Deposition of Cerium-Based Conversion Coatings on Aluminum Alloy 380

Abstract

Cerium-based conversion coatings were deposited on as-cast aluminum alloy 380 substrates by a spontaneous immersion process. In this study, the effects of rinsing temperature prior to immersion in the coating deposition solution were studied with respect to the surface morphology, electrochemical response, and corrosion resistance of the coatings. Panels rinsed at 25°C prior to coating had large cracks and holes in the coating. In contrast, panels rinsed at 100°C prior to coating had a uniform coating morphology with fewer, smaller cracks. Electrochemical testing revealed that coatings deposited on substrates rinsed at 100°C had higher impedance (~80 kΩ·cm2) and lower corrosion current (~0.34 μA/cm2) compared to coatings deposited on substrates rinsed at 25°C, which had 10 kΩ·cm2 impedance and 2.7 μA/cm2 corrosion current. Finally, ASTM B117 salt spray testing showed that rinsing at 100°C prior to coating resulted in cerium-based conversion coatings that could resist the formation of salt tails for at least 8 days.