Organic coil coated aluminum substrates are one of the most widely used materials for construction industry. These coated substrates typically consist of 4 separate layers, the aluminum substrate, the inorganic conversion coating (resulting from the pretreatment application), and the organic coating layers that are called the primer and the topcoat. From industrial experience, it is not clearly and quantitatively determined how these layers contribute to the different processes that occur during corrosion, such as water uptake (diffusion of water through the coating) and the corrosion reactions that take place on the substrate. In this thesis, the formation of the inorganic conversion coating as a function of the pretreatment application parameters, immersion time, temperature and pH, and the individual effects of inorganic and organic coating layers on corrosion are investigated. The structure of the various surfaces formed after coating application and after corrosion testing by Neutral Salt Spray Test (NSST) is investigated by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), X-ray Fluorensence Spectrometer (XRF) and Atomic Force Microscopy (AFM) analysis, while their anticorrosive properties are determined by Electrochemical Impedance Spectroscopy (EIS). The results indicate that the formation of the pretreatment layer is enhanced continuously as function of temperature and immersion time, within the values investigated, while for pH an optimum is observed. The investigation of the corrosion resistance of substrates coated with different coating layers reveal that without organic coating layers, the substrates corrode much faster, indicating the importance of water diffusion on the corrosion reactions.