Effects of rare-earth elements Gd and Y on the solid solution strengthening of Mg alloys

A number of Mg–Gd, Mg–Y binary and Mg–Gd–Y ternary alloys are investigated in terms of solid solution strengthening efficiency in this work. It is found that both gadolinium and yttrium in solid solution give a cn concentration dependence of the yield strength, where c is the solute atom concentration and n = 1/2 or 2/3. This simplified analysis illustrates that we are able to satisfactorily predict the ternary solid solution strengthening in Mg–Gd–Y alloys. Gd and Y in solid solution are found to give a considerably higher strengthening effect than Al and Zn. It is suggested that, in addition to the classical size and/or modulus misfits model, the valency effect may account for the enhanced strengthening of Gd and Y in Mg.