Influence of temperature and strain rate on serration type transition in NZ31 Mg alloy

The process of tensile test at different temperatures and strain rates was used to study the characteristics of serrated flow, i.e., Portevin-Le Chatelier effect (PLC), in NZ31 Mg alloy. The PLC effect in the tensile stress-strain curves was observed at the temperature range of 150-250 °C. Serrated flow during the deformation at 250 °C is prominent, and a lot of slip bands with a specific direction in each grain can be observed in the microstructure. The serration changes from type A to type C with the increase of temperature and the decrease of strain rate. One single serration of type A was described specifically by the processes of partial pinning, absolute pinning and unpinning. The enhancement of pinning ability at high temperature and low strain rate can promote the absolute pinning process and restrain the unpinning process, which explains the serration type transition.