Abstract <p>It was discovered early the that severe plastic deformation (SPD) not only leads to the remarkable grain refinement but also enables effective mechanical mixing of diverse materials, allowing for a high concentration of dissolved components in a solid solution. Later it was observed that this dissolution of the second-phase precipitates and enrichment of a solid solution occurs simultaneously with decomposition of a solid solution. These two processes compete with each other during SPD. After a certain deformation, a steady-state concentration <i>c</i>_ss of the second component is reached in the solution during SPD. This concentration can be found at the solvus line in the phase diagram at the certain temperature <i>T</i>_eff (called usually effective temperature). The effect of SPD on the structure of various Al−Mg-based alloys is analyzed. The similarity and differences of precipitation and dissolution during various severe plastic deformation methods is described. The model describing the change of concentration in a solid solution during high-pressure torsion is developed.</p>