Superplasticity of an Al-Mg alloy : deformation mechanisms and damage behaviour

Superplastic deformation of a fine-grained Al-Mg (5083) alloy has been investigated. The mechanisms of deformation were identified. As expected, the movement of grains is the predominant mechanism. However, from the variations with strain of several features (shape of the grains, dislocation density or crystallographic texture), it is shown that conventional dislocation creep contributes significantly to the macroscopic behaviour. In the studied alloy, superplastic deformation induces damage by nucleation, growth and coalescence of cavities. In this work, a particular attention was given to the coalescence process since it controls fracture, thanks to a three-dimensional characterisation of the population of cavities. It is shown that coalescence occurs in a large strain interval