Dissolution of reactive strontium-containing alloys in liquid aluminum and A356 melts

The dissolutions of commercial purity strontium and a 90 pct Sr-10 pct Al alloy in liquid aluminum and A356 alloys has been investigated. The dissolutions of these alloys was found to be accompanied by the formation of various intermetallic compounds, the type of which depends on the chemistry and temperature of the melt. Additions at low melt temperatures resulted in the exothermic formation of those intermetallics that have the lowest strontium contents, as seen in the relevant phase diagram,i.e., Al₄Sr in liquid aluminum and SrAl₂Si₂ in liquid A356. Due to low reaction rates at these temperatures, these intermetallics formed as dispersed particles that could easily dissolve in the melt, yielding high recoveries. At high melt temperatures, the associated chemical reactions yielded, as products, the higher strontium intermetallics, which formed with little or no exothermicity. These compounds were observed to be scarcely soluble in the melt, resulting in low recoveries. The dissolution time of these alloys were found to show good agreement with calculated values based on a two-stage model comprising an initial exothermic reaction period and a subsequent free dissolution period. In general, the high-strontium alloys were determined to be efficient at low melt temperatures of 675°C to 700°C. These reactive alloys were observed to form thick surface scales in air, which, in the case of commerical purity strontium, proved to be detrimental to dissolutions because they formed a barrier between the solid and the liquid.