Unconventional twinning assisted by pyramidal II stacking faults.

Twinning significantly affects the deformation behavior of hexagonal close-packed Mg, so a thorough understanding of twin nucleation and growth mechanisms is required for enhancing the properties of Mg-based materials. The commonly observed tension twins have been traditionally linked to 〈c + a〉 dislocation dissociation, which results in zonal dislocations with large Burgers vectors several times that of a single twinning dislocation and some residual dislocations. Contrarily, our molecular dynamics simulations reveal twin nucleation from pyramidal II stacking faults through atomic shuffling without shear displacements. This introduces an alternative twin nucleation mechanism, different from the classically accepted mechanism of dislocation dissociation.