Influence of Sc content on the microstructure and mechanical properties of cast Al-2Li-2Cu-0.5Mg-0.2Zr alloy

Highlights: • The grain size was continuously reduced with the increasing Sc content. • No evidence for the formation of the Cu-rich and Sc-containing W phase was observed. • Sc addition could promote the precipitation of S′ in the absence of pre-age stretch. • Sc addition would reduce the growth rate of δ′ and δ′-PFZs. • The highest combinations of strength and ductility were obtained in cast Al-Li alloys. - Abstract: In this work, the influence of Sc content on the microstructure and mechanical properties of cast Al-2Li-2Cu-0.5Mg-0.2Zr alloy was investigated. It was found that the grain size of As-cast alloy was significantly reduced in steps with the increase of Sc addition, accompanied by the arising and increasing of cubic primary Al₃(Sc, Zr) phases. No evidence for the presence of the ternary W (Al_8−xCu_4+xSc) phase was obtained. The volume fraction of nanoscale Al₃(Sc, Zr) dispersoids was improved with the increase of Sc content, and the presence of Sc was observed to refine the S′ (Al₂CuMg) morphology during ageing. The addition of Sc lowered the growth rates of δ′ (Al₃Li) particles and δ′-Precipitate-free zones (δ′-PFZs) of the base alloy. The tensile property results showed that, with the increasing Sc content and ageing times, the yield strength (YS) and ultimate tensile strength (UTS) were continuously increased, and the highest elongation of 6.0% was obtained in the 0.2Sc-containing alloy aged for 32 h at 175 °C. The results indicated that the optimal Sc addition in cast Al-2Li-2Cu-0.5Mg-0.2Zr alloy was 0.2 wt%.