Characterizations of UV aging and atmospheric corrosion on epoxy coated 7A04 aluminum alloy

The aim of this work is to investigate characterizations of corrosion on 7A04 aluminum alloy with epoxy coating under simulated marine atmosphere with/without ultraviolet irradiation. The environment containing Cl^- and sunlight illumination was simulated by salt spray test and UV irradiation/condensation treatment. The corrosion behavior was studied by electrochemical impedance spectroscopy, and level of coating damage was evaluated through gloss measurement. Scanning electron microscope was chosen to observe surface properties of epoxy coating/7A04 aluminum alloy system. The results show that the electrochemical characters are closely related to the aging degree of epoxy coating, which could influence the penetrating process of oxygen and corrosive medium. The coating resistance decrease, while the coating capacitance and the pore rate increase as prolonging of the test time. Along with gloss loss of epoxy coating, pores appear on the surface and the blisters break, which may act as bulk defects of epoxy coating. The coating degradation and substrate corrosion were accelerated by the cooperation of UV irradiation and salt spray. UV aging significant accelerated the deterioration of coating with larger and deeper pores compared to that of non-UV irradiation coating.