Efficient degassing refining agent for magnesium alloy ingot and preparation method thereof

Abstract

The application discloses a kind of high-efficiency degassing refining agent for magnesium alloy ingot and its preparation method in the field of metal melt purification, the refining agent is composed of lanthanum fluoride loaded titanium carbide nanocomposite, calcium zirconate and graphene oxide nanohybrid, and anhydrous magnesium chloride, anhydrous sodium fluoride, anhydrous potassium chloride, metal calcium powder, barium carbonate, aluminum oxide powder and other components in specific ratio.The preparation mainly includes: first, by dispersing titanium carbide nanometer powder and reacting with lanthanum fluoride solution, and by hydrothermal, calcination treatment, lanthanum fluoride loaded titanium carbide nanocomposite is prepared;Second, by mixing zirconium calcium salt solution and graphene oxide dispersion, by urea coprecipitation, hydrothermal reaction and calcination under protective atmosphere, calcium zirconate and graphene oxide nanohybrid are prepared.The application can deeply remove hydrogen and inclusions in magnesium melt through the synergistic effect of two inorganic modified compounds, so as to significantly improve the metallurgical quality and comprehensive performance of magnesium alloy ingot.

Description

Technical Field

[0001] This invention relates to the field of metal melt purification technology, specifically to a high-efficiency degassing refining agent for magnesium alloy ingots and its preparation method. Background Technology

[0002] Magnesium alloys, as the lightest metallic structural materials currently used in engineering applications, hold irreplaceable strategic value in achieving lightweighting goals in aerospace, rail transportation, electronics and communications, and the automotive industry. However, the highly reactive chemical properties of magnesium pose significant challenges during smelting and casting. The melt readily reacts with moisture from the environment and even the furnace charge, absorbing large amounts of hydrogen and generating various oxide inclusions. These defects within the melt, after solidification, evolve into dispersed porosity, shrinkage porosity, and brittle inclusions, directly weakening the alloy's mechanical strength, plasticity, and fatigue life, and significantly deteriorating its corrosion resistance. This becomes a key bottleneck restricting the reliability, safety, and application range of high-end magnesium alloy products.

[0003] To address the aforementioned challenges in melt purification, the industry has long relied primarily on two technologies: flux refining and gas purging. Traditional flux refining typically employs a mixture mainly composed of chloride salts such as magnesium chloride and potassium chloride. It utilizes the density difference and interfacial tension between the molten salt phase and the molten magnesium to adsorb floating inclusions, and degassing is aided by the potential reaction between chloride salts and hydrogen. However, these methods have inherent limitations: firstly, their degassing mechanism relies mainly on physical carryover, resulting in limited efficiency in removing atomic hydrogen deeply dissolved in the melt, making it difficult to achieve a significant reduction in hydrogen content; secondly, fluxes have insufficient ability to capture micron-sized and even smaller oxide inclusions, leading to incomplete purification; and thirdly, some flux components may generate irritating or toxic gases at high temperatures, and if the flux's own properties are not properly controlled, it can easily remain in the molten magnesium, forming new "flux inclusions" and introducing secondary pollution. Although subsequent research has attempted to introduce specific additives to improve flux performance or employ external field enhancement methods such as rotary jetting of inert gases, it has consistently failed to fundamentally revolutionize the mechanism of melt purification.

[0004] With the development of nanoscience and materials design theory, exploring novel additives with special microstructures and surface activities provides a new approach for breakthroughs in magnesium alloy melt purification technology. Research reveals that by precisely designing the crystal structure, surface functional groups, and nanomorphology of inorganic compounds, they can be endowed with high specific surface area, selective adsorption sites, and catalytic decomposition activity not found in traditional materials. If multifunctional nanomodified materials specifically designed for the magnesium melt environment can be developed based on this, and cleverly combined with traditional flux systems, it is hoped that targeted removal of harmful hydrogen atoms and fine inclusions can be achieved from the depths of "molecular capture" and "nano-adsorption." This represents an important direction in the evolution of magnesium alloy refining technology from macroscopic physical purification to microscopic chemical and physical synergistic purification, and is also the most promising technological path to solve the current purity bottleneck in high-end magnesium alloy preparation. Summary of the Invention

[0005] This invention provides a high-efficiency degassing refining agent for magnesium alloy ingots and its preparation method, which solves the technical problems of existing magnesium alloy refining agents that do not completely remove dissolved hydrogen in the melt and have limited adsorption capacity for fine oxide inclusions, thus leading to porosity and inclusion defects and poor overall performance in the ingots.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a high-efficiency degassing refining agent for magnesium alloy ingots, comprising the following steps: S1. By weight, 8-15 parts of lanthanum fluoride-supported titanium carbide nanocomposite, 6-12 parts of calcium zirconate / graphene oxide nanohybrid, 20-30 parts of anhydrous magnesium chloride, 15-25 parts of anhydrous sodium fluoride, 10-20 parts of anhydrous potassium chloride, 3-8 parts of metallic calcium powder, 2-5 parts of barium carbonate, and 1-4 parts of α-alumina micro powder are added into a ball mill and mixed by ball milling under an argon protective atmosphere to obtain a mixed powder. S2. Transfer the mixed powder to a vacuum drying oven and dry it under vacuum at 195-205℃; after cooling, press it into cylindrical ingots under a pressure of 10-20MPa.

[0007] In this invention, the preparation mechanism of the high-efficiency degassing refining agent for magnesium alloy ingots lies in the microscopic-scale uniform composite of two functionally distinct nano-modified compounds with a traditional molten salt matrix through a physical-mechanical method, thereby constructing a multi-component, multi-functional synergistic purification system. The focus of the preparation process is not on chemical reactions, but on achieving fine mixing of phases and the engineered molding of the product. First, the high-energy ball milling process under inert gas protection is key to achieving microscopic uniform composite. During ball milling, the intense collision, shearing, and extrusion between the grinding balls and the materials not only effectively breaks down various raw materials to a finer scale, but more importantly, it allows nanocomposites, metal powders, and salt particles of different densities, hardness, and morphologies to nest, embed, and coat each other, achieving full contact and uniform dispersion of each component, forming a microscopically highly homogeneous composite powder. This step ensures that when the final refining agent ingot is used, each functional component can act synchronously and uniformly on the magnesium melt. The subsequent vacuum drying process aims to completely remove trace amounts of adsorbed moisture that may have been introduced during ball milling, as well as the water of crystallization that some salts may contain. This prevents the refining agent from splashing or intensifying oxidation and hydrogen absorption due to rapid evaporation of water vapor when added to the high-temperature magnesium molten metal. The final pressing and molding process compresses the loose composite powder into dense cylindrical ingots under specific pressure. This gives the refining agent suitable bulk density and strength, facilitating standardized metering, storage, and transportation. It also controls the sinking and melting rate after being added to the melt, ensuring a stable and complete refining reaction. From a mechanistic perspective, the final refining agent is a synergistic system: the matrix composed of traditional chloride and fluoride salts provides the necessary physicochemical environment for coverage, refining, and slag removal after melting; the nano-modified compound acts as the functional center for deep purification. Among them, the lanthanum fluoride-supported titanium carbide nanocomposite mainly functions as a "chemical hydrogen removal agent," with its active fluorine component released at high temperatures reacting with atomic hydrogen in the melt to generate stable gases that escape. Meanwhile, the calcium zirconate / graphene oxide nanohybrid primarily acts as a "physicochemical adsorption center," its large specific surface area and abundant surface active sites providing a strong ability to capture and fix fine oxide inclusions. Under the synergistic transport of the molten salt medium, both components work together in the magnesium melt to achieve synergistic treatment of gas and impurity defects at their source, thereby significantly improving the metallurgical quality of the ingot.

[0008] In this application, the weight parts are measured in grams.

[0009] According to a preferred embodiment of the present invention, in step S1, the ball milling mixing time is 2-4 hours.

[0010] According to a preferred embodiment of the present invention, in step S2, the vacuum drying time at 195-205°C is 4-6 hours.

[0011] According to a preferred embodiment of the present invention, the preparation method of the lanthanum fluoride-supported titanium carbide nanocomposite includes: A1. By weight, 4-6 parts of titanium carbide nanoparticles are dispersed in 15-25 parts of anhydrous ethanol and ultrasonically treated to obtain a titanium carbide ethanol dispersion; 17-18 parts of lanthanum nitrate hexahydrate and 5-6 parts of sodium fluoride are dissolved together in 70-90 parts of deionized water and stirred in a water bath at 58-62℃ to obtain a mixed salt solution; under continuous stirring, the titanium carbide ethanol dispersion is added dropwise to the mixed salt solution, and after the addition is complete, stirring is continued to obtain a suspension; then the suspension is transferred to a high-pressure reactor and hydrothermally reacted at 175-185℃ to obtain a reaction mixture; A2. Cool the reaction mixture to room temperature naturally, filter it to obtain a solid product, wash the solid product with deionized water and anhydrous ethanol in sequence, and dry it under vacuum at 78-82℃ to obtain a precursor powder; place the precursor powder in a tube furnace, heat it to 595-605℃ under a nitrogen atmosphere and calcine it, then cool it with the furnace and grind and sieve it.

[0012] In this invention, the core of preparing the lanthanum fluoride-supported titanium carbide nanocomposite lies in achieving the in-situ generation and firm loading of lanthanum fluoride nanoparticles on the surface of a titanium carbide support. The mechanism encompasses multiple stages, including physical dispersion, chemical precipitation, hydrothermal crystallization, and high-temperature stabilization. First, dispersing the titanium carbide nanoparticles with anhydrous ethanol is a crucial pretreatment step. Titanium carbide has a hydrophobic surface and readily aggregates and settles in pure water, while anhydrous ethanol effectively wets its surface. Ultrasonic cavitation disrupts the van der Waals forces between particles, forming a uniform and stable colloidal dispersion, laying the foundation for subsequent uniform loading. Subsequently, a clear mixed salt solution containing fluoride and lanthanum ions is used as the reaction matrix, and the titanium carbide dispersion is dropwise added to it under continuous stirring. This specific order of addition is crucial, ensuring that when lanthanum and fluoride ions meet and a precipitation reaction occurs, the reaction site is confined to a microscopic liquid domain surrounding the titanium carbide particles. The newly formed lanthanum fluoride nuclei, due to their extremely high surface energy, rapidly adsorb onto the surface of dispersed titanium carbide particles, thereby reducing the total energy of the system. This enables in-situ heterogeneous nucleation of lanthanum fluoride on the titanium carbide surface, effectively avoiding the formation of large free particles during homogeneous nucleation in the bulk solution. The subsequent hydrothermal process is carried out in a closed, high-pressure environment, where the high temperature and pressure conditions greatly promote the dissolution and recrystallization of the particles. During this process, the initially attached precursor undergoes Ostwald ripening, the small and unstable particles dissolve, and recrystallize on larger particles or active sites on the support, allowing the lanthanum fluoride crystals to grow further and form a tighter chemical interface with the titanium carbide substrate, thus strengthening the supported structure. The final high-temperature calcination treatment is carried out under an inert atmosphere. Its main purpose is not a phase transition, but rather to remove residual adsorbed water and crystal water from the material through heat treatment, eliminate impurities such as hydroxyl groups in the precursor, make the lanthanum fluoride lattice more perfect, and further enhance the interfacial bonding force with the titanium carbide support, ultimately obtaining a structurally stable supported nanocomposite with abundant active sites.

[0013] According to a preferred embodiment of the present invention, in step A1, the hydrothermal reaction time at 175-185°C is 12-14 hours.

[0014] According to a preferred embodiment of the present invention, in step A2, the calcination time at 595-605°C under a nitrogen atmosphere is 2-4 hours.

[0015] According to a preferred embodiment of the present invention, the method for preparing the calcium zirconate / graphene oxide nanohybrid includes: B1. By weight, disperse 0.8-1.2 parts of graphene oxide in 80-120 parts of deionized water, and ultrasonically exfoliate to obtain a graphene oxide dispersion; dissolve 10-14 parts of zirconium oxychloride octahydrate and 5-6 parts of calcium nitrate tetrahydrate together in 25-35 parts of deionized water, and stir to obtain a zirconium-calcium salt mixed solution; under continuous stirring, add the zirconium-calcium salt mixed solution dropwise to the graphene oxide dispersion; then add 1-2 parts of urea, and stir at a constant temperature of 68-72℃ to obtain a mixture; B2. Transfer the mixture to a high-pressure reactor and react it solvothermally at 195-205℃. After the reaction is complete, allow it to cool naturally to room temperature, centrifuge to obtain a solid, and wash the solid alternately with deionized water and anhydrous ethanol to obtain a washed solid. Dry the washed solid under vacuum at 58-62℃ to obtain a powder. Place the powder in a muffle furnace and calcine it at 495-505℃ under a nitrogen or argon protective atmosphere. After natural cooling, grind and sieve the powder.

[0016] In this invention, the preparation of the calcium zirconate / graphene oxide nanohybrid aims to grow calcium zirconate nanocrystals in situ on graphene oxide sheets to construct a three-dimensional nanocomposite structure. The mechanism involves the synergistic effect of colloidal dispersion, homogeneous precipitation, hydrothermal crystallization, and controlled thermal reduction. The starting point is to obtain a single-layer or few-layer graphene oxide dispersion. The surface of graphene oxide is rich in oxygen-containing functional groups such as carboxyl and hydroxyl groups, giving it good hydrophilicity in water. The mechanical shear force provided by ultrasonic treatment can effectively overcome the van der Waals forces between sheets, achieving exfoliation and stable dispersion, forming a negatively charged colloidal solution. This provides a two-dimensional template for adsorbing positively charged metal ions and limiting the excessive growth of nanoparticles. Subsequently, a mixed solution of zirconium and calcium sources is introduced, and metal cations are adsorbed onto the surface of the graphene oxide sheets through electrostatic interactions. The addition of urea is crucial in the homogeneous precipitation method. Under heating conditions, urea slowly hydrolyzes, gradually releasing hydroxide and carbonate ions, causing a uniform increase in the pH of the solution. This guides the co-precipitation of zirconium and calcium ions on the graphene oxide surface, generating amorphous zirconium calcium hydroxide or basic carbonate precursors, which are initially anchored on the sheets. The subsequent hydrothermal and solvothermal reactions are the core steps in crystallization and composite formation. In a high-temperature, high-pressure hydrothermal environment, the amorphous precursors gradually dissolve and recrystallize into crystalline calcium zirconate nanoparticles, using functional groups or defect sites on the graphene oxide surface as heterogeneous nucleation sites. This process allows for the formation of strong chemical bonds between the nanoparticles and the graphene oxide substrate, achieving a robust composite. The final heat treatment is carried out in a protective atmosphere and has a dual function: on the one hand, it completely decomposes and dehydrates the precursor and completes the transformation to the target crystalline phase calcium zirconate; on the other hand, the precisely controlled heat treatment conditions can partially reduce graphene oxide, remove some unstable oxygen-containing groups, improve its conductivity and structural stability, while retaining enough functional groups to maintain the interfacial bonding with calcium zirconate, ultimately obtaining a stable hybrid material supported by a conductive carbon network and uniformly loaded with highly active oxide nanoparticles.

[0017] According to a preferred embodiment of the present invention, in step B1, the stirring time at a constant temperature of 68-72°C is 4-6 hours.

[0018] According to a preferred embodiment of the present invention, in step B2, the calcination time at 495-505°C is 3-6 hours.

[0019] The present invention also provides a high-efficiency degassing refining agent for magnesium alloy ingots prepared according to the preparation method of the high-efficiency degassing refining agent for magnesium alloy ingots.

[0020] The beneficial effects of this invention are as follows: This invention provides a highly efficient degassing refining agent for magnesium alloy ingots. By introducing two newly designed inorganic nano-modified compounds, significant and synergistic technical effects are achieved in degassing, impurity removal, and overall performance improvement.

[0021] Firstly, this invention achieves a breakthrough in both mechanism and efficiency in terms of deep and active degassing. The core lies in the application of a lanthanum fluoride-supported titanium carbide nanocomposite. In this composite, nano-lanthanum fluoride is uniformly distributed on the titanium carbide support, creating a high-density active interface. Lanthanum fluoride has a clear purification effect on magnesium alloy melts. In this invention, these active sites can specifically capture hydrogen dissolved in the melt in an atomic state and convert it into easily escaping hydrofluoric acid gas through interfacial chemical reactions, achieving a shift from physical transport to "active chemical capture." This mechanism can significantly reduce the hydrogen content of the melt, fundamentally reducing porosity and micro-shrinkage caused by hydrogen evolution.

[0022] Secondly, this invention demonstrates superior purification capabilities in the efficient adsorption and removal of fine inclusions. Another core component, calcium zirconate, and graphene oxide nanocomposite form a multi-scale purification network. The enormous specific surface area of ​​graphene oxide and its layered structure provide a vast number of physical adsorption sites. The key innovation lies in the in-situ composite calcium zirconate nanoparticles, which endow this hybrid with unique chemical adsorption and conversion capabilities. Patents and research have shown that calcium zirconate can react with common inclusions such as alumina at high temperatures to generate low-melting-point compounds. In this invention, this effect enables the efficient capture, aggregation, and deactivation of micron- and submicron-sized oxide inclusions through interfacial reactions, followed by rapid flotation to the slag phase for removal. This dual mechanism of "physical adsorption" and "chemical conversion" ensures the ultra-high purity of the melt, guaranteeing the acquisition of a clean metallurgical structure.

[0023] Finally, in terms of comprehensively improving ingot performance and process adaptability, this invention achieves a synergistic advantage of "one agent, multiple effects." The combination of the two modified compounds with traditional chloride and fluoride matrices is not a simple functional additive, but rather produces a synergistic and multiplicative purification effect. The combined effect of deep degassing and efficient impurity removal results in clean grain boundaries and uniform composition in the solidified structure. This not only significantly improves the room temperature and fatigue performance of the ingot, but also significantly improves the corrosion resistance of the magnesium alloy. At the same time, the refined agent formula is optimized, with suitable melting point, density, and viscosity, and has both good refining and covering protection effects. During use, it produces less smoke and has good separation from the magnesium melt, avoiding secondary pollution. This makes the magnesium alloy melt treated by this invention have stable purity, which can meet the stringent requirements for internal quality and consistency of materials in high-end fields such as 5G communication base station components and automotive structural parts, representing an important development direction for magnesium alloy melt composite purification technology. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. The drawings are only used to illustrate the implementation methods and are not intended to limit the present invention.

[0025] Figure 1 The images show the electron micrographs of the lanthanum fluoride-supported titanium carbide nanocomposite prepared in Example 1 of this invention and the corresponding EDS elemental mapping diagrams of the regions. Figure 2 The images show the FESEM morphology and XRD pattern of the calcium zirconate / graphene oxide nanohybrid prepared in Example 1 of this invention. Detailed Implementation

[0026] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content.

[0027] Example 1 Preparation of lanthanum fluoride-supported titanium carbide nanocomposites First, a titanium carbide ethanol dispersion was prepared. 5.0 g of titanium carbide nanoparticles were accurately weighed and added to 20 g of anhydrous ethanol. This mixture was placed in an ultrasonic cleaner and ultrasonically treated for 20 min at 40 kHz and 250 W until a uniform, precipitate-free black dispersion was obtained, labeled as dispersion A. Next, a mixed salt solution was prepared. In a beaker, 80 g of deionized water, 17.3 g of lanthanum nitrate hexahydrate, and 5.2 g of sodium fluoride were added sequentially. The beaker was placed in a constant-temperature water bath and stirred continuously at 500 rpm at 60 °C until all solids were completely dissolved, resulting in a clear and transparent solution, labeled as solution B. Under continuous magnetic stirring (600 rpm), dispersion A was slowly added dropwise to solution B using a constant-pressure dropping funnel, with the addition time controlled within 30 min. After the addition was complete, the reaction was continued for 1.5 h under stirring at 60 °C and 600 rpm. At this point, a uniform grayish-white suspension was observed to form. The suspension was transferred entirely to a 200 mL PTFE-lined high-pressure reactor, which was then tightened and placed in a forced-air drying oven. The drying oven program was set to heat to 180 °C at a rate of 5 °C / min and maintain this temperature for a hydrothermal reaction for 13 h. After the reaction, the oven was closed, and the reactor was allowed to cool naturally to room temperature (approximately 25 °C). The reactor was then opened, and all the material inside was poured into a Buchner funnel for filtration. The filter cake was washed three times each with 100 mL of deionized water and 50 mL of anhydrous ethanol. The washed filter cake was transferred to a vacuum drying oven and dried at 80 °C and -0.09 MPa for 12 h to obtain a fluffy white precursor powder. Finally, this precursor powder was placed in an alumina crucible and positioned in the center of a tube furnace. After sealing the tube furnace, nitrogen gas was introduced at a flow rate of 1.0 L / min for 30 min to purge the air. Then, under a continuous nitrogen atmosphere, the furnace temperature was raised to 600 °C at a heating rate of 5 °C / min and held at this temperature for 3 h. After calcination, heating was stopped, and the nitrogen flow rate was maintained to allow the sample to cool to room temperature with the furnace. The product was removed, ground in an agate mortar for 15 min, and passed through a 300-mesh (approximately 48 μm) standard sieve to obtain the lanthanum fluoride-supported titanium carbide nanocomposite, denoted as material M1, and placed in a desiccator for later use.

[0028] Preparation of calcium zirconate / graphene oxide nanohybrids First, a graphene oxide dispersion was prepared. 1.0 g of graphene oxide powder was accurately weighed and added to a beaker containing 100 g of deionized water. This beaker was placed in an ultrasonic cell disruptor and subjected to pulsed ultrasonic treatment at 600 W in an ice-water bath for 40 min (2 s working, 1 s interval) until a homogeneous, stable brownish-red dispersion with no visible particles was obtained; this was labeled dispersion C. Next, a zirconium-calcium salt mixed solution was prepared. In another beaker, 30 g of deionized water, 12.0 g of zirconium oxychloride octahydrate, and 5.6 g of calcium nitrate tetrahydrate were added sequentially and stirred at 400 rpm until completely dissolved, yielding a colorless, clear solution, labeled solution D. Under continuous mechanical stirring (500 rpm), solution D was slowly poured into dispersion C. Then, 1.5 g of urea was added to this mixture, and stirring was continued for 10 min to ensure homogeneity. The mixture was placed on a thermostatic magnetic stirrer and stirred at 70°C and 300 rpm for 5 hours for co-precipitation and aging. Afterwards, the resulting mixture was transferred to a 200 mL PTFE-lined high-pressure reactor and the reactor body was tightened. The reactor was placed in a forced-air drying oven and heated to 200°C at a rate of 3°C / min, and subjected to a solvothermal reaction at this temperature for 27 hours. After the reaction, it was allowed to cool naturally to room temperature. The material in the reactor was transferred to 50 mL centrifuge tubes and centrifuged at 8000 rpm for 5 minutes to separate the solids. The supernatant was discarded, and 40 mL of deionized water was added to the precipitate. The precipitate was resuspended using a vortex mixer and centrifuged again. This washing process was repeated three times. Subsequently, the precipitate was washed twice with 40 mL of anhydrous ethanol. The washed solid was transferred to a petri dish and placed in a vacuum drying oven at 60°C and -0.09 MPa for 10 hours to obtain a black, fluffy powder. Finally, the powder was spread evenly in a corundum ark and placed in a muffle furnace. The furnace temperature was raised to 500°C at a rate of 2°C / min, and calcined at this temperature for 4.5 h under a continuous nitrogen protective atmosphere (flow rate 0.5 L / min). After calcination, heating was stopped, and the mixture was cooled to room temperature under nitrogen protection. The product was removed, ground, and sieved through a 300-mesh sieve to obtain calcium zirconate / graphene oxide nanocomposite, denoted as material M2, which was then placed in a desiccator for later use.

[0029] High-efficiency degassing refining agent for preparing magnesium alloy ingots According to the refining agent formula, accurately weigh the following raw materials: Material M1 12.0g, Material M2 9.0g, anhydrous magnesium chloride 25.0g, anhydrous sodium fluoride 20.0g, anhydrous potassium chloride 15.0g, metallic calcium powder 5.0g, barium carbonate 3.0g, and α-alumina micro powder 2.0g. Place all weighed raw materials into a 500mL zirconia grinding jar, and add 10mm diameter zirconia grinding balls at a ball-to-material mass ratio of 10:1. After sealing the grinding jar, install it on a planetary ball mill. Purge the ball mill chamber with argon gas for 10 minutes to replace the air, then run the ball mill at 300rpm for 3 hours under a continuous argon protective atmosphere. After ball milling, transfer all the mixed powder to a quartz boat and place it in a vacuum drying oven. Close the chamber door, start the vacuum pump to reduce the pressure inside the chamber to below -0.1 MPa, then set the drying temperature to 200℃ and the drying time to 5 hours. After drying, turn off the heating and allow the temperature inside the chamber to cool naturally to below 60℃. Then, turn off the vacuum and remove the dried mixed powder. Finally, weigh 20.0 g of the mixed powder and place it into a cylindrical stainless steel mold with a diameter of 30 mm. Place the mold on a tablet press and press it under a pressure of 15 MPa for 2 minutes to form a dense cylindrical ingot. This ingot is the finished product of the high-efficiency degassing refining agent for magnesium alloy casting described in this invention, denoted as F1.

[0030] The electron micrographs and corresponding EDS elemental mapping images of the lanthanum fluoride-supported titanium carbide nanocomposite prepared in this embodiment are shown below. Figure 1 As shown, by Figure 1 The morphology images show numerous fine particulate loads on the surface of the titanium carbide matrix particles, indicating that the supported phase can form a relatively dispersed covering structure on the surface of the titanium carbide particles. EDS elemental mapping results show that Ti, C, La, and F elements are all distributed within the composite particle region. The La and F element signals show good spatial correlation and overlap with the Ti and C support particle regions, indicating that the lanthanum- and fluorine-containing components have been effectively loaded onto the surface of the titanium carbide particles. These morphological and elemental distribution results demonstrate that the lanthanum- and fluorine-containing components and the titanium carbide support in the lanthanum fluoride-supported titanium carbide nanocomposite prepared in this application have achieved effective composite formation, rather than a simple macroscopic mixing of two powders. Based on this composite structure, the titanium carbide support can improve the dispersion uniformity and interfacial contact area of ​​the lanthanum- and fluorine-containing components in the refining agent system, allowing for more thorough contact with hydrogen-related defects, oxide inclusions, and fine non-metallic inclusions in the magnesium alloy melt during processing. It also promotes the adsorption, migration, aggregation, and flotation removal of inclusions, thereby improving the degassing and purification effects of the magnesium alloy melt.

[0031] The FESEM morphology and XRD pattern of the calcium zirconate / graphene oxide nanohybrid prepared in this embodiment are as follows: Figure 2 As shown, by Figure 2 It can be observed that the surface of the graphene oxide sheets is loaded with a large number of particulate inorganic phases, indicating that the graphene oxide sheets can provide a dispersion and anchoring support for calcium zirconate particles; Figure 2 As can be seen from b, in addition to the characteristic peaks of graphene oxide in the low-angle region, characteristic diffraction peaks matching those of calcium zirconate also appeared in the calcium zirconate / graphene oxide nanohybrid, indicating the formation of a crystalline calcium zirconate phase in the composite. The above FESEM and XRD results can prove from both the microstructure and phase composition aspects that calcium zirconate and graphene oxide have achieved effective composite formation. In this composite structure, the graphene oxide sheets are beneficial to improving the dispersibility of calcium zirconate particles in the refining agent system, while the calcium zirconate particles can provide a stable ceramic phase interface, thereby enhancing the refining agent's ability to capture and remove oxide inclusions, fine non-metallic inclusions, and suspended particles in the melt through interface capture and agglomeration.

[0032] Example 2 The specific implementation method is the same as in Example 1, except that a lanthanum fluoride-supported titanium carbide nanocomposite is prepared. 4.0 g of titanium carbide nanoparticles were accurately weighed and added to 15 g of anhydrous ethanol. The mixture was ultrasonically treated at 40 kHz and 250 W for 15 min to obtain a dispersion. 17.0 g of lanthanum nitrate hexahydrate and 5.0 g of sodium fluoride were accurately weighed and dissolved together in 70 g of deionized water. The solution was stirred at 500 rpm in a 58 °C water bath until completely dissolved to obtain a solution. The titanium carbide dispersion was added dropwise to the salt solution over 25 min with continuous stirring at 600 rpm. After the addition was complete, the mixture was stirred at 58 °C for 1 h. The resulting suspension was transferred to a high-pressure reactor and hydrothermally reacted at 175 °C for 12 h. After the reaction, the mixture was cooled and filtered. The solid was washed three times each with deionized water and anhydrous ethanol, and dried at 78 °C and -0.09 MPa vacuum for 12 h. The dried powder was calcined at 595 °C for 2 h under a nitrogen atmosphere (1.0 L / min) with a heating rate of 5 °C / min. After cooling in the furnace, the material was ground through a 300-mesh sieve to obtain a lanthanum fluoride-supported titanium carbide nanocomposite, denoted as material M3.

[0033] Preparation of calcium zirconate / graphene oxide nanohybrids 0.8 g of graphene oxide was accurately weighed and dispersed in 80 g of deionized water. The mixture was subjected to pulsed sonication in an ice-water bath at 600 W for 30 min to obtain a dispersion. 10.0 g of zirconium oxychloride octahydrate and 5.0 g of calcium nitrate tetrahydrate were accurately weighed and dissolved in 25 g of deionized water to obtain a solution. The salt solution was poured into the graphene oxide dispersion and stirred at 500 rpm. 1.0 g of urea was added, and the mixture was stirred at 300 rpm at 68 °C for 4 h. The mixture was transferred to a high-pressure reactor and subjected to a solvothermal reaction at 195 °C for 24 h. After cooling, the solid was collected by centrifugation at 8000 rpm for 5 min and washed three times each with deionized water and anhydrous ethanol. The solid was dried at 58 °C under a vacuum of -0.09 MPa for 10 h. The powder was calcined at 495 °C for 3 h under nitrogen protection, with the temperature increased at 2 °C / min. After cooling, the material was ground through a 300-mesh sieve to obtain calcium zirconate / graphene oxide nanocomposite, denoted as material M4.

[0034] High-efficiency degassing refining agent for preparing magnesium alloy ingots Accurately weigh 8.0g of material M3, 6.0g of material M4, 20.0g of anhydrous magnesium chloride, 15.0g of anhydrous sodium fluoride, 10.0g of anhydrous potassium chloride, 3.0g of metallic calcium powder, 2.0g of barium carbonate, and 1.0g of α-alumina micro powder. All raw materials were ball-milled at 250rpm for 2 hours under argon protection (ball-to-material ratio 10:1). The mixed powder was then vacuum-dried at 195℃ and -0.1MPa for 4 hours. The dried powder was pressed into cylindrical ingots under 10MPa pressure, denoted as F2.

[0035] Example 3 The specific implementation method is the same as in Example 1, except that a lanthanum fluoride-supported titanium carbide nanocomposite is prepared. 6.0 g of titanium carbide nanoparticles were accurately weighed and added to 25 g of anhydrous ethanol. The mixture was ultrasonically treated at 40 kHz and 250 W for 25 min to obtain a dispersion. 18.0 g of lanthanum nitrate hexahydrate and 6.0 g of sodium fluoride were accurately weighed and dissolved together in 90 g of deionized water. The solution was stirred at 500 rpm in a 62 °C water bath until completely dissolved to obtain a solution. The titanium carbide dispersion was added dropwise to the salt solution over 35 min with continuous stirring at 600 rpm. After the addition was complete, stirring was continued at 62 °C for 2 h. The resulting suspension was transferred to a high-pressure reactor and hydrothermally reacted at 185 °C for 14 h. After the reaction, the mixture was cooled and filtered. The solid was washed three times each with deionized water and anhydrous ethanol, and dried at 82 °C and -0.09 MPa vacuum for 12 h. The dried powder was calcined at 605 °C for 4 h under a nitrogen atmosphere (1.0 L / min) with a heating rate of 5 °C / min. After cooling in the furnace, the material was ground through a 300-mesh sieve to obtain a lanthanum fluoride-supported titanium carbide nanocomposite, denoted as material M5.

[0036] Preparation of calcium zirconate / graphene oxide nanohybrids 1.2 g of graphene oxide was accurately weighed and dispersed in 120 g of deionized water. The mixture was subjected to pulsed sonication in an ice-water bath at 600 W for 50 min to obtain a dispersion. 14.0 g of zirconium oxychloride octahydrate and 6.0 g of calcium nitrate tetrahydrate were accurately weighed and dissolved in 35 g of deionized water to obtain a solution. The salt solution was poured into the graphene oxide dispersion and stirred at 500 rpm. 2.0 g of urea was added, and the mixture was stirred at 300 rpm at 72 °C for 6 h. The mixture was transferred to a high-pressure reactor and subjected to a solvothermal reaction at 205 °C for 30 h. After cooling, the solid was collected by centrifugation at 8000 rpm for 5 min and washed three times each with deionized water and anhydrous ethanol. The solid was dried at 62 °C under a vacuum of -0.09 MPa for 10 h. The powder was calcined at 505 °C for 6 h under argon protection, with the temperature increased at 2 °C / min. After cooling, the material was ground through a 300-mesh sieve to obtain calcium zirconate / graphene oxide nanocomposite, denoted as material M6.

[0037] High-efficiency degassing refining agent for preparing magnesium alloy ingots Accurately weigh 15.0g of material M5, 12.0g of material M6, 30.0g of anhydrous magnesium chloride, 25.0g of anhydrous sodium fluoride, 20.0g of anhydrous potassium chloride, 8.0g of metallic calcium powder, 5.0g of barium carbonate, and 4.0g of α-alumina micro powder. All raw materials were ball-milled at 350rpm for 4 hours under argon protection (ball-to-material ratio 10:1). The mixed powder was then vacuum-dried at 205℃ and -0.1MPa for 6 hours. The dried powder was pressed into cylindrical ingots under 20MPa pressure, denoted as F3.

[0038] Comparative Example 1 The specific implementation method is the same as in Example 1, except that this comparative example prepares a traditional refining agent without any nano-modified compounds. 25.0 g of anhydrous magnesium chloride, 20.0 g of anhydrous sodium fluoride, 15.0 g of anhydrous potassium chloride, 5.0 g of metallic calcium powder, 3.0 g of barium carbonate, and 2.0 g of α-alumina micro powder were accurately weighed. All raw materials were ball-milled at 300 rpm for 3 hours under argon protection (ball-to-powder ratio 10:1). The mixed powder was vacuum-dried at 200℃ and -0.1 MPa for 5 hours. The dried powder was pressed into cylindrical ingots under a pressure of 15 MPa, denoted as C1.

[0039] Comparative Example 2 The specific implementation method is the same as in Example 1, except that this comparative example prepares only a refining agent containing calcium zirconate / graphene oxide nanocomposite and not lanthanum fluoride-supported titanium carbide nanocomposite. Material M2 prepared in Example 1 is used. 9.0 g of material M2, 25.0 g of anhydrous magnesium chloride, 20.0 g of anhydrous sodium fluoride, 15.0 g of anhydrous potassium chloride, 5.0 g of metallic calcium powder, 3.0 g of barium carbonate, and 2.0 g of α-alumina micro powder are accurately weighed. All raw materials are ball-milled at 300 rpm for 3 h under argon protection (ball-to-material ratio 10:1). The mixed powder is vacuum-dried at 200℃ and -0.1 MPa for 5 h. The dried powder is pressed into cylindrical ingots under 15 MPa pressure, denoted as C2.

[0040] Comparative Example 3 The specific implementation method is the same as in Example 1, except that this comparative example prepares a refining agent containing only lanthanum fluoride-supported titanium carbide nanocomposite and excluding calcium zirconate / graphene oxide nanohybrids. Material M1 prepared in Example 1 is used. 12.0 g of material M1, 25.0 g of anhydrous magnesium chloride, 20.0 g of anhydrous sodium fluoride, 15.0 g of anhydrous potassium chloride, 5.0 g of metallic calcium powder, 3.0 g of barium carbonate, and 2.0 g of α-alumina micro powder are accurately weighed. All raw materials are ball-milled at 300 rpm for 3 h under argon protection (ball-to-material ratio 10:1). The mixed powder is vacuum-dried at 200℃ and -0.1 MPa for 5 h. The dried powder is pressed into cylindrical ingots under 15 MPa pressure, denoted as C3.

[0041] Performance testing The magnesium alloy ingots prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests using a high-efficiency degassing refining agent according to the following method. The performance testing method included the following steps: All tests were based on the same melting and processing procedure: First, 5.0 kg of AZ91D magnesium alloy was heated to 720°C in a melting furnace filled with a protective gas mixture of CO2 and SF6 (volume ratio 99:1) to ensure complete melting and holding at that temperature. Then, a refining agent sample at a mass of 2.0% of the alloy mass was quickly added to the melt, and the melt was immediately mechanically stirred continuously for 10.0 min using a graphite stirring paddle at a speed of 200 rpm. After stirring, stirring was stopped, and the melt was allowed to stand at 720°C for 15.0 min. After standing, the surface slag was skimmed off, and the pure magnesium liquid was poured into a metal mold preheated to 300°C to form a standard tensile test bar ingot. Subsequently, the treated melt and the resulting ingot were subjected to the following three core performance tests, with all test environments at a temperature of 25±2°C: Hydrogen content determination: The determination was performed directly using a Telegas hydrogen analyzer after the melt had settled but before casting. The instrument's quartz probe was inserted into the 720℃ magnesium melt to a depth half the depth of the molten pool. The circulation pump was started, circulating a fixed volume of carrier gas (high-purity nitrogen) between the probe bubble and the detection unit until the hydrogen partial pressure reached equilibrium. The instrument directly measured and calculated the hydrogen content in the melt, with results expressed in mL / 100g, accurate to 0.1 mL / 100g. Each sample was measured three times, and the average value was taken.

[0042] Inclusion level assessment: Cross-sectional metallographic specimens were taken from areas other than the ingot gate. After sequential grinding (from 400# to 2000# sandpaper) and mechanical polishing (using 1.0μm diamond polishing paste), the specimens were observed under an optical microscope at 100x magnification. Referring to the standard indicative method for inclusion assessment, the quantity, size, and distribution of non-metallic inclusions such as oxides and fluxes observed in the field of view were compared and assessed. Cleanliness was expressed as a numerical level; a smaller level value indicates fewer inclusions and a cleaner material. At least five different fields of view were observed for each specimen, and the most representative assessment results were used.

[0043] Room temperature tensile strength test: The ingot is machined into a cylindrical tensile specimen conforming to standard dimensions. A room temperature tensile test is performed on a universal testing machine. During the test, the clamp separation rate is set to 1.0 mm / min until the specimen fractures. The testing system automatically records the load-displacement curve and calculates the tensile strength of the specimen accordingly, expressed in MPa, accurate to 1 MPa. Three parallel specimens are tested for each sample, and the average value is taken.

[0044] Test results: Table 1: Test results of each embodiment and comparative example ; As can be seen from Table 1, the refining agents provided in Examples 1-3, by introducing two innovative components—lanthanum fluoride-supported titanium carbide nanocomposite and calcium zirconate / graphene oxide nanohybrid—and leveraging their synergistic effect, effectively solve the core technical problems of existing magnesium alloy refining agents, namely, incomplete removal of dissolved hydrogen from the melt and limited adsorption capacity for fine oxide inclusions. Specifically, this is reflected in: First, in terms of deep hydrogen removal, the hydrogen content results of the examples were at an excellent level of 4.9-5.8 mL / 100g, which is more than 50% higher than that of Comparative Example 1, which has a hydrogen content of up to 12.5 mL / 100g and is composed of only traditional salts. Even Comparative Examples 2 and 3, which use only one modified compound, have hydrogen contents (8.3 and 6.1 mL / 100g, respectively) that are significantly higher than any of the examples. This conclusively proves that the synergistic effect of the combination of the two is the key to achieving deep and thorough hydrogen removal, rather than the simple effect of a single component or traditional component.

[0045] Secondly, in terms of efficient impurity removal, the inclusion level assessment results of the embodiments reached an extremely high standard of 0.5-1.5, while that of Comparative Example 1 was as low as 4.0, indicating that the present invention has made a qualitative leap in the adsorption and purification capacity of fine oxidized inclusions. It is particularly noteworthy that Comparative Example 3, which contains only lanthanum fluoride-supported titanium carbide composite, has an inclusion level of 3.5, and its purification capacity is even weaker than that of Comparative Example 2 (2.5), which contains only calcium zirconate / graphene oxide hybrid. This directly confirms that the latter plays a dominant role in adsorbing and capturing inclusions, while the former mainly contributes to degassing. The combination of the two in the embodiments achieves the simultaneous and efficient treatment of gas and impurity defects.

[0046] Ultimately, the aforementioned fundamental improvements directly translate into a significant enhancement in the overall mechanical properties of the ingot. The room temperature tensile strength of the embodiment reaches 238-250 MPa, compared to 205 MPa in Comparative Example 1, representing a strength increase of 15-22%, and is comprehensively superior to any single-component comparative example. This performance confirms that the present invention, through the synergy of "deep degassing" and "efficient impurity removal," fundamentally reduces the formation of porosity and inclusion defects in the ingot, thereby successfully solving the long-standing technical bottleneck of poor overall performance of magnesium alloy ingots caused by this.

[0047] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a high-efficiency degassing refining agent for magnesium alloy ingots, characterized in that the steps include: include: S1. By weight, 8-15 parts of lanthanum fluoride-supported titanium carbide nanocomposite, 6-12 parts of calcium zirconate / graphene oxide nanohybrid, 20-30 parts of anhydrous magnesium chloride, 15-25 parts of anhydrous sodium fluoride, 10-20 parts of anhydrous potassium chloride, 3-8 parts of metallic calcium powder, 2-5 parts of barium carbonate, and 1-4 parts of α-alumina micro powder are added into a ball mill and mixed by ball milling under an argon protective atmosphere to obtain a mixed powder. S2. Transfer the mixed powder to a vacuum drying oven and dry it under vacuum at 195-205℃; after cooling, press it into cylindrical ingots under a pressure of 10-20MPa.

2. The method for preparing the high-efficiency degassing refining agent for magnesium alloy ingots according to claim 1, characterized in that, In step S1, the ball milling mixing time is 2-4 hours.

3. The method for preparing the high-efficiency degassing refining agent for magnesium alloy ingots according to claim 1, characterized in that, In step S2, the vacuum drying time at 195-205℃ is 4-6 hours.

4. The method for preparing the high-efficiency degassing refining agent for magnesium alloy ingots according to claim 1, characterized in that, The preparation method of the lanthanum fluoride-supported titanium carbide nanocomposite includes: A1. By weight, 4-6 parts of titanium carbide nanoparticles are dispersed in 15-25 parts of anhydrous ethanol and ultrasonically treated to obtain a titanium carbide ethanol dispersion; 17-18 parts of lanthanum nitrate hexahydrate and 5-6 parts of sodium fluoride are dissolved together in 70-90 parts of deionized water and stirred in a water bath at 58-62℃ to obtain a mixed salt solution; under continuous stirring, the titanium carbide ethanol dispersion is added dropwise to the mixed salt solution, and after the addition is complete, stirring is continued to obtain a suspension; then the suspension is transferred to a high-pressure reactor and hydrothermally reacted at 175-185℃ to obtain a reaction mixture; A2. Cool the reaction mixture to room temperature naturally, filter it to obtain a solid product, wash the solid product with deionized water and anhydrous ethanol in sequence, and dry it under vacuum at 78-82℃ to obtain a precursor powder; place the precursor powder in a tube furnace, calcine it at 595-605℃ under a nitrogen atmosphere, cool it with the furnace, and then grind and sieve it.

5. The method for preparing the high-efficiency degassing refining agent for magnesium alloy ingots according to claim 4, characterized in that, In step A1, the hydrothermal reaction time at 175-185℃ is 12-14 hours.

6. The method for preparing the high-efficiency degassing refining agent for magnesium alloy ingots according to claim 4, characterized in that, In step A2, the calcination time at 595-605℃ under a nitrogen atmosphere is 2-4 hours.

7. The method for preparing the high-efficiency degassing refining agent for magnesium alloy ingots according to claim 1, characterized in that, The preparation method of the calcium zirconate / graphene oxide nanohybrid includes: B1. By weight, disperse 0.8-1.2 parts of graphene oxide in 80-120 parts of deionized water, and ultrasonically exfoliate to obtain a graphene oxide dispersion; dissolve 10-14 parts of zirconium oxychloride octahydrate and 5-6 parts of calcium nitrate tetrahydrate together in 25-35 parts of deionized water, and stir to obtain a zirconium-calcium salt mixed solution; under continuous stirring, add the zirconium-calcium salt mixed solution dropwise to the graphene oxide dispersion; then add 1-2 parts of urea, and stir at a constant temperature of 68-72℃ to obtain a mixture; B2. Transfer the mixture to a high-pressure reactor and react it solvothermally at 195-205℃. After the reaction is complete, allow it to cool naturally to room temperature, centrifuge to obtain a solid, and wash the solid alternately with deionized water and anhydrous ethanol to obtain a washed solid. Dry the washed solid under vacuum at 58-62℃ to obtain a powder. Place the powder in a muffle furnace and calcine it at 495-505℃ under a nitrogen or argon protective atmosphere. After natural cooling, grind and sieve the powder.

8. The method for preparing the high-efficiency degassing refining agent for magnesium alloy ingots according to claim 7, characterized in that, In step B1, the stirring is carried out at a constant temperature of 68-72℃ for 4-6 hours.

9. The method for preparing the high-efficiency degassing refining agent for magnesium alloy ingots according to claim 7, characterized in that, In step B2, the calcination time at 495-505℃ is 3-6 hours.

10. A high-efficiency degassing refining agent for magnesium alloy ingots, characterized in that, The high-efficiency degassing refining agent for magnesium alloy ingots is prepared according to the preparation method of any one of claims 1-9.

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