Microstructure strengthening mechanisms in different equal channel angular pressed aluminum alloys

Microstructure characterization and identification of the different nature of boundary formation during severe plastic deformation is the basis for a quantitative analysis of material flow stress. In equal channel angular pressing, the microstructure evolves to form low-angle dislocation boundaries and high-angle boundaries whose origin is different. For this reason, boundary misorientation, size and fraction evolve differently with strain. The Hall-Petch relationship in severe plastic deformed aluminum and aluminum alloys has been extensively discussed by Niels Hansen and others in several published works. It appeared that in such cases, the dislocation boundary strengthening contribution is to be taken into account. This paper deals with further insights into the Hansen's and other authors approach to the Hall-Petch relationship. Present approach is based on a detailed microstructure characterization of the different strengthening contributions in severe plastic deformed aluminum alloys. AA1200, AA3103, AA6000 series, and AA2091 were quantitatively characterized by TEM inspections. The calculated alloys yield strengths were compared to measured tensile yield stresses obtaining a quite satisfactory matching. This, ultimately, confirmed the proposed approach and models. Finally, an experimental value of the hardness-to-yield stress, H/sigma(y) , was found for all the studied alloys and discussed accordingly. (C) 2012 Elsevier B.V. All rights reserved.