Identification and analysis of anomalous {101‾2} twins in an extruded Mg-2wt%Y alloy sheet during uniaxial tensile loading

The deformation behaviors of a hot-extruded Mg-2wt%Y alloy sheet with high activity for basal slip was studied under uniaxial tensile loading along the extrusion direction at room temperature. Using electron backscatter diffraction and crystal plasticity finite element method (CPFEM) simulation, this work proposed the direct evidence for the activation and the role of anomalous { 10 1 ‾ 2 } twinning: (1) In the Mg alloy with high activity for basal slip, anomalous { 10 1 ‾ 2 } twins were indeed identified during tensile loading rather than unloading. The anomalous twins had the highest or the third highest negative Schmid factors of { 10 1 ‾ 2 } twinning, while the normal twins had positive Schmid factors. (2) During tensile loading, the anomalous twins were more easily activated than normal twins. As the true strain increased, the amounts of anomalous twins increased faster than the amounts of normal twins. (3) The normal twins induced positive shear strain along the loading direction while the anomalous twins induced negative shear strain along the loading direction. The role of anomalous twinning was accommodating the plastic compatibility and improving the ductility.