Flow stress behavior of AZ61 magnesium alloy during hot compression deformation

Because of its hexagonal close-packed crystal structures, AZ61 alloy shows low ductility at room temperature and requires thermal activation to increase its ductility and formability. A mathematical model using the amended Fields–Backofen (FB) equation containing a softening item s was established to describe the flow stress behavior of an extruded AZ61 alloy using hot compression tests in temperature and strain rate ranges of 523–673 K and 1 × 10−2 to 10 s−1. The results show that the flow stress of an extruded AZ61 alloy is evidently affected by both deformation temperature and strain rate; i.e., the flow stress decreases as the strain rate decreases and the deformation temperature increases, and a typical characteristic of dynamic recrystallization softening. Optical microstructure evidence shows that dynamic recrystallization takes place in the specimen edge during the deformation process. However, grain growth is only observed at the center of the sample. The flow curves calculated by the amended FB equation fit the experimental results well, not only in the strain-hardening stage but also in the softening stage.