Brazing is a widely used process technology for metal bonding, which achieves firm bonding by heating the filler metal to above its melting point, so that it wets the base material and fills the gap between the joints. In actual application, the selection of filler metal directly affects the quality, performance, and service life of the welding joint. Therefore, the correct selection of filler metal is a crucial link in the brazing process.



1. Select the filler metal according to the properties of the base material



The selection of filler metal should first consider the type and properties of the base material to be welded. Different metal materials have different physical and chemical properties, such as coefficient of thermal expansion, thermal conductivity, and surface wetting properties. For example, when welding metals with good thermal conductivity such as copper and silver, a filler metal with moderate melting point and good fluidity, such as silver-based filler metal, should be selected; while when welding stainless steel or high-temperature alloys, filler metals with high thermal resistance, such as nickel-based or manganese-based filler metals, are needed. In addition, attention should also be paid to whether there will be adverse metallurgical reactions between the filler metal and the base material (such as the formation of brittle phases), in order to avoid affecting the joint strength.



2. Consider the working environment and usage requirements



The environmental conditions in which the workpiece is located during use are also an important basis for selecting the filler metal. If the workpiece needs to operate in a high-temperature environment, a hard filler metal with high melting point and good thermal stability, such as nickel-based or copper-based alloys, should be selected; if used in low or room temperature environments, soft filler metals such as tin-lead alloys or tin-silver-copper alloys can be chosen. In addition, if the workpiece will be exposed to corrosive media, it should be given priority to select filler metals with strong corrosion resistance, such as stainless steel filler metals or filler metals containing precious metals.



3. Match the welding temperature with the process method

　　The melting point of the filler metal must be compatible with the adopted process method. For example, flame brazing is suitable for filler metals with lower melting points, while furnace brazing is suitable for the use of filler metals with higher melting points. At the same time, it should be avoided that the melting point of the filler metal is close to that of the base material to prevent the base material from overheating or deforming. Usually, the melting temperature of the filler metal should be 50-100°C lower than that of the base material to ensure that the structure of the base material is not damaged during the welding process.



4. Pay attention to the wetting and filling ability of the filler metal

　　Good wetting and filling ability are key factors for obtaining high-quality joints. The filler metal should be able to wet the surface of the base material quickly in the molten state and fill the gap between the joints sufficiently under capillary action. For this purpose, an appropriate flux should be selected for use according to the oxidation tendency of the base material, and a filler metal with high surface activity and good fluidity should be chosen.



Conclusion

　　In summary, the reasonable selection of filler metal in the brazing process is not only related to the quality of welding, but also affects the performance and life of the product. Engineers and technical personnel should comprehensively consider factors such as the properties of the base material, working environment, and welding process, and scientifically select the type and specification of filler metal to improve welding efficiency and joint reliability. With the development of material science, new types of filler metals continue to emerge, providing more possibilities for the application of brazing technology. In the future, the selection of filler metal will pay more attention to environmental friendliness, efficiency, and functionality to meet the increasing technical demands of various industrial fields.