Preparation of Zinc-manganese Phosphating Coating on Q235 Steel and Its Environmental-friendly Sealing Treatment

Zinc-manganese phosphating coating was prepared on the surface of Q235 steel, followed by post-treatment via different environmental-friendly sealing processes, such as oil immersion sealing process, silicate sealing process and rare earth salt sealing process. The surface morphology, phase composition, thickness, surface wettability and corrosion resistance of zinc-manganese phosphating coating were tested and analyzed. The results show that the surface of Q235 steel is completely covered with zinc-manganese phosphating coating composed of Zn-3(PO4)(2)center dot 4H(2)O, Mn2Zn(PO4)(2)center dot 4H(2)O and Zn2Fe(PO4)(2)center dot 4H(2)O phases, which can inhibit the corrosion process of Q235 steel. After post-treatment via different environmental-friendly sealing processes, the surface roughness of zinc-manganese phosphating coating is reduced and the corrosion resistance is further improved, but its thickness and phase composition changes are small. The compactness of zinc-manganese phosphating coating after rare earth salt sealing treatment is the best, showing good hydrophobicity and better corrosion resistance for Q235 steel.

Automated summary

The effects of different environmentally friendly sealing processes on the properties of zinc-manganese phosphating coating were studied, and it was found that rare earth salt sealing treatment can significantly improve the compactness and corrosion resistance of the coating.