Silver-based brazing sheet and method of making the same

Abstract

This invention relates to the field of brazing materials technology, specifically to a silver-based brazing sheet and its preparation method, comprising the following raw materials in parts by weight: 50-60 parts silver powder, 20-30 parts copper powder, 15-20 parts zinc powder, 8-10 parts tin powder, 6-8 parts additive A, and 3-5 parts additive B. In this invention, additive A is prepared by synergistically combining composite powder and modified zirconium boride powder with a cerium nitrate aqueous solution. The composite powder is formed by ball milling, pressing, and sintering ceramic fiber powder and silicon carbide micropowder to create a highly stable skeletal structure, effectively improving the high-temperature strength and creep resistance of the brazing sheet, refining the brazing alloy grains, and optimizing interfacial bonding. Simultaneously, additive B is prepared using nano-nickel-cobalt composite metal powder as the core, remaining stable during smelting and rolling, optimizing the microstructure of the brazing sheet, and improving the corrosion resistance of the brazed joint.

Description

Technical Field

[0001] This invention relates to the field of brazing materials technology, specifically to a silver-based brazing sheet and its preparation method. Background Technology

[0002] Silver-based brazing sheets are thin sheet brazing materials made primarily of silver with the addition of elements such as copper and zinc, and are widely used in aerospace, hardware and electrical appliances, instrumentation and other fields.

[0003] In existing technologies, under high-temperature service environments, brazing processes are prone to issues such as unstable melt flow, low interfacial bonding strength, and poor joint mechanical properties. To improve performance, the industry often adds single metal or ceramic particles, but this results in problems such as uneven powder dispersion and poor interfacial compatibility. This not only fails to achieve synergistic strengthening but also reduces the formability of the brazing filler metal and welding stability. Therefore, this invention provides a silver-based brazing sheet and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to provide a silver-based brazing sheet and its preparation method. The silver-based brazing sheet prepared by this invention not only has good high-temperature strength properties, but also good creep resistance, effectively improving the performance of the silver-based brazing sheet.

[0005] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, a silver-based solder sheet comprises the following raw materials in parts by weight: 50-60 parts silver powder, 20-30 parts copper powder, 15-20 parts zinc powder, 8-10 parts tin powder, 6-8 parts additive A and 3-5 parts additive B. The raw materials for additive A include composite powder, modified zirconium boride powder, and cerium nitrate aqueous solution; The raw materials for additive B include composite metal powder, terpineol, and sodium dodecyl sulfate.

[0006] Further, the additive A is prepared by the following method: the composite powder, modified zirconium boride powder and cerium nitrate aqueous solution are mixed at a mass ratio of 1:(0.3-0.5):(3-4), stirred at 300-500 rpm for 40-60 min, silane coupling agent KH-550 is added, and stirring is continued for 20-30 min to obtain a mixed solution. The mixed solution is spray-dried, with the inlet air temperature set at 160-200℃ and the outlet air temperature at 80-100℃ to obtain a dried product. The dried product is then transferred to a grinder and ground to a particle size of 15-20 μm to obtain additive A. The mass concentration of the cerium nitrate aqueous solution is 3-5%, and the mass of the silane coupling agent KH-550 is 1.5-2% of the mass of the composite powder.

[0007] Further, the composite powder is prepared by the following method: ceramic fiber powder and silicon carbide micro powder are mixed at a mass ratio of (3-5):1, placed in a ball mill jar, and ball-milled at a speed of 300-400 rpm for 3-4 hours. A 30-50% aluminum dihydrogen phosphate aqueous solution is added, and ball milling continues for 40-60 minutes to obtain an intermediate product. The intermediate product is placed in a mold and pressed into blocks under a pressure of 15-20 MPa. Then, it is transferred to a furnace at 500-600℃ for sintering for 2-3 hours, cooled, pulverized, and passed through a 200-mesh sieve to obtain the composite powder. The mass of the aluminum dihydrogen phosphate aqueous solution is 8-10% of the total mass of the ceramic fiber powder and silicon carbide micro powder.

[0008] Further, the modified zirconium boride powder is prepared by the following method: dimethylformamide, polyvinylpyrrolidone and deionized water are mixed at a volume ratio of (4-6):1:20 and stirred at 300-500 rpm for 20-30 min at 40-50℃ to obtain a first mixture, which is set aside. The zirconium boride powder is mixed with the first mixture at a mass ratio of 1:(1.5-2.5) and stirred at 300-500 rpm for 30-45 min at room temperature. The mixture is then filtered, and the filter cake is dried at 80-90℃ for 2 h to obtain the modified zirconium boride powder.

[0009] Further, the additive B is prepared by the following method: the composite metal powder and terpineol are mixed at a mass ratio of 1:(2-3), stirred at 200-300 rpm for 20-30 min, sodium dodecyl sulfate is added, and stirring is continued for 15-20 min. The mixture is then centrifuged, the precipitate is collected, dried at 60-80℃ for 8-12 h, and pulverized through a 200-mesh sieve to obtain additive B.

[0010] Further, the composite metal powder is prepared by the following method: nano-nickel powder and nano-cobalt powder are mixed at a mass ratio of (3-4):1, anhydrous ethanol is added, and the mixture is ultrasonically dispersed for 30-40 min to obtain a mixed suspension. Polyvinylpyrrolidone is added to the mixed suspension, and the mixture is ultrasonically dispersed for 15-20 min to obtain a dispersion. The dispersion is centrifuged to separate the precipitate, and the precipitate is washed 2-3 times with anhydrous ethanol and then dried at 50-60℃ for 5-8 h to obtain the composite metal powder.

[0011] Furthermore, the mass of the polyvinylpyrrolidone is 3-4% of the total mass of the nano-nickel powder and nano-cobalt powder.

[0012] Furthermore, the mass of the sodium dodecyl sulfate is 2-3% of the mass of the composite metal powder.

[0013] Furthermore, the zirconium boride powder has a particle size of 35-65 nm.

[0014] Secondly, the present invention provides a method for preparing a silver-based brazing sheet, comprising the following steps: Step 1: Add silver powder, copper powder, zinc powder, tin powder, additive A and additive B into a V-type mixer and mix for 3-4 hours to obtain a premix. Step 2: Transfer the premixed material into the melting furnace, add the rare earth element cerium, heat to 850-950℃ under a protective atmosphere, and hold for 20-30 minutes after it is completely melted to obtain molten alloy liquid; Step 3: Hold the molten alloy liquid at 700-750℃ for 40-60 minutes, then pour the molten alloy liquid into a mold, and then cool it to room temperature at a cooling rate of 20-30℃ / min. After cooling, the alloy ingot is obtained. Step 4: The alloy ingot is subjected to multiple cold rolling passes, during which a high-frequency pulsed current is applied, with a current density of 500-5000 A / cm². 2 The material is rolled into a sheet with a thickness of 0.3-0.5 mm, and then ultrasonically cleaned in an ethanol solution for 15-20 minutes. After being removed, it is rinsed with deionized water and then dried with hot air at 50-60℃ to obtain a brazed sheet. Step 5: Use magnetron sputtering to pre-deposit a metal overcoat on the surface of the brazing sheet. The overcoat material is germanium, and the coating thickness is controlled to be 150-200nm to obtain the coated brazing sheet. Step 6: Perform vacuum low-temperature diffusion annealing on the plated brazed sheet at a temperature of 300-400℃ for 3-4 hours, and then cool it to room temperature in the furnace to obtain the silver-based brazed sheet.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. In this invention, additive A is prepared by synergistically combining composite powder and modified zirconium boride powder with cerium nitrate aqueous solution. The composite powder is formed by ball milling, pressing and sintering ceramic fiber powder and silicon carbide micro powder to form a stable skeleton structure, which effectively improves the high temperature strength and creep resistance of the brazed sheet. The modified zirconium boride powder is uniformly dispersed after dispersion modification, which can refine the brazing alloy grains and optimize the interfacial bonding force. Combined with silane coupling agent modification and spray drying process, the compatibility of each component is improved, and it plays a stable role in the brazing process, effectively improving the mechanical properties of the brazed sheet.

[0016] 2. In this invention, nano-nickel-cobalt composite metal powder is used as the core to prepare additive B. The nano-nickel powder and cobalt powder are ultrasonically dispersed and stabilized with polyvinylpyrrolidone, resulting in high dispersibility and strong activity, which can improve the flowability and oxidation resistance of the brazing filler metal. Terpineol and sodium dodecyl sulfate work synergistically to improve the dispersion stability and formability of the composite metal powder and avoid powder agglomeration. After centrifugation, drying and pulverization, additive B is uniformly mixed with the silver-copper-zinc-tin matrix and exists stably during smelting and rolling, optimizing the microstructure of the brazed sheet, reducing brazing defects and improving the corrosion resistance of the brazed joint.

[0017] 3. In this invention, a composite strengthening method of adding trace amounts of rare earth cerium and high-frequency pulsed current-assisted rolling is adopted in the preparation process. The trace amounts of rare earth can purify the grain boundaries and refine the alloy structure. The pulsed current controls the grain orientation and internal stress in real time during cold rolling, improving the density and surface flatness of the brazed sheet, and solving the problems of easy cracking and uneven structure in traditional rolling. At the same time, through magnetron sputtering pre-plating of an ultra-thin germanium metal overcoat and vacuum low-temperature diffusion annealing, the overcoat significantly optimizes the wetting and bonding of the brazing filler metal and the base material interface. Low-temperature annealing eliminates internal stress without damaging the coating structure, further improving the joint strength and reliability. Attached Figure Description

[0018] Figure 1 The present invention provides a flowchart of a silver-based brazing sheet and its preparation method. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be noted that the raw materials used in the following embodiments are all commercially available.

[0021] Example 1: Preparation of composite powder: Ceramic fiber powder and silicon carbide micro powder are mixed at a mass ratio of 3:1 and placed in a ball mill jar. The mixture is ball-milled at 300 rpm for 3 hours. A 30% aluminum dihydrogen phosphate aqueous solution is added, and the mixture is ball-milled for another 40 minutes to obtain an intermediate product. The intermediate product is placed in a mold and pressed into blocks under a pressure of 15 MPa. The blocks are then sintered in a furnace at 500°C for 2 hours. After cooling, the blocks are pulverized and passed through a 200-mesh sieve to obtain the composite powder. The mass of the aluminum dihydrogen phosphate aqueous solution is 8% of the total mass of the ceramic fiber powder and silicon carbide micro powder.

[0022] Preparation of modified zirconium boride powder: Dimethylformamide, polyvinylpyrrolidone and deionized water were mixed at a volume ratio of 4:1:20 and stirred at 300 rpm for 20 min at 40 °C to obtain a first mixture, which was set aside. Zirconium boride powder was mixed with the first mixture at a mass ratio of 1:1.5 and stirred at 300 rpm for 30 min at room temperature. The mixture was filtered and the filter cake was dried at 80 °C for 2 h to obtain modified zirconium boride powder.

[0023] The zirconium boride powder has a particle size of 35 nm.

[0024] Preparation of Additive A: The composite powder, modified zirconium boride powder, and cerium nitrate aqueous solution were mixed at a mass ratio of 1:0.3:3 and stirred at 300 rpm for 40 min. Silane coupling agent KH-550 was added, and stirring was continued for 20 min to obtain a mixed solution. The mixed solution was then spray-dried at an inlet air temperature of 160℃ and an outlet air temperature of 80℃ to obtain a dried product. The dried product was then ground in a mill until the particle size was 15 μm to obtain Additive A. The mass concentration of the cerium nitrate aqueous solution was 3%, and the mass of silane coupling agent KH-550 was 1.5% of the mass of the composite powder.

[0025] Preparation of composite metal powder: Nano nickel powder and nano cobalt powder were mixed at a mass ratio of 3:1, anhydrous ethanol was added, and ultrasonic dispersion was carried out for 30 min to obtain a mixed suspension. Polyvinylpyrrolidone was added to the mixed suspension, and ultrasonic dispersion was carried out for 15 min to obtain a dispersion. The dispersion was centrifuged to separate the precipitate, and the precipitate was washed twice with anhydrous ethanol and then dried at 50℃ for 5 h to obtain composite metal powder.

[0026] The mass of the polyvinylpyrrolidone is 3% of the total mass of the nano-nickel powder and nano-cobalt powder.

[0027] Preparation of Additive B: The composite metal powder and terpineol were mixed at a mass ratio of 1:2 and stirred at 200 rpm for 20 min. Sodium dodecyl sulfate was added and stirred for another 15 min. The mixture was then centrifuged and the precipitate was collected. The precipitate was dried at 60℃ for 8 h and then pulverized through a 200-mesh sieve to obtain Additive B.

[0028] The mass of the sodium dodecyl sulfate is 2% of the mass of the composite metal powder.

[0029] Preparation of raw materials: 50 parts silver powder, 20 parts copper powder, 15 parts zinc powder, 8 parts tin powder, 6 parts additive A and 3 parts additive B.

[0030] Preparation of silver-based brazing sheets: Step 1: Add silver powder, copper powder, zinc powder, tin powder, additive A and additive B into a V-type mixer and mix for 3 hours to obtain a premix. Step 2: Transfer the premixed material into the melting furnace, add the rare earth element cerium, heat to 850°C under a protective atmosphere, and hold for 20 minutes after it has completely melted to obtain a molten alloy liquid. Step 3: Hold the molten alloy liquid at 700℃ for 40 minutes, then pour the molten alloy liquid into a mold, and then cool it to room temperature at a cooling rate of 20℃ / min. After cooling, the alloy ingot is obtained. Step 4: The alloy ingot is subjected to multiple cold rolling passes, during which a high-frequency pulsed current with a current density of 500 A / cm² is passed through it. 2 The film is rolled into a sheet with a thickness of 0.3 mm, and then ultrasonically cleaned in an ethanol solution for 15 min. After being taken out, it is rinsed with deionized water and then dried with hot air at 50°C to obtain a brazed sheet. Step 5: A metal overcoating layer is pre-plated on the surface of the brazing sheet using magnetron sputtering. The overcoating material is germanium, and the coating thickness is controlled to be 150nm, to obtain the coated brazing sheet. Step 6: Vacuum low-temperature diffusion annealing is performed on the plated brazed sheet at a temperature of 300℃ for 3 hours, followed by furnace cooling to room temperature to obtain the silver-based brazed sheet.

[0031] Example 2: Preparation of composite powder: Ceramic fiber powder and silicon carbide micro powder were mixed at a mass ratio of 4:1 and placed in a ball mill jar. The mixture was ball-milled at 350 rpm for 3.5 h. A 40% aluminum dihydrogen phosphate aqueous solution was added, and the mixture was ball-milled for another 50 min to obtain an intermediate product. The intermediate product was placed in a mold and pressed into blocks under a pressure of 15 MPa. The blocks were then sintered in a furnace at 550 °C for 2.5 h. After cooling, the blocks were pulverized and passed through a 200-mesh sieve to obtain the composite powder. The mass of the aluminum dihydrogen phosphate aqueous solution was 9% of the total mass of the ceramic fiber powder and silicon carbide micro powder.

[0032] Preparation of modified zirconium boride powder: Dimethylformamide, polyvinylpyrrolidone and deionized water were mixed at a volume ratio of 5:1:20 and stirred at 400 rpm for 25 min at 45 °C to obtain a first mixture, which was set aside. Zirconium boride powder was mixed with the first mixture at a mass ratio of 1:2 and stirred at 400 rpm for 35 min at room temperature. The mixture was filtered and the filter cake was dried at 85 °C for 2 h to obtain modified zirconium boride powder.

[0033] The zirconium boride powder has a particle size of 50 nm.

[0034] Preparation of Additive A: The composite powder, modified zirconium boride powder, and cerium nitrate aqueous solution were mixed at a mass ratio of 1:0.4:3.5 and stirred at 400 rpm for 50 min. Silane coupling agent KH-550 was added, and stirring was continued for 25 min to obtain a mixed solution. The mixed solution was then spray-dried at an inlet air temperature of 180℃ and an outlet air temperature of 90℃ to obtain a dried product. The dried product was then ground in a grinder to a particle size of 18 μm to obtain Additive A. The mass concentration of the cerium nitrate aqueous solution was 4%, and the mass of the silane coupling agent KH-550 was 1.8% of the mass of the composite powder.

[0035] Preparation of composite metal powder: Nano nickel powder and nano cobalt powder were mixed at a mass ratio of 3.5:1, anhydrous ethanol was added, and the mixture was ultrasonically dispersed for 35 min to obtain a mixed suspension. Polyvinylpyrrolidone was added to the mixed suspension, and the mixture was ultrasonically dispersed for 18 min to obtain a dispersion. The dispersion was centrifuged, the precipitate was collected, the precipitate was washed three times with anhydrous ethanol, and then dried at 55℃ for 6.5 h to obtain composite metal powder.

[0036] The mass of the polyvinylpyrrolidone is 3.5% of the total mass of the nano-nickel powder and nano-cobalt powder.

[0037] Preparation of Additive B: The composite metal powder and terpineol were mixed at a mass ratio of 1:2.5 and stirred at 250 rpm for 25 min. Sodium dodecyl sulfate was added and stirred for another 18 min. The mixture was then centrifuged and the precipitate was collected. The precipitate was dried at 70℃ for 10 h and then pulverized through a 200-mesh sieve to obtain Additive B.

[0038] The sodium dodecyl sulfate is 2.5% of the mass of the composite metal powder.

[0039] Raw material preparation: 55 parts silver powder, 25 parts copper powder, 18 parts zinc powder, 9 parts tin powder, 7 parts additive A and 4 parts additive B.

[0040] Preparation of silver-based brazing sheets: Step 1: Add silver powder, copper powder, zinc powder, tin powder, additive A and additive B to a V-type mixer and mix for 3.5 hours to obtain a premix. Step 2: Transfer the premixed material into the melting furnace, add the rare earth element cerium, heat to 900℃ under a protective atmosphere, and hold for 25 minutes after it is completely melted to obtain a molten alloy liquid. Step 3: Hold the molten alloy liquid at 730℃ for 50 minutes, then pour the molten alloy liquid into a mold, and then cool it to room temperature at a cooling rate of 25℃ / min. After cooling, the alloy ingot is obtained. Step 4: The alloy ingot is subjected to multiple cold rolling passes, during which a high-frequency pulsed current with a current density of 2000 A / cm² is passed through it. 2 The film is rolled into a sheet with a thickness of 0.4 mm, and then ultrasonically cleaned in an ethanol solution for 18 min. After being taken out, it is rinsed with deionized water and then dried with hot air at 55°C to obtain a brazed sheet. Step 5: A metal overcoating layer is pre-plated on the surface of the brazing sheet using magnetron sputtering. The overcoating material is germanium, and the coating thickness is controlled to be 180nm, to obtain the coated brazing sheet. Step 6: The plated brazed sheet is subjected to vacuum low-temperature diffusion annealing at a temperature of 350°C for 3.5 hours, and then cooled to room temperature in the furnace to obtain a silver-based brazed sheet.

[0041] Example 3: Preparation of composite powder: Ceramic fiber powder and silicon carbide micro powder are mixed at a mass ratio of 5:1 and placed in a ball mill jar. The mixture is ball-milled at 400 rpm for 4 hours. A 50% aluminum dihydrogen phosphate aqueous solution is added, and the mixture is ball-milled for another 60 minutes to obtain an intermediate product. The intermediate product is placed in a mold and pressed into blocks under a pressure of 20 MPa. The blocks are then sintered in a furnace at 600°C for 3 hours. After cooling, the blocks are pulverized and passed through a 200-mesh sieve to obtain the composite powder. The mass of the aluminum dihydrogen phosphate aqueous solution is 10% of the total mass of the ceramic fiber powder and silicon carbide micro powder.

[0042] Preparation of modified zirconium boride powder: Dimethylformamide, polyvinylpyrrolidone and deionized water were mixed at a volume ratio of 6:1:20 and stirred at 500 rpm for 30 min at 50 °C to obtain a first mixture, which was set aside. Zirconium boride powder was mixed with the first mixture at a mass ratio of 1:2.5 and stirred at 500 rpm for 45 min at room temperature. The mixture was filtered and the filter cake was dried at 90 °C for 2 h to obtain modified zirconium boride powder.

[0043] The zirconium boride powder has a particle size of 65 nm.

[0044] Preparation of Additive A: The composite powder, modified zirconium boride powder, and cerium nitrate aqueous solution were mixed at a mass ratio of 1:0.5:4 and stirred at 500 rpm for 60 min. Silane coupling agent KH-550 was added, and stirring was continued for another 30 min to obtain a mixed solution. The mixed solution was then spray-dried at an inlet air temperature of 200℃ and an outlet air temperature of 100℃ to obtain a dried product. The dried product was then ground in a mill until the particle size was 20 μm to obtain Additive A. The mass concentration of the cerium nitrate aqueous solution was 5%, and the mass of silane coupling agent KH-550 was 2% of the mass of the composite powder.

[0045] Preparation of composite metal powder: Nano nickel powder and nano cobalt powder were mixed at a mass ratio of 4:1, anhydrous ethanol was added, and the mixture was ultrasonically dispersed for 40 min to obtain a mixed suspension. Polyvinylpyrrolidone was added to the mixed suspension, and the mixture was ultrasonically dispersed for 20 min to obtain a dispersion. The dispersion was centrifuged, the precipitate was collected, the precipitate was washed three times with anhydrous ethanol, and then dried at 60℃ for 8 h to obtain composite metal powder.

[0046] The mass of the polyvinylpyrrolidone is 4% of the total mass of the nano-nickel powder and nano-cobalt powder.

[0047] Preparation of Additive B: The composite metal powder and terpineol were mixed at a mass ratio of 1:3 and stirred at 300 rpm for 30 min. Sodium dodecyl sulfate was added and stirred for another 20 min. The mixture was then centrifuged and the precipitate was collected. The precipitate was dried at 80℃ for 12 h and then pulverized through a 200-mesh sieve to obtain Additive B.

[0048] The mass of the sodium dodecyl sulfate is 3% of the mass of the composite metal powder.

[0049] Preparation of raw materials: 60 parts silver powder, 30 parts copper powder, 20 parts zinc powder, 10 parts tin powder, 8 parts additive A and 5 parts additive B.

[0050] Preparation of silver-based brazing sheets: Step 1: Add silver powder, copper powder, zinc powder, tin powder, additive A and additive B into a V-type mixer and mix for 4 hours to obtain a premix. Step 2: Transfer the premixed material into the melting furnace, add the rare earth element cerium, heat to 950°C under a protective atmosphere, and hold for 30 minutes after it has completely melted to obtain a molten alloy liquid; Step 3: Hold the molten alloy liquid at 750℃ for 60 minutes, then pour the molten alloy liquid into a mold, and then cool it to room temperature at a cooling rate of 30℃ / min. After cooling, the alloy ingot is obtained. Step 4: The alloy ingot is subjected to multiple cold rolling passes, during which a high-frequency pulsed current with a current density of 5000 A / cm² is passed through it. 2 The film is rolled into a sheet with a thickness of 0.5 mm, and then ultrasonically cleaned in an ethanol solution for 20 min. After being taken out, it is rinsed with deionized water and then dried with hot air at 60°C to obtain a brazed sheet. Step 5: A metal overcoating is pre-plated on the surface of the brazing sheet using magnetron sputtering. The overcoating material is germanium, and the coating thickness is controlled to be 200nm, to obtain the coated brazing sheet. Step 6: Vacuum low-temperature diffusion annealing is performed on the plated brazed sheet at a temperature of 400℃ for 4 hours, followed by furnace cooling to room temperature to obtain the silver-based brazed sheet.

[0051] Comparative Example 1: The difference between this comparative example and Example 1 is that this comparative example does not contain additive A.

[0052] Comparative Example 2 differs from Example 1 in that it does not contain additive B.

[0053] Comparative Example 3 differs from Example 1 in that the preparation steps in this comparative example do not employ high-frequency pulsed current assisted rolling, nor do they involve magnetron sputtering pre-plating of germanium overcoating and vacuum low-temperature diffusion annealing. Instead, conventional cold rolling and direct cleaning and drying processes are used.

[0054] Performance testing: The silver-based brazing sheets prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance testing, and the test data are recorded in the table below: Table 1 In performance testing, the high-temperature tensile strength was determined according to GB / T 228.2-2015, by testing the high-temperature tensile strength of the brazed sheet at 500℃ to evaluate its high-temperature mechanical properties. The elongation after creep rupture was determined according to GB / T... 2039-2024: The specimen is subjected to a constant tensile stress of 50 MPa in a constant temperature environment of 400℃ for 100 hours. The creep strain of the specimen in the steady state stage is measured to evaluate its creep resistance. Determination of mass loss after corrosion: Referring to GB / T10125-2021, the brazed sheet specimens are processed into the same size, with a specimen size of 150 mm × 100 mm × 10 mm. The initial mass is weighed. The corrosion test is carried out according to the neutral salt spray test conditions, test temperature 35℃, sodium chloride solution mass concentration 5%, and continuous spraying for 48 hours. After the test, the corrosion products are removed according to the physical and chemical methods specified in GB / T16545. The mass of the specimen after corrosion is weighed, and the mass loss is calculated. The measured mass loss is divided by the exposed surface area of ​​the reference specimen to obtain the mass loss per unit area.

[0055] The data obtained from the performance tests show that the silver-based brazed sheets prepared in Examples 1-3 are significantly superior to those in Comparative Examples 1-3 in terms of high-temperature tensile strength, creep resistance, and corrosion resistance of the brazed joints. This indicates that additive A, through the synergistic effect of the composite powder and modified zirconium boride powder, constructs a stable skeletal reinforcement structure within the brazed sheet. The composite powder, formed by ball milling, pressing, and sintering ceramic fiber powder and silicon carbide micropowder, creates a rigid skeleton that effectively withstands tensile loads at high temperatures and hinders grain boundary slip, thereby improving high-temperature tensile strength. Simultaneously, the modified zirconium boride powder, after dispersion modification, is uniformly distributed within the matrix, playing a crucial role in... The grain refinement effect increases the number of grain boundaries, making creep deformation more difficult and thus enhancing creep resistance. In contrast, Comparative Example 1, which does not contain additive A, lacks this skeletal support and grain refinement effect in its brazed sheet. During high-temperature tensile testing, grain boundaries are prone to softening and slippage, resulting in a significant increase in elongation after creep fracture and a marked decrease in high-temperature strength. Furthermore, the cerium nitrate component in additive A optimizes the interfacial bonding force between phases, further reducing the performance degradation caused by interfacial weakening at high temperatures. Therefore, the absence of additive A makes Comparative Example 1 inferior to all other examples in terms of high-temperature mechanical properties.

[0056] Comparative Example 2, lacking additive B, exhibited significantly reduced corrosion resistance. Additive B, with nano-nickel-cobalt composite metal powder as its core, underwent ultrasonic dispersion and stabilization treatment with polyvinylpyrrolidone, achieving extremely high dispersibility and surface activity. During smelting and rolling, these nano-metal particles improved the fluidity and spreadability of the brazing filler metal, promoting full filling of the joint gap and effectively reducing microscopic defects such as porosity and inclusions. In contrast, Comparative Example 2, lacking additive B, had numerous microscopic defects inside its brazed joint, resulting in poor microstructure uniformity. During salt spray corrosion, corrosive media easily penetrated along defect channels, leading to rapid joint corrosion and a significant decrease in strength retention.

[0057] Furthermore, Comparative Example 3 did not employ high-frequency pulsed current-assisted rolling in its preparation process, nor did it undergo magnetron sputtering pre-plating of germanium overcoat or vacuum low-temperature diffusion annealing. Test data showed that all three performance indicators of Comparative Example 3 were significantly reduced, especially the high-temperature tensile strength and creep resistance. This is because the trace rare earth cerium element introduced in the preparation process of this invention can purify the alloy grain boundaries and refine the microstructure. However, without the synergistic effect of the subsequent high-frequency pulsed current, the internal stress accumulated during rolling cannot be controlled in real time, making it difficult to optimize grain orientation. This can easily lead to cracking and uneven microstructure in the sheet. The electroplastic effect generated by the pulsed current during cold rolling reduces the deformation resistance and effectively eliminates internal stress, improving the density and surface smoothness of the brazed sheet. The germanium metal overcoat pre-plated by magnetron sputtering, after vacuum low-temperature diffusion annealing, can form a metallurgical bond with the base material, improving the wettability of the brazing filler metal and the interface to be welded.

[0058] By comparing and analyzing the relevant data in the table, it can be seen that the silver-based brazing sheet prepared by this invention not only has good high-temperature strength properties but also good creep resistance. This indicates that the silver-based brazing sheet provided by this invention has a broader market prospect and is more suitable for widespread application.

[0059] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0060] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A silver-based brazing sheet, characterized in that, The raw materials include the following parts by weight: 50-60 parts silver powder, 20-30 parts copper powder, 15-20 parts zinc powder, 8-10 parts tin powder, 6-8 parts additive A and 3-5 parts additive B; The raw materials for additive A include composite powder, modified zirconium boride powder, and cerium nitrate aqueous solution; The raw materials for additive B include composite metal powder, terpineol, and sodium dodecyl sulfate.

2. The silver-based brazing sheet according to claim 1, characterized in that, Additive A is prepared by the following method: composite powder, modified zirconium boride powder and cerium nitrate aqueous solution are mixed at a mass ratio of 1:(0.3-0.5):(3-4), stirred at 300-500 rpm for 40-60 min, silane coupling agent KH-550 is added, and stirring is continued for 20-30 min to obtain a mixed solution. The mixed solution is spray-dried, with the inlet air temperature set at 160-200℃ and the outlet air temperature at 80-100℃ to obtain a dried product. The dried product is then transferred to a grinder and ground to a particle size of 15-20 μm to obtain additive A. The mass concentration of the cerium nitrate aqueous solution is 3-5%, and the mass of the silane coupling agent KH-550 is 1.5-2% of the mass of the composite powder.

3. The silver-based brazing sheet according to claim 2, characterized in that, The composite powder is prepared by the following method: ceramic fiber powder and silicon carbide micro powder are mixed at a mass ratio of (3-5):1, placed in a ball mill jar, and ball-milled at a speed of 300-400 rpm for 3-4 hours. A 30-50% aluminum dihydrogen phosphate aqueous solution is added, and ball milling continues for 40-60 minutes to obtain an intermediate product. The intermediate product is placed in a mold and pressed into blocks under a pressure of 15-20 MPa. Then, it is transferred to a furnace at 500-600℃ for sintering for 2-3 hours, cooled, pulverized, and passed through a 200-mesh sieve to obtain the composite powder. The mass of the aluminum dihydrogen phosphate aqueous solution is 8-10% of the total mass of the ceramic fiber powder and silicon carbide micro powder.

4. The silver-based brazing sheet according to claim 2, characterized in that, The modified zirconium boride powder is prepared by the following method: dimethylformamide, polyvinylpyrrolidone and deionized water are mixed at a volume ratio of (4-6):1:20 and stirred at 300-500 rpm for 20-30 min at 40-50℃ to obtain a first mixture, which is set aside. The zirconium boride powder is mixed with the first mixture at a mass ratio of 1:(1.5-2.5) and stirred at 300-500 rpm for 30-45 min at room temperature. The mixture is then filtered, and the filter cake is dried at 80-90℃ for 2 h to obtain the modified zirconium boride powder.

5. The silver-based brazing sheet according to claim 1, characterized in that, Additive B is prepared by the following method: composite metal powder and terpineol are mixed at a mass ratio of 1:(2-3), stirred at 200-300 rpm for 20-30 min, sodium dodecyl sulfate is added, and stirring is continued for 15-20 min. The mixture is then centrifuged, the precipitate is collected, dried at 60-80℃ for 8-12 h, and pulverized through a 200-mesh sieve to obtain additive B.

6. The silver-based brazing sheet according to claim 5, characterized in that, The composite metal powder is prepared by the following method: nano-nickel powder and nano-cobalt powder are mixed at a mass ratio of (3-4):1, anhydrous ethanol is added, and the mixture is ultrasonically dispersed for 30-40 min to obtain a mixed suspension. Polyvinylpyrrolidone is added to the mixed suspension, and the mixture is ultrasonically dispersed for 15-20 min to obtain a dispersion. The dispersion is centrifuged to separate the precipitate, and the precipitate is washed 2-3 times with anhydrous ethanol and then dried at 50-60℃ for 5-8 h to obtain the composite metal powder.

7. The silver-based brazing sheet according to claim 6, characterized in that, The mass of the polyvinylpyrrolidone is 3-4% of the total mass of the nano-nickel powder and nano-cobalt powder.

8. The method for preparing a silver-based brazing sheet according to claim 5, characterized in that, The mass of the sodium dodecyl sulfate is 2-3% of the mass of the composite metal powder.

9. The method for preparing a silver-based brazing sheet according to claim 4, characterized in that, The zirconium boride powder has a particle size of 35-65 nm.

10. The method for preparing a silver-based brazing sheet according to any one of claims 1-9, characterized in that, Includes the following steps: Step 1: Add silver powder, copper powder, zinc powder, tin powder, additive A and additive B into a V-type mixer and mix for 3-4 hours to obtain a premix. Step 2: Transfer the premixed material into the melting furnace, add the rare earth element cerium, heat to 850-950℃ under a protective atmosphere, and hold for 20-30 minutes after it is completely melted to obtain molten alloy liquid; Step 3: Hold the molten alloy liquid at 700-750℃ for 40-60 minutes, then pour the molten alloy liquid into a mold, and then cool it to room temperature at a cooling rate of 20-30℃ / min. After cooling, the alloy ingot is obtained. Step 4: The alloy ingot is subjected to multiple cold rolling passes, during which a high-frequency pulsed current is applied, with a current density of 500-5000 A / cm². 2 The material is rolled into a sheet with a thickness of 0.3-0.5 mm, and then ultrasonically cleaned in an ethanol solution for 15-20 minutes. After being removed, it is rinsed with deionized water and then dried with hot air at 50-60℃ to obtain a brazed sheet. Step 5: Use magnetron sputtering to pre-deposit a metal overcoat on the surface of the brazing sheet. The overcoat material is germanium, and the coating thickness is controlled to be 150-200nm to obtain the coated brazing sheet. Step 6: Perform vacuum low-temperature diffusion annealing on the plated brazed sheet at a temperature of 300-400℃ for 3-4 hours, and then cool it to room temperature in the furnace to obtain the silver-based brazed sheet.

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