Magnesium alloy was treated by micro-arc oxidation with ultrasound and the discharge phenomenon was studied. The effect of ultrasound on the discharge life and the number of discharge charges was studied asing high speed photography technique. The results indicate that 60 W power ultrasound increases discharge life of single charge and the total number of discharge charges in one discharge period. The size of micro-pore increases and the number of cracks in coating significantly reduce. The dendritic area with a width of 15 μm in magnesium alloy forms during micro-arc oxidation process. Ultrasound eliminates the dendritic structures of micro-arc oxidation magnesium alloy.
The ultrasonic micro-arc oxidation(UMAO)was used to fabricate ceramic coatings on magnesium alloy.UMAO coatings were produced at 60 W input ultrasonic.The effects of the ultrasound on the microstructure,phase composition,elemental distribution and corrosion resistance of the coatings were extensively investigated by scanning electron microscopy(SEM),X-ray diffraction(XRD),energy-dispersive X-ray spectrometry(EDX)and electrochemical workstation.The results showed that ultrasound improved the homogeneous distribution of micro-porous structure.The coatings were mainly composed of MgO ceramic and small amount of calcium and phosphorus with porous structure.The Ca/P ratio of the coatings increased when 60 W ultrasonic was used.The corrosion potential in simulated body fluid(SBF)changed from1.583 V of bare magnesium alloy to -0.353 V of magnesium alloy coated under 60 W ultrasonic.The corrosion resistance of UMAO coatings was better than that of MAO coatings.
