Solute strengthening of basal slip in Mg alloys

Abstract

Strengthening of basal slip could enhance formability of magnesium by decreasing the ratio of pyramidal to basal critical resolved shear stress (P/B CRSS ratio). Here solute strengthening of basal slip is predicted for a wide range of solutes as a function of temperature and solute concentration at experimental strain rates using a recently-developed parameter-free model. The model is simplified by approximating the solute/dislocation interaction energy as the sum of a misfit strain contribution and a stacking fault interaction term, with the dislocation stress field estimated using a Peierls-Nabarro-type model of the basal edge dislocation. The approach is validated against DFT results for both Al and Zn solutes, and the predicted strengths agree well with experiments. The model is then applied to predict basal strengthening of many other solutes versus temperature, with key parameters tabulated for general future use. Comparisons to experimental data on 0.5 at% Dy and 1.0 at% Y versus temperature show moderate agreement, and the predicted effects of deviatoric misfit strains are shown to be small. An analytic formula is developed to predict strengthening as a function of solute misfit volume and stacking fault energies, enabling rapid assessment for many solutes and their combinations because. the model naturally extends to multiple solutes. Predictions are made for a range of existing ternary and higher alloys. Overall, the analysis and models here provide an accurate and easy formulation for estimating basal solute strengthening in dilute multicomponent Mg alloys and thus estimating the P/B CRSS ratio.