Optimization in strength-ductility of heterogeneous Mg-13Gd alloy via small extrusion ratio combined with pre-aging

Abstract

In this work, the extruded Mg-13Gd alloy sheet was fabricated by hot extrusion with small extrusion ratio of 3.9 (ER3.9) combined with the aging prior to extrusion (APE) treatment. The APE-ER3.9 and ER-3.9 samples show apparent heterogeneous lamella structure (HLS) and heterogeneous texture (HT), where fine dynamically recrystallized (DRXed) grains form a random texture and coarse un-DRXed grains exhibit a strong basal texture. Besides, amounts of pre-existing nano-precipitates are introduced in the APE-ER3.9 sample. The APE-ER3.9 sample exhibits the optimal combination of strength and ductility, which is attributed to the synergy of HT between coarse and fine grains, the elevated heterogeneous deformation-induced (HDI) strengthening and hardening, the pre-existing precipitates and the dynamic generation of nanoscale chain-like precipitates during deformation. The coarse grains mainly rely on the activation of basal and prismatic <a> slips to maintain its work hardening. In fine grains, the basal <a> slip dominates the whole deformation process, while the combined effects of activated pyramidal <c + a> slip and cross slip play a significant role in accommodating the late deformation. This work provides a guide for designing Mg-RE alloys with excellent strength and ductility.