Mechanistic insights into the high ductility and limited tension-compression asymmetry of Mg-0.7Sm-0.3Zr alloy

This study aims to elucidate the mechanisms underlying the high room-temperature ductility (EL: 44 %) and limited tension-compression asymmetry (CYS/TYS = 0.96) of a low-alloyed Mg-0.7Sm-0.3Zr (wt.%) alloy. Through a systematic investigation combining electron backscatter diffraction (EBSD) with quasi-in-situ tensile/compressive tests, the intra- and inter-granular deformation behaviors of the alloy were thoroughly examined. The results demonstrated that the extruded bar formed a distinctive fibrous bimodal grain structure with an average grain size of 3.77 μm. The high plasticity of the alloy is attributed to the rare-earth (RE) texture of a significant proportion of grains (69.7 % by area), which facilitates the activation of basal slip and subsequently promotes the coordinated activation of non-basal slip to accommodate deformation in later stages. Furthermore, the intergranular slip transfer behavior plays a crucial role in enhancing plasticity: the basal-to-basal (B–B) slip transfer alleviates stress concentrations, thereby inhibiting crack initiation. Although the basal-to-non-basal (B-nonB) slip transfer induces significant local stress concentrations, it still hinders crack propagation. Based on the experimental data, an equation for yield strength contribution was established: The difference between the calculated compressive and tensile yield strengths is 0.244 τ b -0.136 τ TT + 0.134 τ non-b . The RE texture reduces differences in tensile twinning activity under tension and compression, while grain refinement raises the critical resolved shear stress of tensile twinning beyond basal slip. These factors balance deformation mode variations, resulting in limited tension-compression asymmetry.