Serrated flow and tensile properties of a Mg–Gd–Zn alloy

The tensile deformation behavior of Mg–3Gd–Zn (wt.%) alloy sheets annealed and aged at different temperatures has been studied. Samples annealed at 400 °C for 1 h exhibit serrated flow when they are tensile tested at temperatures ranging from 150 °C to 250 °C and at strain rates of 1 × 10−4 s−1 to 1 × 10−2 s−1. The critical strain for onset of the serrated flow is observed to increase with increasing strain rate but decrease with increasing temperature. The temperature dependences of yield strength and ultimate strength exhibit a plateau, and the expected ductility dips are also observed in the temperature regime of serrated flow. For samples annealed at 480 °C for 1 h, the precipitates and serration both disappear. However, subsequent aging treatments result in the reappearance of a large amount of precipitates and the serration phenomenon, proving that the serrated flow in the Mg–3Gd–Zn sheets is mainly controlled by the shearing of precipitates by gliding dislocations. In addition, the observed static strain aging effect, the negative strain rate sensitivity and the calculated activation energy, combined with observations made by scanning electron microscopy, suggest that dynamic strain aging may also contribute to the serrations in the present alloy.