Grain refinement of magnesium alloys by zirconium: Formation of equiaxed grains

Conical samples of a Mg–3.8%Zn–2.2%Ca alloy undergoing the columnar to equiaxed transition, induced by the addition of 1.5%Zr, have been examined. The zirconium contents in the equiaxed grains just ahead of the columnar front were found to generally vary between 0.2% and 0.3%. Further assessment confirmed that, as the first step towards optimum grain refinement, a zirconium content of 0.22% was necessary for the formation of equiaxed grains in the experimental alloy under conditions similar to sand casting.