Mechanisms of exceptional ductility of magnesium single crystal during deformation at room temperature: Multiple twinning and dynamic recrystallization

Specially oriented magnesium single crystals were subjected to plane strain compression along the 〈112¯0〉 direction in c-axis extension at ambient temperature. The samples deformed up to a logarithmic final strain of −1, illustrating exceptionally high formability, even though basal and prismatic slip were initially inhibited due to the loading orientation with respect to the deformation geometry. Macroscopic {101¯2} extension twins forming massively during early stages of deformation completely consumed the whole sample, resulting in new soft orientations for slip. Additional twinning events took place in the form of secondary and tertiary twinning. At somewhat advanced stages of deformation, newly formed (recrystallized) grains were observed within numerous bands associated with former {101¯1} contraction twins within the primary extension twinned matrix. Recrystallized grains were rotated around the c-axis of their parent twin by an average angle of 30°, resulting in a shift of orientations from the second type (〈112¯0〉) prismatic fiber of ideal twin orientations towards the first type (〈101¯0〉) prismatic fiber of recrystallized grains. This led to a substantial weakening of the texture intensity at the final strain, as well as a high frequency peak of 30° grain boundaries in the misorientation distribution. The obtained results are discussed with respect to the texture evolution during multiple twinning in conjunction with continuous dynamic recrystallization at room temperature.