Vacuum brazing is a method of brazing without flux in vacuum atmosphere. Initially brazed steel and stainless steel were only used in the electronics industry. In the late 1940s, with the development of aviation industry, vacuum brazing successfully solved the welding problem in engine manufacturing. It is widely used in aerospace, atomic energy, electronics, chemical industry, petroleum, medical equipment, tool manufacturing, automobile manufacturing. However, vacuum brazing equipment has high one-time investment, high consumption, complex maintenance, high assembly and positioning requirements, and brazing filler metal should not contain volatile elements, so its application is limited.
Compared with other brazing methods, vacuum brazing has the following advantages:
1. Suitable for brazing stainless steel and superalloys, especially heat-resistant alloys with high aluminium content and high fineness, high quality brazing joints can be obtained. At the same time, it is also suitable for the welding of the same kind of refractory alloys or dissimilar metals such as Qin, Er, Sharp, Keys, Tungsten and Zu.
2. In the process of heating, the parts are in vacuum atmosphere, without oxidation, carburization, decarbonization, pollution and deterioration; and the parts are heated as a whole, with small thermal stress, the deformation can be controlled to a minimum.
3. The matrix metal and filler metal are surrounded by low pressure environment, which can eliminate the volatile impurities and gases released by the metal at the brazing temperature. The performance of the matrix metal itself has also been improved.
4. Vacuum brazing does not use flux, and there will be no porosity and slag inclusion defects. The cleaning procedure after brazing can also be omitted, the time can be saved and the working conditions can be improved. Without flux, it is especially advantageous for welders and their alloys, because the flux left on the parts will cause corrosion.
5. Heat treatment of parts can be carried out together with vacuum brazing, or brazing can be arranged as the final process.
6. The surface of the parts after vacuum brazing is clear and bright, and it is easy to check the quality of the cracks.
7. It is an efficient brazing method that can weld multiple similar brazing seams and braze multiple components in the same furnace according to the capacity of the furnace.
vacuum brazing Principle：
The oxide film on the metal surface during brazing affects the wettability of the liquid solder to the base metal. In the brazing process, it is difficult to form high quality brazed joints if the oxide film on the metal surface of the base metal can not be removed effectively. Different brazing methods adopt different measures to remove oxide film and prevent oxidation. The general brazing method is to remove oxide film by chemical action of brazing flux or reduction action of reducing atmosphere.
Although vacuum brazing has no chemical effect of flux and reduction effect of reducing atmosphere, vacuum reduces oxygen partial pressure in brazing zone, removes oxide film on the surface of welding parts and protects them from oxidation. In this way, high strength, bright and compact joints can be obtained by brazing in a vacuum atmosphere.