Influence of molybdenum disulfide addition on the structure and properties of micro-arc oxidation coatings on LA91 Mg–Li Alloy

Abstract

Magnesium–lithium alloys combine ultra-low density with high specific strength, yet their poor surface hardness and corrosion susceptibility restrict their wider use in advanced engineering fields. In this study, a silicate–phosphate electrolyte containing various concentrations of molybdenum disulfide (MoS₂) particles (0–1.5 g·L⁻¹) was developed to fabricate functional oxide coatings on LA91 Mg–Li alloy via micro-arc oxidation (MAO). Unlike conventional inert additives, MoS₂ was employed here as a semiconducting and lubricating phase to actively regulate plasma discharge behavior and coating growth dynamics. Systematic characterization by SEM, EDS, XRD, and electrochemical tests revealed that MoS₂ incorporation significantly modifies the discharge intensity and distribution, increases the breakdown voltage, and promotes the formation of thicker and denser coatings. MoS₂ particles serve dual roles, namely as active discharge centers and as physical fillers within microdefects, leading to reduced porosity and enhanced coating integrity. The coatings mainly consist of MgSiO₃, MgO, Mg₂SiO₄, and embedded MoS₂ phases. With increasing MoS₂ concentration, the coating thickness, hardness, and corrosion resistance first increase and then decrease, achieving optimal performance at 0.5 g·L⁻¹, where the coating exhibits a thickness of 29.4 μm, hardness of 401.7 HV, and a minimum corrosion current density of 1.085 × 10−⁶ A·cm−². This work provides new insight into the semiconductor-assisted discharge mechanism and the microstructural densification effect induced by MoS₂ during MAO, offering a novel strategy for designing self-lubricating, corrosion-resistant coatings on lightweight Mg–Li alloys.