{10-12} Twin variants selection mechanisms during twinning, re-twinning and detwinning

{10-12} Twinning is one of the main deformation mechanisms in Mg-3Al-1Zn at room temperature. Twin variant activation is reported to follow the Schmid law and be activated as a unidirectional slip system, but local stress states are said to favor other twin variants. In a material containing a first generation of {10-12} twins, subsequent deformation can activate re-twinning and detwinning. In the present paper, a multiple twin structure containing two generations of twins was generated by two successive in-plane compressions along two different directions in a rolled plate. The plate was subsequently loaded to activate detwinning. A grain by grain analysis was performed after each compression to identify the twin variants selection mechanisms. During compression and re-compression, twinning was observed to obey the Schmid law well, with preferential activation of the variants with the highest Schmid factor. Other variants were observed and predicted by constraint models based on the Schmid law and extremum principles. Only a few twins and secondary twins {10-12}-{10-12} were favored by autotwinning and were less dependent on the Schmid factor. The grain boundary misorientations and first generation twin boundaries did not affect the nucleation of new twins statistically. Consequently the twin variant selection and the deformed texture can be predicted by self-consistent crystal plasticity models regardless of the neighboring grains orientations. On the other hand the activation of detwinning after annealing cannot be predicted from the twin orientation.