Papers by Keyword: Microstructural Morphology

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.

Abstract: The mechanical property of magnesium alloy depends on the alloy elements and microstructure strongly. The multiple dependency relations are studied by investigating magnesium alloys with different Al and Zn contents. The semi-continuous casting billets exhibit quite different microstructural morphologies between the centre and edge of the cross section. The centre shows fine and uniform microstructure while the edge is coarse and reticular. However the difference is almost eliminated when the billets were homogenized at 380°C for 15h. The generation mechanism of casting microstructure is also discussed in this paper. The results show that the morphology of second phase and the size of grain have greater effect on the mechanical properties than the element Zn. The alloys with uniform, fine and non-dendrite microstructure exhibit both high strength and elongation when Al content is about 6% and Zn content is various from 0 to 3%. In contrast, the strength increases and elongation decreases significantly as Al content increases from 0 to 6%.