Study on properties of 6061 aluminum alloy coating by two-stage plasma electrolysis in two completely different electrolytes

Abstract

In this paper, an innovative two-stage plasma electrolysis technology was used to prepare a coating with improved properties, and the growth mechanism, wear and corrosion resistance of it were studied. In the first stage, 6061 aluminum alloy discs were fluoridated in a non-aqueous electrolyte (NH₄F-EG) to get a plasma electrolytic fluorination (PEF) coating, and then in the second stage, the samples with fluorinated coatings were transferred to a phosphate electrolyte for plasma electrolytic oxidation (PEO) treatment, resulting in a new coating. Also, two PEF coatings and PEO coatings obtained by processing in a single electrolyte were set up. The roughness, hardness, microstructure, and material composition were analyzed using a surface roughness meter, nano-indentation instrument, scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD), and X-ray photoelectron spectroscopy (XPS). Furthermore, their wear resistance was evaluated through friction tests, and their corrosion resistance was assessed using corrosion tests. The results demonstrate that FF has a lower coefficient of friction (COF) and abrasion width under dry friction than conventional OO, but it has a higher coefficient of friction and abrasion width under water and oil lubrication than under dry friction. Furthermore, FF has a lower corrosion potential and higher corrosion current density than OO. However, FO fully combines and enhances the advantages of both coatings with lower energy consumption, exhibiting the highest corrosion potentials as well as the lowest friction coefficients, abrasion widths, and corrosion current densities in three different samples.