Molecular dynamics (MD) simulation is employed to investigate the deformation behavior under various loading paths and strain rates of nanocrystalline magnesium (NC Mg) with [0001] texture. Atomic-scale structural evolution of NC Mg was performed under uniaxial and biaxial loadings. In tension process, compression twins and basal slip dominate, while the compression process is dominated by tension twins. The activation mechanism of twinning is highly sensitive to the loading path and grain orientation. Meanwhile, the effect of strain rate on the structural evolution of NC Mg was investigated. It is found that the effect of strain rate on the plastic deformation of NC Mg is reflected through the plasticity delays and the way to release the stress. As the strain rate decreases, the plastic deformation mechanism gradually changes from intragranular to grain boundary. Some significant potential deformation mechanisms in the loading process were studied. It is observed that {1121} twins nucleated inside the grains, and the thickening process is completed by basal 〈a〉 slip of the twin boundary. The strain compatibility between twins is automatically optimized with loading. Moreover, the detwinning mechanism caused by the interaction between twins and basal stacking faults is clarified.

The Swift effect of Mg alloy is sensitive to initial texture. However, dislocation slip is the main deformation mechanism during torsion of Mg alloy. The underlying relation of Swift effect and dislocation slip is still not clarified. The effect of stress state and pre-straining on Swift effect was studied experimentally during free-end torsion for an extruded AZ31 alloy. The free-end torsion was performed with axial tension and compression stress which is lower than yield stress. It is found that the transition of axial deformation from contraction to elongation occurs when the axial stress changes from negative to positive. The pre-dislocations introduced by pre-tension promote axial shortening during torsion. While the pre-twins introduced by pre-compression are inhibition of axial shortening. The change of axial deformation is attributed to competition between twinning and prismatic slip. The axial shortening of extruded Mg alloy is generated by tensile twinning leading to c-axis strain. In contrast, the axial elongation can be generated by the activation of prismatic slip. The magnitude of axial strain generated by twinning is larger than that by prismatic slip. Moreover, the occurrence of detwinning results in axial elongation at low shear strain.