Measurement of Oxide Barrier-Film Thickness of Al-Alloy by Electrochemical Impedance Spectroscopy at the Nanometre-Scale

In the present work, the electrochemical behavior and the oxide barrier-film thickness of anodized aluminum-magnesium (Al-Mg) alloy were determined in the as-received and annealed conditions by using electrochemical techniques. Electrochemical parameters such as the polarization resistance, solution resistance, alternating-current (AC) impedance, and the doublelayer capacitance of the anodized Al-Mg alloy were determined in boric acid solutions, with 0 to 10%H3BO3, by using electrochemical impedance spectroscopic (EIS) methods. The oxide barrierfilm thickness of the anodized Al-Mg alloy was then deduced, from the electrochemical parameters obtained, as a function of the boric acid concentration (0 to 10%H3BO3). The optimum thickness of the oxide barrier-film was detected for as received samples (1.17nm) and for annealed samples (1.22nm) at a boric acid concentration of 4%H3BO3.