Transformation to pyramidal Ⅱ slip in 10-12 twin interaction: experiments and molecular dynamics simulations in Mg single crystal

Twinning is an independent deformation system to accommodate strain in magnesium (Mg) alloys. The pyramidal Ⅱ <c+a> slip has a superior capacity to coordinate the deformation along the c-axis direction. However, the intrinsic mechanism of various slip modes transitions to the pyramidal Ⅱ <c+a> slip and their effects on related mechanical properties in cross tensile twins remain unclear. To address this, in this work, cross tensile twins were introduced through room-temperature bidirectional compression of pure Mg single crystals. The basal <a> slip, prismatic <a> slip and pyramidal <a> slip were selected. Molecular dynamics (MD) simulation methods were combined to study the microscopic mechanisms of dislocation slip and atomic motion during the transition of these three types of slip to the pyramidal Ⅱ <c+a> slip. The results show that the cross tensile twins exhibit a penetrating morphology under the basal <a> slip transformation behavior. After the transformation to the pyramidal Ⅱ <c+a> slip, the crystal texture strength weakens, dislocation ordered arrangement forms a dislocation wall, and the regular movement of atoms promotes the migration of the twin boundary and improves room-temperature plasticity. The prismatic <a> slip transformation behavior occurs concurrently with the transition of pyramidal <a> slip. During the transition to the pyramidal Ⅱ <c+a> slip, the internally accumulated dislocations are consumed and severe lattice distortion occurs. This study comprehensively summarizes the slip transformation mechanisms of tensile twins in Mg and its alloys, holding significant implications for developing Mg alloy materials with enhanced mechanical properties.