Effect of aging approaches on the aging behavior of polyurethane coated steels

Four accelerated weathering tests were carried out on polyurethane coated steels. The apparent properties and electrochemical characteristics of the coatings were studied to compare the effects of different accelerated weathering tests on the coating failure behavior. It is found that UV exerts the greatest influence on the glossiness of the coatings and the gloss loss reaches up to 85.7% after 32 d aging. The linear polarization resistance decreases rapidly in the early period of the salt spray test and stabilizes in the later period due to the formation of a salt film. In the mixed aging (xenon light aging+salt spray) test, the variation tendency of both gloss loss and linear polarization resistance are similar to those presented in the early period of xenon light aging and similar to those presented in the later period of salt spray test. Moreover, the equivalent circuit of the mixed aging test shows two time constants in the early period, which is consistent with the single xenon light aging test. In the later period, the failure process of the coatings can be manifested with three time constants, in which the formation of a salt film is the typical feature.