Corrosion behaviour of microarc-oxidisedrnmagnesium alloy in Earle’s balanced saltrnsolution

摘要

Microarc oxidation (MAO) coating is effective in improving the corrosion resistance of magnesium (Mg) alloys in arnsimulated body fluid. MAO coatings were deposited on AZ31 magnesium alloy at different pulse frequencies. Samplesrnwere immersed in Earle’s balanced salt solution (EBSS) up to 21 d. Scanning electron microscopy, potentiodynamicrnpolarisation testing, electrochemical impedance spectroscopy and X-ray diffraction (XRD) were performed to evaluaternthe corrosion behaviour of MAO coatings in EBSS compared to that of the uncoated AZ31. MAO-coated samplesrndemonstrated improved corrosion resistance compared to the bare AZ31 throughout the corrosion period, indicatingrnthat MAO coating exhibited good corrosion protection of AZ31 in EBSS. Given the same immersion time, MAO-coatedrnsamples showed decreased corrosion current density and increased electrochemical impedance with increasing pulsernfrequency. The coating produced at 3000 Hz exhibited the best corrosion resistance compared to the ones produced atrn300, 500 and 1000 Hz due to its uniform and dense structure. The XRD analysis showed that the corrosion productsrnpresented on the surface of the MAO-coated samples after immersion into the EBSS for 21 d were primarily composedrnof magnesium hydroxide, quintinite and hydroxyapatite. The corrosion mechanism of the MAO-coated AZ31 samples inrnEBSS is also discussed.