Influence of initial {10-12} twins on twinning behavior of extruded AZ31 alloys during free-end torsion

In this work, pre-compression along the extrusion direction was used to induce initial {10-12} twins in the extruded AZ31 rod. The effects of initial twins on twinning behavior during free-end torsion were investigated in detail. As-extruded AZ31 rod has a typical extrusion fiber texture. Torsional shear is equal to a bi-axial tensioncompression stress state. Under the stress state, only limited grains with special orientations can be favorably twinned. The c-axis of the twin-texture via torsion is close to the compressive loading direction. Besides, basal slip also greatly contributes to torsion deformation. Basal slip will induce the axes of most grains to rotate towards compressive loading direction during torsion. The c-axes of initial twins via pre-compression have an angle range of 30 deviated from the ED. Torsion deformation causes the twin-texture to rotate towards the compressive loading direction. The transformation mechanisms contain basal slip within twins, growth of initial twins, formation of new twin variants and detwinning. The selection of mechanism depends on the orientation of the parent grains and the initial twins. Moreover, the misorientation of {10-12} twin-boundary can be reduced by 10-20 during torsion owing to the orientation change caused by basal slip. Combining pre-compression and torsion can largely increase the relative proportions of 76 +/- 5/11- 20 twin boundaries and 66 +/- 5/ <11-20 > twin boundaries . Finally, the influence of pre-compression on torsion properties was also discussed.

Automated summary

In this study, initial {10-12} twins were induced in the extruded AZ31 rod through pre-compression along the extrusion direction. The effects of these initial twins on twinning behavior during torsion were thoroughly investigated. The combination of pre-compression and torsion increased the relative proportions of specific twin boundaries. The transformation mechanisms involved basal slip, growth of initial twins, formation of new twin variants, and detwinning. Furthermore, the influence of pre-compression on torsion properties was also discussed.