Evaluation of Corrosion Behaviour of Galvanised, Galvalume and Colour-Coated Steel Sheets

In the present study corrosion behaviour of three coated steel sheets in different corrosive environments was evaluated using various characterisation techniques. Multiple types of corrosion tests, like salt spray test, 100% relative humidity test and chemical resistance test, were performed to report the corrosion resistance of samples in different corrosive environments. Enhanced corrosion resistance properties of the colour-coated samples were obtained from all the studies, followed by galvalume and galvanised samples. Cyclic voltammetry reveals a slightly higher pitting for the galvalume sample. SEM, EDS, XRD and Raman analyses for the salt spray tested and 100% humidity tested galvanised samples shows various corrosion products with their morphologies. XRD analysis reveals Zn5(OH)8Cl2H2O (simonkolleite), ZnO (zinc oxide), β-Zn (OH)2, Zn (OH)2 (zinc hydroxide) and Zn (ClO4)2 for salt spray tested samples whereas for the 100% relative humidity tested samples, main corrosion products are ZnO (zinc oxide), β-Zn (OH)2, Zn (OH)2 (zinc hydroxide), Fe and Zn. Raman spectroscopy reveals the presence of ZnO, β-FeOOH, white rust, green rust, FeCl2, Fe3O4, FeOH, Fe2O3 and δ-FeOH for salt spray tested samples, but for 100% humidity test, only ZnO is revealed.