Study on Mechanical Relaxations of 7075 (Al–Zn–Mg) and 2024 (Al–Cu–Mg) Alloys by Application of the Time-Temperature Superposition Principle

• Published in: Advances in materials science and engineering 2017-01, Vol.2017 (2017), p.1-12
• Main Authors: Rojas, Jose I., Crespo, Daniel, Nicolás, Jorge
• Format: Article
• Language: English
• Subjects: ACTIVATION ENERGY; Aliatges; Alloys; Alumini; Aluminum alloy; Aluminum alloys; ALUMINUM ALLOYS (50 TO 99 AL); Aluminum base alloys; Aluminum-magnesium alloys; Aluminum-magnesium-zinc alloys; Amorphous materials; AMORPHOUS STRUCTURE; Analyzers; Compliance; COPPER ALUMINUM ALLOYS; Dynamic-mechanical analysis; Enginyeria dels materials; Grain boundaries; Internal friction; Intervals; Mechanical properties; Mechanical relaxations; Metal fatigue; Microstructure; MICROSTRUCTURES; Phase shift; Phase transformations; Physics; Temperature; Time-temperature superposition; Viscoelasticity; Viscositat; Àrees temàtiques de la UPC
• ISSN: 1687-8434; 1687-8442
• DOI: 10.1155/2017/2602953

The viscoelastic response of commercial Al–Zn–Mg and Al–Cu–Mg alloys was measured with a dynamic-mechanical analyzer (DMA) as a function of the temperature (from 30 to 425°C) and the loading frequency (from 0.01 to 150 Hz). The time-temperature superposition (TTS) principle has proven to be useful in studying mechanical relaxations and obtaining master curves for amorphous materials. In this work, the TTS principle is applied to the measured viscoelastic data (i.e., the storage and loss moduli) to obtain the corresponding master curves and to analyze the mechanical relaxations responsible for the viscoelastic behavior of the studied alloys. For the storage modulus it was possible to identify a master curve for a low-temperature region (from room temperature to 150°C) and, for the storage and 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.