Unintentional effects of Sr additions in Al-Si foundry alloys

Strontium additions are commonly made to aluminium-silicon based foundry alloys to promote fibrous eutectic silicon morphology. Although this structural modification is the primary goal, it has become apparent that there are several concomitant changes. This paper examines this issue, reviewing the well-known alterations in porosity distribution and eutectic grain size that accompany strontium additions and introducing new research on the effects of strontium on corrosion resistance and as-cast surface finish. It is shown that strontium additions significantly affect both surface finish and corrosion resistance, through a combination of physical and chemical mechanisms. It is concluded that despite being present at only trace levels, strontium has a powerful effect on a variety of casting properties that extends beyond a transition in the morphology of the eutectic silicon phase