Effects of zinc, lithium, and indium on the grain size of magnesium

The grain size of magnesium solid-solution alloys with lithium, indium, and/or zinc has been determined. Lithium, indium, and zinc additions decreased the grain size, D, of magnesium solid-solution alloys cast in a copper mold. The most effective grain refinement was obtained by zinc. In binary Mg-Zn alloys, grain size is related to the Growth restriction factor, Q as D = 94 + 312/Q. In Mg-Li and Mg-In binary alloys, grain size versus growth relationships described as D = a + b/Q indicated that these alloys have lower numbers of nucleants but with higher potency than the Mg-Zn binary system. For Mg-Li and especially Mg-In, grain size could be related to growth restriction as D = 383Q(-n) with higher R-2. Ternary and quaternary alloys based on Mg-Zn with Li and/or In additions also follow the D = a + b/Q relationship with the parameters indicating a larger number of lower potency nucleants than the Mg-Zn binary alloys. Electron probe microanalysis showed that Mg-Zn alloys exhibit pronounced and persistent grain-boundary enrichment of Zn, pointing toward Scheil solidification.