Chemical background of contact corrosion between copper and galvanized steel screws

This research aimed to study of the role of galvanic/contact corrosion between copper and galvanized steel screws.Based on our previous investigations by thermal imaging camera under power, the role of corrosion processes around the fitting were in the focus that could be responsible for the heat evolution.In this multi-metallic system where the metals have different electrode potentials, the chemical processes in the presence of electrolyte were analyzed by different, complementary techniques: the weight loss tests measured at different temperatures gave information about the corrosive metal losses, the analyses of metal ions dissolved during the corrosion processes were performed by inductively coupled plasma optical emission spectrometry (ICP-OES), the change in the surface morphology caused by the corrosive deterioration were visualized by stereo microscopy (SM), by scanning electron microscopy (SEM) and by atomic force microscopy (AFM).These complementary experiments proved numerically that during the function of these fittings the copper dissolution was inhibited by the presence of zinc and iron even at increased temperature.The appearance of iron ions in the electrolyte and the brownish spots on the metal surface indicated that first zinc could inhibit the copper corrosion but after the dissolution of the thin zinc layer on the screw, iron takes over the protection of copper.