Effect of PEO power modes on structure and corrosion resistance of ceramic coatings on AZ91D Mg alloy

Abstract

The aim of this work is to investigate the effects of different power modes [constant current (CC), constant voltage (CV) and constant power (CP)] on the structure and corrosion resistance of the plasma electrolytic oxidation ceramic coatings containing Ca and P on AZ91D Mg alloy. The phase composition, morphology and element distribution of the coatings were studied by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The corrosion resistance of the coatings in the simulated body fluid was examined by electrochemical impedance spectroscopy and polarisation curve methods. The results showed that the coatings were of porous structure and mainly composed of MgO. The thickness, surface roughness, the size of the surface micropores and the amount of MgO were all increased with the cell voltage under the same power mode or increased in the sequence CV.CC.CP under the different power modes. The corrosion resistance of coatings was related to the structure characteristics, which were determined by different power modes. Among the different power modes, the corrosion resistance of the coatings is generally increased in the sequence CV.CP.CC, and under the same mode, the proper increase in the cell voltage is liable for improving the corrosion resistance of the coatings.

Effect of current density on microstructure and properties of PEO ceramic coatings on magnesium alloy

“…All the coatings were observed to have a wavy-jagged interface with the substrate, which is most likely as a result of the dissolution of the substrate in the early stage of the PEO process. 21,22 The coating obtained at low current density was more compact and the coatings produced at higher current density had a higher degree of microcracks. The development of such defects in the PEO coatings is attributed to the thermal stresses during PEO process as a result of melting and solidification of hard ceramic compounds.…”

A review of recent work on discharge characteristics during plasma electrolytic oxidation of various metals

“…Effects of this type are described at various points in Section 'Discharge characteristics', but this review does not encompass detailed consideration of exactly how the electrical power supply can be controlled during PEO processing. Information of this type is available in the literature [23][24][25][26].…”

Properties of Micro-Arc Oxidation Coating Fabricated on Magnesium Under Two Steps Current-Decreasing Mode

“…Our group has previously completed research on the growth mechanism at low-current (Chen et al, 2015). In previous works, it can be found that the structure of these coatings and the voltage curve would change significantly as time goes by (Jiang et al, 2013;Yao et al, 2013;Dehnavi et al, 2015;Sobrinho et al, 2017). Although it is easy to calculate and control the energy consumption using the constant current mode, too much energy input can cause these coatings to peel off during the final repairing stage.…”