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The mechanical relaxation of 7075 (Al Zn mg) and 2024 (Al Cu mg) alloys was studied by using the time temperature superposition principle

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Document pages: 12 pages

Abstract: The viscoelastic response of commercial al – Zn – mg and Al – Cu – Mg alloys was measured using a dynamic mechanical analyzer (DMA) as a function of temperature (30 to 425 ° C) and loading frequency (0.01 to 150 ° C   Hz). The time temperature superposition (TTS) principle has been proved to be useful in studying the mechanical relaxation of amorphous materials and obtaining the master curve. In this work, the TTS principle is applied to the measured viscoelastic data (i.e. storage and loss modulus) to obtain the corresponding master curve, and the mechanical relaxation leading to the viscoelastic behavior of the studied alloy is analyzed. For the storage modulus, the master curve of the low temperature region (from room temperature to 150 ° C) can be determined, and for the storage modulus, the master curve can be determinedd loss moduli, another master curve for a high-temperature region (from 320 to 375°C). These temperature regions are coincidental with the stable intervals where no phase transformations occur. The different temperature dependencies of the shift factors for the identified master curves, manifested by different values of the activation energy in the Arrhenius expressions for the shift factor, are due to the occurrence of microstructural changes and variations in the relaxation mechanisms between the mentioned temperature regions.

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