ABSTRACT
The chromic acid anodize process found increased popularity during World War II for the treatment of aircraft parts and assemblies. Chromic acid anodizing alloys for aircraft parts prior to adhesive bonding and painting is used in Europe without postsealing treatments. In Europe, hot-water sealing and dichromate absorption is never carried out on the parts to be adhesive bonded and/or painted. Hot-water-sealed chromic acid-anodized panels adhesive bonded with Redux show poor bond strength. The alloy composition has a strong influence on the coating thickness after chromic acid anodizing. The unsealed chromic acid anodizing process, as a pretreatment for adhesive bonding and painting, gives satisfactory results in service. Increasing the temperature and voltage during anodizing promotes dissolution of the oxide, and heavy etching of the aluminum might occur in extreme cases, locally burning holes in sheet materials.
