Effects of silicate ion concentration on the formation of ceramic oxide layers produced by plasma electrolytic oxidation on Al alloy

摘要

Plasma electrolytic oxidation (PEO) coatings were fabricated on 5083 Al alloy in KOH electrolyte solution with adding various concentrations of Na2SiO3. Changes in voltage-time response and micro-discharge evolution were analyzed, and the surface and cross-section of the resulting coating layer were further characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The results showed that discharge characteristics were evidently changed with different Na2SiO3 concentrations, particularly higher Na2SiO3 concentrations leading to lower dielectric breakdown voltages. It was found that porous surface structure became prevalent with increasing Na2SiO3 concentration. The EDS analysis confirmed the incorporation of Si element in the PEO coatings. The result of XRD analysis revealed that metastable phases such as gamma-and eta-alumina were produced as a result of PEO, while amorphous phases appeared with excessive Na2SiO3 concentrations (10 and 14 g/L). The coating thickness was significantly increased about 2-8 times with increasing Na2SiO3, almost depending on Na2SiO3 concentration. (C) 2017 The Japan Society of Applied Physics