Preparation and characteristics of oxide films on AA339.1 cast aluminum

Ceramic films on AA339.1 cast aluminum alloys (ANSI) were prepared by high-voltage anodization (HVA) in a mixed electrolyte of glutaric acid, sodium tungstate and phosphoric acid. The characteristics of the films and the effect of various factors, such as peak current density, composition and concentration of the electrolytes, on the properties of the films were investigated in detail. In addition, the structure, chemical composition and morphology of the films were investigated by electron diffraction spectroscopy (EDS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the elements in the film are O, Al, Si, P, S, C and that the structure of the film is non-crystalline. Compared with conventional anodic film on aluminum, the films on AA339.1 show good ornamental property and high microhardness. SEM results indicate that the film appears to be divided into loose and compact layers. Many nano-gaps or cracks are observed in the compact layer, which may be a result of a different film formation mechanism from that of conventional anodic films.