Effect of silicon content and pouring temperature on the shape of eutectic silicon in strip-cast hypoeutectic Al-Si alloys

This study investigated the influence of silicon content and pouring temperature on the shape of eutectic silicon in the hypoeutectic Al-Si strips produced by an unequal-diameter twin-roller strip caster. The strips had three different silicon contents; 6.35wt%, 8.89wt% and 10.67wt%. They were poured at various temperatures from 600°C to 650°C. The results indicate equiaxed cells in the central zone of the strips. While both acicular and granular eutectic silicon can be observed in this equiaxed-cell zone, the area of the zone with granular particles increases with decreasing pouring temperature in the strips of higher silicon content. Al-10.67wt% Si strip, having the highest silicon content, can obtain completely granular particles when poured at the lowest temperature of 600°C. Acicular eutectic silicon particles which lead to crack initiation largely account for the elongation deterioration. Nonetheless, if the particles in the equiaxed-cell zone are partly or all granular, the elongation can be enhanced. Hence, increasing silicon content and lowering pouring temperature to modify the eutectic silicon in the equiaxed-cell zone from acicular to granular can improve the ductility.