Active Corrosion Inhibition of AA2024-T3 by Trivalent Chrome Process Treatment

The trivalent chrome process (TCP) is one of the leading non-chromate conversion coatings and has been shown to provide excellent corrosion protection for Al alloy substrates. The goal of this work was to assess and quantify the self-healing or active corrosion inhibition properties of TCP on AA2024-T3 (UNS A92024). Samples exposed in the artificial scratch cell were characterized using electrochemical impedance spectroscopy (EIS) and x-ray photoelectron spectroscopy (XPS) for assessment of various aspects of active corrosion inhibition. Analysis of the electrolyte exposed to the TCP surface was conducted by inductively coupled plasma-optical emission spectroscopy (ICP-OES). TCP treatment was found to greatly improve the corrosion resistance of AA2024-T3 in corrosive environments. After exposure in dilute Harrison's solution, chromium species were detected in the exposed electrolyte, indicating that chromium is released from the TCP coating. Chromium was found on the surface of the uncoated sheets in the artificial scratch cell, which provided evidence that chromium species can be transported from a TCP coating to a nearby uncoated area as in a scratch. EIS data showed the polarization resistance of the uncoated surface exposed near a TCP surface in the artificial scratch cell was twice as much as uncoated controls, proving that TCP coating can provide active corrosion inhibition to a nearby uncoated Al alloy surface.