Abstract
Anodic oxide films grown on rapidly quenched aluminum alloys containing 2 at% Ti, Zr, Ta, Nb or Hf were characterized. The capacitance of the film on each alloy was found to be related to the dielectric constant of the alloying metal oxide film. In addition, the capacitance was found to depend on the degree of the exposure of the alloyed metal to the electrolyte, due to aluminum dissolution during the anodic oxidation. Capacitance varied with time, temperature and pH of the electrolyte in the anodic oxidation process. An oxide film of the barrier type was observed on Al3Zr by TEM, whereas the oxidation film of the Al–Ti alloy had a dual structure consisting of an inner layer with lower TiO2 content and an outer one with higher TiO2 content. It is considered that these phenomena were caused by the preferential dissociation of aluminum in the anodic oxidation process.
