Intergranular deformation mechanism stimulated by {10-12} extension twins in AZ81-La alloy

Abstract

In polycrystalline Mg-RE magnesium alloys, the lattice parameter, dislocation dynamics and critical resolved shear stress (CRSS) for various deformation modes are altered with the addition of RE atom, finally affecting deformation mode and strain accommodation mechanism among neighboring grains. Uniaxial compression tests were performed on as-extruded AZ81-La Mg alloy samples with the c-axis of the majority of crystals vertical to the compression direction. Twin variants and dominant slip systems were examined by electron backscattered diffraction (EBSD) technique. It is found by in-grain misoriention axis (IGMA) analysis that the plastic deformation is mainly accommodated by a combination of the pyramidal <c+a> slip and the basal <a> slip. The dominant twin variant is $\{0\overline{1}12\}$ <$01\overline{1}1$> and $\{1\overline{1}02\}$ <$\overline{1}101$>. Here, we applied a modified displacement gradient accommodation (m-DGA) method to evaluate the selection mechanism of twin/slip in neighbour grain stimulated by $\{10\overline{1}2\}$ extension twin. It is found that the activated slip system and/or twin variant in the neighbouring grain is determined by the accommodation of the major shear strain induced by $\{10\overline{1}2\}$ extension twin in such a way that strain concentration along grain boundaries can be relaxed.