Diffusion welding of alumina and Al-Sn alloy in the atmosphere

The effects of additions of tin and both tin and magnesium to aluminum on the diffusion weldability of alumina and aluminum alloys in the atmosphere were investigated. Diffusion welding treatments were carried out at temperatures between, 573 and 873K for 1.8, 3.6 and 7.2ks under pressure of 1, 2 and 4MPa. During the welding liquid tin containing magnesium filled the interface and prevented oxidation of the interface. Magnesium in liquid tin reduced a part of the oxidation film at the interface. The combined addition of tin and magnesium to aluminum produced good weldability of the couple at 873K, while the couple was not welded by the single addition of tin. However, the welding treatment in the atmosphere caused undesirable thermal stress which was not observed in vacuum. The couple welded in the atmosphere was fractured at the alumina side in the shear tension test. The thermal stress was found to be caused by the non-uniform distribution of tin at the interface of the welded joint. The uniform distribution of tin was obtained by smoothing rough joint surfaces and resulted in the released thermal stress.