LAUSR

This research was carried out to investigate the influence of Sr modification on the microstructure and mechanical properties of Al-25%Mg2Si. The mechanism of Sr modification was also discussed. Microstructural examination was carried out using optical and scanning electron microscopy. Results showed that 0.05%Sr addition decreases the size of the primary Mg2Si. Further addition of Sr reduces the refinement effect on the primary Mg2Si (Sr > 0.1%). The primary Mg2Si is transformed from dendritic to regular morphology after Sr modification. The distribution of Sr is identical with that of Mg and Si of Mg2Si phase by EDS mapping. The absorption of Sr may be able to explain refinement and morphology transformation of the Mg2Si phase. The formation of Sr-containing compound may be detrimental to the refinement of the primary Mg2Si. Hardness and tensile tests showed that optimum mechanical properties (hardness, ultimate tensile strength and elongation) can be obtained with 0.05 wt.%Sr addition. Fine, regular and homogeneous Mg2Si phase can effectively enhance the mechanical properties of the composite.