Corrosion and wear resistance of micro-arc oxidation coating on glass microsphere reinforced Mg alloy composite

In this study, micro-arc oxidation (MAO) coatings were prepared on a novel glass microsphere reinforced Mg alloy composite to retard the degradation of the composite in the liquid environment containing Cl− for degradable downhole tool applications. The microstructure and chemical composition of the coatings were characterized by SEM, EDS, XPS and XRD. The growth characteristics of the MAO coatings on different matrix regions were analyzed. The corrosion and wear resistance of the coatings were evaluated through the immersion test, electrochemical measurements and friction test. Results showed that the MAO coatings consisted primarily of Mg2SiO4, MgO, little amount of MgAl2O4 and amorphous SiO2. The current density influenced the thickness and structure via affecting the voltage response of the MAO process, afterward influencing the properties of the coatings. The termination voltage of the MAO process and thickness of the coatings increased with the current density. With the current density increased from 8 to 160 mA/cm2, the compactness and microhardness of the coatings were increased, thereby improving the corrosion and wear resistance of the coatings. However, as the current density increased to 200 mA/cm2, the generation of large through-cracks caused the friction coefficient to increase and the corrosion resistance to deteriorate.