Title: The Corrosion Resistance of Organic Composite-Coated Steel Sheets
text: In order to investigate the corrosion resistance of organic composite-coated steel sheets ( OCS ) in a real automotive environment, many kinds of corrosion tests were performed on test pieces and real automotive doors. Tests with a corrosive solution including iron rust were introduced to simulate the real corrosive environment of automotive doors. The relationship between the components of OCS and the corrosion resistance in the rust-including tests was examined. In addition, electrochemical studies were performed. Results indicate OCS has much better corrosion resistance than plated steel sheets with heavier coating weight in all tests. OCS shows excellent corrosion resistance in rust-free corrosive solution, however, some types of OCS do have corrosion concerns in rust-including tests. It became clear that these OCS types have an organic coating with lower cross-linking. With respect to the components of lower cross-linking OCS, Chromate coating has little effect on corrosion resistance in rust-including solution. On the other hand, an organic coating with higher cross-linking shows remarkable improvement of corrosion resistance in rust-including test solutions. Therefore, it is likely that thin organic coatings are susceptible to damage by rust including test solution. Electrochemical measurement actually shows that impedance of OCS after exposing in rust-including solution is lower than before exposing. Consequently, the rust-including tests did simulate the real automotive corrosive environment. It is important to use a proper organic coating with high resistance against rust, because rust exists in real automotive corrosive environments.