Damage sensitivity in a commercial Al alloy processed by equal channel angular extrusion

Abstract A 5083 Al–Mg is processed by equal channel angular extrusion (ECAE) at 150 °C according to various routes. The resulting microstructures are characterised and tested in tensile conditions at high temperature. A particular attention is given to strain induced damage and to the effect of ECAE on the population of second phase particles initially present in the alloy. The relation between the second phase particles and the cavities are investigated by X-ray micro-tomography, which provides three-dimensional (3D) microstructural characterisations. It is shown that the mean size of the particles is progressively reduced by fragmentation when the number of extrusions is increased. Despite this reduction, the damage sensitivity of the alloy is not reduced since during ECAE, some cracks are generated and the average distance between the particles is decreased. Moreover, due to low temperature of deformation, superplastic properties of the ECAE processed microstructures are associated to relatively large stresses, which can promote cavity nucleation. Lastly, it is shown that despite small grain sizes (≈1 μm), the role of diffusion in the control of cavity growth is minor and that the extent of cavity coalescence before fracture remains limited.