Corrosion behavior of carbon steel coated with magnesium electrodeposited from methyl magnesium chloride solution

Magnesium coating was electroplated on carbon steel to improve its corrosion protection. The analytical characterization of the magnesium coating was performed by scanning electron spectroscopy and energy dispersive X-ray spectroscopy. The electrochemical behavior of Mg-coated carbon steel was assessed by electrochemical impedance spectroscopy, open-circuit potential measurements and potentiodynamic polarization curves in 0.03% sodium chloride solution. The electrochemical results showed that the self-corrosion current density (i _corr) of magnesium-coated steel was 0.32 mA cm^?2 (about 1.8% of that of uncoated steel). Impedance results showed an increase of the total impedance when magnesium coating was applied on steel substrate. The corrosion protection was ensured by a two-step mechanism. The first step was cathodic polarization; the second step was the formation of a barrier due to magnesium oxides composed of MgO, Mg(OH₂) and Mg(OH₃)Cl.