The Use of Admittance Measurements for Assessing Quality of Sealing of Anodic Films on Aluminium

SummaryAdmittance measurements are of increasing interest for the rapid quantitative assessment of the quality of sealing of anodized aluminium, and this paper describes a laboratory and production line investigation of this technique made using commercially available instruments. The effect on admittance values of factors such as time of sealing, temperature, pH and contamination level of the sealing water and use of nickel acetate sealing, as well as the effect of anodic film thickness and anodizing temperature, are described in comparison with accepted sealing tests such as the quantitative Kape test and dye stain tests. It is concluded that admittance measurement is a useful production control method for assessing sealing quality and that, under conditions generally used for production anodizing in Britain, a limit of 500/t microsiemens (where t is the anodic film thickness in μm) represents a reasonable acceptance level, which corresponds with the results of accepted sealing tests.