Dislocation structures in a superplastic Zn-40wt% Al alloy

Abstract

In a transmission electron microscope study of the Al-rich phase of a deformed Zn-40wt% Al alloy, the dislocation structures. Burgers vector distributions and dislocation line directions have been determined as a function of strain and strain rate. The Burgers vector distributions are similar at superplastic and higher strain rates, although there is a gradual increase in dislocation density and number of climbing dislocations as the strain rate increases. Contrary to previous results, there is no sharp change in dislocation structure between the superplastic and high strain rate regions and reasons for this are discussed. After deformation at the very lowest strain rate, the Burgers vector distribution is uneven and insufficient dislocations/Burgers vectors are present to maintain grain compatibility by slip alone, and it is concluded that diffusion processes become more important. Mechanisms of superplastic flow in this alloy are discussed with reference to a deformation mechanism map.