A combined electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) approach showed that the corrosion behaviour of 5083 Al alloy was controlled by Mg dissolution at the Mg-rich intermetallic coarse particles (IMCs) that were defects of the passive film. It was thus shown that microstructures with high amount of Mg-rich IMCs were less resistant to corrosion. EIS experimental data were well superimposed with fitted ones calculated using a model proposed in the literature for pure magnesium. The model allowed to plot the resistivity profiles of the passive films, which highlighted their double-layer structure evidenced by XPS.