Comparison between fluoride ions modifier and ceramic AI_2O_3 particles additives on oxide layers produced on magnesium alloys by plasma electrolytic oxidation

摘要

In order to improve the corrosion resistance of the ceramic coatings formed on Mg alloys by plasma-electrolytic oxidation (PEO) method, two kinds of nano-additives (NF and A1_2O_3) were doped in the silicate electrolyte. The surface morphology feature, phase compositionand elemental composition were examined by FESEM, XRD and EDX, respectively. Corrosion resistance of the nano ceramic coatings formed was tested by impedence spectroscopy and potentiodynamic polarization techniques. Our results revealed that all coatings are composed mainly of MgO porous surface structure. Doping of nano additives had little effect on the elementalcomposition, while it influenced the morphological feature of the coating. Electrochemical tests showed that the coatings containing nano-additive have much better corrosion resistance than the plain (no additives) ones. The addition of nano NaF to the electrolyte resulted in formation of thinner and more uniform nano ceramic coatings which are five folds higher corrosion resistance than that deposited with no additive. Surprisingly, addition of Al_2O_3nano-additive improves the corrosion resistance about 20 times than that for no additive which can be attributed to morphological characteristic enhancement.