Competition between the formation and decomposition of a solid solution in Al-Mg alloys during high-pressure torsion

During severe plastic deformation (SPD) of solid solutions, two processes occur simultaneously and compete with each other, namely the decomposition of a solid solution and dissolution of the second-phase precipitates. After a certain deformation, a steady-state concentration css 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 Teff (called usually effective temperature). The effect of high pressure torsion (HPT) on the structure of the Al-10 wt.% Mg alloy is studied. In a sample annealed at a temperature of 420°C, the HPT leads to a noticeable decomposition of the solid solution. In a sample annealed at a temperature of 300°C, a decrease in the concentration at HPT also occurs, but it is less than in the first case. Finally, in a sample annealed at a temperature of 200°C, there is practically no change in the concentration in the solid solution. This means that for Al-Mg alloys css = 3 ± 0.3 wt.% Mg. A comparison with the literature data for equal−channel angular pression (ECAP) of Al-Mg alloys gives approximately the same css value for ECAP. This means that the effective temperature of Teff in the Al-Mg alloys is close to 200°C.