Effect of Strontium on the Oxidation Behavior of Liquid Al–7Si Alloys

The oxidation behavior of small amounts of Al–7Si alloys containing strontium and magnesium has been investigated using thermal gravimetrical analysis (TGA). The results of TGA experiments showed that Sr-additions increase the oxidation rate of the Al–7Si alloys melt significantly. A noticeable content of SrO-containing mixed oxides was found, using scanning electron microscopy (SEM), on the oxidized surfaces after even short oxidation periods. The rapid rate of Sr-loss during the oxidation periods also showed that Sr was highly reactive in the small melts for oxidation. The oxidation of large Al–7Si melts was also studied by analyzing the surface layer at different periods. The surface oxide layers on the large melts consisted of Al₂O₃ and Al₂O₃ · MgO but were found to contain no detectable SrO. Also, in contrast with the small melts, the relatively slow rate of Sr-loss during the oxidation period showed that strontium has good stability in a large melt, revealing that in such cases the tendency of Sr for oxidation is not noticeable.