Effect of heat treatment on the mechanical properties and corrosion behaviour of Al–Si–Mg alloy systems

Abstract: In this study, effects of heat treatment on microstructure, hardness and corrosion behaviour of Al based eutectic alloy systems directionally solidified at different growth rates were investigated. The compositions of alloys were selected as Al–12.95 wt % Si–4.96 wt % Mg and Al–13 wt % Mg2Si. Al–12.95 wt % Si–4.96 wt % Mg and Al–13 wt % Mg2Si alloys were kept at 500 and 540°C for 2 h, respectively, then quenched in cold water and subsequently artificially aged at 180°C for 4 h. The microstructure of Al–12.95 wt % Si–4.96 wt % Mg eutectic alloy consists of irregular Si plates and Mg2Si Chinese script in an aluminium matrix, while the microstructure of Al–13 wt % Mg2Si pseudoeutectic alloy consists of Mg2Si Chinese script in an aluminium matrix phase. Hardness value increased from 83.7 ± 2.0 mm–2 to 125.3 ± 5.2 kg mm–2 and from 82.5 ± 1.0 to 121 ± 2.0 kg mm–2 with the effect of the growth rate and solution heat treatment for Al–12.95 wt % Si–4.96 wt % Mg and Al–13 wt % Mg2Si alloy, respectively. Corrosion behaviour of the samples were investigated by Tafel polarization curves and electrochemical impedance spectroscopy (EIS) techniques. The increasing solidification rate of the alloys and also the heat treatment process increased their corrosion resistance.