The determination of the activation energy varying with the precipitated fraction of β″ metastable phase in an Al-Si-Mg alloy using non-isothermal dilatometry

The kinetic study of the β″ phase precipitation in Al-Si-Mg alloy was carried out through nonisothermal dilatometry. Using Kissinger method, the apparent activation energy was first estimated to be 67 kJ/mol. In order to investigate the variation of the apparent activation energy (Qα) as a function of the formed fraction (α) of β″ phase, differential isoconversional method of Friedman (FR) and integral isoconversional methods of Kissinger-Akahira-Sunose (KAS) were used. The methods showed an increase in Qα with α. However the dependence of Qα is more pronounced for FR method whose Qα values are higher. Qα values were in the range 77-110 kJ/mol and 67-79 kJ/mol for FR and KAS methods, respectively. Some disagreement between these results and those obtained in a previous work using DSC experiments are observed, particularly for FR analysis.