Silicon Nitride Whisker-Reinforced Aluminum Matrix Composites: Twinning and Precipitation Behavior

Aluminum composites reinforced with ceramic whiskers exhibited a unique combination of high specific strength and superior specific modulus. A 20 vol.% Si3N4w/Al-11.5Si-1.0Mg-0.5Cu-0.5Ni (wt.%) composite was fabricated via squeeze casting in the present study. It was observed that the addition of silicon nitride (Si3N4) whiskers in the Al-Si cast alloy promoted extensive twinning in the eutectic silicon particles due to a coupled role of thermal stresses between the matrix and silicon and residual stresses present in the composite. Double aging peaks were present in the age-hardening curves. The precipitation mechanism involved the formation of Mg2Si and Al2CuMg phases. The presence of Si3N4 whiskers in the composite retarded the nucleation process of Mg2Si precipitate while enhancing its growth rate.