Effect of interfacial characteristics on the failure-mechanism mode of a SiC reinforced Al based metal-matrix composite

The present study addresses the interfacial behavior in a SiC reinforced 6061 Al alloy synthesized using the conventional casting route. Microstructural characterization studies carried out on samples subjected to three different controlled heat-treatment cycles revealed the presence of Mg-rich intermetallics and SiC particulates as the two predominant secondary phases distributed in the metallic matrix. The results of scanning electron microscopy revealed the presence of solute-rich zones in the near vicinity of the interface formed between the metallic matrix and the SiC particulates. The dimensions of these solute-rich zones were found to decrease with the decrease in the cooling rate of the samples from the solutionizing temperature. Furthermore, the results of fractographic studies carried out on tensile fractured samples indicated a change in the failure mode from: SiC/Al matrix debonding and cracking of SiC particulates (exhibited by peak-aged samples); to interfacial matrix failure and limited SiC/Al matrix debonding (exhibited by composite samples cooled at 3°C min^-1); to a predominant interfacial matrix failure (exhibited by composite samples cooled at 0.5°C min^-1). This change in the failure mechanism mode is rationalized in terms of the constitutional variation of the interfacial region brought about by the various heat-treatment cycles employed in the present study.