Effect of Mg(OH)₂ layer on the wear and corrosion properties of AZ91 magnesium alloy

Abstract Magnesium and its alloys are characterized by inherently low hardness and inferior tribological properties, resulting in poor wear resistance. Enhancing the wear resistance of these materials is crucial for expanding their potential applications. To address this limitation, various surface treatment techniques have been developed to create protective coatings or surface layers. In this study, a Mg(OH) 2 layer with a thickness 25.5 ± 1.2 μm was synthesized on AZ91 magnesium alloy through oxidation in water vapor at 200 °C for 4 h. The microstructure and phase composition of the resulting layer were systematically characterized using scanning electron microscopy (SEM) and x-ray diffraction (XRD). The tribological properties of the treated magnesium alloy were evaluated using a reciprocating friction and wear test apparatus, with bearing steel balls serving as the counterpart. Comparative analysis revealed that the layer exhibited a friction coefficient 0.12 ∼ 0.15 much lower than those of untreated sample 0.3 ∼ 0.55. The wear rates were also reduced form 64 × 10 −5 mm 3 N −1 m −1 , 81 × 10 −5 mm 3 N −1 m −1 , and 80 × 10 −5 mm 3 N −1 m −1 under 3 N, 5 N, and 10 N loads for untreated sample to 4.0 × 10 −5 mm 3 N −1 m −1 , 3.5 × 10 −5 mm 3 N −1 m −1 and 3.0 × 10 −5 mm 3 N −1 m −1 respectively for treated one. These findings demonstrate the effectiveness of the superheated water vapor oxidation process in enhancing the wear resistance of magnesium alloys.