Characterization and corrosion behaviour of PEO coatings on AM50 magnesium alloy with incorporated particles

摘要

Composite ceramic coatings were formed on a magnesium alloy by AC plasma electrolytic oxidation (PEO) using a phosphate-based electrolyte with α-AI_2O_3, monoclinic ZrO_2 or CeO_2 particles in suspension. Effects of particle concentration (2, 5 and 10 g/L) on the composition/morphology and corrosion behaviour of the coatings were investigated. Findings revealed successful incorporation of particles, which were preferentially located in the outer coating layer. Due to high temperatures at the locations of microdischarges, zirconia particles underwent transformation from monoclinic to tetragonal structure. The majority of alumina and ceria particles remained unaffected, although some of the alumina particles could form MgAl_2O_4 by reaction with the substrate. Porosity and thickness of the coatings tended to decrease with increasing particle concentration in the electrolyte. Coatings formed in the electrolyte containing CeO_2 particles revealed the highest corrosion resistance in 0.5% NaCI solution.