The origin of discontinuous yielding in Mg alloys under slip-dominated condition studied by in-situ synchrotron diffraction and elastic-viscoplastic self-consistent modeling

A discontinuous yielding was observed in the as-extruded Mg-7Gd-2Y-1Zn-0.6Zr (wt. %) alloy under uniaxial tension along the extrusion direction, which was eliminated by the peak-aging treatment. The deformation mechanisms of the as-extruded and peak-aged alloys were studied by in-situ synchrotron diffraction measurement and elastic-viscoplastic self-consistent (EVPSC) modeling. The in-situ synchrotron diffraction results suggest that the unpinning of basal dislocations from solute atmospheres causes the stress relaxation in the basal slip favored grains. The EVPSC modeling results indicate that the discontinuous yielding in the as-extruded alloy is associated with the interaction between basal dislocations and solute atmospheres. After peak-aging treatment, the interaction between basal dislocations and solute atmospheres is weakened due to the consumption of a number of solute atoms. Consequently, the discontinuous yielding is eliminated in the peak-aged alloy.