Diffusion welding of Si3N4 and Al-Sn alloy in the atmosphere

Effects of addition of Sn and combined addition of Sn and other element (Cu, Mg, Zn, Ti, Si, Bi, Cr, Mn or Ni) to aluminum and surface roughness on the diffusion weldability of Si3N4 and aluminum alloys in the atmosphere were investigated. Welding surface was polished either with #800 grinding paper, or with 9μm diamond powder. Diffusion welding treatments were mainly carried out at 873K for 7.2ks under pressure of 2 and 4MPa. The weldability was evaluated by the shear fracture strength. The combined addition of Sn and Mg to aluminum produced the couple showing good weldability with the strength of 45MPa, while by the single addition of Sn the strength was only about 20MPa. The couple of Si3N4/Al-0.5Sn-1Mg showed the strength of 55MPa which was almost same strength as that of Al-0.5Sn-1Mg alloy. The above couple was fractured at the welding interface in the shear tension test. The thermal stress was found to be caused by the non-uniform distribution of Sn at the interface of the welded joint. The uniform distribution of Sn was obtained by smoothing rough joint surfaces and resulted in the released thermal stress.