Formation of rare earth-permanganate conversion coating on AZ61 magnesium alloy and its properties

Abstract

Formation of cerium-lanthanum-permanganate composite conversion coating on AZ61 magnesium has been studied. Morphology of the coated and uncoated alloy samples has been studied by scanning electron microscopy before and after immersion in corrosive media. Energy dispersive X-ray shows that the coatings are composed of oxides and hydroxides of cerium, lanthanum and manganese. The anticorrosive properties of the coatings are investigated by potentiodynamic polarization and electrochemical impedance spectroscopy in diluted sodium sulfate and also in 3.5% sodium chloride solutions. The results indicate that the corrosion resistance of the coated samples is significantly higher than the bare alloy in studied solutions. The effect of plating time on coating resistance is investigated in order to find the optimum treatment time and the best results are found for 60 min plating.