Effect of complex modification of Ca and Sb on the microstructure and mechanical properties of hypoeutectic Al-11Mg2Si alloy

Abstract

The combined addition of 0.2 wt% Ca-Sb in Al-11Mg2Si alloy led to significant refinement of the eutectic Mg2Si from a coarse, needle-like morphology to spherical particles. Specifically, a further increase of Ca-Sb addition to 1.0 wt% resulted in the microstructure transition from hypoeutectic to hypereutectic characteristics. The refinement of eutectic Mg2Si could be attributed to the selective adsorption of Ca and Sb atoms on Mg2Si surfaces, which inhibited the growth of the eutectic phase in the preferential growth direction. Importantly, Ca and Sb elements were involved in the formation of heterogeneous nuclei for primary Mg2Si when Ca-Sb content increased to 1.0 wt%, which introduced the transition of composition from hypoeutectic to hypereutectic structures. Comparing to the unmodified alloy, the Al-11Mg2Si alloy modified with 0.2 wt% Ca-Sb exhibited significantly enhanced elongation to failure of ~7.9% (from ~1.3% of the unmodified alloy) and ultimate tensile strength of ~222 MPa (from ~180 MPa of unmodified alloy). The spheroidization of eutectic Mg2Si after complex modification is believed to be the underlying reason for the greatly enhanced tensile properties.