In the present work, six specimens of hypo-eutectic Al-3Si-0.45Mg-0.45Cu-0.2Sc-0.2Zr cast alloys were made by a traditional casting process. The changes in microstructure and mechanical properties of the alloys at different Sr concentrations were studied using metallographic observation, tensile strength testing, and SEM analysis. The results show that, when the Sr content increased, the grain morphology underwent significant changes, from dendrites to isometric grains, and the Si phase in the eutectic region was greatly transformed and its grain sizes became smaller. However, over-modification, in excessive Sr content samples affected the mechanical performance overall. The best morphology with regards grain size and the silicon phase appeared in 0.06 % and 0.08 % Sr concentration specimens. The mechanical properties of the alloy were maximised and then decreased with increasing Sr concentration. The tensile test results indicated that the alloy with the best mechanical properties was that at 0.08 % Sr addition as evinced by its optimal morphological parameters.