Improvement in Mechanical Properties of Rolled AZ31 Alloy Through Combined Addition of Ca and Gd

In this study, the effects of the combined addition of Ca and Gd on the microstructure and mechanical properties of rolled Mg alloys are investigated by the addition of 0.5 wt% Ca and 0.5 wt% Gd to a commercial AZ31 alloy. The combined addition of Ca and Gd leads to the formation of undissolved second phases such as Al2Ca and Al2Gd, which promote dynamic recrystallization during rolling via the particle-stimulated nucleation phenomenon. As a result, the rolled AZ31-0.5Ca-0.5Gd (wt%) (AZXG3100) alloy shows a finer recrystallized grain structure than the rolled AZ31 alloy; the average grain size of the former (11.9 mu m) is considerably smaller than that of the latter (22.4 mu m). The combined addition of Ca and Gd improves the tensile yield strength of the rolled material from 131 to 144 MPa, which is attributed mainly to the combined effects of Hall-Petch hardening enhanced by grain refinement and dispersion hardening induced by the undissolved particles. The tensile elongation of the rolled material also increases from 14.6 to 18.3% upon the combined addition of Ca and Gd, because the activation of twinning during tension is less pronounced in the rolled AZXG3100 alloy owing to its smaller grain size. These results demonstrate that the combined addition of Ca and Gd simultaneously improves the tensile strength and ductility of the rolled AZ31 alloy.