Unique deformation mechanisms of extruded Mg–Y-Sm-Zn-Zr alloy

Abstract

In present work, the effect of C texture, with the c axis of grains aligned parallel to extrusion direction (ED), on the deformation modes during tension in extruded Mg–Y-Sm-Zn-Zr alloy was investigated. The results indicated that both the extension twins and pyramidal <c+a> dislocations were activated, whereas basal <a> and prismatic <a> dislocations remained dormant during the early stages of tension. With the increase in tensile strain, the number fraction of extension twins increased continuously and rotated their orientation towards the direction perpendicular to ED. Meanwhile, the prismatic slip was activated in the newly orientated grains exhibiting a deviation angle >60°with respect to ED based on the intragranular misorientation axis (IGMA) analysis. Additionally, Viscoplastic self-consistent (VPSC) simulation confirmed that the activation of pyramidal <c+a>, prismatic <a>, extension twin, coupling with the suppression of basal <a> slip attributed to the highest critical resolved shear stress (CRSS) of basal <a> dislocation. Further analysis by TEM revealed that the precipitation of LPSO and γ′ on the basal plane of Mg, along with the increased volume fraction of extension twin actively obstructed the movement of <a> dislocations, consequently elevating the critical resolved shear stress (CRSS) in basal <a> slip.