Evolution of the microstructure and mechanical properties of Al-30 wt. % Zn alloy after the severe plastic deformation (SPD) by the high-pressure torsion has been investigated in detail in dependence on the increasing deformation degree. SPD leads to the gradual grain refinement and decomposition of the Al-based supersaturated solid solution. Measurements of the microhardness reveal a successive softening of the alloy with the increased deformation degree.