The electrochemical and corrosion behaviour of Al-Mg-Zn alloys in 3% sodium chloride and 0.3% sodium sulphate aqueous solution was studied, by means of dc and ac measurements at different polarization conditions. SEM and EDAX analysis were employed in order to characterize the surface structure of the above alloys. The relationship between morphological structure and electrochemical results was examined and particular attention paid to the influence of the secondary phase. Different heat treatments, performed to ensure the dispersion of the fine intermetallic phases, were carried out and the results briefly discussed.