On the planar anisotropy of ductility in a dilute Mg-Zn-Gd alloy

The development of TD-split texture patterns in rare-earth-containing Magnesium (Mg) alloys often produces in-plane mechanical anisotropy of strength and plasticity. In this study, the origins of tensile ductility anisotropy along the rolling direction (RD) and transverse direction (TD) of a Mg-0.1Zn-0.5Gd alloy sheet were quantitatively investigated. The results showed ∼7% and ∼8% higher uniform and fracture elongation, respectively, under TD tension than under RD tension, regardless of the grain size of the material. Microstructural examination and dislocation density analysis revealed a higher fraction of {101‾2} twins and total dislocation density under tension along the TD, accounting for the enhancement of the strain-hardening behavior and improved ductility. Conversely, the increase in prismatic slips rearranged the stress between grains with various orientations, thereby reducing strain hardening and ductility. The higher propensity for the initiation of intergranular and intragranular cracks in the RD-tension samples also contributed to the reduced ductility, whereas crack propagation played a minor role in planar ductility anisotropy. The reasons for the variations in the tendency of microcrack formation along the RD and TD are systematically discussed in terms of intergranular and intragranular strain accommodation, and the main decisive factors are interpreted.