THE MICROSTRUCTURES OF ALUMINUM-ALLOY METAL-MATRIX COMPOSITES MANUFACTURED BY SQUEEZE CASTING

Squeeze-cast metal-matrix composite ingots have been manufactured by recasting A356/10% SiC(p) and by melt infiltrating A357/Al2O3f. The resulting microstructures have been examined by optical and transmission electron microscopy. The primary aluminium in squeeze-cast A356/10% SiC(p) exhibits a dendritic structure with eutectic silicon particles and SiC particulate distributed throughout the interdendritic regions. Unlike squeeze-cast monolithic A357, the primary aluminium dendrite arm spacing and eutectic-silicon particle size in squeeze-cast A356/10% SiC(p) are not strongly affected by an increased cooling rate at high applied pressure. With low die and preform temperature, a high applied pressure is essential to obtain complete melt infiltration in A357/Al2O3f. During melt infiltration, the ceramic preform acts as a filter, preferentially allowing silicon rich liquid to pass through.