Structural changes in aluminum alloys upon severe plastic deformation

The structure and phase composition of Al-Zn, Al-Mg, and Al-Mg-Zn alloys were studied before and after severe plastic deformation of these alloys. The deformation was performed by high pressure torsion with true strain of ∼6. It was established that, as a result of severe plastic deformation, the grains of Al and Zn and also of the β and τ phases revealed in the structure decrease significantly in size and reach nanometer scales. A supersaturated solid solution of Zn in Al decomposes completely in this case and achieves the equilibrium state corresponding to room temperature. The decomposition is less pronounced for the magnesium-containing alloys. Based on the obtained experimental data, a conclusion is drawn concerning the possible mechanisms of this process. Microhardness measurements revealed softening of the alloys as a result of the deformation, which is due to the decomposition of the supersaturated solid solution.