Synergetic modification effects on primary Mg2Si in Al-20Mg2Si alloy induced by the co-addition of beryllium and antimony

Abstract Modifying the primary Mg2Si phase in hypereutectic Al-Mg2Si system with controllable sizes and morphologies is difficult to realize by the single addition of elements, which can only enhance nucleation or control its growth process via adsorption-poisoning. This research provides insights into modification mechanisms of the co-addition of Sb and Be in an Al-20Mg2Si alloy to refine the primary Mg2Si phase by controlling the nucleation and growth process simutaneouly. With 0.5 wt% Be-Sb, truncated octahedrons with rounded corners are obtained, along with the size refinement from ~150 µm to ~10 µm. The formation of Mg3Sb2 particles significantly refines the primary phase by acting as heterogeneous nucleation sites during solidification. Meanwhile, Be could adsorb on the Mg2Si surfaces and restrain the advanced growth of Mg2Si  direction, which contributes to the final morphology of the primary phase. The formation of truncated octahedrons with rounded corners contributes to an improvement in elongation to failure (from ~0.7% to ~1.9%) and ultimate tensile strength (from ~142 MPa to ~198 MPa) comparing to the unmodified alloy, which relieves the stress concentration and restrains the crack source. This study offers a simple methodology to prepare Al-Mg2Si alloys reinforced with close to spherical Mg2Si particles, which is critical to design lightweight Al-Mg2Si alloys with improved performance.