Effect of Cerium Nitrate and Adipic Acid Additives on Anti-Corrosion Resistance and Microstructure of Vanadium Conversion Coating on 2024 Aluminum Alloy

In this research, the effect of inorganic and organic additives of cerium nitrate and adipic acid on anti-corrosion resistance and microstructure of vanadium conversion coating on 2024 aluminum alloy was investigated. First, using the results of electrochemical impedance spectroscopy (EIS) and direct current polarization (DC), optimum value of concentration of both organic and inorganic additives under optimum coating conditions in the absence of additives was determined. Then, in order to properly evaluate the effect of additives, practical process parameters such as immersion time, solution pH and solution temperature were optimized in the presence of additives. Based on the results of direct current polarization and electrochemical impedance spectroscopy, the coated sample with vanadium conversion coating in the presence of 2 gr/lit of cerium nitrate, solution pH of 4, immersion time of 25 minutes and at ambient temperature showed the highest anti-corrosion resistance. This anti-corrosion performance (corrosion current density of 0.026 μA/cm2 and impedance at low frequencies of 85,200 Ω.cm2), displayed significant improvement in anti-corrosion resistance of bare substrate (corrosion current density of 2.28 μA/cm2 and impedance at low frequencies of 18,510 Ω.cm2) by develpoing vanadium conversion coating in the percense of cerium nitrate. Also, in the presence of adipic acid additive the anti-corrosion resistance of substrate increased. In order to investigate the surface characteristics of the vanadium conversion coating in the presence of additives, water contact angle measurment, scanning electron microscopy and energy dispersive X-ray spectroscopy were used.