Simultaneous grain refinement and eutectic Mg2Si modification in hypoeutectic Al-11Mg2Si alloys by Sc addition

Abstract The effect of Sc addition on the microstructure, mechanical properties and fracture behavior of hypoeutectic Al-11Mg2Si alloys were investigated. The results indicate that the trace addition of Sc has significant refine and modification effect on the primary α-Al and eutectic Mg2Si phases in the hypoeutectic Al-11Mg2Si alloy. The morphology of the primary α-Al phase is changed from coarse dendrites to fine spheroidal crystals. Moreover, the morphology of the eutectic Mg2Si phase is changed from a coarse flake-like shape to fine and short fibrous. The mechanical properties, especially the ultimate tensile strength and ductility, can therefore be significantly improved. It is suggested that the simultaneous grain refine of primary α-Al phase and modification of Mg2Si phase are attributed to the formation of Al3Sc heterogeneous nucleus, the Sc segregation and the corresponding composition supercooling in front of the growing Mg2Si phase. This finding implies that simultaneous primary grain α-Al refinement and eutectic Mg2Si modification in hypoeutectic Al-Mg2Si alloys could be achieved by suitable trace or minor Sc alloying.