Modification of Al–Si alloys by metallothermic reduction using submerged SrO powders injection

Aluminum–silicon (Al–Si) casting alloys are the most frequently used alloys in the automotive industry. The modification of its microstructure is an important practice for refining the large needles of the eutectic silicon into fine fibrous or lamellar particles. In this study, the chemical and microstructural analyses of the samples taken during the submerged SrO powders injection tests in magnesium (Mg)-containing molten Al–Si alloys demonstrated the feasibility of Sr uptake in the bath, as SrO is reduced through metallothermic reactions in the molten alloys, producing a suitable silicon eutectic modification effect. The parameters that were evaluated during the experiments included temperature of the molten bath, size of SrO powders, initial Mg concentration in the molten alloy, and injection time. Based on the characterization of the reaction products of partially reacted SrO particles using the scanning electron microscope (SEM) as well as the X-ray diffraction (XRD) analysis of the samples of dross obtained during the injection tests, the sequence of the reaction was proposed. It was observed that the initial Mg content is a key parameter in accelerating the reaction rate through chemical reactions that produce MgAl2O4 as the main reaction product.