Corrosion of aluminum alloy 7A04 under thin electrolyte layers

The corrosion behavior of 7A04 aluminum alloy in 1 mol·L^-1 sodium sulfate solution was investigated by a thin electrolyte layer equipment. The surface morphology was observed by scanning electron microscope (SEM). The corrosion products were analyzed by energy dispersive X-ray detector (EDX) and X-ray photoelectron spectroscopy (XPS). The electrochemical character of 7A04 aluminum alloy was studied by electrochemical impedance spectroscopy (EIS). It is shown that the corrosion is not uniform, and the corrosion product at the edge is more than that at the center. The corrosion products of the specimen surface mainly are Al (OH)₃ and aluminum sulfates. EIS measurements indicate that the corrosion rate of 7A04 aluminum alloy under the thin electrolyte layer of 110μm is the biggest in the initial stage (0-96 h). But in the later stage of corrosion (96-168 h), the corrosion rate in the bulk solution is the biggest.