A conversion coating is applied to a metal by reacting the outer atomic layers with anions from a suitable medium to produce a surface that is normally relatively insoluble in water, and electrically insulating. In the case of chromating, the layer will contain trivalent and hexavalent chromium compounds. The main reasons for applying such coatings are: to increase the corrosion resistance, to decrease the surface liability to fingermarking, to increase the adhesion of paints or other subsequently applied coatings, and to obtain color effects. Here, the corrosion protection aspects of chromating are investigated by comparing treated and untreated aluminum samples using electrochemical and other techniques. The chromating solutions are based on relatively simple formulations using hexavalent chromium compounds, but with added fluoride.
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