OPTICAL TRANSMITTANCE OF ANODICALLY OXIDIZED ALUMINUM-ALLOY

Optical transmittance and anisotropy of anodic oxide films that were m ade from pure aluminum and an aluminum alloy (A5052) were studied. The alloy oxide film exhibits an enhanced polarization function, particul arly when anodization is carried out at a large current density. It wa s revealed by chemical analysis that the alloy oxide film contains a l arger amount of unoxidized aluminum than the pure-aluminum oxide him. The polarization function can be elucidated by considering unoxidized aluminum particles that are arranged in the columnar structure of the alumina film. Electron microscope observation showed that many holes e xist in the alloy oxide film, around which columnar cells are arranged irregularly. Such holes and irregular cell arrangement cause the incr ease in the amount of unoxidized aluminum, and consequently induces sc attering loss.