Effect of phosphate-based sealing treatment on the corrosion performance of a PEO coated AZ91D mg alloy

Abstract

This study investigated the effect of sealing treatment on the corrosion performance of plasma electrolytic oxidation (PEO) coated AZ91D Mg alloy with and without addition of corrosion inhibitor. The microstructure, phase composition and corrosion property of the sealed and unsealed coatings were evaluated by using scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), polarization, and electrochemical impedance spectroscopy (EIS) tests. Electrochemical experiments and salt spray tests showed that, after sealing in phosphate solution containing corrosion inhibitor, the corrosion current density of PEO-coated AZ91D decreased more than 10-fold and the anti-corrosion time in a salt spray environment increased more than three-fold. The corrosion rate of the PEO coating slowed down due to the releasing and adsorbing of the corrosion inhibitors in the pores and cracks of the coating during the corrosion process.

Keywords

• AZ91D magnesium alloy
• Plasma electrolyte oxidation
• Sealing treatment
• Corrosion inhibitor