High temperature damping in Al-Mg-Si industrial alloys

Abstract

The micromechanisms of high temperature damping in an Al-Mg-Si industrial alloy are investigated by mechanical spectroscopy. The alloy in the as-received T6 state shows a relaxation peak at 483 K (1 Hz) with an activation energy H= 1.6 eV and a limit relaxation time τ0 = 1.3 × 10-18 s. It is also found in solubilized, quenched and overaged samples. The internal friction maximum is attributed to a mechanism in which: a) lattice dislocations are firmly pinned by β″ or β′ precipitates and b) lattice dislocation motion is controlled by the dragging of a complex Cottrell cloud composed by Mg and Si solute atoms. A good description of the experimental results is provided considering that the dislocation motion is controlled by transverse diffusion of Mg-Si pairs in the dislocation core. Relaxation mechanisms related with grain boundaries or precipitates can be discarded.