Effect of Al segregation on dislocation transmutation across {1012} twin boundaries in Mg: An atomistic simulation study

Atomistic simulations were adopted to study the solute segregation effect on dislocation transmutation across the {1012} twin boundaries in magnesium. For pure magnesium, the dislocation-twin reaction resulted in the formation of sessile dislocations accompanied by the fast migration of the twin boundary, and no 〈c + a〉 dislocation occurred. With Al segregation, instead, two basal dislocations transmuted into one prismatic 〈c + a〉 dislocation in the twin. Twin migration was significantly impeded, and the resultant twin disconnections stayed localized and had a higher step character than in pure Mg. To reveal the mechanism of the effect of solute segregation, the Peierls barriers of twin disconnections were calculated, and the dynamic evolutions of twin disconnection dipoles were simulated. The results suggested that Al segregation softened the Peierls barrier of twin disconnections but imposed a high pinning force on twin disconnections, thus attenuating their mobility. Moreover, given the same Al segregation, the twin disconnection dipole with a higher step showed greater stability, which explained the presence of localized twin disconnections with a higher step in the cases with Al segregation than in pure magnesium. The solute segregation induced low mobility of twin disconnections contributed to the occurrence of 〈c + a〉 dislocations.