Growth of porous anodic films on FVS0812 aluminium alloy

The formation of porous anodic films on FVS0812 aluminium alloy has been ex amined by transmission electron microscopy in order to elucidate the proces ses of film growth. A complex morphology of film material is revealed conta ining relatively tortuous, branched and terminated porosity and relatively large cavities. The morphology is associated with the differing anodic oxid ation behaviour of the aluminium matrix and silicide dispersion regions of the alloy and the differing chemical stabilities of the resultant film regi ons. The anodic oxidation of the silicide proceeds more slowly than that of the aluminium matrix, with the production of film material of much finer m orphology. The reduced rate of oxidation of the silicide is attributed to t he effects of alloying element species in the anodic fi Im material and por e solution. The rate of oxidation of the silicide is sufficient for most of the particles to be oxidized completely during anodizing. However, the res ultant film material subsequently dissolves in the pore solution leaving re latively large cavities in the film. The differing oxidation rates of the a lloy components, coupled with locally differing film properties, leads to a relatively rough alloy/film interface. (C) 1998 Kluwer Academic Publishers .