In this presentation we will discuss about the stability of ultrafine grained structures subjected to severe plastic deformation with a special emphasis on strain induced phase transformations. In metallic alloys, large strains lead to the creation of a large density of lattice defects that strongly interact with alloying elements. Beyond segregations along dislocations or grain boundaries, some phase transformations may also occur due to an enhanced atomic mobility. For a better understanding of the underlying mechanisms, the structure of various Al-based systems subjected to severe plastic deformation have been investigated using TEM and APT. It is proposed here to make a short review of the most striking results recently collected both on commercial alloys and model systems. A special emphasis will be given on the potentiality offered by deformation induced dynamic phase transformations to design unique nanoscaled structure with optimized properties.