Abstract:Thermal analysis is one of the most used techniques for analyzing the behavior of aluminum alloys in order to analyze the precipitation of Guinier-Preston (GP) zones and different phases formed. In the present work, the behavior of the Al-5.46wt.%Zn- 1.67wt.%Mg alloy was studied. The mechanism and kinetics of precipitation of the GP, the metastable phase η′ and the equilibrium phase η were investigated using DSC carried out between room temperature and 480 °C at heating rates of 5, 10, 15 and 20 °C/min. The apparent activation energies, calculated by DSC from isothermal calculation method using JMAK model, for GP, η′ and η were 56, 79 and 96 kJ/mol, respectively, and those calculated by non-isothermal calculation method using Kissinger methods were 57, 82 and 99 kJ/mol, respectively. The values of Avrami parameter, n, from isothermal calculation, during the precipitation of the GP, η′ and η were 1.103, 1.9075 and 1.92, respectively, and those calculated by non-isothermal were 0.86, 2.30 and 2.24, respectively. The results show that GP zones formation is governed by the migration of Zn and Mg atoms while the precipitation of the η′ metastable phase and the η stable phase is governed by both the migration and the diffusion of the solute atoms.

Key words: Al-Zn-Mg alloys; precipitation kinetics; DSC; JMAK model; activation energy; Avrami parameter