The role of twinning and untwinning in yielding behavior in hot-extruded Mg-Al-Zn alloy

This paper examines the effect of compressive pre-deformation on subsequent tensile deformation behavior in a hot-extruded AZ31 Mg alloy bar with a ring fiber texture, and with the basal planes parallel to the extrusion direction. Such an orientation favors extensive {101¯2} twinning under compressive loading, resulting in a comparably low compressive yield stress. In contrast, the basal slip and {101¯2} twinning are difficult to operate under tensile testing, resulting in a high tensile yield strength. Compressive pre-deformation causes a significant drop in tensile yield strength, from ∼265 to ∼160 MPa, irrespective of the amount of pre-deformation strain. The latter value of ∼160 MPa nearly coincides with the compressive yield strength. The lattice reorientation of 86.3° caused by twinning during compressive loading favors untwinning in the twinned areas during subsequent tensile reloading, leading to a significant drop in tensile yield strength.