Core structure and solute strengthening of second-order pyramidal 〈 c + a 〉 dislocations in Mg-Y alloys

The ability of Y as an alloying agent to improve the ductility of magnesium is explored using a solid solution strengthening model to determine the relative strengthening effect on the available deformation modes. We use density functional theory calculations to determine the interaction energy between an edge 〈 c + a 〉 dislocation and solute atoms surrounding it. We observe that substituting solute atoms directly into the positions closest to the dislocation significantly changes the structure of the dislocation, making the direct calculation and representation of these interaction energies difficult, and necessitating a modification to the calculation of interaction energies. Next, we apply a solution strengthening model to calculate the relative strengthening effect of the solutes and find that the ratio of the critical resolved shear stress of second-order pyramidal 〈 c + a 〉 slip to that of the basal slip, decreases with increasing Y concentration. The resulting, more isotropic plastic response is beneficial for improving the room temperature ductility of Mg alloys.