Unveiling the anomalous enhancement mechanism and the role of tensile twin in DRX of hot-compressed Mg-RE alloys at high strain rates

High-strain-rates typically inhibit dynamic recrystallization (DRX) nucleation, which restricts grain refinement in Mg alloys during hot deformation. In this study, however, an anomalous increase in DRX volume fraction (from 9.5% to 32.9%) is observed in a Mg-7.5Gd-1Y-2Nd-0.4Zr (wt.%) alloy as the strain rate increases from 0.001 s -1 to 1 s -1 . This anomalous behavior is attributed to a transition in the dominant DRX mechanism. At low strain rates, intragranular precipitates hinder the evolution of dislocation rearrangement toward subgrain boundaries, thus inhibiting the dominant continuous dynamic recrystallization (CDRX). With increasing strain rate, intragranular precipitation diminishes and dislocation density rises, a synergistic effect between discontinuous dynamic recrystallization (DDRX) and CDRX promoting the formation of multi-layer DRXed grains near grain boundaries. Furthermore, at 1 s -1 , deformation bands induce the nucleation of numerous banded DRXed grains. These deformation bands originate from the growth and coalescence of tensile twins. Even at 450 °C, stable grain boundary precipitates suppress grain boundary sliding and dislocation accumulation at boundaries, inducing profuse tensile twins in the early deformation stage. With increasing strain, these tensile twins indirectly promote DRX nucleation by using deformation bands as a medium. The clarification of this anomalous DRX response provides new insights for alloy design and the preparation of fine-grained Mg-RE alloys.