Advanced Trivalent Chromium Seals for Hard-coat Anodized Aluminum Alloys

Hard-coat (Type III) anodized aluminum alloys have been used by the military, aerospace, automotive, and petroleum industries for applications where superior hardness and wear resistance are required. In recent years there has been a great interest in sealing and dyeing hard-coated aluminum in order to improve the corrosion resistance and appearance of the oxide film. Although hard-coated aluminum has very high wear resistance, it has to be sealed to ensure a desirable level of corrosion resistance. However, conventional industrial seals for hard-coated aluminum cause a dramatic reduction in abrasive wear resistance. A novel room temperature trivalent chromium based seal was found to be an excellent post-treatment for hard-coated aluminum to provide enhanced corrosion resistance without compromising the wear characteristics. In this study, a comparison of post treatments including trivalent chromium based seal, DI water, nickel acetate, sodium dichromate, sodium silicate, nickel fluoride, black dye, black dye and nickel seals was made. The quality of the oxide film was evaluated by microhardness, wear resistance, corrosion resistance, and dielectric strength. The effects and possible mechanisms of the post-treatment processes on the anodic film are discussed.