Vacuum brazing of aluminum radiator for automobile engine
Due to its light weight, good corrosion resistance, good thermal conductivity and other characteristics and widely used in aerospace, construction, electrical appliances, automobiles, ships and other industries, its consumption is increasing. Aluminum alloys have long been considered a structural material for heat exchangers, waveguides and many other complex components. The study of aluminum alloy brazing first focuses on its metallurgical properties and then on the role of adding elements in the brazing process. At present, the special purpose aluminum alloy brazing research mainly focuses on the aluminum alloy welding. Many special purpose aluminum alloys are being developed and applied in engineering practice. Lt-3 aluminum alloy is designed for vacuum brazing of aluminum alloys. It is made of 4004 aluminum alloy and double bread rolling on the basis of 3003 aluminum alloy. Cladding material ACTS as solder in brazing process. The material is widely used in the manufacture of radiators and condensers. The vacuum brazing scheme of lt-3 coated aluminum alloy was introduced.
Vacuum brazing is carried out in a vacuum furnace and flux is not used in the brazing process. Although there is no chemical action of flux or reduction effect of reducing atmosphere, the oxidation film on the surface of the welding part can be removed to protect the welding part from oxidation due to the reduction of oxygen partial pressure in the brazing area.
Mechanism of removing oxide film from metal surface
1. The oxide film can be decomposed by itself under high temperature and high vacuum: oxygen partial pressure in > vacuum.
2. Magnesium vapor damages the oxide film on the metal surface. Vacuum brazing usually USES metal instead of flux in place of oxygen, which is more reactive than aluminum, to prevent flux corrosion and post-brazing cleaning. Mainly magnesium. However, with the addition of Mg, the solder has a serious corrosive effect on the base metal, and the content of Mg in the solder is generally controlled at 1.0%-2.5%.
3. The expansion force of aluminum trioxide first cracks, so that the liquid-filled metal from the cracks into the oxide film, opened the oxide film.
Requirements for brazing alloys
The filler metal used for vacuum brazing is silicon-aluminum, which requires strict composition. Filler metals shall not contain elements with high vapor pressure and elements with significant surface oxide decomposition at vacuum and high temperature. Otherwise, the process and quality of vacuum brazing will be affected.