Microstructure evolution during multidirectional solidification of Al-Cu-SiC composites

The present investigation is aimed at understanding the solidification behaviour of Al-Cu-SiCp composites under multidirectional solidification conditions. Macro-and microstructures of composites solidified using small and large size moulds have been studied. It was observed that an increase in particle volume fraction and/or an increase in cooling rate reduced the extent of macrosegregation of reinforcements in the composites. In the case of composites solidified in large size permanent moulds, the differentia!cooling rate along the transverse direction led to the formation of a conical-shaped particle-depleted zone in the bottom part of the casting. Columnar grains were observed in the particle-depleted zone, while the particle-containing region exhibited equiaxed grain morphology. SiC particles did not facilitate heterogeneous nucleation of matrix phases. In the absence of convection, SiC particles promoted grain refinement in the matrix. However, when there was a significant amount of convection, he presence of SiC particles led to a coarser grain structure, matrix dendrite arm spacing (DAS) was not significantly altered by the presence of SIC particles. (C) 1998 Published by Elsevier Science Limited. All rights reserved.