Corrosion behavior of MoS2-incorporated PEO coatings prepared on Al alloy

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 alpha-aluminum oxide (alpha-Al2O3), gamma-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 mu A/cm(2) in the bare aluminum alloy to 581 and 30.1 mu A/cm(2) 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.