Corrosion resistance investigation of nanostructured Si- and Si/TiO2-coated Mg alloy in 3.5% NaCl solution

Si/TiO2 nano-composite and Si were coated on Mg-Ca alloy by physical vapour deposition (PVD). The surface morphology of specimens was characterised by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray spectroscopy (EDS) and atomic-force microscopy (AFM). The AFM results indicated that the average surface roughness of the nano-Si/TiO2 coating is lower than that of the mono-layered Si coating. However, the nanocomposite coating presented a more compact structure with fewer pores, pinholes and cracks than the Si coating. Nano-Si/TiO2 composite coating consisted of TiO2 (110) as the outer layer and Si (111) as the inner layer, producing a greater thickness (1.765 μm) than the Si coating (1.139 μm). Electrochemical studies reveal that there is a less significant reduction in the corrosion rate for the nano-Si/TiO2 and Si coatings. However, the nano-Si/TiO2 coating considerably enhanced the corrosion resistance of bare Mg alloy in NaCl solution.