Negligible effect of twin-slip interaction on hardening in deformation of a Mg-3Al-1Zn alloy

Extruded magnesium alloys with a strong basal texture present a strong tension-compression asymmetry in deformation due to the fact that dislocation slips dominate plastic deformation in tension along the extrusion direction (ED) whereas twinning dominates plastic deformation in compression along the ED. The deformation characteristics allows for a study of the twin-slip interaction by introducing dislocations in the material before activating twinning. In the current work, dislocations of different densities are first introduced by prestraining in tension an extruded Mg-3Al-1Zn alloy along the ED to 5% and 10% of total strain, respectively. Then the loading direction is reversed to compression such that deformation twinning is activated. The results show that the hardening rate after different prestrains remains nearly unchanged, indicating that twin-slip interaction produces negligible effect on strain hardening. The yield stress in the reversed compression increases only slightly with increasing prestrain: ~20 MPa at every 5% increase in prestrain. Electron backscatter diffraction results show that prestraining can retard twin nucleation at the very early stage of plastic deformation, but it has little effect on twin growth.