Influence of Alloying Element Mg on Na and Sr Modifying Al-7Si Hypoeutectic Alloy

The influence of alloying element Mg on Na and Sr modifying Al-7Si hypoeutectic alloys was investigated. The residual content of Na and the morphology of modified eutectic silicon were characterized. It was found that the alloying element Mg had an enhanced effect on the uptake of sodium in the Al-7Si hypoeutectic alloy modified by the Na-contained modifier. Moreover, the morphology of eutectic silicon of the modified Al-7Si alloys was significantly different from that of Al-7Si-0.4Mg alloys in the present research. When the addition of the modifier is enough, both modifiers could entirely modify the eutectic silicon phase of Al-7Si alloys, while incompletely modified eutectic silicon was observed in both Na-modified and Sr-modified Al-7Si-0.4Mg alloy. It was observed that there was an adhering relationship between the partially modified eutectic silicon with Mg-rich phases. According to the results, it can be proposed that the addition of Mg will affect the solidification behavior of alloys, thereby, leading to the incomplete modification of eutectic silicon phases.