Migration mechanism of sessile like (c plus a) pyramidal edge-dislocations dissociated along the basal plane of magnesium

The pyramidal II (c +a) edge-dislocation in Mg causes a transformation into the basal-dissociated (c +a) dislocation, in which two partial (c +a) dislocations aligned along the (a) direction on a basal plane are connected by an I1 type basal stacking fault. This paper investigates the mobility of basal-dissociated dislocations, which are considered as sessile, through molecular dyanmics simulations. We demonstrate that the dislocation migrates smoothly along the (c +a) direction even at very low temperatures. We also clarify the unique migration mechanism: two terminating 1/2(c +a) partial dislocations exchange a Shockley's partial dislocation at every 1/2(c +a) migration. By revealing the glissile nature of the basal-dissociated (c +a) dislocation, we provide new insights into the plasticity mechanisms of Mg. Further decompositions with basal-dissociated (c) dislocations occur when the strain is applied perpendicularly to the slip plane. Under higher shear stress, the dissociated (c) dislocations cannot easily migrate and instead decompose into heterogeneous structures.