High-strength high-corrosion-resistance low-silver brazing filler metal

Abstract

The invention belongs to the field of welding materials, and particularly relates to high-strength high-corrosion-resistance low-silver brazing filler metal. The chemical components comprise, by mass, 10%-20% of Ag, 30%-50% of Cu, 0.5%-6% of Sn, 2%-3% of Ga, 2%-3% of In, 1%-5% of Ni, 0.05%-0.1% of Si3N4 nanoparticles and the balance Zn. Ga, In, Ni and Si3N4 nanoparticles are cooperatively added, so that the strength and corrosion resistance of the brazing filler metal are remarkably improved while the low silver content is guaranteed.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of welding materials, and particularly relates to a high-strength high-corrosion-resistance low-silver brazing filler metal. BACKGROUND

[0002] Silver brazing filler metal can form reliable metallurgical bonding with copper, stainless steel and other base materials due to its moderate melting point, excellent wettability, good electrical conductivity and excellent mechanical properties, and the obtained welded joint can meet the use requirements in various service environments and is widely used in precision welding in the fields of microelectronics, refrigeration appliances, new energy vehicles, aerospace devices and the like.

[0003] At present, the silver content of silver brazing filler metal used in domestic industrial production is usually 30% to 70%, and the total annual demand exceeds 8000 tons according to incomplete statistics. However, China is poor in silver resources, and silver as an important strategic raw material in silver brazing filler metal is easily affected by international political situation. In the first half of 2025, the price rose by as high as 36%, significantly higher than the 25% increase in the price of gold during the same period.

[0004] Reducing the silver content in silver brazing filler metal is a common practice to reduce the cost of expensive silver raw materials, but the problems such as reduced weld strength, poor corrosion resistance and poor processing performance that follow make the unqualified rate of welded products rise, causing resource waste. In order to improve the performance of low-silver brazing filler metal, methods such as adding trace amounts of rare earth elements or adjusting the Cu / Zn ratio are usually used. However, the amount of rare earth elements is difficult to control accurately, and excessive addition may form brittle phases, which in turn damage the performance. Simply adjusting the Cu / Zn ratio has limited effect on the improvement of strength and corrosion resistance, and may worsen the processing performance.

[0005] Patent CN112108790A discloses a cadmium-free low-silver brazing filler metal and a preparation method thereof. The cadmium-free low-silver brazing filler metal is composed of Ag, Cu, Zn, In, Sn, Ni and trace element R, and the weight percentages of the components are as follows: 13.5-20wt.% of Ag, 40-48wt.% of Cu, 1-3wt.% of In, 1-3wt.% of Sn, 0.1-1.0wt.% of Ni, and 0.001-0.2wt.% of trace element R, which is composed of one or more of lanthanum, cerium, silicon, antimony, zirconium and yttrium, and the balance is Zn. The invention solves the problems of insufficient silver content and difficult control of trace element addition in low-silver brazing filler metal, realizes low melting point and high processing performance of the cadmium-free low-silver brazing filler metal, and is suitable for brazing red copper, brass and stainless steel, meeting the high strength and environmental protection requirements of equipment such as four-way valves.

[0006] However, the current manufacturing industry is highly competitive and faces dual pressure of improving product performance and reducing manufacturing cost. Therefore, it is urgent to develop a new type of brazing filler metal with high strength, high corrosion resistance and low silver content. SUMMARY

[0007] The present application provides a high-strength and high-corrosion-resistance low-silver brazing filler metal with high strength and good corrosion resistance, which can be widely used in automatic or semi-automatic welding of laser welding, flame brazing, vacuum welding and composite heat source welding methods. Under the premise of maintaining low silver content, the synergistic effect of specific components Ga, In, Ni and Si3N4 in specific component ratio significantly improves the comprehensive mechanical properties and processing performance of the welding wire, and at the same time improves the shear strength and corrosion resistance of the welded joint.

[0008] The object of the present application can be achieved by the following technical measures: A high-strength and high-corrosion-resistance low-silver brazing filler metal, the chemical composition of which is as follows: 10-20% of Ag, 30-50% of Cu, 0.5-6% of Sn, 2-3% of Ga, 2-3% of In, 1-5% of Ni, 0.05-0.1% of Si3N4 nanoparticles, and the balance of Zn.

[0009] Further, in order to control the solid solution amount of Ni in CuZn compound, the Ni accounts for 1.3-7.7% of the sum of the mass of Cu and Zn.

[0010] Further, the total mass fraction of Ga and In is 4.5-5.5%.

[0011] Further, the Si3N4 is a nanoparticle with an average particle size of 100-300 nm, and the Si3N4 accounts for 1-2% of the sum of the mass of Ga and In.

[0012] The preparation method of the present application is as follows: Commercially available high-purity metal Ag ingot, electrolytic Cu plate, Zn ingot, Sn ingot, Ga metal block, In metal block, Ni particles and nano-sized Si3N4 particles are used, and conventional Ag-based smelting method is used in a medium frequency furnace for smelting. During the smelting process, the Ag ingot and the electrolytic Cu plate are first placed in the crucible, and the covering agent is added to prevent oxidation and evaporation loss of the metal, and the frequency of the medium frequency furnace is controlled at 35-45 kW, and then the required metal and Si3N4 nanoparticles are sequentially added, and the ingot blank is obtained after stirring, refining, ultrasonic melt breaking treatment, standing, slagging and casting. By annealing, peeling, extruding, pickling, polishing and coiling, a coiled high-strength and high-corrosion-resistance low-silver brazing filler metal with a diameter of 0.8-2.0 mm is obtained; or by annealing, straightening, strip making, pickling and polishing, a straight strip high-strength and high-corrosion-resistance low-silver brazing filler metal with a diameter of 1.6-3.2 mm is obtained.

[0013] Further, the covering agent is a mixture of charcoal and borax.

[0014] The mechanism of each element in the brazing filler metal is as follows: (1) Ag (10%~20%), as a basic element, ensures good wettability and spreadability of the brazing filler metal, reduces the melting point of the brazing filler metal, improves the welding performance, and a lower content is also a key element for controlling the production cost.

[0015] (2) Cu (30%~50%), as a main constituent element, ensures good compatibility of the brazing filler metal with copper, stainless steel and other base materials, avoids the formation of brittle intermetallic compounds, and helps to improve the elongation and processing performance.

[0016] (3) Zn (balance), as an effective melting element, forms CuZn compounds to participate in solid solution strengthening, reduces the surface tension of the brazing filler metal melt and improves the flowability, and enhances the affinity with Fe, Co and Ni elements.

[0017] (4) Sn (0.5%~6%), which can reduce the solid-liquid phase line temperature of the silver brazing filler metal, reduce the brazing temperature, prevent the excessive growth of the heat-affected zone base material grains, and at the same time, dissolve in copper to improve the weld strength.

[0018] (5) Ga (2%~3%) and In (2%~3%), both of which have a melting point much lower than the main constituent elements, and appropriate addition can significantly reduce the solid-liquid phase line temperature of the brazing filler metal, greatly improve its wettability and spreadability on copper, stainless steel and other base materials, fill small capillary gaps, cooperate with Ag and Sn, further widen the welding temperature range, and optimize the process. However, excessive Ga or In is easy to form brittle CuGa2 and Cu4In phases, which reduces the mechanical properties of the brazed joint, so the total amount of the two should be controlled.

[0019] (6) Ni (1%~5%), the preferred content design is one of the innovations in the present application, as a core strengthening and corrosion-resistant element, it also ensures good processing performance. Specifically, Ni can form a substitutional solid solution with Cu and inhibit grain growth to refine the structure of the brazing filler metal and the weld, thereby improving the strength and toughness; Ni has a high electrode potential, which can increase the open circuit potential of the brazing filler metal, reduce its electrochemical corrosion tendency, promote the formation of a dense and stable passivation film on the surface, and inhibit the selective dissolution of Zn and the overall pitting phenomenon of the solder and the weld in a high-salt environment; in addition, Ni has good compatibility with Cu and Fe, which reduces the interfacial tension between the brazing filler metal and copper, stainless steel and other base materials, thereby improving the wettability and spreadability of the brazing filler metal on the surface of copper or stainless steel, and improving the reliability of copper / copper, copper / stainless steel and stainless steel / stainless steel welding. Excessive Ni will significantly deteriorate the processing plasticity of the silver brazing filler metal, leading to difficulty in drawing into wire. Therefore, the suitable mass ratio of Ni to Cu / Zn is determined through exploration and research, thereby ensuring the good drawing formability of the brazing filler metal.

[0020] (7) Si3N4 nanoparticles (0.01%~0.05%) are another key innovation point in the present application, which are used as heterogeneous nucleation and grain refinement agent in the solidification process of the brazing filler metal. Specifically, the high melting point and high stability nano-sized Si3N4 particles are introduced as non-spontaneous nucleation core in the solidification of the silver brazing filler metal and brazing process, which significantly increases the nucleation rate, thereby greatly refining the microstructure of the brazing filler metal and the weld; since Si3N4 does not chemically react in the smelting process of the silver brazing filler metal, the dispersed nanoparticles preferentially precipitate at the grain boundaries, play a pinning strengthening role, and also can inhibit the growth of the grains during the welding thermal cycle, obtaining a uniform and fine equiaxed crystal structure. However, excessive Si3N4 will be enriched with CuGa2 and Cu4In at the grain boundaries, resulting in the appearance of large particle compound phases in the microstructure, which makes the fracture morphology of the brazing filler metal and the brazing seam change from ductile fracture to cleavage fracture, and deteriorates the mechanical properties. Therefore, the addition amount of Si3N4 nanoparticles and Ga and In needs to be strictly controlled.

[0021] Compared with the prior art, the present application has the following beneficial effects: (1) Synergistic improvement of strength and plasticity By introducing the Ni element to form a solid solution and creatively adding Si3N4 nanoparticles as a grain refinement agent, a multiple synergistic strengthening mechanism of "Ni solid solution strengthening + Si3N4 pinning strengthening + fine grain strengthening" is constructed. This mechanism not only realizes the tensile strength ≥580MPa, but also keeps the elongation at more than 15%, effectively improving the extrusion difficulty and wire breakage problem of traditional silver brazing filler metal in the processing process, and improving the production efficiency.

[0022] (2) Reduction of brazing temperature and optimization of joint performance By adding Ga and In together, the solidus and liquidus temperatures of the low-silver brazing filler metal are controlled within 750℃ and 810℃, respectively. In various automatic or semi-automatic welding processes such as laser welding, flame brazing, vacuum welding and composite heat source, the brazing temperature can be stably controlled below 850℃, which effectively inhibits the grain coarsening of the base material in the joint area. The mechanical properties of the copper / copper and copper / stainless steel joints are better than those of the copper base material, and the shear strength of the stainless steel / stainless steel joint can reach more than 350MPa, showing excellent reliability.

[0023] (3) Significant enhancement of electrochemical corrosion resistance The synergistic effect of Ga-In-Ni ternary component system fundamentally improves the electrochemical properties of the brazing filler metal. The preferred content of Ni solid-solved in CuZn compound is beneficial to inhibit the preferential dissolution of Zn, and Si3N4 nanoparticles refine the grains while reducing the microelectrochemical heterogeneity, and the combined effect of the two reduces the electrochemical corrosion tendency of low-silver brazing filler metal, improves and ensures that the welding wire and weld have higher electrochemical corrosion resistance, and the brazing filler metal has significantly enhanced resistance to chloride ion pitting corrosion, thereby prolonging the service life of the welded components in harsh environments. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Electron micrograph of Example 3; Figure 2 Electron micrograph of Comparative Example 3. DETAILED DESCRIPTION

[0025] The present application can be further understood by the specific examples of the present application and the comparative examples given below. However, they are not a limitation of the present application.

[0026] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application can be purchased through commercial channels.

[0027] Main raw materials: commercially available high-purity Ag ingots (GB / T 39810-2021), electrolytic Cu plates (GB 30080-2025), Zn ingots (GB / T 470-2008), Sn ingots (GB / T 728-2020), Ga metal blocks (GB / T 10118-2023), In metal blocks (YS / T257-2009), and Ni particles (GB / T 26016-2021), Si3N4 nanoparticles (GB / T 34216-2017) that meet national standards.

[0028] The performance of the brazing filler metal and the welded joint was tested according to the following standards: mechanical properties of the brazing filler metal: GB / T 228.1-2021; electrochemical properties of the brazing filler metal: GB / T 24196-2009; wettability of the brazing filler metal: GB / T 11364-2008; strength of the brazing seam: GB / T 11363-2008; salt spray test: GB / T 10125-2021.

[0029] Example One A high-strength and high-corrosion-resistant low-silver brazing filler metal, the chemical composition of which is as follows: 10.0% Ag, 47.3% Cu, 0.5% Sn, 2% Ga, 3% In, 1.1% Ni, 0.05% Si3N4 nanoparticles, and the balance being Zn.

[0030] Based on the test results of 5 test pieces, the welding wire has excellent processability, the tensile strength is 590 MPa, the elongation is 18.3%, the spreading areas on red copper and 316L stainless steel are 318 mm 2 and 291 mm 2 respectively, and the self-corrosion potential of the welding spot reaches -0.183V (vs. SCE).

[0031] The vacuum brazing method is adopted, the brazing temperature is set to 845℃, and the filler material with a diameter of 2mm is used to weld the red copper / red copper lap test plate, the red copper / 316L stainless steel lap test plate and the 316L stainless steel / 316L stainless steel lap test plate with a thickness of 5mm respectively. The red copper / red copper and red copper / 316L stainless steel lap test plates are broken on the side of the red copper base material, and the shear strength of the 316L stainless steel / 316L stainless steel lap test plate is 363MPa.

[0032] After all the test pieces are subjected to salt spray corrosion for 720 hours, no obvious rust is observed.

[0033] The electrochemical performance test is carried out in a 3.5wt.% NaCl simulated seawater solution at room temperature, the test piece is placed at an open circuit potential for 1 hour to ensure that the surface reaches an electrochemical steady state, the polarization curve proves that the self-corrosion potential is increased from -0.25V (vs. SCE) to above 0.2V (vs. SCE), the corrosion rate is reduced by 60%, and the resistance to chloride ion pitting corrosion is significantly improved.

[0034] Example Two A high-strength and high-corrosion-resistant low-silver filler material, the chemical composition of which is as follows in terms of mass percentage: 12% of Ag, 43.6% of Cu, 1.2% of Sn, 3% of Ga, 2% of In, 1.5% of Ni, 0.07% of Si3N4 nanoparticles, and the balance of Zn.

[0035] Based on the test results of 5 test pieces, the welding wire has excellent processability, the tensile strength is 603MPa, the elongation is 19.5%, the spreading areas on red copper and 316L stainless steel are 326 mm 2 and 299 mm 2 respectively, and the self-corrosion potential of the welding spot reaches -0.176V (vs. SCE).

[0036] The vacuum brazing method is adopted, the brazing temperature is set to 840℃, and the filler material with a diameter of 2mm is used to weld the red copper / red copper lap test plate, the red copper / 316L stainless steel lap test plate and the 316L stainless steel / 316L stainless steel lap test plate with a thickness of 5mm respectively. The red copper / red copper and red copper / 316L stainless steel lap test plates are broken on the side of the red copper base material, and the shear strength of the 316L stainless steel / 316L stainless steel lap test plate is 384MPa.

[0037] All the test pieces have no obvious rust after salt spray corrosion for 720 hours.

[0038] Example Three A high-strength and high-corrosion-resistance low-silver solder with a chemical composition in terms of mass percentage of 15% of Ag, 41.3% of Cu, 1.8% of Sn, 2.5% of Ga, 3% of In, 2% of Ni, 0.08% of Si3N4 nanoparticles, and the balance of Zn.

[0039] Based on the test results of 5 test pieces, the welding wire has excellent processability, the tensile strength is 628 MPa, the elongation is 25.9%, the spreading areas on red copper and 316L stainless steel are 335 mm 2 and 303 mm, and the self-corrosion potential of the welding spot reaches -0.171 V (vs. SCE).

[0040] The vacuum brazing method is adopted, the brazing temperature is set to 840 ℃, and the solder with a diameter of 2 mm is used to weld the red copper / red copper lap test plate, the red copper / 316L stainless steel lap test plate and the 316L stainless steel / 316L stainless steel lap test plate with a thickness of 5 mm. The red copper / red copper and red copper / 316L stainless steel lap test plates are broken at the side of the red copper base material, and the shear strength of the 316L stainless steel / 316L stainless steel lap test plate is 392 MPa.

[0041] All the test pieces have no obvious rust after salt spray corrosion for 720 hours.

[0042] Example Four A high-strength and high-corrosion-resistance low-silver solder with a chemical composition in terms of mass percentage of 18% of Ag, 39.7% of Cu, 3% of Sn, 3% of Ga, 2.5% of In, 3.2% of Ni, 0.08% of Si3N4 nanoparticles, and the balance of Zn.

[0043] Based on the test results of 5 test pieces, the welding wire has excellent processability, the tensile strength is 646 MPa, the elongation is 21.3%, the spreading areas on red copper and 316L stainless steel are 344 mm 2 and 312 mm 2 , and the self-corrosion potential of the welding spot reaches -0.166 V (vs. SCE).

[0044] The vacuum brazing method is adopted, the brazing temperature is set to 830 ℃, and the solder with a diameter of 2 mm is used to weld the red copper / red copper test plate, the red copper / 316L stainless steel test plate and the 316L stainless steel / 316L stainless steel test plate with a thickness of 5 mm. The red copper / red copper and red copper / 316L stainless steel test plates are broken at the side of the red copper base material, and the shear strength of the 316L stainless steel / 316L stainless steel test plate is 381 MPa.

[0045] No obvious rust was observed in any of the test specimens after 720 hours of salt spray corrosion.

[0046] Example 5 A high-strength, high-corrosion-resistant, low-silver brazing filler metal has the following chemical composition by mass percentage: 20% Ag, 38.2% Cu, 5% Sn, 3% Ga, 2% In, 5.0% Ni, 0.1% Si3N4 nanoparticles, with the balance being Zn.

[0047] Based on the test results of 5 specimens, the welding wire exhibits excellent processing performance, with a tensile strength of 622 MPa, an elongation of 20.8%, and a spreading area of ​​352 mm² on both copper and 316L stainless steel. 2 and 324mm 2 The self-corrosion potential of the solder joint reaches -0.173V (vs. SCE).

[0048] Vacuum brazing was used at a temperature of 830℃. Using 2mm diameter brazing filler metal, 5mm thick copper / copper lap joint test plates, copper / 316L stainless steel lap joint test plates, and 316L stainless steel / 316L stainless steel lap joint test plates were welded. Both the copper / copper and copper / 316L stainless steel lap joint test plates broke on the copper base material side. The shear strength of the 316L stainless steel / 316L stainless steel lap joint test plate was 359MPa.

[0049] No obvious rust was observed in any of the test specimens after 720 hours of salt spray corrosion.

[0050] Example 6 A high-strength, high-corrosion-resistant, low-silver brazing filler metal has the following chemical composition by mass percentage: 13% Ag, 30% Cu, 6% Sn, 2.5% Ga, 2.5% In, 1% Ni, 0.1% Si3N4 nanoparticles, with the balance being Zn.

[0051] Based on the test results of 5 specimens, the welding wire exhibits excellent processing performance, with a tensile strength of 613 MPa, an elongation of 22.6%, and a spreading area of ​​331 mm² on both copper and 316L stainless steel. 2 and 302mm 2 The self-corrosion potential of the solder joint reaches -0.179V (vs. SCE).

[0052] Vacuum brazing was used at a temperature of 845℃. Using 2mm diameter brazing filler metal, 5mm thick copper / copper lap joint test plates, copper / 316L stainless steel lap joint test plates, and 316L stainless steel / 316L stainless steel lap joint test plates were welded. Both the copper / copper and copper / 316L stainless steel lap joint test plates broke on the copper base material side. The 316L stainless steel / 316L stainless steel lap joint test plate had a shear strength of 377MPa.

[0053] All the test pieces have no obvious rust after salt spray corrosion for 720 hours.

[0054] Example Seven A high-strength and high-corrosion-resistance low-silver solder with a chemical composition in terms of mass percentage of 17% of Ag, 50% of Cu, 3% of Sn, 2.5% of Ga, 2% of In, 3% of Ni, 0.05% of Si3N4 nanoparticles, and the balance of Zn.

[0055] Based on the test results of 5 test pieces, the welding wire has excellent processability, a tensile strength of 634 MPa, an elongation of 21.1%, and a spreading area on red copper and 316L stainless steel of 348 mm 2 and 315 mm 2 respectively, and a self-corrosion potential of the welding point of -0.169 V (vs. SCE).

[0056] The vacuum brazing method is used, the brazing temperature is set to 830℃, and the diameter of the filler metal is 2 mm. The red copper / red copper lap joint test plate, the red copper / 316L stainless steel lap joint test plate, and the 316L stainless steel / 316L stainless steel lap joint test plate with a thickness of 5 mm are welded. The red copper / red copper and red copper / 316L stainless steel lap joint test plates are broken on the side of the red copper base material, and the shear strength of the 316L stainless steel / 316L stainless steel lap joint test plate is 372 MPa.

[0057] All the test pieces have no obvious rust after salt spray corrosion for 720 hours.

[0058] Example Eight A high-strength and high-corrosion-resistance low-silver solder with a chemical composition in terms of mass percentage of 13% of Ag, 30% of Cu, 0.5% of Sn, 2% of Ga, 2.5% of In, 5% of Ni, 0.1% of Si3N4 nanoparticles, and the balance of Zn.

[0059] Based on the test results of 5 test pieces, the welding wire has excellent processability, a tensile strength of 597 MPa, an elongation of 15.5%, and a spreading area on red copper and 316L stainless steel of 312 mm 2 and 288 mm 2 respectively, and a self-corrosion potential of the welding point of -0.194 V (vs. SCE).

[0060] Vacuum brazing was used at a temperature of 850℃. Using 2mm diameter brazing filler metal, 5mm thick copper / copper test plates, copper / 316L stainless steel test plates, and 316L stainless steel / 316L stainless steel test plates were welded. Both the copper / copper and copper / 316L stainless steel test plates broke on the copper base material side. The 316L stainless steel / 316L stainless steel test plate had a shear strength of 351MPa.

[0061] No obvious rust was observed in any of the test specimens after 720 hours of salt spray corrosion.

[0062] Comparative Example 1 A high-strength, high-corrosion-resistant, low-silver brazing filler metal has the following chemical composition by mass percentage: 10.0% Ag, 47.3% Cu, 0.5% Sn, 2% Ga, 3% In, 0.05% Si3N4 nanoparticles, with the balance being Zn.

[0063] Based on the test results of 5 specimens, the welding wire's processing performance is generally average, with a tensile strength of 526 MPa, an elongation of 11.4%, and a spreading area of ​​263 mm² on both copper and 316L stainless steel. 2 and 207mm 2 The self-corrosion potential of the solder joint reaches -0.273V (vs. SCE).

[0064] Vacuum brazing was used, with the brazing temperature set at 880℃. Using brazing filler metal with a diameter of 2mm, copper / copper lap joint test plates, copper / 316L stainless steel lap joint test plates, and 316L stainless steel / 316L stainless steel lap joint test plates with a thickness of 5mm were welded respectively. The shear strengths were 237MPa, 244MPa, and 281MPa, respectively.

[0065] All specimens showed obvious rust after 720 hours of salt spray corrosion.

[0066] Comparative Example 2 A high-strength, high-corrosion-resistant, low-silver brazing filler metal has the following chemical composition by mass percentage: 12% Ag, 43.6% Cu, 1.2% Sn, 1.5% Ni, 0.07% Si3N4 nanoparticles, with the balance being Zn.

[0067] Based on the test results of 5 specimens, the welding wire's processing performance is generally average, with a tensile strength of 534 MPa, an elongation of 10.2%, and a spreading area of ​​248 mm² on both copper and 316L stainless steel. 2 At 187mm, the self-corrosion potential of the solder joint reaches -0.247V (vs. SCE).

[0068] The vacuum brazing method was used, the brazing temperature was set to 910℃, the brazing filler metal with a diameter of 2mm was used to weld the 5mm-thick red copper / red copper lap joint test plate, red copper / 316L stainless steel lap joint test plate and 316L stainless steel / 316L stainless steel lap joint test plate, and the shear strengths were 241MPa, 248MPa and 293MPa respectively.

[0069] After 720 hours of salt spray corrosion, all the test pieces had no obvious rust.

[0070] Comparative Example Three A high-strength high-corrosion-resistance low-silver brazing filler metal, the chemical components of which are as follows in terms of mass percentage: 15% of Ag, 41.3% of Cu, 1.8% of Sn, 2.5% of Ga, 2.5% of In, 2% of Ni, and the balance of Zn.

[0071] Based on the test results of 5 test pieces, the wire processing performance was general, the tensile strength was 552MPa, the elongation was 10.9%, the spreading areas on red copper and 316L stainless steel were 277mm 2 and 232mm 2 respectively, and the self-corrosion potential of the welding point reached -0.231V (vs. SCE).

[0072] The vacuum brazing method was used, the brazing temperature was set to 885℃, the brazing filler metal with a diameter of 2mm was used to weld the 5mm-thick red copper / red copper lap joint test plate, red copper / 316L stainless steel lap joint test plate and 316L stainless steel / 316L stainless steel lap joint test plate. The red copper / red copper and red copper / 316L stainless steel lap joint test plates were broken at the side of the red copper base material, and the shear strength of the 316L stainless steel / 316L stainless steel lap joint test plate was 314MPa.

[0073] After 720 hours of salt spray corrosion, all the test pieces had no obvious rust.

[0074] Comparative Example Four A high-strength high-corrosion-resistance low-silver brazing filler metal, the chemical components of which are as follows in terms of mass percentage: 18% of Ag, 39.7% of Cu, 3% of Sn, 3% of Ga, 2.5% of In, 6% of Ni, 0.08% of Si3N4 nanoparticles, and the balance of Zn.

[0075] Based on the test results of 5 test pieces, the wire processing performance was general, the tensile strength was 563MPa, the elongation was 8.1%, the spreading areas on red copper and 316L stainless steel were 282mm 2 and 254mm 2 respectively, and the self-corrosion potential of the welding point reached -0.213V (vs. SCE).

[0076] The vacuum brazing method was used, the brazing temperature was set to 890℃, the brazing filler metal with a diameter of 2mm was used to weld the red copper / red copper test plate, the red copper / 316L stainless steel test plate and the 316L stainless steel / 316L stainless steel test plate with a thickness of 5mm. The red copper / red copper and red copper / 316L stainless steel test plates were broken on the side of the red copper base material, and the shear strength of the 316L stainless steel / 316L stainless steel test plate was 331MPa.

[0077] After 720 hours of salt spray corrosion, all test pieces showed no obvious rust.

[0078] Comparative Example 5 A high-strength, high-corrosion-resistant, low-silver brazing filler metal, the chemical composition of which is as follows: 20% Ag, 38.2% Cu, 5% Sn, 3% Ga, 2% In, 2.0% Ti, 1% Nd, and the balance Zn.

[0079] Based on the test results of the 5 test pieces, the wire processing performance is general, the tensile strength is 558MPa, the elongation is 9.7%, the spreading area on red copper and 316L stainless steel is 305mm 2 and 281mm 2 , respectively, and the self-corrosion potential of the welding point reaches -0.279V (vs. SCE).

[0080] The vacuum brazing method was used, the brazing temperature was set to 890℃, the brazing filler metal with a diameter of 2mm was used to weld the red copper / red copper test plate, the red copper / 316L stainless steel test plate and the 316L stainless steel / 316L stainless steel test plate with a thickness of 5mm. The red copper / red copper and red copper / 316L stainless steel test plates were broken on the side of the red copper base material, and the shear strength of the 316L stainless steel / 316L stainless steel test plate was 331MPa.

[0081] After 720 hours of salt spray corrosion, all test pieces showed no obvious rust.

[0082] Examples 1-8 demonstrate an optimized multi-component alloy design that achieves a balance of high strength, high elongation, excellent spreadability, high brazing joint strength, and outstanding corrosion resistance, etc. while maintaining a low silver content. The electrochemical test results further confirm that the brazing filler metal has significantly improved self-corrosion potential and pitting resistance, for example, the excellent electrochemical stability exhibited in Example 1.

[0083] Through comparison between Examples 1-8, the brazing filler metal that meets the following three conditions has better performance: Ni accounts for 1.3% to 7.7% of the sum of the mass of Cu and Zn, the total mass fraction of Ga and In is 4.5% to 5.5%, and Si3N4 accounts for 1% to 2% of the sum of the mass of Ga and In.

[0084] By comparing Example 1 with Comparative Example 1, and Example 5 with Comparative Example 5, it can be clear that the self-corrosion potential of the comparative examples without Ni is significantly lower, at -0.273 V and -0.279 V, respectively, and "obvious rusting" occurs after the salt spray test. This strongly proves that Ni is the most critical element for improving the corrosion resistance of the solder.

[0085] By comparing Example 4 with Comparative Example 4, it can be known that although Ni is an important strengthening element, an excess amount will lead to the formation and increase of brittle intermetallic compounds. These hard and brittle phases seriously damage the plasticity of the material, causing the elongation to decrease sharply. At the same time, due to the significant decrease in plasticity, the tensile strength also decreases instead of increasing, and the optimal strength level cannot be achieved. Therefore, the nickel content used in the examples is in the optimal range, and the composition design is both scientific and balanced.

[0086] By comparing Example 2 with Comparative Example 2, it can be known that a high-performance solder formula is an organic whole. Only Ni and Si3N4 can achieve acceptable strength and corrosion resistance, but cannot achieve excellent processability. Therefore, Ga and In work together with Ni, Si3N4, and other elements to produce a "1+1>2" synergistic effect, which ultimately realizes the overall superior performance exhibited in the examples.

[0087] In addition, the comparison between Comparative Example 3, which does not add Si3N4, and Example 3, which has a similar composition, shows that the self-corrosion potential of the former is -0.231 V, which is much lower than that of the latter, which is -0.171 V. Combined with the fact that the microstructure of the former is coarser than that of the latter, it can be concluded that the addition of Si3N4 nanoparticles refines the microstructure and makes an important contribution to improving the corrosion resistance of the material. Figure 1 and Figure 2 It can be concluded that the addition of Si3N4 nanoparticles refines the microstructure and makes an important contribution to improving the corrosion resistance of the material.

[0088] The specific examples described in the present document are merely illustrative of the spirit of the invention. Those skilled in the art to which the present invention belongs can make various modifications or supplements to the described specific examples or replace them with similar ways, without deviating from the spirit of the present invention or exceeding the scope defined by the appended claims.

Claims

1. A high-strength, high-corrosion-resistant, low-silver brazing filler metal, characterized in that, Its chemical composition by mass percentage is: 10%–20% Ag, 30%–50% Cu, 0.5%–6% Sn, 2%–3% Ga, 2%–3% In, 1%–5% Ni, 0.05%–0.1% Si3N4 nanoparticles, with the balance being Zn.

2. The high-strength, high-corrosion-resistant, low-silver brazing filler metal according to claim 1, characterized in that, The mass of Ni accounts for 1.3% to 7.7% of the sum of the masses of Cu and Zn.

3. The high-strength, high-corrosion-resistant, low-silver brazing filler metal according to claim 1, characterized in that, The total mass fraction of Ga and In is 4.5% to 5.5%.

4. The high-strength, high-corrosion-resistant, low-silver brazing filler metal according to claim 1, characterized in that, The average particle size of the Si3N4 nanoparticles is 100-300 nm, and the mass of Si3N4 accounts for 1%-2% of the sum of the masses of Ga and In.

5. The high-strength, high-corrosion-resistant, low-silver brazing filler metal according to claim 1, characterized in that, Its chemical composition by mass percentage is: 15% Ag, 41.3% Cu, 1.8% Sn, 2.5% Ga, 3% In, 2% Ni, 0.08% Si3N4 nanoparticles, with the balance being Zn.

6. A method for using a high-strength, high-corrosion-resistant, low-silver brazing filler metal according to any one of claims 1-5, characterized in that, Includes the following steps: (1) High-purity metal Ag ingots, electrolytic Cu plates, Zn ingots, Sn ingots, Ga metal blocks, In metal blocks, Ni particles and nano-sized Si3N4 particles are used as raw materials; (2) Melting is carried out in an intermediate frequency furnace. First, Ag ingots and electrolytic Cu plates are placed in a crucible and a covering agent is added to prevent metal oxidation and evaporation loss. (3) Control the frequency of the medium frequency furnace at 35-45kW, and add the required metal and Si3N4 nanoparticles in sequence; (4) The ingot is obtained by stirring, refining, ultrasonic melt crushing, settling, slag removal and casting; The ingot is annealed, peeled, extruded, pickled, polished, and placed on a tray to obtain a tray-packed brazing filler metal with a diameter of 0.8 mm to 2.0 mm; or it is annealed, straightened, made into strips, pickled, and polished to obtain a straight strip brazing filler metal with a diameter of 1.6 mm to 3.2 mm.

7. The method for using high-strength, high-corrosion-resistant, low-silver brazing filler metal according to claim 6, characterized in that, The covering agent is a mixture of charcoal and borax.

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