An Optimized Trivalent Chromium Conversion Coating Process for AA2024-T351 Alloy

Abstract

© The Author(s) 2017. Published by ECS. All rights reserved. In this work, a trivalent chromium conversion coating applied on AA2024-T351 alloy has been optimized for corrosion protection in sodium chloride solutions. Scanning electron microscopy, energy dispersive X-ray spectroscopy and electrochemical measurements were employed to characterize the coating. An immersion post-treatment of the coated alloy in 40°C deionized water for 120 s considerably enhanced the corrosion protection properties, compared with a post treatment at 20°C, or the absence of a post-treatment. Electrochemical noise measurements, combined with real time imaging, and potentiodynamic polarization experiments indicated a conversion treatment for 300 or 600 s provides optimal corrosion protection. Relatively long conversion treatments decreased the corrosion protection due to an increase in coating defects and cracks, especially around the second-phase particles.