Abstract:Differential scanning calorimetric (DSC) study was carried out at different heating rates to examine the solid state reactions in a 7150 Al-Zn-Mg alloy in water-quenched (WQ) state, naturally and artificially aged tempers. The exothermic and endothermic peaks of the thermograms indicating the solid state reaction sequence were identified. The shift of peak temperatures to higher temperatures with increasing heating rates suggests that the solid state reactions are thermally activated and kinetically controlled. The artificial aging behaviour of the alloy was assessed by measuring the variations of hardness with aging time. The fraction of transformation (Y), the rate of transformation (dY/dt), the transformation function f(Y), and the kinetic parameters such as activation energy (Q) and frequency factor (k₀) of all the solid state reactions in the alloy were determined by analyzing the DSC data, i.e. heat flow involved with the corresponding DSC peaks. It was found that the kinetic parameters of the solid state reactions are in good agreement with the published data.

Key words: 7150 Al-Zn-Mg alloy; DSC; aging behaviour; activation energy; transformation function