Effect of SiC and borosilicate glass particles on the corrosion and tribological behavior of AZ91D magnesium alloy after PEO process

In this work, Plasma Electrolytic Oxidation (PEO) coatings were produced on AZ91D Mg alloy, using as electrolyte an aqueous solution containing both silicates and phosphates. SiC particles, or borosilicate glass particles or a combination of them (SiC + borosilicate glass) were suspended into the electrolyte. The PEO-treated samples were characterized through Scanning Electron Microscope (SEM) (both on the surface and in cross section), X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS) in order to study the morphology, thickness, adhesion, structure and composition of the coating as well as particle distribution. The corrosion behavior was analyzed by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The wear resistance was evaluated by dry sliding tests vs. AISI 52100 bearing steel (block-on-ring contact geometry). The results showed that both SiC and borosilicate glass particles were incorporated into the PEO layers. Glass particles contributed to enhance corrosion resistance, whereas SiC particles decreased it. On the other hand, SiC particles improved the wear resistance (due to enhanced load support), leading to an increase of the friction coefficient (due to an increase of the abrasive component of friction). The best combination of properties was obtained with the addition of glass particles for 3 min treatment time. In this way, both the corrosion and wear resistance were increased, minimizing the detrimental effects of SiC particles on the corrosion properties and the friction coefficient.