Unusual F₃ stacking fault in magnesium

An unusual F₃ basal stacking fault resulting from twin-dislocation interaction in magnesium is observed in molecular dynamics simulation. The F₃ fault is produced in the twin lattice from the interaction between a migrating (1012) twin boundary and a partial dislocation of either a prismatic <c> edge, or a prismatic <c+a> mixed dislocation in the matrix. The condition is that the partial dislocation needs to have a negative sign and lie on a plane intersecting a compression site of the twin boundary. The F₃ fault can also be generated when a positive basal <a> mixed dislocation in the twin lattice, with slip plane intersecting a compression site of the twin boundary, interacts with a basal-prismatic twinning disconnection. The F₃ fault comprises two I₁ faults that have the same character but are separated by two basal layers. It has one end connected to the twin boundary, and the other end bounded by a lattice defect with a Burgers vector identical to that of a 30° Shockley partial dislocation. The formation frequency of the F₃ fault is higher at a lower shear stress (below ~400 MPa) and/or a lower temperature (100 K and 200 K). The F₃ fault can decompose into a glissile 30° Shockley and a T₂ fault at a temperature above ~400 K. The relationships between the F₃ fault and other types of basal stacking faults such as I₂, T₂ or paired I₁ faults that are separated by multiple basal layers are discussed.