Effect of heat treatment on the intermetallic phase transformation and corrosion performance of Zn-Al-Mg alloy coated steel sheets in chloride-containing environments

A heat-treated Zn-Al-Mg alloy-coated steel sheet is studied to investigate its corrosion resistance in chloride-containing environments. The study focuses on the intermetallic phase transformation and its influence on corrosion performance. Corrosion resistance is evaluated using salt spray tests and electrochemical tests, along with an analysis of corrosion product formation. The heat treatment facilitates the transformation of MgZn₂ to Mg₂Zn₁₁, resulting in a more balanced area distribution between Zn and Mg₂Zn₁₁ phases. This structural balance promotes the formation of a protective Zn₅(OH)₈Cl₂·H₂O layer on the surface. This protective layer acts as an effective barrier to chloride ions, preventing further corrosion. These findings demonstrate that heat treatment enhances the durability and corrosion resistance of Zn-Al-Mg alloy-coated steel sheets by stabilizing the surface structure and promoting the formation of corrosion-resistant phases.