We conducted molecular dynamics simulations to study the interactions between a migrating {1011} twin boundary (TB) and prismatic 〈 c 〉 and 〈 c + a 〉 dislocations in magnesium. In the simulations, the 〈 c + a 〉 dislocation comprises 〈 c 〉 edge and 〈 a 〉 screw components. Both of these 〈 c 〉 and 〈 c + a 〉 dislocations are observed to exhibit a dissociated core comprising two partial dislocations. Upon interaction with a (1011) TB, these partials pin the TB and reside on a pyramidal-basal (PyB) or basal-pyramidal (BPy) twin interface. It was found that one of the two partials transmutes into a basal 〈 a 〉 dislocation inside the (1011) twin, and the other transforms into a Frank partial dislocation that is inside the twin and linked with a single-atomic-layer-height disconnection on the TB. The basal 〈 a 〉 dislocation has its extended core bounded by two Shockley partial dislocations. The simulations reveal that when the 90° Shockley is positioned close to the TB, the full 〈 a 〉 dislocation easily detaches. In contrast, when the 30° Shockley is located close to the TB, the 〈 a 〉 connects to the TB and migrate with the TB synchronously. It was observed that connection of the 〈 a 〉 to the (1011) TB leads to a configuration comprising an I₂ fault with one end linked to a two-atomic-layer-height disconnection on the TB through a 30° Shockley partial dislocation. Further examination suggested that such a two-atomic-layer-height disconnection has its riser plane parallel to a PyB interface when the shear direction of the connected I₂ points towards the TB, while has its riser plane parallel to a BPy interface when the shear direction of the connected I₂ points away from the TB.

Single-atomic-layer-height disconnections that connect with I₁ stacking faults are produced on {1011} twin boundaries in pure magnesium through transmutation of basal 〈a〉 mixed dislocations across the twin boundaries, and their stabilities are examined using molecular dynamics simulations. The stable configuration for a single-atomic-layer-height disconnection is a pyramidal-basal (PyB) disconnection connecting an I₁ fault associated with a stacking sequence change of ABACA, or a basal-pyramidal (BPy) disconnection connecting an I₁ fault associated with a stacking sequence change of BABCB. A stable single-atomic-layer-height disconnection can transform to a less stable single-atomic-layer-height disconnection when its step orientation changes solely. A stable single-atomic-layer-height disconnection can also transform to another stable single-atomic-layer-height disconnection, when the step orientation of the disconnection and the type of the I₁ fault that connects with the disconnection change synchronously, and this process is accompanied with the emission of a Shockley partial dislocation from the twin boundary.

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.

In this work a new nanoscale surface marking technique, namely electron beam damage induced surface marking (EBDISM), is developed and tested for the first time on a fine-grained pure Mg surface. This technique utilizes focused high-energy electron beam of a scanning electron microscope to “burn” dense arrays of nano-scale grid patterns on the sample surface, and it is proved to be very effective for identifying and measuring localised deformation behaviours. However, the surface marking deposited by EBDISM is not permanent and it tends to deteriorate overtime. Cheap, easy to use and versatile, the EBDISM technique has a huge potential for quantitative measurement of strain field and nano-scale deformation analysis.