Effect of Sr on the Microstructure of Electromagnetically Stirred Semi-solid Hypoeutectic Al–Si Alloys

The present study investigated the effects of Sr addition on the microstructure of semi-solid Al A356 alloy during electromagnetic stirring. Different amounts of Sr (0–350 ppm) were added to the alloy, and the effect of Sr on eutectic nucleation and growth temperature of the eutectic silicon phase was determined. The results indicate that the addition of the Sr up to 90 ppm increased the solidification range (TL–TS) of the alloy and the further addition of Sr decreased the value of TL–TS. Image analysis revealed that increasing of Sr up to 90 ppm increased the globularity (roundness) of primary aluminum particles. However, the further addition of the Sr reduced the roundness of particles. Also, it was found that the addition of Sr in all amounts increased the area percentage of primary aluminum particles compared to the non-modified alloy. The mechanisms for changes in TL–TS, roundness and area percentage of primary aluminum phase are also discussed.