Grain Refinement, Texture Evolution, and Tensile Performance Improvement of AZ91D Magnesium Alloy Processed by Multi‐Cycle Accumulative Back Extrusion

Abstract

Accumulative back extrusion (ABE) process is performed on an AZ91D Mg alloy at 310 °C. Microstructure, texture, and mechanical properties affected by the ABE cycles are elucidated in detail. Results reveal that the initial as‐cast grain structure (≈190 μm) is significantly refined (≈2.98 μm) after being imposed by six ABE cycles. The β‐Mg17Al12 phases undergo fragmentation and spheroidization. The dynamic recrystallization (DRX) process is accelerated through the particle stimulated nucleation (PSN) mechanism during initial deformation. Meanwhile, twins are inclined to occur in barren areas of the second phases and play a role of twinning‐induced dynamic recrystallization (TDRX). Grain refinement is governed by the combined function of PSN, TDRX, continuous dynamic recrystallization (CDRX), and discontinuous dynamic recrystallization (DDRX). Basal textures with low intensities are developed due to the fully developed recrystallized grains. Schmid factor analysis indicates that the {0001} <11–20> basal slip and the {11–22} <11–23> pyramidal slip contribute to ABE deformation. Finally, excellent ultimate tensile strength and fracture elongation are obtained after a three‐cycle ABE process, which are estimated to be 296 MPa and 21.43%, respectively. The resulting tensile performance is attributed to the refined grains, fragmented β‐Mg17Al12 particles, and the weakened basal texture.