Abstract
Cold rolled steel, electrogalvanized steel (60 g/m2 coating), and three aluminum-alloy (2036, 5182, and 6111) sheet products were painted with a full automotive paint system. These materials were tested in two laboratory cyclic corrosion test environments, namely, GM9540P(B) and CCT-IV. Resistance to cosmetic corrosion was measured in terms of underfilm paint delamination on scribed, flat panels. Crevice corrosion resistance was determined in terms of pitting on lapped panels of like materials, and galvanic corrosion resistance in terms of pitting on lapped panels of unlike materials. Cosmetic corrosion of the aluminum alloys was found to be much better than that of cold rolled, and slightly better than that of electrogalvanized steel. The CCT-IV test was found to be more severe than GM9540P(B) for cosmetic corrosion, but GM9540P(B) was more severe for galvanic corrosion. Galvanic current measurements indicate that the difference is related to the salt solutions used in each test. Aluminum alloys were found to be prone to crevice corrosion and to galvanic corrosion when coupled to steel. These results indicate that comparative evaluations of the corrosion resistance of these materials must take into account the possibility of crevice and galvanic effects.
