Effect of Er Addition and Solution Treatment on the Microstructure and Mechanical Properties of Hypoeutectic Al–10%Mg₂Si–3.5%Cu Alloy

The effects of Er addition and solution treatment on the microstructure characteristics, tensile properties, and fracture behavior of a hypoeutectic Al–10%Mg₂Si–3.5%Cu alloy were systematically studied. The results showed that the addition of 0.45 wt% Er to hypoeutectic Al–10Mg₂Si alloy without and with the addition of 3.5 wt% Cu can significantly reduce the grain sizes of the eutectic Mg₂Si phase and α-Al/Mg₂Si eutectic cell, and transform the morphology of the eutectic Mg₂Si from coarse Chinese characters to thin stripes, dots, and fibers. The modification of eutectic Mg₂Si is attributed to the inhibition of Er on the heterogeneous nucleation of AlP by forming Er, P-containing phases, and the enrichment of Er atoms around eutectic Mg₂Si, which inhibits the growth of eutectic Mg₂Si and promotes a change in its growth direction. The solid solution treatment causes the eutectic Mg₂Si to tend towards spheroidization, which is promoted by the addition of Er. The addition of 0.45 wt% Er simultaneously improves the strength and plasticity of the cast alloys without and with the addition of 3.5 wt% Cu. The solid solution treatment further improved the tensile properties of the studied alloys. The improvement in strength of the alloy after as-cast and T6 treatment is due to the obstruction of fine eutectic Mg₂Si and containing-Er/Cu intermetallic compound particles on dislocations, while the improvement of plasticity mainly lies in the reduction of stress concentration and stress uniformity around eutectic Mg₂Si and intermetallic compounds caused by the regularity and spheroidization of their morphology.