Under normal circumstances, alumina ceramics have high temperature resistance, wear resistance, corrosion resistance, high strength, high hardness, good insulation and other characteristics, but its processing performance, welding performance is poor. However, metal materials have the advantages of high temperature resistance, corrosion resistance, high strength, good electrical conductivity, and good machining performance and welding performance. With the continuous expansion of the application field of high-performance structural ceramics and the development of high-tech needs, many components often require the comprehensive properties of ceramic and metal materials. Ceramic and metal can be organically combined through ceramic metallized vacuum brazing process, and composite structural parts with the advantages of both ceramic and metal can be obtained.
Because the structure of ceramic materials is different from the microstructure of metal materials, the filler metal often cannot wet the ceramic surface, nor can it act on it to form a firm bond, so the sealing of ceramics and metals is a special process method, that is, the method of ceramic metallization: first firmly adhere to a layer of metal film on the surface of the ceramic that needs brazing, so that the surface has metal characteristics. Then realize the brazing of ceramic and metal. After the introduction of relevant information, the existing molybdenum and manganese method, gold plating method, copper plating method, tin plating method, nickel plating method, LAP method (laser metal plating) and other ceramic metallization processes.
Vacuum brazing alumina metallized ceramic is a process in which the solder with a melting point lower than the base metal is melted and the joint gap is filled by capillary action to obtain a non-removable joint. The vacuum brazing process has the advantages of no need to use flux aid and good toughness of brazing spot due to deoxidation. In recent years, with the continuous development of science and technology, brazing technology occupies an increasingly important position in various industrial sectors, especially in electrical instrumentation and national defense and other industries has become an irreplaceable process method. For example, large oxygen generators, heat exchangers with complex shapes (oil coolers, evaporators and radiators, etc.) used in automobiles and ships, honeycomb structures with complex shapes in jet engines, electrical parts, precision machinery parts, etc., must be brazed.
In this paper, a series of technological tests and production applications of vacuum brazing have been carried out. The key of brazing is the fitting gap of joint, the correct choice of brazing process parameters and vacuum brazing process.
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