Evolution of unidirectional solidification microstructure of the Al-In monotectic alloys in high temperature gradient

High temperature gradient is employed under the directional condition to examine the influence of the ratio of gradient to solidification rate, G/R, on the microstructure of Al-17.5%In (mass fraction) alloys. The experimental results show that the microstructure evolution of monotectic alloy under the directional solidification is similar to the one of eutectic alloy. When steady growth is formed, there exists an In-rich zone in the front of α phase and vice versa. The diffusion process plays a dominate role in the steady growth due to the small lamella distance. Unidirectional solidification microstructure of the alloys changes from fibrous structure to regular droplet-like array and finally random dispersion of In droplets in the aluminum matrix with increasing growth rate or decreasing temperature gradient. The change suggests that the transition of monotectic solidification structure has a closed relation to the morphological transition of solid-liquid interface.