The characteristics and application of brazing, the common method of metal alloy welding.

【Summary Description】 The energy source for brazing can be chemical reaction heat or indirect heat energy. It is the use of lower than the melting point of the melting point of the material to be welded metal as solder, after heating the solder melting, capillary action will be the solder and into the gap between the contact surface of the joint, wetting the surface of the metal to be welded, so that the liquid phase and the solid phase between the diffusion and the formation of brazing joints. Therefore, brazing is a solid phase and liquid phase welding method. 1. Characteristics and application of brazing Brazing uses an alloy with a melting point lower than that of the base metal as a brazing filler metal. When heated, the brazing filler metal melts and fills and remains in the joint gap by wetting and capillary action. The base metal is in a solid state and relies on the mutual diffusion between the liquid brazing filler metal and the solid base metal to form a brazing joint. Brazing has little effect on the physical and chemical properties of the base metal, the welding stress and deformation are small, and the dissimilar metals with large differences in welding performance can be welded at the same time. The joint appearance is beautiful and neat, the equipment is simple, and the production investment is small. However, the strength of the brazed joint is low and the heat resistance is poor. Applications: Carbide cutting tools, drill bits, bicycle frames, heat exchangers, conduits and various containers; in the manufacture of microwave waveguides, electronic tubes and electronic vacuum devices, brazing is even the only possible connection method. 2. Solder and flux The brazing filler metal is the filler metal that forms the brazed joint, and the quality of the brazed joint depends to a large extent on the brazing filler metal. The brazing filler metal should have suitable melting point, good wettability and caulking ability, can diffuse with the base metal, and should also have certain mechanical properties and physical and chemical properties to meet the performance requirements of the joint. According to the melting point of the solder, brazing is divided into two categories: soft brazing and brazing. (1) Soldering. The melting point of the solder is lower than 450 ℃, which is called soldering. The commonly used solder is tin-lead solder, which has good wettability and electrical conductivity, and is widely used in electronic products, electrical appliances and auto parts. The joint strength of soldering is generally 60 to 140MPa. (2) Brazing. The melting point of the brazing filler metal is higher than 450 ℃, which is called hard brazing, and the commonly used brazing filler metal is brass brazing filler metal and silver-based brazing filler metal. The joint with silver-based solder has high strength, electrical conductivity and corrosion resistance, the melting point of the solder is low, the process is good, but the price of the solder is high, and it is mostly used for welding parts with higher requirements. Brazing is mostly used for the brazing of steel and copper alloy workpieces with large forces and tools. The joint strength of brazing is 200 ~ 490MPa, Note: the contact surface of the base metal should be very clean, so use flux. The function of flux is to remove the oxide and oil impurities on the surface of the base metal and the brazing material, protect the contact surface of the brazing material and the base metal from oxidation, and increase the wettability and capillary fluidity of the brazing material. The melting point of the flux should be lower than that of the solder, and the flux residue should be less corrosive to the base metal and the joint. The flux commonly used in soldering is rosin or zinc chloride solution, and the flux commonly used in brazing is a mixture of borax, boric acid and alkaline fluoride. According to the heat source or heating method, brazing can be divided into: flame brazing, induction brazing, furnace brazing, dip brazing, resistance brazing and so on. Due to the low heating temperature during brazing, the performance of the workpiece material is less affected, and the stress deformation of the weldment is also small. However, the strength of the brazed joint is generally low and the heat resistance is poor. Brazing heating method: almost all heating heat sources can be used as brazing heat sources, and according to this will be brazed. Classification. Flame brazing: heating with gas flame, used for brazing of carbon steel, stainless steel, hard alloy, cast iron, copper and copper alloy, aluminum and aluminum alloy. Induction brazing: The use of alternating magnetic field in the parts of the induction current of resistance heat heating weldments, used for welding parts with a symmetrical shape, especially the tube shaft type of brazing. Dip brazing: the weldment is partially or entirely immersed in molten salt mixture or solder melt, and the brazing process is realized by the heat of these liquid media, which is characterized by rapid heating, uniform temperature and small deformation of the weldment. Furnace brazing: the use of resistance furnace heating weldments, resistance furnace by vacuum or the use of reducing gas or inert gas to protect the weldments. In addition, there are soldering iron brazing, resistance brazing, diffusion brazing, infrared brazing, reaction brazing, electron beam brazing, laser brazing, etc. Brazing can be used for welding carbon steel, stainless steel, high temperature alloy, aluminum, copper and other metal materials, but also can connect dissimilar metal, metal and non-metal. Suitable for welding joints with little load or working at room temperature, especially for precision, miniature and complex multi-brazed weldments.

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