Origin of tension–compression yield asymmetry in wrought magnesium alloys enhanced by zinc solid solution

Tension-compression yield asymmetry (TCYA) is an inherent and prevalent feature of wrought magnesium (Mg) alloys, while zinc (Zn) is one of the most widely used alloying elements for developing high-performance Mg alloys. To elucidate the underlying mechanism by which Zn solid solution affects TCYA, this study compared the microstructures and room-temperature tensile/compressive mechanical properties of Mg–xZn alloys ( x = 0, 1, 2, 4 wt%). Zn solid solution moderately reduced the c/a axial ratio of Mg, resulting in a weakened basal texture after hot extrusion. Concurrently, Zn segregation at grain boundaries suppressed the growth of dynamically recrystallized grains, leading to a refined microstructure. Benefiting from the synergistic effects of grain refinement and solid solution strengthening, both tensile yield strength (TYS) and compressive yield strength (CYS) of Zn-containing alloys were significantly higher than that of pure Mg, and increased monotonically with rising Zn content. During deformation, compressive loading along extrusion direction activated tensile twinning and dislocation slip in more grains compared to tensile loading, which accounted for the inherently lower CYS. Hence, Zn solid solution exacerbated the TCYA of Mg alloys. The fundamental reason is that despite grain refinement and texture randomization, Zn increases the critical resolved shear stress (CRSS) of basal slip much more significantly than that of non-basal slip. This differential strengthening effect is more pronounced in tensile deformation (where basal slip dominates), thereby reducing the CYS/TYS. Therefore, the solid-solution Zn content should be carefully controlled during the development of high-strength Zn-containing Mg alloys to avoid excessive TCYA.