Coatings are used to enhance appearance and assure functional requirements. High performance and cost reduction during vehicle manufacturing are the main requirements, leading to increased use of pre-primed automotive sheet in recent years. Costs may be significantly reduced if the conventional electrophoretic primer is eliminated or its usage reduced. Conductive primers also offer the advantage of welding facility. The behaviour of two conductive pre-primers applied on galvannealed steel was studied and compared with that of a conventional electrophoretic primer. Before pre-priming a nonchrome pre-treatment was applied. Pre-primer 1 is an organic zinc rich silicate with a low thickness and pre-primer 2 is a very thin water based primer filled with graphite. The behaviour of two finish coat systems was also studied. These finish coats were applied on not primed and pre-primed galvannealed steel sheets. Two activation treatments were used, a conventional zinc phosphate and an experimental one. Finish coat system 1 included a powder intercoat, a waterborne base coat and a clear coat, and finish coat system 2 included the same powder intercoat, a solvent based base coat and a clear coat. Formability capabilities of pre-primers were evaluated through cupping and stone chipping tests. To evaluate corrosion protection, these samples were submitted to a cyclic corrosion test (CCT). Corrosion mechanisms were studied by scanning electron microscopy (SEM) with associated X-ray microanalysis by dispersive energy spectrometry (EDS) and by electrochemical impedance spectroscopy (EIS). To evaluate the performance of finish coats, the samples were also submitted to the same cyclic corrosion test, and the paint coating adhesion was evaluated, before and after exposure, by cross-cut test method. Both pre-primers applied with a low thickness seem to be good alternatives to the conventional electrophoretic primers. In agreement with results previously obtained for preprimed electrogalvanized steel substrate, submitted to CCT, electrochemical studies showed that less protection was achieved by primer 2. Regarding finish coats better adhesion was verified for the one with waterborne base coat, a more environmentally convenient system. Both finish coats presented good anticorrosive behaviour, without significant defects on undamaged areas.
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