Mechanical property and corrosion resistance evaluation of AZ31 magnesium alloys by plasma electrolytic oxidation treatment: Effect of MoS₂ particle addition

Magnesium alloys have been used in a wide range of lightweight applications in industries such as aerospace, automotive, and personal computing due to their high strength to weight ratio; however, high chemical reactivity, poor corrosion and wear resistance limit their widespread uses in many fields. The plasma electrolytic oxidation (PEO) process can produce a protective oxide layer on the magnesium alloy to improve the mechanical properties that limit more widespread application of magnesium alloys. In this work, molybdenum disulphide (MoS₂) nanoparticles in concentrations ranging from 0 to 10 g/L were added into the PEO electrolyte. The aim of this study is to investigate the influence of incorporating MoS₂ nanoparticles on the microstructure, phase, as well as short- and long-term corrosion resistance, and other mechanical properties of PEO grown oxides. While the MgAl₂O₄ phase was formed for all PEO grown oxide, the addition of MoS₂ nanoparticles in the electrolyte reduced the formation of MgAl₂O₄ phase and enhanced the growth of MgO phase in the oxide coating. A higher hardness, 16.6 GPa, was obtained for the oxide layer grown with 10 g/L MoS₂ nanoparticles added. The corrosion resistance, wear resistance, and adhesion of the PEO grown oxide layer were strongly influenced by the porosity defect, phase, and microstructure of the coating. It appears that the addition of 2.5 g/L MoS₂ nanoparticle in electrolyte provided an oxide layer with the best short-term corrosion resistance, excellent adhesion, and the lowest wear rate; however, the addition of MoS₂ nanoparticles to the PEO electrolyte was disadvantageous to the long-term anticorrosion performance of an oxide layer because of its reduced formation of MgAl₂O₄ phase.