The modified phosphate conversion coating on Zn-Mg alloy coated steel for corrosion protection

摘要

Zinc phosphate conversion coatings have been widely used industrially as an undercoating for paint to improve the adhesion of the paint and to improve corrosion resistance.Tri-cation type phosphating bath consisting of Zn, Mn and Ni ions have been developed in order to increase the properties such as corrosion resistance, alkaline stability and paint adhesion. The modified phosphate conversion coatings were formed on Zn-Mg alloy coated steel which was manufatured with the Electro Magnetic Levitation-Physical Vapour deposition(EML-PVD) process in order to increase the corrosion resistance of coating layer. The characteristic changes and corrosion resistance of coatings were investigated with varying concentrations of Mo & Ni in phosphating solution. Surface morphology and crystal size were observed by SEM. Salt spray test, potentiodynamic polarization and electrochemical impedance spectroscopy were used to evaluate the corrosion resistance.