Prohesion and outdoors tests on corrosion products developed over painted galvanized steel sheets with and without Cr(VI) species

Abstract Galvanized steel sheets pre-treated with a new product and then painted with a polyester topcoat without primer were submitted to Prohesion G-85 test (PT) and to outdoor marine exposure test (OT). The new product that replaces standard inorganic chromium pre-treatment + primer consists in a water based resin which applied directly to the properly cleaned metal substrate is then dried in place. This scheme sets aside Cr(VI) compounds which cause severe damages on human health. Goethite, lepidocrocite, magnetite, akaganeite and silicates were found in OT samples coinciding with the usual corrosion products obtained for conventional painting schemes (with Cr(VI)). Surprisingly in PT samples greigite was detected, showing that the new painting scheme is susceptible to microbiological corrosion. Goethite, lepidocrocite, pyrite, magnetite and akaganeite were also found. This study allows the conclusion that in the PT the corrosion mechanism is different from that in the OT for the analyzed samples and should not be used to predict the performance of this kind of outdoor exposed materials.