Effect of Al-8Sr-8Ce master-alloy content on microstructure and mechanical properties of Al-15Mg2Si alloy

Abstract

Al-Mg 2 Si alloys exhibit broad application prospects in automotive, aerospace, and electronics fields. However, the coarse morphology of Mg 2 Si constrains their applications. In this study, an Al-8Sr-8Ce modifier was proposed to improve the Mg 2 Si morphology and mechanical properties of Al-15Mg 2 Si alloys. The experimental results show that the addition of Al-8Sr-8Ce modifier transforms coarse, irregular flaky primary Mg 2 Si phases into fine polygonal grains and refines the coarse Chinese-script-like eutectic Mg 2 Si phases into fine fibrous structures. As the addition of Al-8Sr-8Ce increases from 0 to 0.4wt.%, both primary and eutectic Mg 2 Si phases are gradually refined with enhanced distribution uniformity. When the Al-8Sr-8Ce content further increases to 0.5wt.%, the average size of primary Mg 2 Si phase increases nearly by 100% compared to that with 0.4wt.% modifier, and the eutectic Mg 2 Si transforms into a thin-sheet interconnected dendritic structure. Therefore, the optimal content of Al-8Sr-8Ce is 0.4wt.%. Under this condition, the average diameter of the primary Mg 2 Si phase decreases to 11.95 µm, and the ultimate tensile strength and elongation attain 184 MPa and 4.0% respectively, which are 7.6% and 60.0% higher than those of the unmodified alloy. Excessive addition of the Al-8Sr-8Ce induces massive precipitation of Al 2 Si 2 Sr with a high formation temperature, which consume Sr and Ce elements and weaken the poison adsorption effect. This results in a decrease in both the strength and ductility of the alloy.