Thermal Analysis of the Mechanism and Kinetics Parameters of the Metastable Phases Precipitation in the Al-Mg-Si Alloy

Abstract

In this experimental study, the mechanism and kinetic parameters of the metastable phases precipitation in the Al-Mg-Si alloy were determined thermally by differential scanning calorimetric (DSC) analysis. All samples were treated up to 550 °C at heating rates of 5, 10, 20 and 30 °C/min. The apparent activation energy (56.74 kJ/mol) and the Avrami exponent (0.99), were determined by DSC from the non-isothermal method, using the Ozawa, Boswell and Kissinger methods while those obtained by isothermal method using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model were 51.04 kJ/mol and 1.18. The activation energies values indicate that the formation of the metastable phases was mainly controlled by the migration of Mg and Si. The values of n, are characteristics of a growth of plate after saturation of nucleation. The frequency factor (ko) calculated by the isothermal method is found to be 8.36×107 s-1.