Effect of bismuth on microstructure of unmodified and Sr-modified Al-7Si-0.4Mg alloys

The effects of bismuth and the combination of bismuth and strontium on the eutectic silicon structure in Al-7Si-0.4Mg alloys were investigated under different solidification conditions. The results show that bismuth has a refining effect on the eutectic silicon and its refinement behavior increases with increasing Bi content up to 0.5% (mass fraction). When bismuth is added into the molten alloy modified with strontium, a higher Sr/Bi mass ratio of at least 0.45 is required to attain full modification of the eutectic silicon.