Tribological and corrosion behavior of PEO coatings with graphite nanoparticles on AZ91 and AZ80 magnesium alloys
(1. Department of Industrial Engineering, University of Padua, Via Marzolo 9, 35131 Padova, Italy;
2. Department of Industrial Engineering, Alma Mater Studiorum, University of Bologna, V. le Risorgimento 4, 40136 Bologna, Italy)
Abstract: The effect of the addition of graphite nanoparticles into the electrolyte used to produce plasma electrolytic oxidation (PEO) coatings on AZ91 and AZ80 magnesium alloys was studied. The corrosion and wear resistances of the obtained coatings were investigated. A solution that contained both phosphates and silicates was used as electrolyte. Moreover, two different PEO treatment times were studied. The corrosion resistance was analyzed with potentiodynamic polarization and EIS tests; the wear resistance was investigated with a flat on ring tribometer. The results were related to the morphology, microstructure, elemental composition and thickness evaluated with SEM analysis. The presence of the graphite nanoparticles increased the thickness, produced a densification of the coating and sealed the pores on the surface, thus improving both the corrosion and wear resistance. The increase in the corrosion and wear resistances was more evident for AZ91 than for AZ80 due to the higher aluminum content.
Key words: plasma electrolytic oxidation; wear resistance; corrosion resistance; magnesium alloy; graphite nanoparticles