CHROMATE CONVERSION COATINGS

摘要

Chromate conversion coatings are produced on various metals by chemical or electrochemical treatment with mixtures of hexavalent chromium and certain other compounds. These treatments convert the metal surface to a superficial layer containing a complex mixture of chromium compounds. The coatings are usually applied by immersion, although spraying, brushing, swabbing, or electrolytic methods are also used. A number of metals and their alloys can be treated; notably, aluminum, cadmium, copper, magnesium, silver, and zinc. The appearance of the chromate film can vary, depending on the formulation of the bath, the basis metal used, and the process parameters. The films can be modified from thin, clear-bright and blue-bright, to the thicker, yellow iridescent, to the heaviest brown, olive drab, and black films. A discussion of specific formulations is not included in this article because of the wide variety of solutions used to produce the numerous types of finishes. It is intended to present sufficient general information to permit proper selection and operation of chromating baths. Proprietary products, which are designed for specific applications, are available from suppliers.