Effect of carbon nanotubes on the microstructure and properties of plasma electrolytic oxidized ceramic coatings on high silicon aluminum alloy

Ceramic coatings with carbon nanotubes were prepared on high silicon aluminum alloy by plasma electrolytic oxidation. The microstructure, phase, and elemental compositions of the matrix and ceramic coatings were characterized by metallographic microscope, X-ray diffraction, field emission scanning electron microscope, micro confocal Raman spectrometer and energy dispersive spectrometer. The functional groups contained in the coating were characterized using Fourier infrared spectrometer and X-ray photoelectron spectroscopy. The electrochemical workstation and thermal conductivity meter were employed to study the corrosion resistance and thermal conductivity of ceramic coatings. The effect of CNTs on the morphology, microstructure, coating formation and growth, corrosion resistance and thermal conductivity of PEO coatings on ADC12 Al alloy was investigated. The results showed that the micropores on the surface of the PEO coating can be used as discharge channels for various migrating ions and particle groups in the electrolyte to participate in the formation and inward and outward growth of the coatings. CNTs participated in the formation and growth of ceramic coating by surface adsorption, melt wrapping and fusion reaction during the plasma electrolytic oxidation process. The coating contains mainly α-Al2O3, γ-Al2O3, SiO2 and small amount of SiC phases. The changes of electrochemical corrosion and thermal conductivity of the PEO coatings are related to the regulation of the coating microstructure by CNTs.