Estimation of Peierls-Nabarro stress of dislocations by the first-principles calculation in Mg alloys and their effects on plasticity

• The model for Peierls-Nabarro stress (σ p ) of edge and screw 〈a〉 and 〈 c + a 〉 dislocations in hcp-Mg alloys are firstly established based on the first-principles calculation. • Specific alloying elements prefer to simultaneously decrease σ p of both the prismatic 〈a〉 and the pyramidal 〈 c + a 〉 slips and promote their activations. • The relationship between the Δσ p , i.e., the difference of σ p in the mg alloy and pure Mg, and plasticity of Mg alloys is explored for the first time. • Cooperative activation of prismatic 〈a〉 and pyramidal 〈 c + a 〉 dislocations effectively contribute to enhanced ductility by providing additional pathways for dislocation movement. Poor plasticity is an intrinsic disadvantage of magnesium (Mg) alloys, which limits their wide application at room temperature. Alloying is an accepted method to tune the plastic deformation mode and improve plasticity. However, the effect of solute atoms on the activation of different dislocations is still unclear and has rarely been systematically investigated in Mg alloys. In this work, the formulations of Peierls-Nabarro stresses (σ p ) for edge and screw dislocations along various slip planes in Mg-X (X = Y, Ca, Nd, Zn, Al and Sn) alloys are firstly derivate, as well as the calculation of the parameter K (energy factor) based on the first-principles calculation. The effects of solute atoms on the σ p of various types of dislocations are systematically studied. The difference of the σ p between the Mg-X alloy and pure Mg, i.e., Δσ p , is determined, which is strongly influenced by the solute atoms. The negative Δσ p reflects the promotion of dislocation activation. The relationship between the Δσ p of different non-basal dislocations and elongation in eight Mg-X alloys is explored. The simultaneous improvement of the activation of the prismatic 〈a〉 and the pyramidal 〈c + a〉 dislocations is discovered, which can be achieved by specific alloying elements. Cooperative activation of the prismatic 〈a〉 and the pyramidal 〈c + a〉 dislocations owing to the reduced Δσ p is shown to closely correlate with the significant increased plasticity of the Mg alloys. These findings advance a novel perspective on alloy design strategies for Mg alloys with improved plasticity.