Unraveling the formation of enhanced long-term durability chromate-phosphate conversion coatings with a Cr(III) complex dye

The role of additives in surface treatments is pivotal for enhancing the functionality and performance of coatings. While the impact of additives on the functionality and performance of various types of coatings has been mechanistically investigated, the specific influence of additives on the durability of chromate-phosphate conversion coatings remains less understood. This study introduces a novel Cr(III) complex dye, which significantly improves the long-term durability of such coatings. Through comprehensive experimentation, it is demonstrated that the application of this dye markedly influences the morphology, chemical composition, element distribution, and modulus of the conversion film, with negligible effects on the film thickness. The paramount effectiveness of the dye is predominantly realized through the mitigation of bound water in the conversion film and the formation of a more stable structure via interaction with phosphate ions. This work contributes to the nuanced understanding of additive-coating interactions, highlighting the potential of specific chemical agents in advancing the durability of protective coatings.