Evaluation of the corrosion protection of defective polyaniline/epoxy coating by localized electrochemical impedance spectroscopy

Defective epoxy varnish and hydrofluoric acid-doped polyaniline/epoxy (PANI-HF/EP) coatings were coated on the surface of an AZ91D magnesium alloy. The corrosion protection of the defective coatings was evaluated in 0.05 M NaCl by localized electrochemical impedance spectroscopy. Then, the surface of AZ91D magnesium alloy beneath the coating was analyzed by scanning electron microscopy- and energy dispersive X-ray spectroscopy. The results indicated that the defective epoxy varnish coating could not protect the magnesium alloy because it only served as an electrolyte barrier. By contrast, the PANI-HF/EP coating served not only as an electrolyte barrier, but also facilitated the formation of a protective layer by redox processes. Therefore, the defective PANI-HF/EP coating could protect magnesium alloy from corrosion.