Abstract: The kinetics of film-forming course, the surface morphology, structure, composition and valence of element, phase constituent and the corrosion resistance of anodic films were studied by the ways of voltage-time curve, thickness-time curve, SEM, EDS, XPS, XRD, total immersion test and polarization curve respectively. The results show that there are relativity among the structure, composition and corrosion resistance of anodic films on AZ91D Mg alloy; the film-forming course can be divided into four stages, and the corrosion resistance of the anodic films in different stages have great difference because of its variation of thickness, structure and composition; the films that have the best corrosion resistance is the films formed on the boundary of stages Ⅲ and Ⅳ during the anodic course. The anodic oxidation film contains Mg, O, Si, B and a small amount of Al and Na. The dense layer is composed mainly of MgO, while the porous layer is composed of MgO, MgSiO₃ and Mg₃B₂O₆.

Key words: Mg alloy, Anodizing, Corrosion resistance