Cr2O3 sealing of anodized aluminum alloy by heat treatment

Abstract

Anodized films of aluminum alloys are composed of an inner thin barrier layer and an outer thick porous layer. A sealing process as a post treatment of anodizing, the porous layer achieves improved mechanical and chemical performance as well as decorative color. Nevertheless, dramatically increased hardness could not be achieved using traditional sealing processes. In this study, the sealing of anodized aluminum alloy was carried out by repetition of dipping in a hexavalent chromium oxide solution and heat treatment. The changes in the anodized layer before and after the sealing were analyzed by XRD and SEM. Electrochemical corrosion and wear rate test were also carried out. The hardness, wear resistance and corrosion resistance were compared with traditional sealing methods, such as boiling water and cold nickel fluoride. By heat treatment after dipping in a hexavalent chromium oxide solution, Cr2O3 was formed and filled the pores in the porous layer of the anodized film. Therefore, the hardness of the anodized film was increased with an improvement in wear resistance. In addition, improvement in corrosion resistance was achieved by Cr2O3 sealing.