Ellipsometric Analysis of Growth Process of Oxidation Films on Magnesium and its Alloys in Neutral Aqueous Solutions

摘要

The growth process of oxidation films on pure Mg, and AZ31B and AZ91D alloys in pure water, Na_2SO_4 and NaCl solutions has been analyzed by in-situ ellipsometry. The films with a refractive index of 1.42 - 1.47 grew rapidly in two consecytive stages; stage Ⅰ where the film thickness increases approximately linearly with time, and stage Ⅱ where the growth rate decreases with time. In every solution, the film growth rate of 6N-Mg was higher than that of AZ91D. The oxidation films were mainly composed of Mg(OH)_2. The films formed on 6N-Mg and AZ91D have protective ability, while they suffer local breakdown at high potentials.