Low Temperature Sealing of Anodized Aluminum for Enhancing Corrosion Resistance

Abstract

Aluminum and it alloys has various advantages for industrial and application fields, such as high specific strength, thermal conductivity and machinability. However, due to its relatively high reactivity, the low corrosion resistance should be improved for practical uses. In order to improve the corrosion resistance of aluminum, various technologies have been employed to passivate against corrosion. Especially, anodic oxidation (or anodizing) is one of the most effective method to create passive layer on aluminum, which enhance the corrosion resistance. The anodic oxidation creates a thick oxide layer with nanoscale high-aspct-ration cylindrical pores on aluminum substrate, and the pores provide paths of corrosive media to aluminum substrate causing the corrosion. Therefore, the pores in the oxide layer should be sealed to inhibit the absorption of corrosive media in the pores. Hot sealing methods requires relatively short time for process, but there is a energy cost for boiling water during the sealing. Cold sealing doesn’t need to heat the solution, but the processing time is longer and some expensive chemicals are required, such as nickel fluoride. In this study, we designed a new solution for cold sealing of anodized aluminum as an alternative of cold nickel fluoride sealing. We mixed ammonium based chemicals and nicke based chemicals, so that the active ion spices will be similar with nickel fluoride. With respect to the concentration of mixed solution, we could reduce the processing time to maximize the corrosion resistance. Moreover, the corrosion resistance of the anodized aluminum sealed with mixed solution showed better corrosion resistance than previous cold sealing and hot sealing.