Research Progress on Chromium-free Passivation Technology for Galvanized Steel Sheets
Galvanized steel sheets are widely used in construction, automotive, appliance, and power industries due to their corrosion resistance, which can be further enhanced by passivation. Traditional chromate passivation, while effective due to self-repairing ability and chemical stability, poses severe health and environmental risks from hexavalent chromium. This review systematically categorizes recent chromium-free passivation technologies into inorganic, organic, and organic/inorganic composite systems. Inorganic systems include molybdates, rare earth salts (e.g., cerium, lanthanum), titanium salts, and silicates; organic systems include silanes, tannic acid, and acrylic resins. Film formation mechanisms and anticorrosion properties are examined. Individual systems exhibit limitations: molybdate films have micro-defects and limited thickness uniformity; rare earth films crack upon drying; organic films offer flexibility and adhesion but insufficient barrier properties. Organic/inorganic composite passivation integrates inorganic barrier function with organic interfacial binding and functional regulation, significantly improving film integrity and durability. The review concludes with challenges and prospects for chromium-free passivation.