This chapter presents a study in which the growth process of oxidation films on pure magnesium (Mg), and AZ31B, and AZ91D alloys in pure water, Na2SO4, and NaCl solutions are analyzed by in-situ ellipsometry. The films with a refractive index of 1.42 - 1.47 grew rapidly in two consecutive stages. In stage I, the film thickness increases approximately linearly with time, and in stage II, 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 film growth rate of Mg-based materials depended on their purity and composition and the kind of electrolyte. The results of XPS analysis suggested that the oxidation films formed on AZ91D alloy in air and aqueous solutions are mainly composed of MgCO3 and Mg(OH)2, respectively. Anodic polarization curves measured after immersion in 0.1M NaCl suggested that the films formed on high purity Mg and AZ91D alloy have protective ability, while they suffer local breakdown at high potentials. The intrinsic passivity region of Mg was clearly observed on high purity Mg.
ASJC Scopus subject areas
- Chemical Engineering(all)