Effect of Hg²⁺ on the corrosion behavior of Al-2%Zn coatings on AA5083 in 3.5 Wt.% NaCl solution

Purpose This paper aims to study the effect of Hg 2+ on the corrosion behavior of Al–2%Zn coatings on AA5083 in 3.5 Wt.% NaCl solution. Design/methodology/approach Potentiodynamic polarization and electrochemical impedance spectroscopy are used to investigate the effect of Hg 2+ on the corrosion behavior. The surface and cross-sectional morphology are characterized by scanning electron microscopy and energy dispersive spectroscopy (EDS) to further reveal the corrosion mechanism of Hg 2+ . Findings The results show that the corrosion behavior of the coating changes significantly as the concentration of Hg 2+ increases from 5 to 30 μg/L. The corrosion production film can inhibit the corrosion process when Hg 2+ concentration is in the range of 0.5–5 μg/L, while Hg 2+ can promote the corrosion process significantly when its concentration reaches to 30 μg/L. The generation rate of dense oxide film on the coating surface is faster than dissolution rate when the concentration of Hg 2+ is in the range of 0–5 μg/L, which makes the coating “self-healing” and thus slightly slows down the corrosion rate. The EDS analysis shows that excessive Hg 2+ are preferentially deposited at locations with inhomogeneous electrochemical properties, which in turn accelerates corrosion. Originality/value The corrosion resistance of Al-based coatings is significantly affected by Hg 2+ in seawater. Thus, it is important to explain the corrosion mechanism of Al–2%Zn coatings under the combined effect of Hg 2+ and Cl − in 3.5 Wt.% NaCl solution.