An Appropriate Specimen Configuration for Evaluating the Perforation Corrosion Resistance of Automotive Coated Steel Sheets in Accelerated Corrosion Tests

A variety of metallic coatings have been developed for automotive steel sheet panels to achieve better corrosion resistance. Accelerated corrosion tests are used to develop and select coated steel sheets in a short period. In addition to the test conditions, a specimen configuration simulating the lapped portion of vehicles is another important issue when evaluating resistance to perforation corrosion in the laboratory since the specimen must reproduce the unique environment inside the lapped portion. In this study, lapped specimens with different configurations were prepared and the influence of a bare area in a large crevice on the corrosion behavior of zinc coatings was systematically analyzed by comparing the results of laboratory tests with the corrosion observed in vehicles in service. It was found that the controlling factor of resistance to perforation corrosion was influenced by the configuration of the test specimen. A large crevice gap and bare area in the crevice of the lapped portion changed the corrosion behavior of the coatings and solution within the crevice. As a result of this, the corrosion of pure zinc was accelerated in comparison with zinc alloy coatings due to the rapid corrosion rate of the coating and the rapid consumption of corrosion product in the crevice. On the basis of the experimental findings, an appropriate specimen configuration and specimen preparation procedure for evaluating perforation corrosion resistance were proposed.