The microstructures of locally reinforced squeeze-cast Al-alloy metal-matrix composites

Locally reinforced metal-matrix composites (MMCs) have been manufactured by squeeze casting an A357 Al alloy into a die containing a reinforcement insert of either steel, an A356/10 vol.% SiC_p MMC, or a 20 vol.% Al₂O₃ short-fibre preform. The temperatures of the Al-alloy matrix, reinforcement insert and die were monitored continuously during squeeze casting, and the microstructures of the ascast MMCs were examined. Application of high pressure caused intimate contact along the insert-matrix interface with refinement of the matrix microstructure. There was little bonding between the matrix and the steel insert, while good bonding was obtained between the matrix and the A356/SiC_p MMC insert, which was partially melted at the interface. The Al₂O₃ short-fibre preform insert was fully infiltrated at high pressure, with a band of high Si content in the matrix microstructure near the interface.