EFFECT OF MAGNESIUM ON THE CAST MICROSTRUCTURE OF EUTECTIC AND HYPEREUTECTIC ALUMINUM-SILICON ALLOYS

The modification of eutectic aluminium - silicon alloys by sodium is well established. It is prone to under or overmodification, both of which are deleterious to properties. Its effects fades away rapidly leading to variation in properties. Magnesium is a popular alloying element for aluminium alloys, whose effect on improving the age-hardening characteristics of aluminium alloys is well established. Its effect on the cast microstructure in eutectic and hypereutectic alloys is, however, not widely reported. Its effect on the morphology of the silicon phase is not also well established. Experiments conducted to study the effect of magnesium on aluminium - silicon alloys confirm that it does modify the eutectic silicon in both eutectic and hypereutectic alloys. Its effects are comparable to and in some respects superior to that of sodium.