Abstract
Differential scanning calorimetry was used to study the energetics and the dissolution kinetics of Guinier-Preston zones and η′ phases in Al-4.5at.%Zn-1.75at.%Mg alloys aged for various times at 298 or 393 K. The results show that for samples aged at 298 K the dissolution enthalpies, which are proportional to the pre-existing particle volume fractions, increase with the aging time, whereas for samples aged at 393 K the ΔH r values exhibit a maximum after aging for 16 days. However, the peak and reversion temperatures always increase with the aging time regardless of the aging temperature. Using an integrated kinetic function, developed on the basis of a difusion-limited dissolution kinetic model under non-isothermal conditions, the calculated curves were fitted to the experimental data, allowing precipitate sizes to be computed. Furthermore, good correlation was observed between the strength of these alloys and the measured particle size.
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