Aluminum (Al) alloys are used widely in the automotive and aerospace industries, but their corrosion resistance is insufficient in long-term service, particularly in a high-salinity environment. The incorporation of molybdenum disulfide (MoS2) particles into plasma electrolytic oxidation (PEO) coatings formed on an aluminum alloy was investigated in this work. After oxidation, the coatings were investigated by a series of structural, morphological and electrochemical corrosion tests to understand the effect of molybdenum disulfide addition to the base electrolyte. The phase compositions and surface morphology of coatings were analyzed through X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM), respectively. The XRD results showed that all coatings were primarily composed of α-aluminum oxide (α-Al2O3), γ-aluminum oxide and molybdenum disulfide phases. The FESEM observations indicated that molybdenum disulfide particles were successfully incorporated in the ceramic coating and the apparent porosities decreased with increasing molybdenum disulfide concentration. The electrochemical corrosion tests indicated that the amount of coating porosity decreased and the corrosion current density decreased from 79·6 μA/cm2 in the bare aluminum alloy to 58·1 and 30·1 μA/cm2 in the PEO coatings without and with the molybdenum disulfide additive, respectively. This behavior could be attributed to the beneficial effect of the molybdenum disulfide particles, which might play an important role in blocking micropores and microcracks.

This study has investigated the dry sliding wear behaviour of aluminium (Al)–silicon (Si) alloy matrix hybrid composites reinforced with nanosized alumina (Al2O3) and zirconia (ZrO2) in cast and heat-treated conditions. Dry sliding wear tests were performed on a pin-on-disc apparatus under a normal load of 10 N. Optical microscopy, X-ray diffraction and scanning electron microscopy examination were used to investigate the microstructures and tribological properties of the composites and the base alloy. For comparison of the wear behaviours of the samples, the wear constant (K) was measured based on the wear rate data. The lowest wear constant was observed in the heat-treated composite containing 2 wt.% zirconia, which shows a decrease of around 65% in comparison to the non-reinforced base alloy. It has been suggested that the wear process is controlled by nucleation and propagation of cracks; however, in the case of heat-treated composites, the fragmentation of layers decreases due to the spherical nature of silicon particles.