Corrosion protection of AZ91D magnesium alloy by a cerium-molybdenum coating-The effect of citric acid as an additive

In order to improve the corrosion resistance of AZ91D magnesium alloy, a coating was formed by a potentiostatic technique from a solutions containing Ce(NO3)3, Na2MoO4 and citric acid (H3Cit). The degree of corrosion protection achieved was evaluated in simulated physiological solution by monitoring the open circuit potential, polarization techniques and electrochemical impedance spectroscopy (EIS). Surface analysis techniques (SEM, EDS, X-ray diffraction and X-ray photoelectron spectroscopy (XPS)) were used for coating characterization. The film is mainly composed by cerium and molybdenum oxides and magnesium oxides and hydroxides. The obtained results show that the corrosion resistance of the coated electrodes has been increased significantly. This improvement in the anticorrosive performance is in part due to the corrosion inhibition properties of H3Cit.