Fabrication of Self-Lubricating Composite Coating on Al-Si-Cu-Ni-Mg Casting Alloy for Automotive Applications and the Influence of Heat Treatment

Self-lubricating Al2O3/MoS2 composite films were prepared on Al-Si-Cu-Ni-Mg casting alloys through successive anodization and anodic electrolysis. Changes of the high-temperature oxidation resistance of the composite films were investigated using heat treatments in argon and air atmospheres at 250-350 ℃ for 2 hr. Friction tests confirmed that the filling of molybdenum disulfide （MoS2） into porous anodic oxide films improved the composite films' lubricity and wear resistance effectively. Moreover, results demonstrated that heat treatment in Ar atmosphere greatly enhanced the oxidation resistance of MoS2 on the composite film surface while maintaining the excellent lubricity and wear resistance of composite films. The improved oxidation resistance of MoS2 was attributed mainly to MoS2 crystallization under oxygen-free conditions during heat treatment, which slowed the chemical transformation from MoS2 to crystalline molybdenum trioxide （MoO3） effectively. These findings were confirmed using field emission scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy.