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

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 mm) 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.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study investigates the influence of initial grain size on the formation of bimodal-grained microstructure and mechanical properties of a Mg-11Gd-3Y-0.5Nd-Zr alloy. It is found that the fraction of unrecrystallized grains in the bimodal-grained microstructure is determined by the initial grain size, with a higher fraction observed in samples with larger initial grain size. The formation of unrecrystallized grains in samples with small initial grain size is caused by the uneven distribution of grain sizes, while in samples with large initial grain size, it is mainly influenced by the difference in orientation among grains. The strength of the alloy increases with increasing initial grain size, while the elongation decreases. The sample with the largest initial grain size exhibits the highest ultimate tensile strength. The higher strength is attributed to the texture strengthening and hetero-deformation induced by the higher fraction of unrecrystallized grains.