Improved Corrosion Resistance of AZ91D Mg Alloy by Cerium-Based Films. Formation of a Duplex Coating with Polypyrrole

Abstract

In order to improve the corrosion resistance of die-cast AZ91D magnesium alloy in simulated physiological solution, two cerium-based coatings were synthesized. The coatings were electrodeposited from solutions containing Ce(NO3)3, H2O2 and C6H8O7 or C4H4O6Na2. The influence of the presence of sodium tartrate and citric acid in the preparation solution on the morphology, composition and anticorrosive perfor- mance of the generated coatings was evaluated. The corrosion properties were examined in Ringer solution by polarization studies, open circuit measurements and faradaic impedance spectroscopy. Results showed that the incorporation of additives improves the anticorrosive properties of the films formed without sodium tartrate or citric acid. The coating formed in the presence of sodium tartrate showed the best anticorrosive performance. Subsequently, the possibility of forming duplex coatings employing the cerium-based films as inner layers and polypyrrole as top coating was evaluated. At this point, it was found that polypyrrole can be electropolymerized on top of the formed cerium-based film modified with sodium tartrate.