Evolution of Nanometer Precipitates in AA7050 Alloy Subjected to Overaging Treatment and Warm Deformation

The aim of this work was to develop a new processing method that can be utilized to refine grain structures. In order to produce sufficiently large dispersed precipitates to obstruct the dislocation sliding, the precipitation behaviors of AA7050 alloy during overaging and warm deformation were investigated. The results show that the size and quantity of the needle-like precipitates increased with increasing aging temperatures and times during overaging. The strain can induce the dissolution of needle-like precipitates and the re-precipitation of the spherical and refined precipitates, which were wrapped around by high density dislocation cells. The size and distribution of the precipitates and dislocation density were stable during the stress relaxation processing at 300 °C with a strain rate of 10 s-1. The sub-grains and fine-grained structures were obtained owing to the pinning effect of the precipitates, resulting in both improved strength and ductility.