Determination of kinetic parameters of the hardening phases in Al–Mg–Si alloy using DSC analysis and its photo-electrochemical protection

Abstract

Differential scanning calorimetric (DSC) is a good tool for investigating the phases transformation, since it permits the determination of the kinetic parameters such as activation energy and reaction order. The hardening phase precipitation in the Al–Mg–Si alloy was investigated by using DSC and isothermal and non-isothermal calculation models. All specimens were treated up to 550 °C with heating rates (ν) of 5, 10, 20 and 30 °C/min. The shift from the temperature peak to a higher for high heating rate indicates that the precipitation reactions are thermally activated. The results showed that the activation energy and the reaction orders, obtained from both methods are similar. The decreased activation energy is attributed to the saturation of the previous phase, which acts as precursor for the metastable phases. The pre-exponential factor (ko) calculated by the isothermal calculation method is equal to 8.36 × 107 s−1. On the other hand, the corrosion resistance of the alloy is significantly enhanced by photoelectrochemical cathodic protection. This was achieved by short-circuiting the alloy to n-CdS under visible irradiation where the corrosion current decreases by 88%.