Diffusion welding is usually a solid-phase welding method using indirect heat energy as energy source. It is usually carried out in a vacuum or in a protective atmosphere. When welding, the surface of the two welders is exposed to and heat for a certain time under high temperature and pressure to reach the distance between atoms and combine with the atom’s simple diffusion. Before welding, it is not only necessary to clean the impurities such as oxides on the workpiece surface, but also the surface roughness should be lower than a certain value to ensure the welding quality. Under the protection of vacuum or protective atmosphere, the diffusion welding is under a certain temperature (lower than the melting point of the parent material) and the pressure condition, so that the smooth and smooth surface of the surface is contact with the smooth and smooth surface of the contact, and the atoms are diffused each other. After a long time, the original interface disappears to achieve complete metallurgical bonding. Welding method. Diffusion welding has the following advantages: (1) in the case of almost no damage to the properties of the welded material, the welding of all kinds of materials and different materials can be achieved, which can be used to make double or multilayer composite materials. (2) it is capable of welding complex structures with large thickness difference. (3) the joint composition and microstructure are uniform, and the stress corrosion tendency is reduced. (4) the welding deformation is small and the joint precision is high. It can be used as the final assembly connection method of components. (5) it can be carried out at the same time with other processing technologies, such as vacuum heat treatment, etc., and the welding of multiple joints can be completed at the same time, thereby increasing productivity. Insufficient: diffusion welding requires high surface welding and cleaning, long welding time, low productivity, high cost and large investment in equipment. Applications: welding between different melting points or incompatible metals between metallurgy, welding of metal and ceramics, and welding of titanium, nickel and aluminum alloy structures. It has been applied not only to the advanced technology fields such as atomic energy, aerospace and electronics industry, but also to the general machinery manufacturing industry.