Abstract
The micromechanisms of high temperature damping in an AlMgSi 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 MgSi pairs in the dislocation core. Relaxation mechanisms related with grain boundaries or precipitates can be discarded.
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