Effect of electrolyte systems on plasma electrolytic oxidation coatings characteristics on LPSO Mg-Gd-Y-Zn alloy

Abstract

In order to solve the problem of poor corrosion resistance of Mg-Gd-Y-Zn alloy with high strength and high toughness. In this paper, two-step plasma electrolytic oxidation (PEO) was implemented on Mg-Gd-Y-Zn alloy with long period stacking ordered (LPSO) phase in seven different electrolyte systems. Optical microscope (OM), Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) were used to characterize the structure distribution and composition of the LPSO phase. X-ray diffraction (XRD), SEM, EDS, Mott-Schottky test (M-S), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and immersion hydrogen evolution were used to study the morphology, composition, structure and corrosion resistance of the PEO coatings prepared using the various electrolytes. The PEO coating prepared by the mixed electrolyte of sodium aluminate, sodium phosphate and sodium silicate, referred to as PEO-APS coating, had the most excellent structure and corrosion resistance. The coating was dense and uniform, the coating thickness was 3.5 μm, the open porosity was 4.4 %, the average pore size was 0.12 μm, and the corrosion current density icorr was 2.09 × 10−8 A cm−2. In addition, the formation mechanism and corrosion resistance mechanism of the PEO-APS coating were discussed, and the effect of LPSO phase on the PEO-APS coating was proposed.