The effect of Sr modification on the eutectic structure of AlSi7Mg alloys at different purity levels

The effect of different Sr levels on the solidification path and the microstructure of the Al-Si eutectic in AlSi7Mg alloys at 3 different levels of purity (high purity, commercial purity, and secondary alloy) was investigated. Thermal analysis technique was performed to obtain the cooling curves and characteristic temperatures of the eutectic reactions. Microstructural investigations were carried out to study the variation of the eutectic structure due to Sr addition and alloy’s purity. The results indicate how the commercially pure alloy shows the highest nucleation and growth temperatures among the unmodified alloys, while the secondary alloy has the lowest ones. Sr addition decreases the characteristic eutectic temperatures. Even though the growth temperature is similar after Sr modification in the commercial and high purity alloys, this last shows a finest eutectic structure. Different levels of Sr are required to fully modify the eutectic of the AlSi7Mg alloy at different purity grade.