Fusion welding is a method of heating the workpiece interface to a molten state without increasing pressure during welding. When welding, the heat source quickly heats and melts the interface between two workpieces to be welded, forming a molten pool. The molten pool moves forward with the heat source, and after cooling, it forms a continuous weld to connect the two workpieces into a whole.
In the welding process, if the atmosphere is in direct contact with the high-temperature molten pool, the oxygen in the atmosphere will oxidize metals and various alloy elements. Nitrogen and water vapor in the atmosphere enter the molten pool, and defects such as porosity, slag inclusion and cracks will also be formed in the weld during the subsequent cooling process, which will worsen the quality and performance of the weld.
Pressure welding is to combine two workpieces in solid state under pressure, which is also called solid state welding. The commonly used pressure welding process is resistance butt welding. When the current passes through the connection end of two workpieces, the temperature there rises due to the large resistance, and when it is heated to a plastic state, it is connected into a whole under the action of axial pressure.
The common feature of various pressure welding methods is that pressure is applied during welding without filling materials. Most pressure welding methods, such as diffusion welding, high frequency welding and cold pressure welding, have no melting process, so there are no problems of beneficial alloy elements burning and harmful elements invading the weld seam like fusion welding, thus simplifying the welding process and improving the welding safety and hygiene conditions. At the same time, because the heating temperature is lower than that of fusion welding, the heating time is short and the heat affected zone is small. Many materials that are difficult to weld by fusion welding can often be welded by pressure welding into high-quality joints with the same strength as the parent metal.
Brazing is a method that uses a metal material with a melting point lower than that of the workpiece as a brazing filler metal, heats the workpiece and the brazing filler metal to a temperature higher than or lower than the melting point of the workpiece, wets the workpiece with liquid brazing filler metal, fills the interface gap, and realizes mutual diffusion between atoms with the workpiece, thus realizing welding.
The weld formed when welding two connectors is called weld. When welding, both sides of the weld will be affected by welding heat, and the structure and properties will change. This area is called the heat affected zone. When welding, due to the difference of workpiece material and welding current, etc. After welding, the weld seam and heat affected zone may be overheated, brittle, hardened or softened, which will also reduce the performance of the weldment and worsen the weldability. Therefore, it is necessary to adjust the welding conditions. Preheating the interface of weldment before welding, keeping temperature during welding and heat treatment after welding can improve the welding quality of weldment.