Corrosion resistance properties of colored zirconium conversion coating and powder coating on cold-rolled steel

Jiuhe Corporation developed a new surface pretreatment for producing a phosphate-free and colored zirconium conversion coating on cold-rolled steel (CRS). Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were applied to study the surface morphology and elemental composition of the golden yellow-colored conversion coating. Electrochemical impedance spectroscopy (EIS) was used to investigate the electrochemical performance of the conversion coatings with different colors. The corrosion resistance properties of the powder coatings were characterized using the neutral salt spray test (NSS) and the tape adhesion test. The EIS and NSS results demonstrate that the colored zirconium conversion coatings exhibit excellent corrosion resistance properties compared with the bare CRS. The golden yellow-colored conversion coating has a maximum EIS value (748 Ω·cm 2 ) and achieves 0 mm degree of corrosion, as stipulated by EN ISO 4628-8. This paper proposes a hypothesis concerning the ZrO 2 –(β-FeOOH)-polymer conversion reaction to explain the color changes.