The critical roles of twinning and prismatic 〈a〉 slipping in affecting the dynamic recrystallization of hot-rolled Mg-Gd-Zr thick plate

• Effect of Prismatic 〈a〉 dislocations on recrystallisation/texture was studied. • Recrystallisation process of pure Prismatic 〈a〉 dislocations was observed using TEM and TKD. • First-principles calculations explain why Prismatic 〈a〉 dislocations are activated. • Prismatic < a >dislocations dominate Mg-Gd-Zr alloy deformation processes. In this study, the typical Mg-14Gd-0.3Zr alloy was rolled at the high-temperature range of 450–500 °C. The rolled Mg alloy plate with thickness of 30 mm exhibits an ultra-high ultimate tensile strength of 428 MPa and elongation of 3.4 %, which has rarely been reported, and the strong fiber texture played a critical role in strengthening. The mechanisms underlying the evolution of texture during rolling were systematically investigated. At the early stage of rolling, alloys (450 °C and 475 °C) exhibited a [10 1 ¯ 0] texture due to twinning assisted by Prismatic 〈a〉 slipping. At 500 °C, the alloy underwent nearly complete dynamic recrystallization (DRX) process. With increasing the rolling reduction, the DRX occurred in the whole temperature range, exhibiting the typical [10 1 ¯ 0]–[11 2 ¯ 0] double fiber texture. For continuous DRX, Prismatic 〈a〉 dislocations accumulate to form grains with 30°[0001] grain boundaries, which exhibit a [10 1 ¯ 0] fiber texture. During discontinuous DRX, Prismatic 〈a〉 slip induced grain rotation around the [0001] axis, stabilizing either the 〈10 1 ¯ 0〉//RD (rolling direction) or 〈11 2 ¯ 0〉//RD orientations, leading to the formation of [10 1 ¯ 0]–[11 2 ¯ 0] double fiber texture. TEM observations confirmed that Prismatic 〈a〉 dislocations can accumulate to form sub-grain lamellae, which gradually transform into high-angle grain boundaries by absorbing more Prismatic 〈a〉 dislocations. First-principle calculation demonstrated that with increasing Gd content, the unstable stacking fault energy of prismatic slipping significantly decreases, promoting the activation of Prismatic 〈a〉 slipping. These findings elucidate the critical role of twinning and Prismatic 〈a〉 dislocations in texture evolution and the DRX process during thick plate rolling of the high-Gd content Mg-Gd-Zr alloy.