Synergistic Passivation of Zinc Phosphate and Aluminum Tripolyphosphate for Enhanced Long‐Term Protection of Epoxy Polyurethane Rust‐Tolerant Coatings

ABSTRACT Steel structures subjected to long‐term exposure in marine and industrial environments are prone to corrosion. Traditional derusting methods are often costly and technically challenging. Hence, the development of rust‐tolerant coatings possessing dual functions of “rust stabilization” and “barrier protection” is of great significance. Currently, zinc phosphate (ZP) and aluminum triphosphate (ATP) have attracted attention as environmentally friendly rust converters. However, when used individually, they exhibit limitations such as delayed release or insufficient durability. Based on the concept of synergistic passivation between ZP and ATP, an epoxy‐polyurethane composite rust‐tolerant coating was developed in this study. The coatings were prepared by combining ZP and ATP at a 1:1 ratio, with the filler content adjusted within 10–20 wt% Structural characterization revealed that ZP and ATP act synergistically to convert active corrosion products into stable iron phosphate complexes, while ATP nanoparticles fill the interlayer gaps of ZP, resulting in the formation of a dense passive layer. Performance evaluations demonstrated that at a 15 wt% filler content, the coating maintained a hardness retention rate of 72%, exhibited minimal loss of adhesion, and achieved the lowest water absorption. After 960 h of salt spray testing, the coating retained high impedance (1.84 × 10 4 Ω cm 2 ) and low corrosion current density (4.249 × 10 −5 A cm −2 ). This study demonstrates that the ZP‐ATP hybrid system significantly enhances the long‐term protective performance of rust‐tolerant coatings through a synergistic “chemical conversion–physical barrier” mechanism, offering a new strategy for the corrosion protection of steel structures.