Recent progress in surface modification of metals coated by plasma electrolytic oxidation: Principle, structure, and performance

Oxide coatings were produced on a 6061 aluminum alloy using a pulsed unipolar plasma electrolytic oxidation (PEO) process. The effect of electrical parameters including pulse frequency, duty cycle and current density on phase formation in the coatings was revealed using conventional and glancing angle X-ray diffraction. The results show that PEO coatings are mainly composed of γ-Al2O3. Depending on the electrical parameters employed, the coatings can also contain α-Al2O3 and mullite with varying concentrations. Higher current densities and higher duty cycle were found to favor the formation of mullite. Under the experimental conditions used, the ratio of the integrated XRD peaks for α- and γ-Al2O3 varied from 0 to about 0.6, indicating that the relative content of α-Al2O3 in the PEO coatings varied over a wide range. Longer pulse on-times and higher current densities promoted the gamma to alpha-alumina phase transformation. Depth profiling of PEO ceramic coatings using glancing angle XRD with different incident beam angles revealed that mullite was more concentrated in the top surface of the coatings. No significant variation in α-Al2O3 concentration across the coatings could be concluded in this study, unlike the results of some other studies.

/pdf/phase-transformation-in-plasma-electrolytic-oxidation-45wh2xex2o.pdf

Phase transformation in plasma electrolytic oxidation coatings on 6061 aluminum alloy

Corrosion, wear and tribocorrosion performance of a thermally sprayed aluminum coating modified by plasma electrolytic oxidation technique for offshore submerged components protection

Fabrication and characterization of hydrophobic microarc oxidation/poly-lactic acid duplex coating on biodegradable Mg-Ca alloy for corrosion protection

Study plasma electrolytic oxidation process and characterization of coatings formed in an alumina nanoparticle suspension

Effect of ultrasonic on microstructure and growth characteristics of micro-arc oxidation ceramic coatings on 6061 aluminum alloy

Evolution of micro-arc oxidation behaviors of the hot-dipping aluminum coatings on Q235 steel substrate

Effect of high temperature oxidation prefab film on formation of micro-arc oxidation coatings on 6061aluminum alloy

In this paper, the composite coatings on the surface of magnesium alloy were successfully prepared by the combination of micro-arc oxidation (MAO) and sol–gel method. Oxide ceramic layers were formed on AZ91D magnesium alloy using MAO process. The sol–gel layers were coated on MAO ceramic layers. The composition of the composite coatings was analyzed by x-ray diffraction and x-ray photoelectron spectroscopy. The microstructure of the composite coatings was analyzed by scanning electron microscope. The results show that the composite coatings can reduce the gap membrane effectively. The polarization curves and electrochemical impedance spectroscopy were used to evaluate the corrosion resistance. The results of corrosion tests show that the sol–gel layer enhances the corrosion resistance of the magnesium alloys significantly.

Corrosion Performance of Composite MAO/TiO 2 Sol–Gel Coatings on Magnesium Alloy AZ91D

The pressure dependence of the crystallisation temperature of amorphous Zr 70 Cu 30 alloy and the variation of its crystallisation phases under high pressure annealing were investigated by electrical resistivity measurement and X-ray diffraction method. The results show that pressurising generally raises the crystalisation temperature, but slightly decreases it at the early stage of compression. Evident changes in crystallisation phase in the alloy were also observed under high pressure annealing. At atmosphere pressure, the crystallisation products are CuZr 2 with a modicum of α-Zr, while at a pressure of 2 GPa, the alloy crystallises into a mixture consisting of CuZr 2 , Cu 10 Zr 7 and an appreciable amount of α-Zr. The origin of these observations is discussed.

Shen Dejiu

Papers

Effect of ultrasonic on microstructure and growth characteristics of micro-arc oxidation ceramic coatings on 6061 aluminum alloy

Evolution of micro-arc oxidation behaviors of the hot-dipping aluminum coatings on Q235 steel substrate

Effect of high temperature oxidation prefab film on formation of micro-arc oxidation coatings on 6061aluminum alloy

Corrosion Performance of Composite MAO/TiO 2 Sol–Gel Coatings on Magnesium Alloy AZ91D

The influence of pressure on crystallisation of amorphous Zr70Cu30 alloy—I. Crystallisation temperature and the crystallisation phases