Corrosion electrochemical behavior of arc sprayed Al coatings

The Al coating was prepared on the surface of steel samples by arc spraying. The corrosion behavior of Al coating was analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), electromotive potential polarization and electrochemical impedance spectroscopy (EIS). The impedance data were fitted into an appropriate equivalent circuit to explain the electrochemical corrosion behavior of the coating in different stages. The micro morphology of arc sprayed Al coating surface was observed by SEM. It was found that the Al coating surface was in tentacle and layered structure, and the coating was porous and rough, which was related to the process of thermal spraying coating. XRD results showed that the oxide content in the coating was very small, and Al was the main component. The corrosion resistance of the coating was tested by EIS. The results showed that the Al coating had high corrosion resistance at the initial stage of corrosion, and a large number of bubbles were generated on the surface of the coating when it was immersed. Because there were many pores in the coating, which facilitated the penetration of Cl-. However, with the extension of corrosion time, the coating first appeared pitting behavior. At this time, the outer surface of the corrosion hole formed an oxygen-rich area and became a cathode, and the concentration cell was formed outside the corrosion hole due to the decrease of oxygen concentration in the corrosion hole, which promoted the activation and dissolution of aluminum. The corrosion products of the coating will block the pores in the coatings, and the corrosion rate will decrease.