Electrochemical Impedance Spectroscopy of Trivalent Chromium Pre-Treated Aluminum Alloys

A chemical conversion coating on aluminum alloys was developed using a trivalent chromium bath. Electrochemical impedance spectroscopy (EIS) was made to characterize the corrosion resistant properties of the surface films formed. The results showed a 10 to 100 fold increase in the polarization resistance of the surface films compared to the untreated aluminum alloy. These electrochemical results compared well with the corrosion behavior in salt spray tests. The trivalent chromium-treated surfaces showed no corrosion for up to 200 hours in 5% salt spray. A post-treatment with an oxidizer even further raised the coating's resistance due to an improved corrosion protection. Corrosion protection, Conversion coatings, Ac-impedance, Chromate, Aluminum alloys.