Creep and microstructure in ultrafine-grained 5083 Al

Creep and microstructure in ultrafine-grained (UFG) 5083 Al were investigated at 473 K. UFG 5083 Al was prepared by consolidating the cryomilled alloy powders via hot isostatic pressing followed by extrusion. The creep microstructure developed in the alloy was examined by means of transmission electron microscopy. The results show that the relationship between stress and strain is sigmoidal. Such a sigmoidal behavior is similar in trend to those reported for solid-solution alloys and superplastic alloys. An analysis of the mechanical data along with the consideration of several microstructural findings related to dislocation activity and configuration indicates that the alloy behaves as a superplastic alloy and not as a solid-solution alloy. Also, it is shown that the superplastic behavior of UFG 5083 Al is characterized by the presence of a threshold stress whose origin is most likely related to an interaction between impurities, which are able to segregate at nanoscale dispersion particles introduced as a result of processing, and dislocations, which are captured at the departure side of the particles.