Electrochemical corrosion behavior of arc sprayed Al–Zn–Si–RE coatings on mild steel in 3.5% NaCl solution

Abstract

Al–Zn–Si–RE coating with high Al content was deposited on mild steel by arc spraying. The electrochemical behavior of Al–Zn–Si–RE coating in 3.5 % NaCl solution was systematically studied by potentiodynamic polarization, corrosion potential (φcorr) and electrochemical impedance spectroscopy techniques (EIS). The impedance data were fitted to appropriate equivalent circuits to explain the different electrochemical processes occurring at the electrode-electrolyte interface. The results indicate that Al–Zn–Si–RE coating reveals the similar polarization behavior as Zn–15Al coating. The coating has no passive region in the anodic polarization, but far lower corrosion current and much higher corrosion potential. Al–Zn–Si–RE coating provides effective sacrificial protection for steel substrate and the sacrificial anodic protection plays dominant role during the immersion process. In addition, the φcorr evolution and EIS plots indicate that the corrosion process can be divided into five stages: pitting–dissolution–redeposition, activation corrosion, cathodic protection, physical barriers and the coating failure.