Formation of Micro Spot-Welding Joint of Rapidly Solidified Ni-19.8%Sn Alloy Foils

Abstract

In this study, the spot welding of rapidly solidified Ni-19.8%Sn alloy foils has been conducted by a micro-type capacitor discharge welder. The configuration and microstructural morphology of the joint were examined experimentally and he temperature of the micro nugget was analyzed numerically. The results show that the micro-joint consists of an oblate spheroid nugget and a 2.0~3.0 m thick bond zone. The microstructure of the joint is fine and homogeneous and there is no coarsening sign in the parent materials near nugget. During solidification, the cooling rate of nugget is so high to the order of 106K/s that the eutectic reaction of L  α-Ni + Ni3Sn was suppressed or at least partly suppressed and almost all of the liquid within the joint solidified into supersaturated α-Ni. Therefore, the joint microstructure which is consistent with the microstructure of the alloy foils shows the characteristics of rapid solidification. In addition，a kind of streamline due to vortex flow in micro nugget, with dispersed dross distributes in cluster along the streamline, is formed under electromagnetic force and electrode pressure.