Comparison of progressive sealing methods of anodized aluminium as potential substitute for the chromate sealing

Comparison of progressive sealing methods of anodized aluminium as potential substitute for chromate sealing was analysed. Among them sealing in rare earth metal salt solution (Ce³⁺), so called cold impregnation and sealing in zirconium solution were compared to the standard sealing in boiling water. The sealed specimens were exposed to a corrosive environment (1 wt.% NaCl solution). The decisive qualitative parameters of the sealing layers were the sealing coefficient K_p applying the standard ISO 3210 and the resistance inside the pores applying EIS measurements (filling resistance). Based on the proposed equivalent circuit, the filling resistance can be considered as the indicator of the sealing quality for anodized aluminium. The results of EIS analysis are supported by EDX and IR measurements. It can be concluded that the sealing in zirconium solution provides the most satisfactory results and it can be used as an adequate substitute for chromate sealing.