The role of initial grain size on bimodal-grained microstructure and mechanical properties of an extruded Mg-Gd-Y-Nd-Zr alloy

Abstract

Influence of initial grain size on the formation of bimodal-grained microstructure and mechanical properties of a Mg-11Gd-3Y-0.5Nd–Zr alloy was investigated. The results indicate that the fraction of unrecrystallized (un-DRXed) grains in bimodal-grained microstructure was governed by the initial grain size, and the fraction increases with the increasing of initial grain size. Formation of un-DRXed grains in samples with a small initial grain size is induced by the uneven distribution of grain size, in which coarser grains is more difficult to recrystallize. However, the recrystallization behavior in samples with large initial grain size is mainly affected by the difference in orientation among grains, and grains with orientation that are not favored for slip are difficult to recrystallize. The strength increases while the elongation decreases with the increasing of initial grain size. The sample with the highest initial grain size (178 μm) accordingly shows the best ultimate tensile strength of 459 MPa. The higher strength is mainly due to the higher texture strengthening and hetero-deformation induced (HDI) strengthening provided by higher fraction of un-DRXed grains.