AlSi2Sc2 intermetallic formation in Al-7Si-0.3Mg-xSc alloys and their effects on as-cast properties

Abstract

The influences of 0–0.65 wt% Sc additions on microstructure evolution during solidification, and on as-cast tensile properties and fracture behavior have been investigated in Al-7Si-0.3Mg foundry alloys. The results show that the addition of Sc significantly refines both the primary α-Al grain size and the eutectic silicon particle size, and Sc also results in the formation of AlSi2Sc2 in up to two eutectic reactions. The as-cast yield strength was improved by the addition of Sc, however, at high Sc level (0.65 wt%) the ultimate tensile strength decreased, owing to the formation of relatively large AlSi2Sc2 crystals in the Al-AlSi2Sc2 eutectic. The fracture path in the tensile samples is shown to pass through the eutectic AlSi2Sc2 intermetallic and eutectic silicon. The Sc level should not be higher than 0.40 wt% Sc to avoid the deleterious effect of AlSi2Sc2.