On the role of non-basal deformation mechanisms for the ductility of Mg and Mg-Y alloys

Mg-Y alloys show significantly enhanced room temperature ductility compared to pure Mg and other classical Mg wrought alloys. The presented study focuses on understanding the mechanisms for this ductility improvement by microstructure analysis, texture analysis and slip trace analysis based on electron backscatter diffraction and transmission electron microscopy. As expected, pure Mg mainly deforms by basal slip and tensile twinning. In contrast, Mg-Y shows a high activity of compression twinning, secondary twinning and pyramidal slip. These additional deformation modes cause a homogeneous deformation with a weaker basal texture, more balanced work hardening and enhanced ductility. Additionally, in Mg-Y shear bands are much more frequent and carry less strain than those in pure Mg. As a consequence, failure in shear bands occurs at significantly higher strain. The experimental results are discussed focusing on the mechanisms effecting the observed high activation of pyramidal deformation modes in Mg-Y.