Environmentally Friendly Solutions as Potential Alternatives to Chromium-Based Anodization and Chromate Sealing for Aeronautic Applications

Abstract

The adoption of chrome-free anodizing and sealing systems for aluminum alloys, particularly AA2024, is gaining prominence due to environmental and health concerns associated with traditional Cr(VI)-based processes. This study evaluates the environmental and economic impacts of sulfuric acid anodizing (SAA) combined with sealing based on fluorozirconate, molybdate, and cerate. Comparative analyses were conducted against conventional Cr(VI) systems and SAA with Cr(III) sealing, focusing on corrosion resistance, energy consumption, washing steps and material flows. The entire anodizing process was examined, including pretreatment, anodization, and sealing. Electrochemical analyses and surface characterization through SEM/EDS, FIB, and XPS were conducted. The results demonstrate that the chromium-free system offers competitive corrosion resistance while significantly reducing environmental and economic costs. Furthermore, fluorozirconate, molybdate, and cerate-based post-treatments broaden its application spectrum in corrosion science and warrant further exploration. However, adopting new sealing technologies in aerospace requires extensive certification involving corrosion resistance, durability assessments, and stringent environmental simulations. Compliance with regulatory standards set by the FAA (Federal Aviation Administration) and EASA (European Union Aviation Safety Agency) necessitates thorough documentation, third-party validation, and testing to ensure safety and performance before industrial implementation. These challenges underscore the complexity of transitioning to more sustainable anodizing and sealing technologies in the aerospace industry.