Kinking Nonlinear Elasticity and the Deformation of Magnesium

Despite a large body of work devoted to understanding the deformation of polycrystalline magnesium, there are still some outstanding questions, not the least of which are the nature of its microyielding and the nature of its fully reversible, hysteretic, stress-strain curves. In this article, we provide further evidence that Mg is a kinking nonlinear solid by showing excellent agreement between the predictions of our microscale model, in which fully reversible, dislocation-based incipient kink bands (IKBs) are the key microscale element, the experimental results obtained in our study, and, just as important, the results obtained by others. It follows that microyielding and the fully reversible hysteresis loops are most likely to be due to IKB formation, with the propensity for kinking being enhanced for coarse-grained samples up to a grain size of ≈50 μm, after which further increases in grain size have little effect. From the areas of the reversible loops, the critical resolved shear stresses (CRSSs) associated with the movement of basal plane dislocations are obtained and are shown to scale with the maximum flow stresses at which the loops are obtained. We also make the case that, at least for low strains, strains along the c-axis can be accommodated by invoking the formation of IKBs, mobile dislocation walls, and kink boundaries and should be included in future modeling of the deformation of polycrystalline Mg.