High damping capacity after precipitation in some commercial aluminum alloys

Three commercial aluminum alloys, Al-4 wt.% Cu (2017), Al-5 wt.% Zn-3 wt.% Mg-0.5 wt.% Cu (7022) and Al-0.9 wt.% Mg-1 wt.% Si (6082), have been studied by mechanical spectroscopy. In the as-received state, AlMgSi presents the highest damping capacity among these three light alloys. In order to favour dislocation damping, the solid solution concentration has been lowered by ageing. Annealing treatments were chosen in such a way that the alloy thermoelectric power was decreased to its lowest value, which means that the solute concentration was the lowest. No obvious damping change was observed after ageing in AlCu and AlZnMgCu. On the other hand, both the damping capacity and the elastic modulus have been increased by ageing in AlMgSi alloys. Moreover, a much stronger dependence of damping on the vibration amplitude was observed in the aged AlMgSi than in AlCu and AlZnMgCu alloys. This amplitude effect leads to a high damping capacity for high strain amplitudes in AlMgSi. Consequently, AlMgSi is the most promising grade for developing high damping light materials among the existing aluminum alloys.