Extended ductility due to kink band formation and growth under tensile loading in single crystals of Mg-Zn-Y alloy with 18R-LPSO structure

The deformation behaviour of single crystals of an Mg85Zn6Y9 alloy with an 18R-LPSO structure was experimentally and numerically investigated using a micro-tensile testing method and a crystal plasticity finite element method, respectively. The deformation microstructure was characterised using optical and electron microscopy. The experimental results indicated that kink band was formed in the specimens depending on the initial crystal orientation relative to the loading direction. The kink banding was accompanied with remarkable ductility of over 50% nominal strain. The deformation behaviour observed was successfully reproduced in a crystal plasticity finite element analysis. The numerical results indicated that the kink band was formed by the accumulation of basal slip, which was enhanced by the geometrical softening owing to the lattice rotation. The growth of a kink band, which was reasonably explained by the changes in Schmid factor for a basal slip system due to lattice rotation, suppressed the localised failure at low strain. This resulted in the observed extended ductility, even in the LPSO structure with strong plastic anisotropy.