Removing basal-dissociated [formula omitted] dislocations by [formula omitted] deformation twinning in magnesium alloys

Abstract

Reactions of {101¯2} twin boundaries (TBs) with dislocations in a Mg alloy subjected to cyclic deformation were studied and modeled, based on atomic-resolution observations, theory of interfacial defects and molecular dynamics (MD) simulations. Atomic-resolution observations provide evidence for occurrence of reactions of {101¯2} TBs with basal 〈a60〉 and basal-dissociated 〈c+a〉 dislocations upon back and forth migration of {101¯2} TBs, respectively, during cyclic deformation. MD simulations show that immobile basal-dissociated 〈c+as〉, 〈c+a60〉 and 〈c〉 dislocations in Mg can be incorporated into {101¯2} TBs to produce steps which can move together with the TBs upon twinning/detwinning under low shear stresses. And such steps can usually emit 〈a60〉 dislocations under simultaneous application of shear and normal stresses. Importantly, the normal stresses required to transmute immobile basal-dissociated 〈c+a〉 dislocations to glissile 〈a60〉 dislocations are much lower than those required to transmute basal 〈a60〉 dislocations to 〈c+a〉 dislocations during {101¯2} deformation twinning. Our results may have implications for comprehensive understanding of the roles of deformation twinning, 〈c+a〉 dislocations, and their interactions/reactions in plastic deformation of Mg alloys.