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 {10(1) over bar 2} twinning under compressive loading, resulting in a comparably low compressive yield stress. In contrast, the basal slip and {10(1) over bar 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 similar to 265 to similar to 160 MPa, irrespective of the amount of pre-deformation strain. The latter value of similar to 160 MPa nearly coincides with the compressive yield strength. The lattice reorientation of 86.3 degrees 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. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.