Activation of zinc phosphate coating by silver nitrate pretreatment

ABSTRACT

The effects of a new activation pretreatment based on silver nitrate solution on the formation and protection characteristics of zinc phosphate coating on mild steel surface were studied. The surface morphology of coated samples and microstructural evolution were analysed by the scanning electron microscopy (SEM) and the energy-dispersive spectroscopy. The protection characteristics were evaluated using potentiodynamic polarisation curves and the electrochemical impedance spectroscopy in a 3.5% NaCl solution. Experimental results revealed that the activation pretreatment with silver nitrate solution promotes the nucleation of zinc phosphate coating on steel surface which produced compact coatings with full surface coverage. Introducing the pretreatment with silver nitrate solution prior to the phosphating step strongly influences the surface morphology and corrosion resistance of the phosphate layer. The corrosion resistance of activated phosphate coatings was improved, where the corrosion potential shifted positively, and the corrosion current density was markedly reduced.

KEYWORDS:

• Zinc phosphating
• surface pretreatment
• protection coating
• corrosion resistance
• EIS

Acknowledgements

The authors would like to acknowledge the support of Universiti Sains Malaysia for this research under post-doctoral fellow scheme (USM 1228/15). The authors also gratefully acknowledge the continual support provided by the staff at Universiti Sains Malaysia.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by Universiti Sains Malaysia: [Grant Number Post-doctoral fellow scheme (USM 1228/15)].