Microstructure and mechanical properties of ceramic coatings formed on 6063 aluminium alloy by micro-arc oxidation

The microstructure and mechanical properties of ceramic coatings formed on 6063 aluminium alloy obtained in silicate-, borate- and aluminate-based electrolyte without and with nanoadditive Al2O3 and TiO2 by micro-arc oxidation (MAO) were studied by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), microhardness and friction-abrasion tests, respectively. SEM results show that coatings with nanoadditive have less porosities than those without nanoadditive. XRD results reveal that nanoadditive-containing coatings contain more oxides compared with nanoadditive-free coatings in all cases, which are consistent with the EDS analysis. Mechanical properties tests show that nanoadditive Al2O3-containing coatings have higher microhardness values compared with the other coatings obtained in silicate-, borate- and aluminate-based electrolyte. On the other hand, nanoadditive has a positive effect on improving the wearing-resistance of MAO coatings in all cases. Furthermore, the borate-MAO coatings present an inferior anti-wearing property compared with the silicate- and aluminate-MAO coatings for both the nanoadditive-free and nanoadditive-containing coatings.