Grain orientation design via gradient strain path for enhanced strength-ductility synergy in AZ31 Magnesium alloy sheets
Qingshan Yang, Guanglin Liu, Hongwei Yan, Dan Zhang, Jianyue Zhang, Rulong Du, Liyang Yue
Abstract
• The gradient compressive strain produces an inhomogeneous stress-strain distribution in the sheet. • The strain gradient-induced twinning mechanism forms a gradient texture orientation, which promotes the activation of basal and non-basal slip. • The gradient GNDs introduce the interface structure, triggering the HDI strengthening mechanism. • The gradient texture orientation and HDI hardening mechanism synergistically improve the ductility and strength of AZ31. The room-temperature ductility of magnesium (Mg) alloys is fundamentally limited by preferential basal slip activation—a challenge directly addressable through strategic grain orientation tailoring. In this study, gradient compressive strain paths are utilized through a 25° inclined die to tailor the crystallographic textures of AZ31 sheets. Precisely controlled deformation induces a triaxial stress state that rotates basal-oriented grains into gradient {10–12} twin-dominated configurations, while concurrently generating gradient geometrically necessary dislocations (GNDs). This microstructural duality synergistically activates pyramidal 〈 c + a 〉 slip systems, demonstrated by Schmid factor (SF) elevation from 0.12 to 0.38, and triggers the hetero-deformation-induced (HDI) strengthening mechanism. The engineered sheets achieve 422 MPa ultimate tensile strength (UTS) with 32.7% elongation (EL), representing 13% and 76% enhancements over conventional counterparts. Twin-mediated strain delocalization enables uniform thickness deformation, culminating in a record 7.7 mm limiting dome height at room temperature. These results indicate that grain orientation design is a critical pathway to transcend magnesium's intrinsic deformation constraints.