A coating flux for recycled Al-Li alloys, its preparation method and application

Abstract

This application relates to the field of aluminum-lithium alloy waste recycling technology, and in particular to a covering flux for recycled Al-Li alloys, its preparation method, and its application. The raw materials for preparing this recycled Al-Li alloy flux are lithium chloride, lithium fluoride, aluminum fluoride, and calcium fluoride. This covering flux is used in the remelting and recycling of recycled aluminum-lithium alloys, simultaneously providing covering, slag removal, degassing, and refining functions. It results in minimal lithium loss, is sodium-free and potassium-free, and exhibits excellent melt purification. This achieves high purity of the melt in the remelting and recycling of recycled aluminum-lithium alloys. Aluminum-lithium alloy ingots prepared from the recycled aluminum-lithium alloy melt using the covering flux of this application exhibit high purity and excellent production quality.

Description

Technical Field

[0001] This application relates to the field of aluminum-lithium alloy waste recycling technology, and in particular to a covering flux for recycled Al-Li alloys, its preparation method and application. Background Technology

[0002] Aluminum-lithium alloys are widely used in the aerospace field due to their lightweight, high strength, and high elastic modulus. With technological advancements, a significant amount of aluminum-lithium alloy waste has been generated. Recycling this waste has substantial economic value. However, the smelting of recycled aluminum-lithium alloys presents several challenges: 1. The waste surface contains oxide layers such as Al2O3, Li2O, and LiAlO2, and after machining and use, it retains a wider variety of complex inclusions, including oil stains and carbides; 2. Lithium is highly reactive and easily burns during smelting, forming products such as Li2O, LiAlO2, and LiH; 3. Aluminum-lithium alloys are extremely sensitive to potassium and sodium, requiring the potassium and sodium content in the alloy to not exceed 5 ppm; 4. During remelting of recycled materials, the original inclusions are difficult to completely remove using conventional refining methods.

[0003] Current purification technologies for aluminum-lithium alloy melts mainly include inert gas protection, rotor blowing degassing, and vacuum melting. Rotor blowing degassing can remove inclusions and hydrogen to some extent, but it is difficult to guarantee the stability of the alloy melt quality. While vacuum melting can ensure the cleanliness of aluminum-lithium alloys, it is difficult to remove previous inclusions from recycled aluminum-lithium alloys, and lithium loss is severe, resulting in high costs. In comparison, flux protection remains the most economical and applicable method, but it requires targeted development based on alloy composition and inclusions.

[0004] In the prior art, CN110004328B discloses an aluminum-lithium alloy flux containing only LiCl and LiF. While it can provide basic coverage, its ability to dissolve complex oxides such as LiAlO2, which are abundant in recycled materials, is limited. Patent CN113430412A uses lithium fluoride, lithium chloride, aluminum fluoride, potassium fluoride, hexachloroethane, ammonium chloride, and ammonium fluoride. Although this formula provides some purification effect, it cannot meet the requirements for preparing recycled aluminum-lithium alloys. Furthermore, the use of potassium chloride introduces potassium elements into the recycled aluminum-lithium alloy. In addition, the use of ammonium chloride and ammonium fluoride will decompose into ammonia and hydrogen chloride gas during the smelting process. The hydrogen chloride gas will further react with aluminum in the melt to generate hydrogen gas, resulting in excessive hydrogen content in the melt. Moreover, the decomposition of ammonium salts is very rapid, instantly generating a large amount of gas, which can easily cause the melt to boil. Patent CN112760515A uses potassium chloride, magnesium chloride, sodium chloride, barium chloride, lithium chloride, aluminum fluoride, and calcium chloride. The combination of various chloride salts can form complex eutectic mixtures, which, while offering some purification, introduce various uncontrollable and harmful impurity elements into the aluminum-lithium alloy, severely impacting the cleanliness of the recycled aluminum-lithium alloy melt. Therefore, there is an urgent need to develop a specialized flux that can efficiently purify the complex inclusions in recycled aluminum-lithium alloys without introducing harmful elements.

[0005] In summary, while some development and research have been conducted on protective fluxes for aluminum-lithium alloys, these fluxes introduce other impurity elements and are unsuitable for the preparation of recycled aluminum-lithium alloys. Therefore, there is an urgent need to develop a dedicated protective flux for recycled aluminum-lithium alloys that can effectively purify various oxides and carbides. Summary of the Invention

[0006] Therefore, the purpose of this application is to overcome the shortcomings of the prior art and provide a covering flux for recycled Al-Li alloys, its preparation method, and its application. This aims to solve the problems of difficult removal of complex inclusions, severe lithium burn-off, easy hydrogen absorption, and sensitivity to Na and K impurities in the smelting of recycled aluminum-lithium alloys.

[0007] To achieve the above objectives, this application adopts the following technical solution:

[0008] First, this application provides a covering flux for recycled Al-Li alloys, using lithium chloride, lithium fluoride, aluminum fluoride, and calcium fluoride as raw materials.

[0009] Preferably, the raw materials for preparing the covering flux for recycled Al-Li alloys, by mass parts, are: 33-85 parts of lithium chloride, 15-67 parts of lithium fluoride, 10-52 parts of aluminum fluoride, and 10-52 parts of calcium fluoride.

[0010] Preferably, the covering flux is in powder form with a particle size ≤1.0mm.

[0011] Preferably, the H2O content in the covering flux is ≤2.0wt%.

[0012] Based on a general inventive concept, this application provides a method for preparing a covering flux for recycled Al-Li alloys, comprising the following steps:

[0013] S1. Lithium chloride, lithium fluoride, and aluminum fluoride are mixed and melted, then condensed to obtain the first mixed salt;

[0014] S2. The first mixed salt is mixed with calcium fluoride, and then ball-milled and dried to obtain a powdered coating flux.

[0015] Preferably, in step S1, the mixing and melting temperature is 700~800℃.

[0016] Preferably, the target temperature for condensation is 20~50℃.

[0017] Preferably, the condensation step includes first cooling the furnace to 500°C, then removing it and cooling it under argon protection.

[0018] Preferably, the first mixed salt is first ball-milled to obtain granular first mixed salt, and then mixed with the calcium fluoride; wherein the particle size of the granular first mixed salt is ≤1.0mm.

[0019] Preferably, the ball milling is performed using a dry ball mill made of zirconia or Hastelloy.

[0020] Preferably, in step S2, the drying conditions include a temperature of 120~200℃ and a time of 8~9h.

[0021] Based on a general inventive concept, this application provides an application of a covering flux for recycled Al-Li alloys in the recycling of aluminum-lithium alloy waste, comprising the following steps:

[0022] The aluminum-lithium alloy waste to be recycled is melted into a waste aluminum melt. Then, under stirring conditions, the above-mentioned recycled Al-Li alloy is added to the waste aluminum melt with a covering flux. After standing, it is then refined and slag is removed in sequence to obtain the recycled aluminum-lithium alloy.

[0023] Preferably, the aluminum-lithium alloy waste to be recycled is melted at 730~760℃ under argon protection and held at that temperature for 10~30 minutes.

[0024] Preferably, the covering flux for the recycled Al-Li alloy is added uniformly along the surface of the melt in 2-3 portions; the amount of covering flux added is 1.0-1.5 wt% of the mass of the waste melt.

[0025] Preferably, after the regenerated Al-Li alloy is completely added with the covering flux, it is gently stirred for 3 to 10 minutes, and then allowed to stand for 10 to 20 minutes.

[0026] Preferably, after settling, high-purity argon gas is used for refining, and after refining, the slag is removed and the mixture is poured.

[0027] The mechanism of the covering flux for recycled Al-Li alloys provided in this application is as follows:

[0028] The covering flux of this application is composed of lithium chloride, lithium fluoride, aluminum fluoride, and calcium fluoride. Lithium chloride serves as the base carrier, forming a liquid covering layer that effectively isolates air and prevents oxidation and hydrogen absorption. The combination of lithium fluoride and aluminum fluoride forms a highly active fluorochlorate system, which can effectively dissolve dense alumina, lithium oxide, and lithium alumina oxide oxides in recycled aluminum-lithium alloys, and effectively remove inclusions from aluminum-lithium alloy waste. Finally, calcium fluoride alters the surface tension of the flux and inclusions, causing fine inclusions to aggregate into larger particles, forming easily removable slag, thereby improving slag removal efficiency and melt cleanliness.

[0029] The covering flux of this application is prepared by first mixing and melting lithium chloride, lithium fluoride, and aluminum fluoride, ball milling them into particles, then mixing them with calcium fluoride, ball milling them, and drying them to obtain the finished product. Because the components of the covering flux are highly hygroscopic, strict water avoidance is required during the preparation process, ensuring it is carried out in an anhydrous environment. This covering flux is used in the remelting and recycling of recycled aluminum-lithium alloys, combining functions of covering, slag removal, degassing, and refining. It results in minimal lithium loss, is free of sodium and potassium, and has excellent melt purification effects. It achieves high purity of the melt in the remelting and recycling of recycled aluminum-lithium alloys. Aluminum-lithium alloy ingots prepared from the recycled aluminum-lithium alloy melt using the covering flux of this application exhibit high purity and excellent production quality.

[0030] Compared with the prior art, this application has the following advantages:

[0031] (1) This application combines lithium chloride, lithium fluoride, aluminum fluoride, and calcium fluoride in a specific ratio. Through the synergistic effect of different components, a continuous coating layer can be formed on the surface of the melt, reducing the contact between the melt and the surrounding atmosphere, and promoting the contact, migration, and removal of oxide inclusions in the recycled aluminum-lithium alloy at the flux interface, thereby improving the cleanliness of the melt. At the same time, it has a certain refining effect, improving the performance of the recycled aluminum-lithium alloy while ensuring the cleanliness of the melt.

[0032] (2) The results show that, compared with the existing production process that uses a flux-covered ingot, the lithium loss of the recycled aluminum-lithium alloy ingot produced using the flux of this application can be controlled within 3%, while the inclusion content is within 0.8 mm² / kg-Al and the hydrogen content can be controlled below 0.14 mL / 100g Al, which has good melt purification ability, thereby effectively improving the quality of recycled aluminum-lithium alloy ingots. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some implementation methods of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0034] Figure 1 The diagram shows the isothermal phase equilibrium of the LiCl-LiF-AlF3 system at 873 K.

[0035] Figure 2 The diagram shows the isothermal phase equilibrium of the LiCl-LiF-AlF3 system at 973 K.

[0036] Figure 3 The diagram shows the isothermal phase equilibrium of the LiCl-LiF-AlF3 system at 1013 K.

[0037] Figure 4 The wetting evolution process of the eutectic 79wt%LiCl-21wt%LiF system on the α-Al2O3 surface; among which, Figure 4 a~ Figure 4 h shows the wetting images of the eutectic 79wt%LiCl-21wt%LiF system on the α-Al2O3 surface at times of 0, 50, 100, 150, 200, 250, 300 and 350 ps, ​​respectively.

[0038] Figure 5 The wetting evolution process of the 48.9wt%LiF-51.1wt%AlF3 system on the α-Al2O3 surface; among which, Figure 5 a~ Figure 5 h shows the wetting images of the 48.9wt%LiF-51.1wt%AlF3 system on the α-Al2O3 surface at times of 0, 50, 100, 150, 200, 250, 300 and 350 ps, ​​respectively.

[0039] Figure 6 The wetting evolution process of the 60wt%LiCl-15wt%LiF-25wt%CaF2 system on the α-Al2O3 surface; among which, Figure 6 a~ Figure 6 h shows the wetting images of the 60wt%LiCl-15wt%LiF-25wt%CaF2 system on the α-Al2O3 surface at times of 0, 50, 100, 150, 200, 250, 300, and 350 ps.

[0040] Figure 7 The radial distribution function of Li-Cl and Li-F ion pairs in different covering flux systems.

[0041] Figure 8 The integral curves of Li-Cl and Li-F ion pairs in different covering flux systems are shown.

[0042] Figure 9 SEM image of the recycled aluminum-lithium alloy prepared in Example 1.

[0043] Figure 10 The EDS spectrum corresponding to the +1 position point in the SEM image of the recycled aluminum-lithium alloy prepared in Example 1.

[0044] Figure 11 The EDS spectrum corresponding to the +2 position point in the SEM image of the recycled aluminum-lithium alloy prepared in Example 1.

[0045] Figure 12 The EDS spectrum corresponding to the +3 position point in the SEM image of the recycled aluminum-lithium alloy prepared in Example 1.

[0046] Figure 13 The image shows the XRD phase diagram of the recycled aluminum-lithium alloy prepared in Example 1. Detailed Implementation

[0047] The embodiments described in this specification are merely for explaining this application and are not intended to limit this application.

[0048] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0049] Those skilled in the art will understand that the order in which the steps are written in the various embodiments or examples does not imply a strict execution order and does not limit the implementation process in any way. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but sequentially is preferred.

[0050] The present application is further illustrated below with reference to embodiments. It should be understood that these embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0051] All raw materials used in the embodiments and comparative examples of this application have a purity of ≥99.7%; all smelting experiments were conducted under argon protection; and the recycled aluminum-lithium alloy waste was 2195 and 2050 alloy machining chips.

[0052] In the embodiments and comparative examples of this application, the chemical composition of the aluminum-lithium alloy melt and samples was detected using a spark direct-reading emission spectrometer, and verified by ICP-OES when necessary. The lithium content could be further determined by flame atomic absorption spectrometry. The lithium burn-off rate was calculated according to Formula 1: Lithium element burn-off rate = [(Total lithium element in the melt before treatment - Total lithium element in the melt after treatment) ÷ Total lithium element in the melt before treatment] × 100%. The magnesium burn-off rate was calculated according to Formula 2: Magnesium element burn-off rate = [(Total magnesium element in the melt before treatment - Total magnesium element in the melt after treatment) ÷ Total magnesium element in the melt before treatment] × 100%. At the same time, the total content of inclusions in the recycled aluminum-lithium alloy ingot was detected by the PoDFA method, and the hydrogen content in the recycled aluminum-lithium alloy ingot was detected by the inert gas melting method.

[0053] The following is an example of an investigation into the screening of coating flux components for recycled Al-Li alloys:

[0054] Experimental Example 1

[0055] This experimental example uses FactSage software to calculate the isothermal phase equilibrium diagrams of the ternary system formed by LiCl, LiF, and AlF3 at 873 K, 973 K, and 1013 K. The results are as follows: Figures 1-3 As shown, specifically, Figure 1 Isothermal phase equilibrium diagram of the LiCl-LiF-AlF3 ternary system at 873 K and 1 atm; Figure 2Isothermal phase equilibrium diagram of the LiCl-LiF-AlF3 ternary system at 973 K and 1 atm; Figure 3 This is the isothermal phase equilibrium diagram of the LiCl-LiF-AlF3 ternary system at 1013 K and 1 atm. In the diagram, s2 represents solid AlF3, s3 represents solid Li3AlF6; Salt-liquid represents salt melt; Rocksalt represents rock salt; and Slag-liq represents slag melt. Figures 1-3 It can be seen that as the temperature increases, the liquid phase region in the system gradually appears and expands; under conditions close to the melting temperature of recycled aluminum-lithium alloy, the preferred composition enters the salt-containing liquid phase region or the region dominated by the salt liquid phase, indicating that the system has the thermodynamic conditions to form a molten overlay layer. Therefore, LiCl-LiF-AlF3 was selected as the first mixed salt system.

[0056] Experimental Example 2

[0057] This experimental example uses molecular dynamics calculations to obtain the wetting process of α-Al₂O₃ by different components of the covering flux. Specific results are as follows: Figures 4-6 As shown. Figure 4 a~ Figure 4 h shows the wetting images of the eutectic 79wt%LiCl-21wt%LiF system on the α-Al₂O₃ surface at times of 0, 50, 100, 150, 200, 250, 300, and 350 ps, ​​respectively; from Figure 4 It can be seen that the eutectic 79wt%LiCl-21wt%LiF system gradually approaches and spreads on the α-Al2O3 surface during the simulation, indicating that the LiCl-LiF binary system has a certain interfacial coverage ability and initial wetting effect. Figure 5 a~ Figure 5 h shows the wetting images of the 48.9wt%LiF-51.1wt%AlF3 system on the α-Al2O3 surface at times of 0, 50, 100, 150, 200, 250, 300, and 350 ps, ​​respectively; Figure 5 It is evident that the 48.9wt%LiF-51.1wt%AlF3 system exhibits significant atomic migration and rearrangement in the interfacial region during wetting, indicating a strong interaction between this system and the α-Al2O3 interface. Figure 6 a~ Figure 6 h shows the wetting images of the 60wt%LiCl-15wt%LiF-25wt%CaF2 system on the α-Al2O3 surface at times of 0, 50, 100, 150, 200, 250, 300, and 350 ps, ​​respectively; Figure 6As can be seen, the 60wt%LiCl-15wt%LiF-25wt%CaF2 system exhibited a significant spreading trend and a large interfacial contact range during the simulation, indicating that introducing CaF2 into the LiCl-LiF-based system is beneficial for improving the wetting behavior of the flux on the α-Al2O3 surface. (Comprehensive comparison) Figures 4-6 It is evident that different salt systems exhibit significant differences in interfacial coverage, wetting and spreading, and interfacial interactions. Among them, the LiCl-LiF system provides basic coverage, the LiF-AlF3 system shows a strong tendency for interfacial interactions, while the LiCl-LiF-CaF2 system demonstrates good overall characteristics in terms of coverage and wettability. This provides mechanistic support for its formation of a continuous coating layer and its promotion of contact, migration, and subsequent aggregation and removal of oxide inclusions at the flux interface during the remelting and recycling of Al-Li alloys.

[0058] Experimental Example 3

[0059] This experiment uses molecular dynamics to calculate the viscosity of different components covering the flux, and the specific results are shown in Table 1.

[0060] Table 1. Viscosities of different coated flux systems at 1013K

[0061]

[0062] As can be seen from Table 1, although the simple LiCl-LiF system has a certain covering ability, its purification effect on complex inclusions is limited; the LiF-AlF3 and LiCl-LiF-AlF3 systems have low viscosity, which is conducive to contact and dissolution with oxide inclusions, but the slag phase is easy to disperse, which is not conducive to subsequent slag removal; after adding CaF2, the viscosity of the system is in a more suitable range, which is conducive to the aggregation and flotation of inclusions and improves the slag-aluminum separation effect.

[0063] Experiment Example 4

[0064] This experimental example uses molecular dynamics simulations to analyze the radial distribution function and integral curves of Li-Cl and Li-F ion pairs in fluxes with different components. Specific results are as follows: Figure 7 and Figure 8 As shown, where Figure 7 It is a radial distribution function. Figure 8 This is the integral curve of the function.

[0065] from Figure 7It can be seen that the first peak of the Li-F ion pair in different flux systems appears in a relatively small r range, and the peak value is generally higher than that of the Li-Cl ion pair, indicating that there is a stronger short-range interaction and a more obvious local coordination feature between Li and F. In contrast, the first peak of the Li-Cl ion pair is larger in position and has a lower peak intensity, indicating that the Li-Cl interaction is relatively weaker. Further combining... Figure 8 It can be seen that the integral curve of the Li-F ion pair increases faster in the first coordination layer, indicating that F - Easier to enter Li + The near-neighbor coordination environment allows for the formation of a relatively more stable local structure. Comparative results between different flux systems indicate that the introduction of fluorine-containing components can enhance the Li... + The degree of local ordering in the surrounding area, and changes Li + The coordination environment of the Li-Cl system is beneficial for improving the structural stability of the flux system and its ability to interact with oxide interfaces. In summary, Li-Cl primarily helps maintain the flow and coverage characteristics of the basic salt system, while the enhanced Li-F interaction provides structural mechanistic support for flux wetting oxide inclusions, promoting interfacial reactions, and subsequent inclusion removal.

[0066] Based on the analysis results of the above two-component and three-component systems, it can be seen that different salt components play different roles in the flux covering system. The LiCl-LiF binary system mainly exhibits lower melting characteristics and basic covering effect, which can form an initial protective layer on the melt surface; the LiF-AlF3 system shows strong interfacial interaction characteristics, indicating that the fluorine-containing active component has a positive significance in enhancing the interaction between the flux and oxide interface; the LiCl-LiF-CaF2 ternary system further shows that the introduction of CaF2 on the LiCl-LiF basis is beneficial to improving the wetting and spreading behavior of the flux on the oxide surface and increasing the degree of interfacial contact.

[0067] To balance low melting temperature, continuous coverage, interfacial interaction with oxide inclusions, and process adaptability during the remelting and recycling of Al-Li alloys, LiCl, LiF, AlF3, and CaF2 are further combined and optimized to construct a four-component covering flux system of LiCl-LiF-AlF3-CaF2. This four-component system balances basic coverage, interfacial wettability, and interaction with oxide interfaces. Its specific performance and technical effects will be further explained in the following examples.

[0068] The following are examples of the application of covering fluxes made from lithium fluoride, lithium chloride, aluminum fluoride, and calcium fluoride in the recycling of recycled aluminum-lithium alloys.

[0069] Example 1

[0070] (1) Weigh the raw materials according to the following mass ratio: 50 parts lithium chloride, 25 parts lithium fluoride, 15 parts aluminum fluoride and 10 parts calcium fluoride.

[0071] (2) Weigh the lithium chloride, lithium fluoride and aluminum fluoride powders and place them in a Hastelloy crucible. Melt them at 800℃ for 2 hours and cool them to about 50℃ to obtain a blocky mixed salt. Then ball mill the blocky mixed salt for 30 minutes. After ball milling, mix the granular mixed salt with calcium fluoride in proportion and put it into a ball mill for 1 hour to obtain a powdered flux. Then put it into a drying oven and dry it at 180℃ for 8 hours. After drying, a covering flux is obtained and sealed for later use.

[0072] (3) 6 kg of 2195 waste was put into the melting furnace and melted into a melt at 740°C. The above-mentioned covering flux was added under stirring, wherein the amount of covering flux added was 1.0 wt% of the mass of the waste melt. After the covering flux was added, it was left to stand for 10 minutes, and then air blowing was carried out for refining. When the impurity components floated to the surface of the melt, the slag was removed. After the slag was removed, it was poured out of the furnace to obtain a recycled aluminum-lithium alloy ingot.

[0073] in, Figure 9 This is a SEM image of the recycled aluminum-lithium alloy ingot prepared in Example 1. Figures 10-12 Here are EDS plots at three different locations in the SEM image, where... Figure 10 EDS spectrum corresponding to point +1 in the SEM image of recycled aluminum-lithium alloy; Figure 11 The EDS spectrum corresponding to point 2 in the SEM image of the recycled aluminum-lithium alloy. Figure 12 The EDS spectrum corresponding to point 3 in the SEM image of the recycled aluminum-lithium alloy. Figure 13 The image shows the XRD phase diagram of the recycled aluminum-lithium alloy prepared in Example 1. From... Figures 9-13 It can be seen that the inclusions in the recycled aluminum-lithium alloy ingot are mainly alumina, lithium oxide, lithium aluminum oxide, and carbides. Samples were taken during the casting process, and the inclusion content in the recycled aluminum-lithium alloy ingot was analyzed using the PoDFA method. The results showed that the inclusion content (preferably Al2O3, Li2O, LiAlO2, and a small amount of carbide inclusions in this embodiment) in the recycled aluminum-lithium alloy ingot was 0.6 mm. 2 / kg-Al. This indicates that the covering flux prepared in this embodiment can effectively suppress elemental loss during the remelting process of recycled aluminum-lithium alloy and improve melt cleanliness. Furthermore, in this example, the lithium loss rate is 2.1%, and the magnesium loss rate is 1.2%.

[0074] The hydrogen content in the recycled aluminum-lithium alloy ingot was measured and found to be 0.12 mL / 100g Al, which effectively removes gas and hydrogen and controls the hydrogen content in the alloy. The sodium and potassium content is ≤4 ppm, which avoids sodium embrittlement and potassium embrittlement in the recycled aluminum-lithium alloy and ensures the mechanical properties of the alloy ingot.

[0075] Example 2

[0076] (1) Weigh the raw materials according to the following mass ratio: 60 parts lithium chloride, 20 parts lithium fluoride, 10 parts aluminum fluoride, and 10 parts calcium fluoride.

[0077] (2) Weigh the lithium chloride, lithium fluoride and aluminum fluoride powders and place them in a Hastelloy crucible. Melt them at 800℃ for 2 hours and cool them to about 50℃ to obtain a blocky mixed salt. Then ball mill the blocky mixed salt for 30 minutes. After ball milling, mix the granular mixed salt with calcium fluoride in proportion and put it into a ball mill for 1 hour to obtain a powdered flux. Then put it into a drying oven and dry it at 180℃ for 8 hours. After drying, a covering flux is obtained and sealed and packaged for later use.

[0078] (3) 4 kg of 2050 waste was put into a melting furnace and melted into a molten material at 740°C. After the waste material was in molten form, it was kept at a temperature of 10 min. The protective flux was added in batches and stirred gently. The amount of protective flux added was 1.5 wt% of the mass of the waste molten material. After standing for 10 min, it was refined with high-purity argon gas for 6 min to better control lithium burn-off, hydrogen content, and Na and K content. When the impurity components floated to the surface of the molten material, the slag was removed. After the slag was removed, it was cast to obtain a recycled aluminum-lithium alloy ingot.

[0079] During the recycling and remelting process, lithium loss was 2.7%, and magnesium loss was 1%. Analysis of the inclusion content in the recycled aluminum-lithium alloy ingots revealed that the inclusion content (alumina, lithium oxide, and lithium alumina) in the ingots was 0.8 mm. 2 / kg-Al. This indicates that the covering flux prepared in this embodiment can also effectively suppress elemental loss during the remelting process of recycled aluminum-lithium alloy and improve melt cleanliness.

[0080] The hydrogen content in the recycled aluminum-lithium alloy ingot was measured and found to be 0.14 mL / 100g Al, which effectively removes gas and hydrogen and controls the hydrogen content in the alloy. The sodium and potassium content is ≤4 ppm, which avoids sodium embrittlement and potassium embrittlement in the recycled aluminum-lithium alloy and ensures the mechanical properties of the alloy ingot.

[0081] Comparative Example 1

[0082] (1) Weigh the raw materials according to the mass ratio: 40 parts lithium fluoride and 60 parts lithium chloride.

[0083] (2) Weigh the lithium fluoride and lithium chloride powders and place them in a Hastings alloy crucible. Melt them at 800°C for 2 hours and cool them down to about 50°C to obtain a blocky mixed salt. Then, ball mill the blocky mixed salt for 1 hour to obtain a powdered flux. Then, put it into a drying oven and dry it at 180°C for 8 hours. After drying, a covering flux is obtained and sealed for later use.

[0084] (3) 6 kg of 2195 waste was added to a smelting furnace and melted into a molten body at 740°C. The protective flux was added under stirring, with the amount of protective flux being 1 wt% of the mass of the molten waste. After the protective flux was added, the mixture was allowed to stand for 10 minutes, then refined by blowing air. When the impurities floated to the surface of the molten body, the slag was removed, and the mixture was poured to obtain a recycled aluminum-lithium alloy ingot. During the slag removal process, separation of the slag layer from the molten aluminum was difficult, and a large amount of paste-like material remained on the surface of the molten body after slag removal. This indicates that binary fluxes with only a covering function cannot meet the purification requirements of recycled alloys.

[0085] Among them, the lithium burn-off rate reached 6.8%, and the magnesium burn-off rate was 3.9%. Analysis of the inclusion content in the recycled aluminum-lithium alloy ingot revealed that the inclusion content (alumina, lithium oxide, lithium alumina, and magnesium-containing spinel) in the recycled aluminum-lithium alloy ingot was 2.8 mm. 2 / kg-Al.

[0086] The hydrogen content in the recycled aluminum-lithium alloy ingot was measured and found to be 0.50 mL / 100 g Al.

[0087] Comparative Example 2

[0088] (1) Weigh the raw materials according to the mass ratio: 25 parts lithium fluoride, 55 parts lithium chloride, and 20 parts aluminum fluoride.

[0089] (2) Weigh the lithium fluoride, lithium chloride and aluminum fluoride powders and place them in a Hastings crucible. Melt them at 800°C for 2 hours and cool them down to about 50°C to obtain a blocky mixed salt. Then ball mill the blocky mixed salt for 1 hour to obtain a powdered flux. Then put it into a drying oven and dry it at 180°C for 8 hours. After drying, a covering flux is obtained and sealed for later use.

[0090] (3) 6 kg of 2195 waste was put into the smelting furnace and melted into a melt at 740°C. The above-mentioned protective flux was added under stirring, wherein the amount of protective flux added was 1 wt% of the mass of the waste melt. After the protective flux was added, it was left to stand for 10 minutes, and then air blowing was carried out for refining. When the impurity components floated to the surface of the melt, the slag was removed and the melt was poured to obtain a recycled aluminum-lithium alloy ingot.

[0091] Measurements revealed a lithium burn-off rate of 4.2%, a magnesium burn-off rate of 2.6%, a hydrogen content of 0.30 mL / 100g Al, and an inclusion content of 1.6 mm. 2 / kg-Al. Although the LiF-AlF3 combination enhanced the oxide dissolution capacity and reduced the burn-off, the slag phase was dispersed and had a high viscosity, resulting in incomplete slag removal and a significant increase in the final inclusion content.

[0092] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. The application of a covering flux for recycled Al-Li alloys in the recycling of aluminum-lithium alloy waste, characterized in that, Includes the following steps: The aluminum-lithium alloy waste to be recycled is melted into a waste aluminum melt. Then, under stirring conditions, the recycled Al-Li alloy covering flux is added to the waste aluminum melt. After settling, the mixture is then refined and slag is removed to obtain the recycled aluminum-lithium alloy. The amount of the recycled Al-Li alloy covering flux added is 1.0~1.5 wt% of the mass of the waste aluminum melt. The raw materials for preparing the coating flux for the recycled Al-Li alloy, by mass fraction, are: 50-60 parts lithium chloride, 20-25 parts lithium fluoride, 10-15 parts aluminum fluoride, and 10 parts calcium fluoride.

2. The application according to claim 1, characterized in that, The covering flux is in powder form with a particle size ≤1.0mm.

3. The application according to claim 1, characterized in that, The method for preparing the covering flux for the recycled Al-Li alloy includes the following steps: S1. Lithium chloride, lithium fluoride, and aluminum fluoride are mixed and melted, then condensed to obtain the first mixed salt; S2. The first mixed salt is mixed with calcium fluoride, and then ball-milled and dried to obtain a powdered coating flux.

4. The application according to claim 3, characterized in that, In step S1, the mixing and melting temperature is 700~800℃; the target condensation temperature is 20~50℃.

5. The application according to claim 3, characterized in that, The first mixed salt is first ball-milled to obtain granular first mixed salt, and then mixed with calcium fluoride; wherein the particle size of the granular first mixed salt is ≤1.0mm.

6. The application according to claim 3, characterized in that, In step S2, the drying conditions include a temperature of 120~200℃ and a time of 8~9h.

7. The application according to claim 1, characterized in that, The aluminum-lithium alloy waste to be recycled was melted at 730~760℃ under argon protection.

8. The application according to claim 1, characterized in that, After adding the covering flux to the recycled Al-Li alloy, let it stand for 10-20 minutes, and then refine it with inert gas.

9. The application according to claim 1, characterized in that, After refining, the slag is removed and the mixture is poured.

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