The role of solute in grain refinement of magnesium

The effect of separate solute additions of Al, Zr, Sr, Si, and Ca on grain size of Mg has been investigated. Increasing the Al content in hypoeutectic Mg-Al alloys resulted in a continuous reduction in grain size up to 5 wt p et Al, reaching a relatively constant grain size for higher Al contents (ab ove 5 wt pet). The effect of Sr additions was investigated in both low- and high-Al content magnesium alloys, and it was found that Sr had a significa nt grain refining effect in low-Al containing alloys but a negligible effec t on grain size in Mg-9Al. Additions of Zr, Si, and Ca to pure magnesium re sulted in efficient grain refinement. The grain refinement is mainly caused by their growth restriction effects, i.e., constitutional undercooling, du ring solidification, but the effect of nucleant particles, either introduce d with the alloying additions or as secondary phases formed as a result of these additions, may enhance the grain refinement. A brief review of grain refinement of magnesium alloys is included in this article to provide an up date on research in this field.