The aerospace industry uses a variety of metal alloys as structural components in aircraft. Corrosion and degradation of these metals in service is typically inhibited using a multi-layer coating system (conversion coating + primer + topcoat). Historically used conversion coatings and primers contain Cr(VI) as the active corrosion inhibitor. Due to human health and environmental concerns, there is a world-wide effort to eliminate chromate from use and to replace these coatings with more environment-friendly and equally-as-effective coatings. The trivalent chromium process (TCP) conversion coating is the leading replacement candidate. A challenge with implementing this conversion coating for protecting high Cu aluminum alloys is that it is not as good as the legacy chromate coatings for reasons that remain poorly understood. In this dissertation project, fundamental research was conducted to better understand how to improve the anti-corrosion properties of TCP on AA2024-T3, a high Cu containing aerospace alloy. A focus was on understanding system-level interactions between the coating and alloy surface, and how it correlates with early-stage failure of alloys. The overall objective of this dissertation project was to improve the corrosion performance of TCP conversion coatings through: (i) process parameter optimization (ii) a better understanding of early-stage failure mechanisms, specifically, the sites where alloy corrosion initiates and the coating composition and structure on and around these sites. The final chapters of this dissertation also focus on the use of TCP as a sealant for surface modified (anodized) AA2024-T3 and comparing the effectiveness of a TCP seal against other industrially used sealing methods.
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