Magnesium (Mg) alloys are usually subjected to torsion deformation during processing or manufacturing. However, the torsional behavior remains underexplored at the atomic level compared to uniaxial deformation. In this work, atomistic simulations are employed to understand the deformation mechanism during torsion around \(\langle 10\overline{1 }0\rangle\) and \(\langle 11\overline{2 }0\rangle\) axes of Mg. We reveal that the onset of plasticity occurs near the surface due to stress-gradient effect and the deformation mechanisms are highly dependent on torsion axis. Specifically, the prismatic and basal slip dominate torsion around \(\left[ {11\overline{2}0} \right]\) axis. During torsion around \(\left[10\overline{1 }0\right]\) axis, \(\left\{ {11\overline{2}1} \right\}\) twinning can be activated, whereas \(\left\{ {10\overline{1}1} \right\}\) twinning is formed due to local stress but detwinned eventually. Moreover, extensive cross slip and interactions between basal and prismatic dislocations are observed and the associated mechanisms are discussed. These novel atomic-scale insights provide deeper understanding of the plastic deformation mechanisms of Mg under torsional loading.
