Preparation And Properties Of Composite Ceramic Layer On Magnesium Alloy By Ultrasonic Assisted Micro-Arc Oxidation

Magnesium alloy as a light structure metal has a wide application prospect in the fields of aerospace,electronic communications and so on,but its poor corrosion resistance limits its practical application.At present,as an environmental protection surface technology,micro-arc oxidation technology has been used to improve the corrosion resistance of magnesium alloys.But the layer prepared by the technology is loose and porous,which has an adverse effect on the improvement of the corrosion resistance of magnesium alloys.Adding particulate additives in the electrolyte can effectively reduce the microporosity of the ceramic layer and improve the corrosion resistance of the magnesium alloy.However,if the particle is directly added to the electrolyte,there exists a problem of poor dispersion due to its own gravity effect.Ultrasonic with its unique effect can effectively improve the dispersibility of the particles and promote micro-arc oxidation.In this paper,AZ31B magnesium alloy was used as the matrix material.Ultrasonic-assisted method was introduced into the micro-arc oxidation process.Based on the optimized aluminate-phosphate composite electrolyte,a composite ceramic layer was prepared by adding Al₂O₃colloid in the optimized composite electrolyte.The effect of the addition amount,the addition time of the Al₂O₃colloid and the ultrasonic assisted effects on the microstructure and properties of the composite ceramic layer were studied.The following conclusions were obtained:?1?Through series univariate experiments,the effect of the concentration of each component in the composite electrolyte on the micro-arc oxidation voltage and corrosion resistance of the magnesium alloy was studied,and an optimum value of the concentration of each component was determined,NaAlO₂=15 g/L,Na₃PO₄=5 g/L,NaB₄O₇=2 g/L.?2?The porosity of the composite ceramic layer was reduced by doping Al₂O₃ colloids in the electrolyte during the ultrasonic-assisted micro-arc oxidation process comparing the undoping one.The thickness of the layer was increased.Al₂O₃ phase was presented in the layer.Both the corrosion and wear resistances of the magnesium alloy sample were improved by doping Al₂O₃ colloids.?3?The ceramic layer prepared by adding 500 mL Al₂O₃ colloid in the composite electrolyte in the middle period of micro-arc oxidation?about 3/5 of the total oxidation time?showed the smallest porosity,tiny cracks and the best sealing effect.The layer with the largest thickness presented the best corrosion and wear resistances.?4?The dispersion effect of Al₂O₃ colloid is best when the ultrasonic frequency is 45 kHz and the power ratio is 60%.After the micro-arc oxidation sealing,the porosity of the ceramic layer surface is minimum,there is no obvious micro-cracks,and the film thickness is large.The improvement of microscopic quality lead to the corrosion resistance optimal.