Technical Note: Impedance Spectroscopy as Quality Control and Corrosion Test for Anodized Al Alloys

The corrosion resistance of anodized Al alloys prepared for military applications is presently evaluated in a 300-hour salt spray test. The alloy “passes” the test if it shows less than a certain number of pits at its completion.¹  Recent success in applying impedance spectroscopy to the characterization of the corrosion behavior of polymer-coated metals²  suggests that this technique could be developed into a quality control test for Al alloys Bodu, et al.,³  have used the DC limit of the impedance for anodized Al 2024 as a criterion for its corrosion resistance and have observed very good agreement with salt spray test results. ASTM B457 describes a procedure to measure the impedance at 1000 Hz to determine the quality of sealing. However, the impedance value, which is to be used to judge the quality of the processing operation, is left to a decision of the user and producer....