Work-softening and anneal-hardening behaviors in fine-grained Zn–Al alloys

In this study work-softening and anneal-hardening behaviors were explored and compared in fine-grained Zn–22 Al and Zn–22 Al–0.3 Cu alloys. It was found that the work-softening behavior is enhanced by a decrease in grain size and an increase in the relative amount of high-angle boundaries. A model based on the absorption of dislocation pile-up by grain boundary is proposed to explain the work-softening behavior in these alloys. When subjected to a grain-coarsening heat treatment, ultra-fine-grained Zn–Al and Zn–Al–Cu alloys exhibit an unusual anneal-hardening behavior. But once their grain size exceeds a critical value, the Zn–Al and Zn–Al–Cu alloys resume the normal anneal-softening behavior.