A brazing filler metal for magnesium alloy brazing and a method for manufacturing the same

Abstract

The application relates to a brazing filler metal for magnesium alloy brazing and a preparation method thereof. In order to solve the problems of large brittleness and high impurity content of magnesium alloy brazing filler metals prepared by a traditional melting and casting method, the technical scheme of combining a multi-element mixed powder brazing filler metal component design and an argon protection mixed powder preparation process is adopted to prepare high-purity alloy brazing filler metals, the component proportion of the multi-element powder can be flexibly regulated, the powder after mixing does not need to pass through plastic processing procedures such as melting and casting and rolling, and the powder can be directly prepared into thin brazing filler metal sheets and brazing filler metal pastes, meanwhile, the powder can also be customized according to a weld shape to meet the thin gap filling requirements of precise structural parts. Meanwhile, the component segregation can be reduced, the brazing filler metal organization uniformity is improved, the processing difficulty is low, the finished product rate is high, the mixed powder process batch performance is stable, and the process can accurately adapt to high-end scenes such as aerospace, high-end automobile manufacturing and electronic devices.

Description

Technical Field

[0001] This invention relates to a brazing filler metal and its preparation method. Background Technology

[0002] Magnesium alloys, as the lightest metallic structural materials currently used in engineering applications, possess high specific strength and specific stiffness, excellent thermal conductivity, and electromagnetic shielding properties, making them promising candidates for applications in 5G communications, new energy vehicles, and aerospace. However, with the rapid development of these fields, higher demands are being placed on the reliable joining of magnesium alloys, and the high-precision forming of complex components often requires brazing processes.

[0003] The inherent physicochemical properties of magnesium alloys present numerous bottlenecks in their welding process. For instance, magnesium alloys have a low melting point (approximately 650°C), making them highly sensitive to brazing temperatures. Therefore, in practical applications, low-melting-point brazing filler metals are often required. However, when prepared using traditional smelting and casting methods, these filler metals are prone to compositional segregation. Furthermore, filler metals adapted to the low melting point of magnesium alloys often exhibit high brittleness and poor plasticity, making it difficult to process them into thin sheets. This hinders the filling and bonding requirements of complex structural components, significantly limiting the application of brazing technology in precision magnesium alloy joining applications. Traditional alloy smelting processes are also susceptible to introducing metallic impurities such as Fe and Cr, as well as oxide slag, due to furnace erosion and high-temperature oxidation. Summary of the Invention

[0004] In order to solve the problems of high brittleness and high impurity content of magnesium alloy brazing filler metal prepared by traditional melting and casting methods, this invention proposes a brazing filler metal for magnesium alloy brazing and its preparation method.

[0005] The brazing filler metal of the present invention for magnesium alloy brazing consists of 10-90 wt.% Al, 10-90 wt.% Ag, 1-10 wt.% SiC, 0.5-2 wt.% Mn, 0.5-1.5 wt.% Zr, 0.2-2 wt.% La, 0.2-1.5 wt.% Ce and the balance Mg.

[0006] The preparation method of the brazing filler metal for magnesium alloy brazing according to the present invention is carried out according to the following steps:

[0007] 1. Modify SiC particles, and then use Mg powder, Al powder, Ag powder, Mn powder, Zr powder, La powder, Ce powder and modified SiC particles as raw materials and vacuum dry them;

[0008] The process for modifying SiC particles is as follows: First, SiC particles are placed in a 5-10% NaOH solution and stirred at 80-100℃ for 1-2 hours for hydroxylation pretreatment. The SiC particles are filtered out and washed with deionized water until neutral. After filtration, they are dried at 100-120℃ to obtain hydroxylated silicon carbide. Then, a mixed solvent of anhydrous ethanol and deionized water is prepared at a volume ratio of 9:1. The pH of the mixed solvent is adjusted to 3.5-5.5, a silane coupling agent is added, and the mixture is stirred and hydrolyzed for 15-30 minutes until clear to obtain a hydrolysate. The hydroxylated silicon carbide is added to the hydrolysate, ultrasonically dispersed for 10-15 minutes, and stirred and refluxed at 80-120℃ for 2-6 hours to allow the silane coupling agent to form covalent bonds by condensation with the hydroxyl groups on the surface of silicon carbide. After the reaction, the mixture is separated by centrifugation or vacuum filtration, washed with anhydrous ethanol, and finally vacuum dried at 80-120℃ for 4-8 hours.

[0009] 2. Load Mg powder, Al powder, Ag powder, Mn powder, Zr powder, La powder, Ce powder, modified SiC particles, and spherical abrasive into a ball mill jar with a ball-to-powder ratio of 5-8:1; seal the ball mill jar and purge the air; then ball mill, first premixing at a speed of 150-200 r / min for 0.5-1 h to initially and uniformly disperse the metal powder and overcome the agglomeration problem caused by density differences, then adjust the speed to 200-250 r / min and continue mixing for 1-2 h to obtain a mixed powder;

[0010] 3. The mixed powder obtained in step 2 is cold-pressed to prepare a solder sheet or mixed with a binder to prepare a solder paste, thus completing the process;

[0011] The cold pressing process is as follows: pressure is 50-600MPa, pressure is held for 1-3 minutes, and the thickness of the brazing filler metal sheet is 0.1-1mm.

[0012] The principles and beneficial technical effects of this invention are as follows:

[0013] 1. This invention employs a technical solution combining multi-component mixed powder brazing filler metal composition design with an argon-protected powder mixing preparation process to produce high-purity alloy brazing filler metal. The powder mixing process completely eliminates the high-temperature stage, and the use of high-purity argon gas for full-process sealed protection prevents oxidation and contamination from external impurities at the source. Furthermore, segmented mixing and precise batching provide core assurance for the quality of low-temperature brazed joints. On one hand, the composition ratio of the multi-component powders can be flexibly controlled, and reinforcing particles can be added for reinforcement, shortening the brazing filler metal development cycle. On the other hand, after powder mixing, there is no need for plastic processing steps such as melting, casting, and rolling; thin brazing filler metal sheets and pastes can be directly prepared. Custom molding based on weld shape is also possible, perfectly adapting to the thin gap filling requirements of precision structural components. Simultaneously, it reduces component segregation and improves the uniformity of the brazing filler metal structure, laying the foundation for subsequent optimization of brazed joint performance.

[0014] 2. The powder mixing process used in this invention allows for flexible control of the composition ratio of Mg, Al, Ag, Mn, Zr, La, and Ce. Mg serves as the matrix phase, ensuring good compatibility with the magnesium alloy base material. Al acts as a melting point regulator, working synergistically with Ag and Zr to stably control the brazing temperature below 500℃, preventing overheating damage to the base material and optimizing the wetting and spreading properties of the brazing filler metal. La and Ce, two rare earth elements, work together to purify grain boundaries, refine grains, and remove impurities, inhibiting the excessive growth of brittle intermetallic compounds and significantly improving the toughness and mechanical uniformity of the joint. Mn can remove harmful impurities, improve the corrosion resistance of the joint, and simultaneously refine the microstructure and enhance high-temperature stability. Zr, as a highly efficient grain refiner, can significantly refine the liquid phase of the weld, inhibit crack propagation during solidification, improve weld density and toughness, and optimize melt flowability. SiC, as a particulate reinforcement, refines the matrix microstructure and interrupts the formation of continuous metal compounds due to its high hardness and high thermal stability, improving the joint strength. Combined with silane coupling agent modification, it achieves uniform dispersion, ultimately achieving a high-quality brazing effect with low temperature and high strength.

[0015] 3. The mixed powder of this invention can be flexibly prepared into 0.1-1mm thin solder sheets or solder paste according to requirements, suitable for complex welds and precision structural parts. Compared with the melting process, it has a wider range of applications, lower subsequent processing difficulty, and higher yield. At the same time, the batch performance of the powder mixing process is stable. With the advantages of high purity, low impurities, and flexible form brought by the powder mixing process, it can be precisely adapted to high-end scenarios such as aerospace, high-end automobile manufacturing, and electronic devices. Attached Figure Description

[0016] Figure 1 This is a metallographic diagram of the weld after brazing in Example 1;

[0017] Figure 2 This is a schematic diagram of SiC agglomeration at the weld after brazing in Comparative Example 2.

[0018] Figure 3 The shear stress-strain curve of the brazed compression-shear specimen obtained in Example 2;

[0019] Figure 4 The image shows the fracture morphology of the weld obtained by brazing in Example 2. Detailed Implementation

[0020] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any reasonable combination of the specific embodiments.

[0021] Specific Implementation Method 1: The brazing filler metal used in this implementation method for magnesium alloy brazing consists of 10-90 wt.% Al, 10-90 wt.% Ag, 1-10 wt.% SiC, 0.5-2 wt.% Mn, 0.5-1.5 wt.% Zr, 0.2-2 wt.% La, 0.2-1.5 wt.% Ce, and the balance Mg.

[0022] This embodiment has the following beneficial effects:

[0023] This embodiment uses a powder mixing process to flexibly adjust the composition ratio of Mg, Al, Ag, Mn, Zr, La, and Ce. Mg serves as the matrix phase, ensuring good compatibility with the magnesium alloy base material. Al acts as a melting point regulator, working synergistically with Ag and Zr to stably control the brazing temperature below 500℃, preventing overheating damage to the base material and optimizing the wetting and spreading properties of the brazing filler metal. La and Ce, two rare earth elements, work together to purify grain boundaries, refine grains, and remove impurities, inhibiting the excessive growth of brittle intermetallic compounds and significantly improving the toughness and mechanical uniformity of the joint. Mn can remove harmful impurities, improve the corrosion resistance of the joint, and simultaneously refine the microstructure and enhance high-temperature stability. Zr, as a highly efficient grain refiner, can significantly refine the liquid phase of the weld, inhibit crack propagation during solidification, improve weld density and toughness, and optimize melt flowability. SiC, as a particulate reinforcement, refines the matrix microstructure and interrupts the formation of continuous metal compounds due to its high hardness and high thermal stability, improving the joint strength. Combined with silane coupling agent modification, it achieves uniform dispersion, ultimately achieving a high-quality brazing effect with low temperature and high strength.

[0024] Specific Implementation Method Two: The preparation method of the brazing filler metal for magnesium alloy brazing in this implementation method is carried out according to the following steps:

[0025] 1. Modify SiC particles, then use Mg powder, Al powder, Ag powder, Mn powder, Zr powder, La powder, Ce powder and modified SiC particles as raw materials and vacuum dry them;

[0026] The process for modifying SiC particles is as follows: First, SiC particles are placed in a 5-10% NaOH solution and stirred at 80-100℃ for 1-2 hours for hydroxylation pretreatment. The SiC particles are filtered out and washed with deionized water until neutral. After filtration, they are dried at 100-120℃ to obtain hydroxylated silicon carbide. Then, a mixed solvent of anhydrous ethanol and deionized water is prepared at a volume ratio of 9:1. The pH of the mixed solvent is adjusted to 3.5-5.5, a silane coupling agent is added, and the mixture is stirred and hydrolyzed for 15-30 minutes until clear to obtain a hydrolysate. The hydroxylated silicon carbide is added to the hydrolysate, ultrasonically dispersed for 10-15 minutes, and stirred and refluxed at 80-120℃ for 2-6 hours to allow the silane coupling agent to form covalent bonds by condensation with the hydroxyl groups on the surface of silicon carbide. After the reaction, the mixture is separated by centrifugation or vacuum filtration, washed with anhydrous ethanol, and finally vacuum dried at 80-120℃ for 4-8 hours.

[0027] Drying the raw materials completely removes anhydrous ethanol and volatilizes trace amounts of volatile groups in the coupling agent. Because the coupling agent is added in extremely low amounts and is firmly bonded to SiC, it will not detach or decompose to generate contaminants during subsequent powder mixing and brazing. Modification with silane coupling agents allows the coupling agent molecules to covalently bond with the hydroxyl groups on the SiC surface, forming a uniform coating layer without introducing free impurities. The silane coupling agent forms a covalent coating layer on the surface of SiC particles, improving the interfacial compatibility between inorganic SiC particles and metal powder, inhibiting SiC particle agglomeration, and increasing the dispersion uniformity in the brazing filler matrix. It also strengthens the interfacial bonding force between SiC and the metal matrix, preventing interfacial peeling and particle segregation defects during brazing, and improving the mechanical properties of the joint. The modified SiC particles, as an inorganic particle reinforcing phase, have high hardness and good thermal stability. They can refine the microstructure of the brazing filler matrix, inhibit grain growth and joint deformation during brazing, and improve the shear strength, wear resistance, and high-temperature stability of the joint. Simultaneously, they can prevent crack propagation and improve the toughness of the brazed joint.

[0028] 2. Load Mg powder, Al powder, Ag powder, Mn powder, Zr powder, La powder, Ce powder, modified SiC particles, and spherical abrasive into a ball mill jar with a ball-to-powder ratio of 5-8:1; seal the ball mill jar and purge the air; then ball mill, first premixing at a speed of 150-200 r / min for 0.5-1 h to initially and uniformly disperse the metal powder and overcome the agglomeration problem caused by density differences, then adjust the speed to 200-250 r / min and continue mixing for 1-2 h to obtain a mixed powder;

[0029] 3. The mixed powder obtained in step 2 is cold-pressed to prepare a solder sheet or mixed with a binder to prepare a solder paste, thus completing the process;

[0030] The cold pressing process is as follows: pressure is 50-600MPa, pressure is held for 1-3 minutes, and the thickness of the brazing filler metal sheet is 0.1-1mm.

[0031] 1. This embodiment employs a technical solution combining multi-component mixed powder brazing alloy composition design with argon-protected powder mixing preparation process to produce high-purity alloy brazing alloy. The powder mixing process completely eliminates the high-temperature stage, and the use of high-purity argon gas for full-process sealed protection prevents oxidation and contamination from external impurities at the source. Furthermore, segmented mixing and precise batching provide core assurance for the quality of low-temperature brazed joints. On one hand, the composition ratio of the multi-component powders can be flexibly controlled, and reinforcing particles can be added for reinforcement, shortening the brazing alloy development cycle. On the other hand, after powder mixing, there is no need for plastic processing processes such as melting, casting, and rolling; thin brazing alloy sheets and brazing alloy paste can be directly prepared. Custom molding based on weld shape is also possible, perfectly adapting to the thin gap filling requirements of precision structural components. Simultaneously, it reduces component segregation and improves the uniformity of the brazing alloy structure, laying the foundation for subsequent optimization of brazed joint performance.

[0032] 2. The powder mixing process used in this embodiment allows for flexible control of the composition ratio of Mg, Al, Ag, Mn, Zr, La, and Ce. Mg serves as the matrix phase, ensuring good compatibility with the magnesium alloy base material. Al acts as a melting point regulator, working synergistically with Ag and Zr to stably control the brazing temperature below 500℃, preventing overheating damage to the base material and optimizing the wetting and spreading properties of the brazing filler metal. La and Ce, two rare earth elements, work together to purify grain boundaries, refine grains, and remove impurities, inhibiting the excessive growth of brittle intermetallic compounds and significantly improving the toughness and mechanical uniformity of the joint. Mn can remove harmful impurities, improve the corrosion resistance of the joint, and simultaneously refine the microstructure and enhance high-temperature stability. Zr, as a highly efficient grain refiner, can significantly refine the liquid phase of the weld, inhibit crack propagation during solidification, improve weld density and toughness, and optimize melt flowability. SiC, as a particulate reinforcement, refines the matrix microstructure and interrupts the formation of continuous metal compounds due to its high hardness and high thermal stability, improving the joint strength. Combined with silane coupling agent modification, it achieves uniform dispersion, ultimately achieving a high-quality brazing effect with low temperature and high strength.

[0033] 3. This embodiment of the mixed powder can flexibly prepare 0.1-1mm thin solder sheets or solder paste according to requirements, suitable for complex welds and precision structural parts. Compared with the melting process, it has a wider range of applications, lower subsequent processing difficulty, and higher yield. At the same time, the batch performance of the powder mixing process is stable. With the advantages of high purity, low impurities, and flexible form brought by the powder mixing process, it can be precisely adapted to high-end scenarios such as aerospace, high-end automobile manufacturing, and electronic devices.

[0034] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 2 in that the Mg powder, Al powder, Ag powder, Mn powder, Zr powder, La powder, and Ce powder mentioned in step one are spherical powders with a particle size of 1-80μm.

[0035] Specific Implementation Method Four: This implementation method differs from Specific Implementation Method Two or Three in that the particle size of the SiC particles mentioned in Step One is 50nm-50μm.

[0036] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods Two to Four in that the vacuum drying process described in step one is as follows: First, the vacuum drying oven is evacuated to a vacuum degree of -0.05~-0.08MPa, and then argon gas is introduced while heating to 80-120℃, and the temperature is maintained for 2-4 hours. After vacuum drying, the moisture, oil, and volatile impurities adsorbed on the powder surface are removed, avoiding porosity defects caused by the volatilization of impurities during powder mixing and brazing; an argon gas environment is maintained throughout the drying process to prevent oxidation of Mg powder and Al powder.

[0037] Specific Implementation Method Six: This implementation method differs from one of Specific Implementation Methods Two to Five in that the amount of silane coupling agent added in step one is 0.1-2% of the weight of the SiC particles.

[0038] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods Two to Six in that the mass ratio of hydroxylated silicon carbide to the volume of hydrolysate in step one is 1g:5-20mL.

[0039] Specific Implementation Method Eight: This implementation method differs from one of Specific Implementation Methods Two to Seven in that the air removal process in step two is as follows: the ball mill jar is evacuated to a vacuum degree of -0.08 to -0.1 MPa, and then argon is introduced. The evacuation and argon introduction are repeated 3-5 times; the purity of the argon is ≥99.99%.

[0040] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods Two to Eight in that the binder in step three is ethyl cellulose or polyvinyl butyral; the binder accounts for 0.5%-2% of the weight of the mixed powder. The binder has a low volatilization temperature, decomposes completely during subsequent brazing, leaves no carbon residue, and is suitable for low-temperature brazing conditions.

[0041] Specific Implementation Method 10: This implementation method differs from Specific Implementation Methods 2 to 9 in that: the silane coupling agent in step one is KH-550; and the sieving is done using a 200-2000 mesh standard sieve.

[0042] Example 1:

[0043] The brazing filler metal used for magnesium alloy brazing in this embodiment consists of 50 wt.% Al, 15 wt.% Ag, 7.0 wt.% SiC, 1.5 wt.% Mn, 1.0 wt.% Zr, 0.8 wt.% La, 0.5 wt.% Ce and the balance Mg.

[0044] The preparation method of the brazing filler metal for magnesium alloy brazing in this embodiment is carried out according to the following steps:

[0045] 1. Modify SiC particles, then use Mg powder, Al powder, Ag powder, Mn powder, Zr powder, La powder, Ce powder and modified SiC particles as raw materials and vacuum dry them;

[0046] The Mg powder, Al powder, Ag powder, Mn powder, Zr powder, La powder, and Ce powder are spherical powders with a particle size of 10-30 μm; the SiC particles have a particle size of 50 nm-100 nm.

[0047] The vacuum drying process is as follows: First, the vacuum drying oven is evacuated to a vacuum degree of -0.07MPa, and then argon gas is introduced while heating to 100℃ and kept at that temperature for 3 hours.

[0048] The SiC particle modification process is as follows: SiC particles are placed in anhydrous ethanol, then a silane coupling agent is added, and the mixture is stirred at 30°C for 4 hours for modification. After modification, the mixture is dried in a vacuum drying oven at 60°C for 3 hours, and finally sieved. The amount of silane coupling agent added is 0.5% of the weight of the SiC particles; the silane coupling agent is KH-550; the sieve is a 1000-mesh standard sieve; the volume ratio of SiC particles to anhydrous ethanol is 1:1.5.

[0049] The process for modifying SiC particles is as follows: First, SiC particles are placed in a 5% NaOH solution and stirred at 80°C for 2 hours for hydroxylation pretreatment. The SiC particles are filtered out and washed with deionized water until neutral. After filtration, they are dried at 100°C to obtain hydroxylated silicon carbide. Then, a mixed solvent of anhydrous ethanol and deionized water is prepared at a volume ratio of 9:1. The pH of the mixed solvent is adjusted to 4, and a silane coupling agent is added. The mixture is stirred and hydrolyzed for 30 minutes until clear to obtain a hydrolysate. The hydroxylated silicon carbide is added to the hydrolysate, ultrasonically dispersed for 15 minutes, and stirred and refluxed at 120°C for 5 hours to allow the silane coupling agent to form covalent bonds by condensation with the hydroxyl groups on the surface of silicon carbide. After the reaction, the mixture is separated by centrifugation or vacuum filtration, washed with anhydrous ethanol, and finally vacuum dried at 100°C for 6 hours. The mass ratio of hydroxylated silicon carbide to the volume of the hydrolysate is 1 g: 10 mL.

[0050] 2. Mg powder, Al powder, Ag powder, Mn powder, Zr powder, La powder, Ce powder, modified SiC particles, and spherical abrasive are loaded into a ball mill jar with a ball-to-powder ratio of 6:1. The ball mill jar is sealed and air is purged. Ball milling is then carried out. First, the mixture is premixed at a speed of 150 r / min for 0.5 h to initially and uniformly disperse the metal powder and overcome the agglomeration problem caused by density differences. Then, the speed is adjusted to 200 r / min and the mixture is continued for 1 h to obtain a mixed powder.

[0051] The air removal process is as follows: the ball mill jar is evacuated to a vacuum level of -0.1 MPa, and then argon gas is introduced. The evacuation and argon gas introduction are repeated 3 times.

[0052] The purity of the argon gas is ≥99.99%;

[0053] 3. The mixed powder obtained in step 2 is cold-pressed to prepare a solder sheet or mixed with a binder to prepare a solder paste, thus completing the process;

[0054] The cold pressing process is as follows: pressure is 250MPa, holding pressure is 1min, and the thickness of the brazing filler sheet is 103μm;

[0055] The binder is ethyl cellulose;

[0056] The brazing process for AZ40 magnesium alloy prepared in this embodiment is as follows: brazing is performed in an argon-protected furnace. Before brazing, the surface of the AZ40 magnesium alloy to be brazed is degreased, sanded, and cleaned. The brazing filler metal sheet is placed at the gap between the base materials, a clamping force of 0.1 MPa is applied, high-purity argon gas is introduced for protection, the temperature is raised to 350°C at a rate of 20°C / min, and held for 20 minutes to ensure that the brazing filler metal and the base material are in full contact under the action of temperature and pressure. Then, the temperature is raised to 480°C at a rate of 10°C / min to complete the brazing. Subsequently, the furnace is cooled to 300°C, and the workpiece is removed to complete the brazing.

[0057] Figure 1 This is a metallographic diagram of the weld after brazing in Example 1; Figure 1 The weld is dense and free of pores, with a small amount of metallic compounds distributed at the weld and fine SiC particles dispersed throughout. In Example 1, the brazed magnesium alloy compression-shear specimen exhibited a weld shear strength of 52 MPa and a weld ratio of 96.4%.

[0058] Example 2:

[0059] The brazing filler metal used in this embodiment for magnesium alloy brazing consists of 15 wt.% Al, 50 wt.% Ag, 2.5 wt.% SiC, 1.0 wt.% Mn, 1.0 wt.% Zr, 1.2 wt.% La, 0.8 wt.% Ce and the balance Mg.

[0060] The preparation method of the brazing filler metal for magnesium alloy brazing in this embodiment is carried out according to the following steps:

[0061] 1. Modify SiC particles, then use Mg powder, Al powder, Ag powder, Mn powder, Zr powder, La powder, Ce powder and modified SiC particles as raw materials and vacuum dry them;

[0062] The Mg powder, Al powder, Ag powder, Mn powder, Zr powder, La powder, and Ce powder are spherical powders with a particle size of 10-30 μm; the SiC particles have a particle size of 50 nm-100 nm.

[0063] The vacuum drying process is as follows: First, the vacuum drying oven is evacuated to a vacuum degree of -0.08MPa, and then argon gas is introduced while heating to 110℃ and kept at that temperature for 2 hours.

[0064] The process for modifying SiC particles is as follows: First, SiC particles are placed in a 10% NaOH solution and stirred at 90°C for 2 hours for hydroxylation pretreatment. The SiC particles are filtered out and washed with deionized water until neutral. After filtration, they are dried at 110°C to obtain hydroxylated silicon carbide. Then, a mixed solvent of anhydrous ethanol and deionized water is prepared at a volume ratio of 9:1. The pH of the mixed solvent is adjusted to 4.5, and a silane coupling agent is added. The mixture is stirred and hydrolyzed for 20 minutes until clear to obtain a hydrolysate. The hydroxylated silicon carbide is added to the hydrolysate, ultrasonically dispersed for 10 minutes, and stirred and refluxed at 90°C for 5 hours to allow the silane coupling agent to form covalent bonds with the hydroxyl groups on the surface of silicon carbide through condensation. After the reaction, the mixture is separated by centrifugation or vacuum filtration, washed with anhydrous ethanol, and finally vacuum dried at 110°C for 7 hours. The mass ratio of hydroxylated silicon carbide to the volume of the hydrolysate is 1 g: 15 mL.

[0065] 2. Mg powder, Al powder, Ag powder, Mn powder, Zr powder, La powder, Ce powder, modified SiC particles, and spherical abrasive are loaded into a ball mill jar with a ball-to-powder ratio of 7:1. The ball mill jar is sealed and air is purged. Ball milling is then performed. First, the mixture is premixed at a speed of 150 r / min for 0.5 h to initially and uniformly disperse the metal powders and overcome the agglomeration problem caused by density differences. Then, the speed is adjusted to 200 r / min, and the mixture is continued for 1 h to obtain a mixed powder.

[0066] The air removal process is as follows: the ball mill jar is evacuated to a vacuum level of -0.08 MPa, and then argon gas is introduced. The evacuation and argon gas introduction are repeated 3 times.

[0067] The purity of the argon gas is ≥99.99%;

[0068] 3. The mixed powder obtained in step 2 is cold-pressed to prepare a solder sheet or mixed with a binder to prepare a solder paste, thus completing the process;

[0069] The cold pressing process is as follows: pressure is 300MPa, pressure is held for 1 minute, and the thickness of the brazing filler sheet is 105μm;

[0070] The binder is ethyl cellulose;

[0071] The brazing process for AZ80 magnesium alloy prepared in this embodiment is as follows: brazing is performed in an argon-protected furnace. Before brazing, the surface of the AZ40 magnesium alloy to be brazed is degreased, sanded, and cleaned. The brazing filler metal sheet is placed at the gap between the base materials, a clamping force of 0.1 MPa is applied, high-purity argon gas is introduced for protection, the temperature is raised to 350°C at a rate of 20°C / min, and held for 20 minutes to ensure that the brazing filler metal and the base material are in full contact under the action of temperature and pressure. Then, the temperature is raised to 490°C at a rate of 10°C / min to complete the brazing. Subsequently, the workpiece is cooled to 300°C with the furnace and then removed to complete the brazing.

[0072] Figure 3 The shear stress-strain curve of the brazed compression-shear specimen obtained in Example 2 is shown. Figure 3 It can be seen that as the strain increases, the shear stress at the weld increases continuously. When it reaches 62 MPa, the weld fractures due to shear. Figure 4 The image shows the fracture morphology of the weld obtained by brazing in Example 2. It can be seen that there are obvious dimples at the fracture surface, indicating that the weld has a certain degree of plasticity. This is because the amount of metallic compounds in the weld was reduced through composition optimization. The shear strength of the magnesium alloy compression-shear specimen obtained by brazing in Example 2 is 62 MPa, and the weld strength is 98.7%.

[0073] Example 3:

[0074] The brazing filler metal used in this embodiment for magnesium alloy brazing consists of 35 wt.% Al, 35 wt.% Ag, 1.7 wt.% SiC, 1.6 wt.% Mn, 1.2 wt.% Zr, 1.5 wt.% La, 1.1 wt.% Ce and the balance Mg.

[0075] The preparation method of the brazing filler metal for magnesium alloy brazing according to the present invention is carried out according to the following steps:

[0076] 1. Modify SiC particles, then use Mg powder, Al powder, Ag powder, Mn powder, Zr powder, La powder, Ce powder and modified SiC particles as raw materials and vacuum dry them;

[0077] The Mg powder, Al powder, Ag powder, Mn powder, Zr powder, La powder, and Ce powder are spherical powders with a particle size of 10-30 μm; the SiC particles have a particle size of 50 nm-100 nm.

[0078] The vacuum drying process is as follows: First, the vacuum drying oven is evacuated to a vacuum degree of -0.07MPa, and then argon gas is introduced while heating to 100℃ and kept at that temperature for 3 hours.

[0079] The process for modifying SiC particles is as follows: First, SiC particles are placed in a 5% NaOH solution and stirred at 100°C for 2 hours for hydroxylation pretreatment. The SiC particles are filtered out and washed with deionized water until neutral. After filtration, they are dried at 110°C to obtain hydroxylated silicon carbide. Then, a mixed solvent of anhydrous ethanol and deionized water is prepared at a volume ratio of 9:1. The pH of the mixed solvent is adjusted to 5, and a silane coupling agent is added. The mixture is stirred and hydrolyzed for 30 minutes until clear to obtain a hydrolysate. The hydroxylated silicon carbide is added to the hydrolysate and ultrasonically dispersed for 15 minutes. The mixture is stirred and refluxed at 100°C for 6 hours to allow the silane coupling agent to form covalent bonds by condensation between silanol groups and hydroxyl groups on the surface of silicon carbide. After the reaction, the mixture is separated by centrifugation or vacuum filtration, washed with anhydrous ethanol, and finally vacuum dried at 110°C for 7 hours. The mass ratio of hydroxylated silicon carbide to the volume ratio of the hydrolysate is 1 g: 20 mL.

[0080] 2. Mg powder, Al powder, Ag powder, Mn powder, Zr powder, La powder, Ce powder, modified SiC particles, and spherical abrasive are loaded into a ball mill jar with a ball-to-powder ratio of 6:1. The ball mill jar is sealed and air is purged. Ball milling is then carried out. First, the mixture is premixed at a speed of 150 r / min for 0.5 h to initially and uniformly disperse the metal powder and overcome the agglomeration problem caused by density differences. Then, the speed is adjusted to 200 r / min and the mixture is continued for 1 h to obtain a mixed powder.

[0081] The air removal process is as follows: the ball mill jar is evacuated to a vacuum level of -0.1 MPa, and then argon gas is introduced. The evacuation and argon gas introduction are repeated 3 times.

[0082] The purity of the argon gas is ≥99.99%;

[0083] 3. The mixed powder obtained in step 2 is cold-pressed to prepare a solder sheet or mixed with a binder to prepare a solder paste, thus completing the process;

[0084] The cold pressing process is as follows: pressure is 250MPa, pressure is held for 1 minute, and the thickness of the brazing filler sheet is 105μm;

[0085] The binder is ethyl cellulose;

[0086] The brazing filler metal prepared in this embodiment is used for welding ZK61 magnesium alloy. The brazing process is as follows: brazing is performed in an argon-protected furnace. Before brazing, the surfaces of the AZ40 magnesium alloy to be brazed are degreased, sanded, and cleaned. The brazing filler metal sheet is placed at the butt joint gap of the base material, and a clamping force of 0.1 MPa is applied. High-purity argon gas is introduced for protection, and the temperature is raised to 350°C at a rate of 20°C / min and held for 20 minutes to ensure full contact between the brazing filler metal and the base material under the action of temperature and pressure. Then, the temperature is raised to 470°C at a rate of 10°C / min to complete the brazing. Subsequently, the furnace is cooled to 300°C, and the workpiece is removed to complete the brazing. The shear strength of the brazed butt joint is 43 MPa, and the joint weld rate is 95.8%.

[0087] Comparative Example 1:

[0088] The alloy brazing filler metal was prepared using an atmosphere-protected melting process: First, magnesium ingots were preheated and placed in a crucible. Vacuum was drawn and argon gas was introduced for protection. The magnesium matrix was induction heated to -700℃ to melt. Then, the temperature was raised to 720℃, Al was added, and the mixture was stirred thoroughly. The temperature was then raised to 740℃, and Mn and sponge zirconium were added sequentially to promote the dissolution of high-melting-point elements and grain refinement. After that, the temperature was lowered to -720℃, pure silver foil and Mg-La and Mg-Ce master alloys were added, and the mixture was stirred to reduce burn-off. The melt was then cooled to 595℃, and SiC particles preheated to 250℃ were added. Mechanical stirring was started for 10 minutes (700 rpm) to force the SiC particles to disperse evenly using a high-viscosity slurry. The temperature was then raised to 700℃ to restore fluidity. After standing, the mixture was cast into molds. The resulting ingots were brittle and difficult to roll into brazing filler metal sheets of the target thickness.

[0089] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that the SiC particles used in Comparative Example 2 were not modified with silane coupling agents. Other steps and parameters were the same as in Example 1. Figure 2 This is a schematic diagram of SiC agglomeration at the weld after brazing in Comparative Example 2. Figure 2 It can be seen that the SiC particles that have not been modified by silane coupling agent exhibit local agglomeration at the weld, which affects the shear performance of the weld, and the shear strength of the weld is only 21 MPa.

Claims

1. A brazing filler metal for magnesium alloy brazing, characterized in that: The brazing filler metal for magnesium alloys consists of 10-90 wt.% Al, 10-90 wt.% Ag, 1-10 wt.% SiC, 0.5-2 wt.% Mn, 0.5-1.5 wt.% Zr, 0.2-2 wt.% La, 0.2-1.5 wt.% Ce, and the balance Mg.

2. The method for preparing the brazing filler metal for magnesium alloy brazing as described in claim 1, characterized in that: The preparation method of the brazing filler metal for magnesium alloy brazing is carried out according to the following steps:

1. Modify SiC particles, and then use Mg powder, Al powder, Ag powder, Mn powder, Zr powder, La powder, Ce powder and modified SiC particles as raw materials and vacuum dry them; The process for modifying SiC particles is as follows: First, SiC particles are placed in a 5-10% NaOH solution and stirred at 80-100℃ for 1-2 hours for hydroxylation pretreatment. The SiC particles are filtered out and washed with deionized water until neutral. After filtration, they are dried at 100-120℃ to obtain hydroxylated silicon carbide. Then, a mixed solvent of anhydrous ethanol and deionized water is prepared at a volume ratio of 9:

1. The pH of the mixed solvent is adjusted to 3.5-5.5, a silane coupling agent is added, and the mixture is stirred and hydrolyzed for 15-30 minutes until clear to obtain a hydrolysate. The hydroxylated silicon carbide is added to the hydrolysate, ultrasonically dispersed for 10-15 minutes, and stirred and refluxed at 80-120℃ for 2-6 hours to allow the silane coupling agent to form covalent bonds by condensation with the hydroxyl groups on the surface of silicon carbide. After the reaction, the mixture is separated by centrifugation or vacuum filtration, washed with anhydrous ethanol, and finally vacuum dried at 80-120℃ for 4-8 hours.

2. Load Mg powder, Al powder, Ag powder, Mn powder, Zr powder, La powder, Ce powder, modified SiC particles, and spherical abrasive into a ball mill jar with a ball-to-powder ratio of 5-8:1; seal the ball mill jar and purge the air; then ball mill, first premixing at a speed of 150-200 r / min for 0.5-1 h to initially and uniformly disperse the metal powder and overcome the agglomeration problem caused by density differences, then adjust the speed to 200-250 r / min and continue mixing for 1-2 h to obtain a mixed powder; 3. The mixed powder obtained in step 2 is cold-pressed to prepare a solder sheet or mixed with a binder to prepare a solder paste, thus completing the process; The cold pressing process is as follows: pressure is 50-600MPa, pressure is held for 1-3 minutes, and the thickness of the brazing filler metal sheet is 0.1-1mm.

3. The method for preparing brazing filler metal for magnesium alloys according to claim 1, characterized in that: The Mg powder, Al powder, Ag powder, Mn powder, Zr powder, La powder, and Ce powder mentioned in step one are spherical powders with a particle size of 1-80 μm.

4. The method for preparing brazing filler metal for magnesium alloys according to claim 1, characterized in that: The particle size of the SiC particles mentioned in step one is 50nm-50μm.

5. The method for preparing brazing filler metal for magnesium alloys according to claim 1, characterized in that: The vacuum drying process described in step one is as follows: First, the vacuum drying oven is evacuated to a vacuum degree of -0.05~-0.08 MPa. Then, argon gas is introduced while heating to 80-120℃, and the temperature is maintained for 2-4 hours. After vacuum drying, the moisture, oil, and volatile impurities adsorbed on the powder surface are removed to avoid porosity defects caused by the volatilization of impurities during powder mixing and brazing. An argon gas environment is maintained throughout the drying process to prevent oxidation of Mg powder and Al powder.

6. The method for preparing brazing filler metal for magnesium alloys according to claim 1, characterized in that: The amount of silane coupling agent added in step one is 0.1-2% of the weight of SiC particles.

7. The method for preparing brazing filler metal for magnesium alloys according to claim 1, characterized in that: The mass ratio of hydroxylated silicon carbide to the volume of hydrolysate in step one is 1g:5-20mL.

8. The method for preparing brazing filler metal for magnesium alloys according to claim 1, characterized in that: The air removal process described in step two is as follows: the ball mill jar is evacuated to a vacuum level of -0.08 to -0.1 MPa, and then argon gas is introduced. The evacuation and argon gas introduction are repeated 3-5 times; the purity of the argon gas is ≥99.99%.

9. The method for preparing brazing filler metal for magnesium alloys according to claim 1, characterized in that: The binder mentioned in step three is ethyl cellulose or polyvinyl butyral; the binder accounts for 0.5%-2% of the weight of the mixed powder.

10. The method for preparing brazing filler metal for magnesium alloys according to claim 1, characterized in that: Step 1: The silane coupling agent is KH-550; the sieving process uses a 200-2000 mesh standard sieve.

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