After severe plastic deformation (SPD) processing, aluminum alloys show increased strength but low ductility. However, the ductility of the materials obtained during tensile tests does not reflect the full plastic deformation ability of the materials. This work presents the results of a more comprehensive plasticity analysis, which is applied first time to material after SPD processing. The current study considers an aluminum alloy 5083 before and after equal channel angular pressing (ECAP). The plasticity analysis was implemented based on the fracture locus, which was plotted in the space of the equivalent strain to fracture, the stress triaxiality parameter, and the Lode angle parameter using the Hosford–Coulomb (H–C) model. The parameters of the H–C model were determined using a combined experimental–numerical approach. It was found that the plasticity of the 5083 alloy strongly depended on a combination of the stress triaxiality and Lode angle parameter. However, the fracture locus of the material after ECAP processing showed slightly higher values of equivalent strain to fracture than that of the initial material. This approach makes it possible to estimate the ultimate plasticity of the materials after ECAP processing for a wide range of stress-strain states and can be used to predict fracture in plastic deformation processes.