Influence of uniaxial deformation on the corrosion performance of pre-coated packaging steel

The influence of uniaxial deformation on the corrosion performance of electrolytic chromium-coated steel (ECCS) in both the presence and absence of a polymer coating was studied using scanning electron microscopy (SEM), open circuit potential (OCP), potentiodynamic polarization (PP) measurements and electrochemical impedance spectroscopy (EIS). The individual and combined contribution of chromium-chromium(III) oxide and the polymer coating was investigated. Specimens were uniaxially deformed to maximum strains of 5, 10 and 25%, respectively. After deformation Lüders bands were observed on the surface of the metal substrates. The corrosion resistance of the ECCS was shown to be better than that of the bare steel, due to the protective properties of the chromium-chromium(III) oxide layer on the surface. The corrosion resistance of the ECCS was found to decrease with strain, to be attributed to the introduction of local defects in the coating leading to increasing exposure of the more active underlying steel with deformation. The PETG (a glycol-modified amorphous PET) coating as such proves to be a very effective barrier layer in protecting the underlying substrate, however, in combination with the bare steel its protective properties decrease with time of exposure and deformation. Combining the individual contributions of the chromium-chromium(III) layer and the PETG coating it was shown that the corrosion performance of the polymer-coated ECCS is significantly better than the polymer-coated bare steel after deformation, which can be also attributed to the good corrosion resistance of the chromium-chromium(III) oxide layers and the improved adhesion of the coating.