Mechanical spectroscopy was employed to investigate the microstructure evolution of a Zr-modified 6082 Al-Mg-Si alloy and the same alloy with Sc addition after ageing and following severe plastic deformation through equal channel angular pressing. Measurements of the internal friction and dynamic young modulus have been performed in isothermal and isochronal runs in the frequency range 0.1 - 104 Hz. The anelasticity spectra reveal in the temperature range 470-870 K both structural and anelastic relaxation processes. Two structural damping maxima connected with inverse temperature trend of the modulus occur in the alloys submitted to equal channel angular pressing, the first one is strongly suppresed by Sc and Zr addition. An anelastic relaxation peak whose strength depends on the nature and morphology of precipitates and dispersoids and on the deformation and ageing condition was observed in all samples investigated. The high background damping occurring before the first structural damping maximum is analyzed with reference to a superplastic behavior of the equal channel angular pressing processed alloys.