A Study on Microstructure Formation during Directional Solidification of a Hypoeutectic Al-ll.3Si-3.5Cu alloy

摘要

Directional solidification experiments were carried out in a hypoeutectic Al-ll.3Si-3.5Cu system to investigate the microstructural evolution with the solidification rate. At a fixed temperature gradient, a dendritic microstructure was observed at a constant speed of more than 25μms~(-1), a cellular interface developed at 5 urns'1 and the growth rate of 0.5 μms~(-1) led to the stability of the planar interface. The results revealed that primary silicon phases formed among cells, even though the studied Al-Si alloy system formed the composition within a hypoeutectic silicon composition. This suggests that the liquid concentration among cells during solidification reached a higher concentration, i.e., the eutectic concentration. It is, however, interesting that primary silicon phases did not form during a dendritic growth of more than 25 μms~(-1). These experimental observations are explained using the theoretical models on the interface temperatures.