Effect of particulate type on the microstructure and heat-treatment response of Al-Cu-based metal-matrix composites

In the present study, an aluminum-based metallic matrix (Al-2wt.%Cu) was reinforced with graphite and silicon carbide particulates using conventional casting techniques. Microstructural characterization studies conducted on the composite samples revealed a columnar-equiaxed type of grain morphology, a finite amount of non-interconnected porosity, the presence of interdendritic/intercellular Al-Cu phase and a predominantly grain-boundary-segregated distribution of the ceramic particulates. Further, the results of scanning electron microscopy revealed the enrichment of the copper and the presence of secondary phases in the immediate vicinity of the ceramic (C/SiC) particulates. Results of ageing studies demonstrate accelerated ageing kinetics in the case of the Al-Cu/SiC samples when compared to the Al-Cu/C samples. This difference in ageing kinetics was finally rationalized in terms of variations in the constitutional and structural features of the Al-Cu matrix due to the presence of the graphite and the silicon-carbide particulates. (C) 1997 Elsevier Science S.A.