Modeling of the Effect of Temperature, Frequency, and Phase Transformations on the Viscoelastic Properties of AA 7075-T6 and AA 2024-T3 Aluminum Alloys

The viscoelastic response of commercial aluminum alloys 7075-T6 and 2024-T3 as a function of temperature is presented. Experimental data are obtained with a dynamic-mechanical analyzer (DMA) at different loading frequencies and compared with the available transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) data. The effect of successive microstructural transformations (particle precipitation and redissolution) is revealed. An analytical model is developed, which fits the mechanical response up to 573 K (300 C). The model takes into account the concentration of Guinier-Preston Zones (GPZ) and metastable precipitates (g¢ in AA 7075-T6 and h¢/S¢ in AA 2024-T3), allowing us to determine the kinetic parameters of these transformations. The activation energies were previously obtained by several authors from DSC measurements and other techniques, showing considerable dispersion. The presented data, obtained with a completely different technique, allow us to reduce the uncertainty on these data and show the potential of DMA measurements in the study of microstructural transformations.