In this work, super saturated solid solution Al–30 wt%Zn alloy was subjected to high pressure torsion (HPT). The material properties and microstructural evolution were experimentally studied. Despite strong grain refinement during HPT, the process of softening is observed. Such a material behavior is captured by a proposed model (MBWG) that takes into consideration the effects of solid solution hardening, Orowan looping and evolution of the dislocation density. Namely, the softening process occurred during HPT is attributed to decomposition of super saturated solid solution and evolution of the dislocation mean free path with plastic strain. Our simulation shows that the proposed model describes well the softening and saturation processes, and the decomposition of solid solution plays a significant role during the HPT process.