Corrosion protection performance of Mo-incorporated 2-hydroxyphosphonoacetic acid-Zn2+ complex conversion layers on the cold-rolled steel substrate

A coordination-induced film-forming method was developed to construct 2-hydroxyphosphonoacetic acid (HPAA)-Zn2+ complex conversion layer (HPAA-Zn2+ layer for short) on cold-rolled steel (CRS) substrate. Moreover, the incorporation of Mo component into the HPAA-Zn2+ layer can significantly improve the uniformity and anticorrosion properties. The results showed that Mo-incorporated HPAA-Zn2+ layer displayed the best anticorrosion performance when the molar ratio of HPAA/Zn2+ was 1:1, the film-forming time was 10 min, and the concentration of molybdate was 0.1 wt%. In addition, energy dispersive spectroscopic (EDS) and X-ray photoelectron spectroscopic (XPS) results demonstrated that the Mo-incorporated HPAA-Zn2+ layer was mainly composed of ZnO and HPAA-Zn2+ complex and also confirmed that Mo-O-P bonds occurred between molybdate anion and HPAA molecule.