Experimental study of electrochemical corrosion behaviour of bilayer on AZ31B Mg alloy

A bilayer on AZ31B magnesium alloy was prepared by first applying anodization to modify the substrate, and then depositing a self-assembled nanophase particle (SANP) film. Structure and corrosion behaviour are characterized by scanning electron microscopy, energy dispersion spectrometry, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscope and electrochemical impedance spectroscopy. Experimental results indicate that the bilayer consists of a SNAP/loose layer and a dense layer, and provides the corrosion protection of Mg substrate for more than 354 h in 0.005 M NaCl solution. Therefore, the bilayer is effective to protect Mg alloy against corrosion for a long time.

Research highlights
► The bilayer consists of a SANP/loose layer and a dense layer.
► The bilayer provides the corrosion protection of AZ31B Mg alloy in 0.005MNaCl solution for more than 354 h.
► Before 165 h, the corrosion protection of SANP/loose layer is due to its good compactness, strong adhesion and high thickness.
► After 165 h, thecorrosion protectionof inner dense layer is due to its compacter structure and the limit recovery.