Contribution of extension twinning to plastic strain at low stress stage deformation of a Mg-3Al-1Zn alloy

Extruded magnesium alloys present a typical sigmoidal shaped stress-strain curve when compressed along the extrusion direction due to the activation of {101̅2}〈101̅1̅〉 extension twinning. Quantitative measurements of the contribution of twinning to plastic strain at the low stress stage deformation are incomplete in the literature. In this work, we carefully measured the evolution of twin volume fraction during low stress stage plastic deformation of an extruded Mg-3Al-1Zn alloy by electron backscatter diffraction, and calculated the contribution of twinning to the plastic strain. Our results show that, at the very beginning of yielding, basal dislocation slip is the main contributor to the plastic strain, but twin nucleation is already activated. The contribution from twinning rapidly increases as the plastic strain increases. After the plastic strain exceeds 1.0%, extension twinning contributes 80-90% of the plastic deformation until twinning is saturated.