Twin-assisted precipitation during hot compression of an Mg-Gd-Zn-Zr magnesium alloy

Abstract

Dynamic precipitation in an Mg-Gd-Zn-Zr alloy during hot compression at 350°C and 450°C and at strain rates of 0.001-0.1s−1 is investigated. The deformation conditions were designed such as to promote twinning or slip of dislocations. The results indicated that both twinned and non-twinned grains were present at 350°C, with the extent being a function of the applied strain rate. The formation and propagation of {101̅2}〈1̅011〉 primary tensile twins within the twinned grains was identified as being at root of the twin-assisted precipitation phenomenon. The precipitates had spherical-morphology in the twinned grains whereas parallel arrays of rod-shaped precipitates formed in the non-twinned grains due to dynamic precipitation on the slip bands and the stacking faults. Twin-assisted precipitates were suppressed by increases in the strain rate at 350°C because of the shorter time required for solute element diffusion towards the nucleated precipitates at that temperature. Increasing the deformation temperature to 450°C changed the dominant deformation mechanism from twinning to slip of dislocations, resulting in the formation of rod-shaped precipitates similar to those observed in non-twinned grains at 350°C. An EBSD analysis was used to study the dominant deformation mechanism as a function of the Schmid factor, and the twinning deformation mechanism was found to be predominant in the grains having a lower Schmid factor.