Effect of High Cl^- Environment on Corrosion Behavior of Aluminum Rich Phosphate Coating

Abstract

To study the effect of high Cl- environment on the corrosion of aluminum rich phosphate coatings, the corrosion behavior of phosphate coatings in high Cl- environments was analyzed using electrochemical testing methods such as open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy, combined with scanning electron microscopy and laser confocal microscopy. Results showed that the aluminum-rich phosphate coating had a double-layer structure. Phosphate coated Al powder inside the coating provided excellent shielding performance. With the increase of Cl- concentration in the solution, the corrosion tendency and corrosion rate increased, and the corrosion resistance of the coating decreased. Moreover, aluminum-rich phosphate coatings corroded first at cracks and defects when the concentration of Cl- was low. With the increase of Cl- concentration, the corrosion of phosphate would cause the Al powder in the outer surface and the inner of coatings to fall off, and then the corrosion pits were formed. Furthermore, the corrosion pits tended to expand outward and increase in size, accelerating the corrosion of the coating and the substrate.

Keywords

• phosphate coating|aluminum rich|high cl- environment|corrosion behavior|electrochemical corrosion