An industrial Al-Mg alloy was processed by Equal Channel Angular Extrusion. The resulting microstructures were studied and the mean orientation between cells were measured by transmission electron microscopy. The as-processed materials were deformed at high temperature. The effects of the number of extrusions on the mean grain size, the rheology at high temperature and the associated damage behaviour of the as-processed microstructures were investigated. It is shown that some damage occurs nearby second phase particles and the effect of ECAE processing on the size and the spatial distribution of these particles is discussed.