Formation of an anti-corrosive chemical conversion coating on aluminium substrate under low temperature

Abstract

Abstract Improving the anti-corrosive performance of aluminium (Al) and its alloys is essential in its industrial applications. In this work, a green trivalent chromium conversion (TCC) coating was prepared on the surface of commercial high-purity Al without phosphate in the conversion solution under low temperature. The surface morphology of the TCC coating prepared with various immersion time was characterized. A compact TCC coating without pinholes and cracks was obtained with the immersion time of 1.5 min. The potentiodynamic polarization curves of the specimens with TCC coating were also recorded and analysed to evaluate the influence of immersion time and conversion process temperature on the protection performance of the TCC coatings. The results showed both the immersion time and temperature have obvious effects in the corrosion current (J corr) and corrosion potential (E corr). According to the measured J corr, E corr, and pitting potential (E p), an optimized immersion time of 1.5 min and temperature of 40 °C was obtained to form a compact and effective TCC coating on Al substrate.