Removing basal-dissociated 〈 c + a 〉 dislocations by { 10 1 ¯ 2 } deformation twinning in magnesium alloys

Reactions of { 10 1 ¯ 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 { 10 1 ¯ 2 } TBs with basal 〈 a 60 〉 and basal-dissociated 〈 c + a 〉 dislocations upon back and forth migration of { 10 1 ¯ 2 } TBs, respectively, during cyclic deformation. MD simulations show that immobile basal-dissociated 〈 c + a s 〉 , 〈 c + a 60 〉 and 〈 c 〉 dislocations in Mg can be incorporated into { 10 1 ¯ 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 〈 a 60 〉 dislocations under simultaneous application of shear and normal stresses. Importantly, the normal stresses required to transmute immobile basal-dissociated 〈 c + a 〉 dislocations to glissile 〈 a 60 〉 dislocations are much lower than those required to transmute basal 〈 a 60 〉 dislocations to 〈 c + a 〉 dislocations during { 10 1 ¯ 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.