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

Highlights: • Sc refines both the α-Al grain and the eutectic Si in hypoeutectic Al-Si alloy. • Sc results in the formation of AlSi₂Sc₂ in two eutectic reactions. • The AlSi₂Sc₂ were significantly larger when they grew in the L→Al+AlSi₂Sc₂ reaction. • The as-cast yield strength was improved by the addition of Sc. 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.