Effect of Current Density on Microstructure, Corrosion Resistance, and Wear Resistance of Micro-arc Oxidation Coatings on 2195 Al-Li Alloy in a Silicate-Phosphate Electrolyte Solution

Abstract:

Ceramic coatings were prepared on 2195 Al-Li alloy by micro-arc oxidation (MAO) in a silicate-phosphate electrolyte solution under different current densities. The effect of current density varying from 200 A/m² to 800 A/m² on the microstructure, corrosion resistance, and wear resistance of MAO coatings was investigated. The surface and cross-sectional morphologies, composition, and roughness of MAO coatings were analyzed by scanning electron microscope, energy disperse spectrometer, X-ray diffractometer, X-ray photoelectron spectroscope, and surface roughness tester. The results show that with the increase in current density, the roughness and thickness of MAO coating increase. MAO coatings are mainly composed of γ-Al₂O₃ and a small amount of α-Al₂O₃. MAO coatings prepared under the maximum current density is the densest. Potentiodynamic polarization tests indicate that the corrosion resistance of coatings increases with the increase in current density. When the current density is 800 A/m², MAO coating exhibits the best corrosion resistance, with a corrosion potential of -0.536 V and a corrosion current density of 4.32×10^-7 A/cm², which is two orders of magnitude lower than that of the substrate. Electrochemical impedance spectroscopy results indicate that, at a current density of 800 A/m², the sample possesses the largest capacitive arc radius and the highest impedance magnitude in the low-frequency region. The wear resistance of MAO coatings increases with the increase in current density. When the current density is 200 A/m², the wear mechanism is dominated by abrasive wear. With further increase in current density, the wear mechanism remains abrasive wear. MAO coatings prepared at 800 A/m² show the best wear resistance with a wear rate of 1.355×10^-4 mm³/(N?m).