Calculation of critical shear stress for binary magnesium alloys: A first-principles study

Abstract

The selection of alloying elements with the effect of “Solid solution strengthening and ductilizing” (SSDD) is an important way to develop high-performance magnesium (Mg) alloys recently, and the critical shear stress (CRSS) is an intrinsic parameter that characterizes the effect of SSDD. In this study, the CRSS of four slip systems in Mg-X (X = Al, Zn, Ca, Li, Mn, Sn, Bi, Ag Ga, In, Zr), all of which have a solid solubility (>0.5 at%) in Mg, are calculated using a combination of first-principles and the Peierls-Nabarro (P–N) model, and the SSDD effect of the alloying elements is studied systematically and experimentally verified. Calculations indicate that solid solutions of Mn, Ag, and Li can increase the CRSS of basal system and reduce the difference between the three non-basal and basal systems. Solid solutions of Zn, Ca and Zr can narrow the CRSS gap between at least one non-basal slip system and the basal slip system, but other elements have no positive effect. A smaller equilibrium volume and larger charge density around Mn or Ag element than that of Li, which makes CRSS larger. At the same time, the simulation results are validated by experiment. Mg–Ag alloy exhibits improved strength and plasticity, as well as a large number of <c+a> dislocations under TEM, which is consistent with the calculation finding that Ag promotes < c+a> dislocation slip. This study can provide guidance for the selection of solid solution elements for Mg alloys.