Severe plastic deformation by Equal Channel Angular Pressing (ECAP) has now been used on several occasions to develop fine microstructure, typically reaching below the micron level and sometimes reaching the nano-level, in ductile metals and alloys. Such microstructures offer the possibility of improved strength, ductility and toughness, for example in Aluminium-base alloys and composites, while allowing flexibility of choice of alloy composition and the improvement of other material characteristics. The present study examines the changes of structure and mechanical properties found after ECAP-processing of Al-Mg alloy and during subsequent annealing to relax the microstructure. The creation of an elongated microstructure with a high proportion of low-angle boundaries and high retained dislocation density is demonstrated. The importance of these parameters in determining material behaviour, but especially strength, is discussed. Recent studies are underway to examine the use of ECAP processing for the consolidation and structural refinement of metastable Al powders and Al-base composite powders. The importance of hydrostatic pressure and shear straining in the consolidation and microstructural refinement is discussed.