mm. After melting for 5 minutes, mechanically stir for 25 minutes, cool to 710℃, and semi-continuously cast into an ingot to obtain an aluminum-lithium alloy ingot. The analysis results of the prepared aluminum-lithium alloy ingot showed that the lithium metal yield was 94.82%, and the lithium metal content in different parts of the aluminum-lithium alloy was 1.12±0.01%. There was no segregation of lithium metal in the alloy, the ingot surface was smooth, and its elemental composition met the high-quality standard of GB / T 1196-2008.

[0070] One of the key aspects of the technical method in this application is the first preparation of high-quality lithium-magnesium alloy elements (i.e., the intermediate product obtained in step S4). The main technical indicators of the prepared lithium-magnesium alloy elements are lithium yield, Li+Mg content, and Li content. Based on Example 1, the results of the lithium yield, (Li+Mg) content, and Li content of the lithium-magnesium alloy elements were analyzed for different technical parameters in steps S1 (calcination section), S2 (vacuum thermal reduction section), and S3 (paraffin purification section), as shown in Table 1. Except for the variable parameters in the table, the rest of the preparation process and detection and analysis process are exactly the same as in Example 1.

[0071] Table 1:

[0072]

[0073] As shown in Table 1, the high-quality lithium-magnesium alloy element first obtained using the technical method of this application has a Li content of not less than 85%, a Li+Mg content of not less than 99.5%, and a Li yield of over 90%, with the Li yield even exceeding 96% in Examples 4 and 5. These examples demonstrate that the process route of the technical method of this application is smooth, and the process parameters and selected equipment can meet the requirements for preparing lithium-magnesium alloy elements. The lithium-magnesium alloy produced by this method costs only 2 / 3 of the traditional lithium metal manufacturing cost, significantly reducing the manufacturing cost of magnesium-lithium alloys and aluminum-lithium alloys. The alloying preparation process does not require expensive vacuum melting furnaces, reducing fixed asset investment by 1 / 3 compared to the same lithium production, and there is no chlorine pollution.

[0074] In step S2, the high-temperature vacuum thermal reduction reaction is a solid-solid reaction, meaning the reactants are all solids, producing a gas. For a solid-solid reaction to proceed, the contact area must be increased, so the materials need to be finely ground. However, if the material is too fine, the surface energy increases, leading to natural polymerization. Therefore, a specific particle size must be selected to improve the reaction rate and yield. Similarly, applying pressure also helps to bring the molecules closer together for the reaction to occur. Thus, the particle size of the lithium salt in step S1 of the calcination section is generally 75-90 μm (D50), the particle size of the calcium, magnesium, and aluminum oxides is generally 85-100 μm (D50), and the particle size of the raw material in step S2 of the vacuum thermal reduction section is 80-90 μm (D50).

[0075] To further verify the effectiveness and advantages of the technical method of this application, the technical method of this application is compared with the method of preparing magnesium-lithium alloys and aluminum-lithium alloys with different melting amounts by doping. The comparative analysis results of preparing LA141 magnesium-lithium alloy are shown in Table 2, and the comparative analysis results of preparing 2195 aluminum-lithium alloy are shown in Table 3.

[0076] Table 2:

[0077]

[0078] Table 3:

[0079]

[0080] The specific preparation processes for Comparative Example 1 in Table 1 and Comparative Examples 4 and 5 in Table 2 are as follows:

[0081] Comparative Example 1

[0082] Magnesium-lithium alloy was prepared using a doping method: 200 kg of cleaned and dried magnesium ingots were placed in a crucible in a vacuum induction furnace. The furnace was evacuated and filled with argon to maintain a slight positive pressure. The furnace was heated to 750°C, and after 45 minutes, the magnesium was completely melted. 37.90 kg of lithium metal obtained by electrolysis and vacuum-packed in aluminum foil was then removed to prepare LA141A magnesium-lithium alloy ingots. The aluminum foil-wrapped lithium metal was placed 300 mm below the molten magnesium using a bell jar method. After melting for 5 minutes, argon gas was passed through and the mixture was stirred for 25 minutes. The mixture was then cooled to 710°C and cast into cylindrical castings. Analysis of the prepared magnesium-lithium alloy ingots showed a lithium metal yield of 74.1%, with a maximum lithium content of 16.63% and a minimum of 12.36%, indicating severe lithium segregation in the alloy. The electrolysis method used in this comparative example is a known technique and will not be elaborated upon in this application.

[0083] Comparative Example 4

[0084] Preparation of aluminum-lithium alloy by doping: 200 kg of cleaned and dried aluminum ingots were placed in a crucible in a vacuum induction furnace. The furnace was evacuated and filled with argon to maintain a slight positive pressure. The furnace was heated to 750°C. After 45 minutes, the aluminum was completely melted. 2.89 kg of metallic lithium obtained by electrolysis and vacuum-packed in aluminum foil was taken out. The target alloy was 2195 aluminum-lithium alloy ingot. The metallic lithium wrapped in aluminum foil was placed 300 mm below the molten aluminum using the bell jar method. After melting for 5 minutes, argon gas was passed through and stirred for 25 minutes. The mixture was cooled to 710°C and semi-continuously cast into an ingot. The results of sampling and analysis of the prepared aluminum-lithium alloy ingot showed that the yield of metallic lithium was 73.82%, with the highest lithium content being 1.96% and the lowest being 0.74%. The metallic lithium was severely segregated in the alloy.

[0085] Comparative Example 5

[0086] Preparation of aluminum-lithium alloy by doping: 400 kg of cleaned and dried aluminum ingots were placed in a crucible in a vacuum induction furnace. The furnace was evacuated and filled with argon to maintain a slight positive pressure. The furnace was heated to 750°C. After 45 minutes, the aluminum was completely melted. 5.83 kg of metallic lithium obtained by electrolysis and vacuum-packed in aluminum foil was removed to prepare 2195 aluminum-lithium alloy ingots. Using a bell jar method, the foil-wrapped metallic lithium was placed 300 mm below the molten aluminum. After melting for 5 minutes, argon gas was passed through and stirred for 25 minutes. The mixture was then cooled to 710°C and semi-continuously cast into ingots. Analysis of the prepared aluminum-lithium alloy ingots showed a lithium yield of 72.39%, with a maximum lithium content of 1.98% and a minimum of 0.84%. Severe segregation of lithium in the alloy was observed. Several black grooves, 2-4 mm deep, 1-3 mm wide, and 100-600 mm long, appeared on the surface, as shown in Figures 6 and 7. These grooves are flammable during subsequent machining of the ingots on a lathe.

[0087] In Table 2, Examples 1-7 are based on Example 1, where LA141A magnesium-lithium alloy ingots were prepared. Steps S1-S4 are identical to those in Example 1. The difference in step S5 compared to Example 1 is the single-furnace melting amount (i.e., the weight of the magnesium ingots used) and the weight of the added lithium-magnesium alloying element; the rest of the preparation process is the same. Similarly, in Table 3, Examples 8-14 are based on Example 2, where 2195 aluminum-lithium alloy ingots were prepared. Steps S1-S4 are identical to those in Example 2. The difference in step S5 compared to Example 1 is the single-furnace melting amount (i.e., the weight of the aluminum ingots used) and the weight of the added lithium-magnesium alloying element; the rest of the preparation process is the same. Furthermore, the testing standards and methods for all examples, test cases, and comparative examples in Tables 2 and 3 are the same.

[0088] As shown in Tables 2 and 3, the traditional doping method can only produce Mg-Li alloy ingots and Al-Li alloy ingots with small melting volumes (around 50 kg). When producing alloy ingots with large melting volumes, the surface quality of the alloy may be substandard, with cracks and even black grooves. For details, please refer to Figures 4 and 5, which show the appearance of a 400 kg LA141 magnesium-lithium alloy product, and Figures 6 and 7, which show the appearance of a 400 kg 2195 aluminum-lithium alloy product. Products with substandard surface quality, as shown in Figures 4-7, require machining to remove cracks and black grooves during subsequent use, resulting in significant waste. Furthermore, the alloys prepared by the doping method have low lithium yields, leading to lithium waste, and severe segregation, which directly affects the product's strength, stiffness, and modulus. The Mg-Li alloy ingots and Al-Li alloy ingots prepared by the method of this application, whether in small melting amounts of 50 kg or large melting amounts of 600 kg, all meet the national standards for high-quality products in terms of appearance and elemental analysis. This effectively meets the needs of large alloy casting applications such as aerospace, and significantly improves lithium yield. The appearance of the Mg-Li alloy ingots and Al-Li alloy ingots prepared by the method of this application can be seen in Figure 2 (400 kg LA141 magnesium-lithium alloy product) and Figure 3 (400 kg 2195 aluminum-lithium alloy product).

[0089] In summary, this application provides a process for preparing high-quality Mg-Li and Al-Li alloys with large melting capacity under atmospheric pressure. The process involves first producing Li-Mg binary alloying elements through a reduction reaction using lithium salts and oxides of Ca, Mg, and Al. Then, the Li-Mg binary alloying elements are smelted with magnesium or aluminum ingots under atmospheric pressure to obtain the corresponding Mg-Li or Al-Li alloys. This method can prepare large castings of high-quality Mg-Li and Al-Li alloys under atmospheric pressure, while simultaneously improving lithium yield. It eliminates the need for electrolytic lithium metal as a raw material for producing magnesium-lithium or aluminum-lithium alloys, thus avoiding the chlorine pollution generated by traditional lithium electrolysis.

[0090] The above are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A process for preparing high-quality Mg-Li and Al-Li alloys with large melting capacity under normal pressure, characterized in that... Includes the following steps: S1. Preparation of composite oxide containing lithium metal: Lithium salt and oxide are thoroughly mixed and pressed into cylinders, which are then calcined under vacuum at high temperature to obtain composite oxide containing lithium metal; S2. Preparation of Li-Mg binary alloy: The composite oxide obtained in step S1 is fully mixed with reducing agent and flux and then pressed into pellets. The pellets are subjected to high-temperature vacuum thermal reduction reaction to generate lithium and magnesium metal mixture gas. The metal mixture gas is cooled in a cooling collector to form metastable Li-Mg binary alloy condensed phase with metallic bonds. S3. Paraffin purification: The Li-Mg binary alloy condensed phase collected in step S2 is placed into the molten paraffin along with the collector, so that the Li-Mg binary alloy condensed phase is completely melted and floats on the surface of the paraffin, while the high melting point impurities sink to the bottom of the paraffin. The temperature of the paraffin is reduced, and the Li-Mg binary alloy liquid phase floating on the surface of the paraffin solidifies into a solid phase, which is then removed. S4. Distillation purification and ingot casting: The solidified Li-Mg binary alloy condensate phase retrieved in step S3 is purified by distillation in an argon-protected distillation furnace. The purified Li-Mg binary alloy is then melted in a melting furnace with flux added, and cast into Li-Mg binary alloy ingots under argon protection. The ingots are packaged in aluminum foil and stored in argon-filled containers. S5. Magnesium and aluminum alloying: The cleaned and dried magnesium or aluminum ingots are heated and melted in an electric furnace. The Li-Mg binary alloy ingots obtained in step S4 are placed into the molten magnesium or aluminum liquid for melting, so that the Li-Mg binary alloy ingots are melted quickly. The mixture is stirred, cooled, and then cast into the corresponding magnesium-lithium alloy ingots or aluminum-lithium alloy ingots.

2. The preparation process of high-quality Mg-Li and Al-Li alloys with large melting capacity under normal pressure according to claim 1, characterized in that, In step S1, the mass ratio of lithium salt to oxide is (35-45):(65-55); the lithium salt is one, two, or three of anhydrous lithium carbonate, lithium nitrate, and lithium hydroxide; the oxide is a mixture of calcium oxide and magnesium oxide, or a mixture of aluminum oxide and magnesium oxide; the particle size of the lithium salt is selected to be D50 of 75-90 μm, and the particle size of the oxide is selected to be D50 of 85-100 μm.

3. The preparation process of high-quality Mg-Li and Al-Li alloys with large melting capacity under normal pressure according to claim 2, characterized in that, The vacuum high-temperature calcination mentioned in step S1 refers to calcination at a vacuum degree of 5-20 Pa and a temperature of 850-950 °C for 6-8 hours.

4. The preparation process of high-quality Mg-Li and Al-Li alloys with large melting capacity under normal pressure according to claim 1, characterized in that, In step S2, the mass ratio of the composite oxide, reducing agent, and flux is (80-83):(15-17):(2-4), and the particle size of the composite oxide, reducing agent, and flux is selected to be 80-90 μm with a D50.

5. The preparation process of high-quality Mg-Li and Al-Li alloys with large melting capacity under normal pressure according to claim 4, characterized in that, The reducing agent in step S2 is any one of ferrosilicon, aluminum powder or carbon powder, and the flux is fluorite.

6. The preparation process of high-quality Mg-Li and Al-Li alloys with large melting capacity under normal pressure according to claim 1, characterized in that, The high-temperature vacuum thermal reduction reaction of the pellets in step S2 is carried out at a pressure of 5-10 Pa and a temperature of 1100-1200 °C for 8-10 hours.

7. The preparation process of high-quality Mg-Li and Al-Li alloys with large melting capacity under normal pressure according to claim 1, characterized in that, In step S3, the melting temperature of the Li-Mg binary alloy condensed phase in the cooling collector in paraffin is controlled to be 7-10°C higher than the melting point of the Li-Mg binary alloy, and the melting time is 2-2.5 hours.

8. The preparation process of high-quality Mg-Li and Al-Li alloys with large melting capacity under normal pressure according to claim 1, characterized in that, In step S4, the Li-Mg binary alloy is purified by three-stage distillation in a distillation furnace. The distillation vessel in the furnace is made of stainless steel, and the temperatures of the three distillations are controlled to be 15°C, 30°C, and 45°C higher than the melting point of the Li-Mg alloy, respectively.

9. The preparation process of high-quality Mg-Li and Al-Li alloys with large melting capacity under normal pressure according to claim 1, characterized in that, When the Li-Mg binary alloy is melted in step S4, and when the magnesium ingot or aluminum ingot is heated and melted in step S5, a flux is added and protected with argon gas. The flux is a mixture of three compounds: LiCl, MgCl2 and LiF, and the mass ratio of the three compounds is LiCl:MgCl2:LiF = (55-65):(4-21):(25-31).

10. The preparation process of high-quality Mg-Li and Al-Li alloys with large melting capacity under normal pressure according to claim 1, characterized in that, The metastable metallic bonded Li-Mg binary alloy condensed phase consists of compounds Mg2.49Li and Mg4.72Li. In step S5, after the Li-Mg binary alloy reaches its melting point and melts, at approximately 600°C, the compounds Mg2.49Li and Mg4.72Li decompose into atomic Li and atomic Mg. By stirring, the atomic Li and atomic Mg are uniformly distributed in the corresponding magnesium or aluminum liquid.

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