Architecting optimized heterostructure for exceptional strength-ductility synergy in Mg-Gd-Y-Zn-Mn alloy

Abstract

Achieving a superior combination of strength and ductility in magnesium (Mg) alloys remains challenging. Heterogeneous microstructures have been demonstrated as an effective strategy to overcome this dilemma. In this study, a remarkable strength-ductility synergy is sustained in an extruded Mg-8Gd-4Y-1Zn-0.5Mn (GWZ841M, wt.%) alloy via optimizing bimodal structure. By reducing the width of coarse grain by nearly an order of magnitude while maintaining similar fine grain and secondary phase characteristics, the alloy exhibits a twofold increase in elongation to 17.3% and an increased ultimate tensile strength of 372 MPa. Multi-scale characterization reveals that the refined heterostructure facilitates balanced stress-strain partitioning and generates a high and continuous gradient of geometrically necessary dislocations (GNDs) near hetero-interfaces. The spatial GNDs gradient maintains hetero-deformation induced (HDI) hardening, which delays necking and promotes the activation of multiple slip systems, collectively improving deformation compatibility. In contrast, excessive coarse grains width leads to strain localization, limited slip coordination, and premature microcrack nucleation, resulting in early failure. These findings demonstrate that controlling the heterogeneity length scale plays a decisive role in regulating strain hardening and damage evolution, providing a robust strategy for developing high-performance Mg alloys.