Stress Gradient-Driven Deformation Mechanisms in Cold-Rolled AZ31 Magnesium Alloy Sheets

Abstract AZ31 magnesium alloy, with limited slip systems at room temperature, is prone to non‑uniform stress/strain distribution during cold rolling. This study combines finite‑element simulation, rolling experiments, and multi‑scale TEM characterization including in‑situ tensile testing to reveal that roll speed‑to‑feed rate matching governs through‑thickness stress partitioning. A critical feed rate of 200 mm/s eliminates “zipper‑like” stress concentration and significantly reduces peak equivalent stress; deviation intensifies stress gradients and causes rolling force surges up to ~930 kN at 300 mm/s. A pronounced stress gradient exists along the thickness direction: the surface layer, sub-jected to high shear strain from roll friction, exhibits dense dislocation tangles and lattice distortion, whereas the core coordinates deformation predominantly via twinning, with twin boundaries redistributing strain. In‑situ TEM dy-namically corroborates this stress‑partitioning mechanism, revealing a competitive “tangling versus slipping” be-havior—high‑shear zones promote dislocation entanglement and blockage, while transition zones accommodate strain through dislocation slip. This multi‑scale study establishes a direct linkage from macroscopic stress gradients to microscopic deformation mechanisms, providing a theoretical basis for optimizing rolling parameters and micro-structure control in AZ31 sheets.