Grain refinement of commercial purity Mg-9%Al alloys by superheating

An investigation has been made into the grain refinement of commercial purity Mg-9%Al alloys by superheating. The results obtained from analyzing the cooling curves of commercial purity Mg-9%Al alloys before and after superheating reveal that superheating increases the nucleation temperature of commercial purity Mg-9%Al alloys, and the resultant grain size corresponds to the change in the nucleation temperature. Detailed microscopic examination suggests that superheating does not obviously change the chemistry of the intermetallic particles in the Mg-9%Al alloys studied. The temperature-solubility theory can reasonably explain the observations about superheating made in this study. It follows that an increase in the number density of nucleant particles is probably the key reason responsible for grain refinement by superheating.