The viscoelastic response of pure Al and commercial 6082 and 6082-T6 (Al–Mg–Si)
alloys is measured with dynamic–mechanical analyzer as a function of temperature
(ranging from 35 to 425°C) and loading frequency (ranging from 0.01 to 100 Hz).
The measured data (the storage modulus, loss modulus, and mechanical damping)
are compared to available transmission electron microscopy and differential
scanning calorimetry data, to ascertain whether unexplained variations of the
viscoelastic behavior of the alloys can be correlated to phase transformations.
The results suggest that some of these variations may be controlled by the
formation and dissolution of metastable phases, such as Guinier–Preston (GP)
zones and phases β″, β′, and B′. Indeed, GP zones and phase β″ have been
reported to control other mechanical properties. However, due to the high
complexity of the aging path of Al–Mg–Si alloys, with formation and dissolution
reactions of many precipitate types overlapping along wide temperature
intervals, further research is necessary to establish unequivocally the
contribution of each individual phase transformation to the overall viscoelastic
behavior. Finally, an internal friction peak related to grain boundary sliding
is significantly smaller in the alloys compared to pure Al, probably because the
precipitates pin the grain boundaries.
