Achieving excellent strength-ductility synergy in orientation-heterostructured Mg-Y alloy via element segregation-assisted pinning of twin boundary

Abstract

The low strength, poor ductility, and limited cold formability of Magnesium (Mg) alloys have restricted their wide application as structural materials. The "heterostructure" design is a promising strategy for developing high-performance materials. In this work, four orientation-based heterostructured materials were fabricated by modulating bulk Mg-2.9Y (wt%) alloy to a single-pass strain of 10% for five complete triaxial cyclic compression (TCC) cycles along planes A, B, and C, followed by an additional compression on plane A. This process was combined with the subsequent annealing at 200°C for 1 h, leading to the hard-oriented 10%-5 cycles and 10%-5 cycles-200°C/1 h materials together with the soft-oriented 10%-5 cycles+A and 10%-5 cycles+A-200°C/1 h materials. They were characterized by dense refined twins and fragmented grains embedded in coarse-grained matrix. Compared to the TCC-processed materials, the annealed materials showed more pronounced strengthening. The 10%-5 cycles+A-200°C/1 h material exhibited the optimal combination of strength and ductility, with the periodic segregation of Y atoms at dense twin boundaries strengthening the hard domains and increasing deformation incompatibility between the soft and hard domains. The geometrically necessary dislocations significantly accumulated at the twin boundaries, resulting in pronounced hetero-deformation induced (HDI) strengthening. At high strains, the pinning effect of Y atoms gradually weakened, and $\left\{10\overline{1}2\right\}$$\left\{10\overline{1}2\right\}$ twinning was triggered. This also facilitated the activation of non-basal <a> slip systems, providing more persistent HDI hardening and excellent ductility. These findings provide novel insights into the development of high-strength and ductile hexagonal close-packed metallic materials.