Preparation and characterization of a cerium conversion film on magnesium alloy

Abstract

Purpose – The purpose of this paper was to prepare the cerium-based conversion coating on AZ91D magnesium alloy, and its compositions, micro-morphology, corrosion resistance and the chemical valence state of the film elements were investigated. Design/methodology/approach – The methodology comprised preparation of coatings at different temperatures, which then were characterized using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, an electrochemistry workstation and by means of X-ray photoelectron spectroscopy. Findings – The conversion coating had a micro-cracked morphology. The conversion coatings were composed of MgO (or Mg-OH), CeO2 and Ce2O3. The best corrosion resistance of the cerium passivation film appeared when the treatment temperature was about 35°C. Originality/value – The corrosion current densities of conversion coatings were lower by one to two orders of magnitude than the corrosion current density of the blank sample. The rare earth passivation coating prepared under the best condition could reduce the corrosion current to 3.548 × 10−6 A/cm2.