Deformation heterogeneity in textured magnesium AZ31 under reversed loading

Abstract

The evolution of heterogeneous deformation fields in rolled Mg AZ31 under compres- sion -tension-compression loading along the rolling direction is investigated with multiscale digital image correlation. Full-field deformation maps with sub-grain resolution are obtained at each analysis point. Heterogeneous shear bands are found to govern the deformation be- havior through all stages of loading. On the compressive loading stages, ±45 shear bands, generated by collaborative activity of {1012}h1011i tensile twin mechanism, dominate the plastic behavior. At all length scales, these bands are observed to have an abrupt and sudden nature in agreement with the abrupt and sudden nature of deformation twinning. Besides, these shear bands are concluded to be the products of macroscale and microscale simple shear processes. Upon reversal of loading, ±45 shear bands are recovered in a reversible fashion due to detwinning. Further tensile loading after the detwinning mechanism has fin- ished lead to the formation of very localized and intense shear bands that appear slanted at approximately 60 . On the second compression stage, new ±45 shear bands form and intermingle with the preexisting high angle shear bands. A possible mechanism for cyclic hardening in Mg AZ31 materials due to this intermingling effect is discussed. Volumetric information is deduced by inspection of an orthogonal face to the primary observation face of the sample with another set of DIC optics. Volumetric information confirms volumetric nature of ±45 simple shear processes that form during compression stages. For the tensile stages, macro-DIC analysis of primary and secondary surfaces and micro-DIC analysis of the primary surface point to change of dominant deformation mechanisms during different loading stages.