Ultrasonic Assisted Preparation And Properties Of Magnesium Alloy Micro-arc Oxidation Composite Coating

Magnesium alloys have excellent properties,low density,good thermal conductivity,good cutting performance and casting performance,and have important applications in the fields of transportation,electronics industry,aerospace and chemical engineering.However,the poor corrosion resistance of magnesium alloys limits its application,and its performance can be effectively improved through the micro-arc oxidation process.A micro-arc oxidation process can form a dense ceramic layer on the surface of the magnesium alloy,effectively improving the corrosion resistance of the magnesium alloy.Since the formation process of the composite film layer must have a hole structure,which will affect the performance of the magnesium alloy,it needs to be treated to reduce the hole.This paper aims to improve the sealing problem of micro-arc oxidation composite film.Taking AZ31D magnesium alloy as the base material,Al₂O₃powder and graphite powder were added to the electrolyte separately.Because it is insoluble in the electrode liquid,it is fully diffused and penetrated in the electrolyte by the aid of the stirring system and the ultrasonic auxiliary system In the process of arc oxidation film formation,it participates in the formation of the composite film and improves the performance of the micro-arc oxidation composite film.The basic electrolyte composition selected for the experiment was15 g/L Na Al O₂,5 g/L Na₃PO₄,and 2 g/L Na₂B₄O₇.The following conclusions were drawn through the experiment:（1）Add 4 g/L Al₂O₃ powder to the electrolyte.When the ultrasonic auxiliary frequency is 25 kHz and the power is 90%,the sample has the best corrosion resistance.The corrosion rate is 0.01707 g/m²h;when the ultrasonic auxiliary frequency is 45 kHz,the power is at 60%,the sample has the best corrosion resistance,with a corrosion rate of 0.00590 g/m²h;（2）Al₂O₃ powder and graphite powder are added to the electrolyte at the same time.The experiment has the best effect when the voltage is 500 V.When the amount of graphite powder is 7 g/L,the sample has the best corrosion resistance and wear resistance.The selected ultrasonic auxiliary parameters are the same as when only Al₂O₃ powder is added.Under this process,the corrosion rate of the sample is 0.00216 g/m²h;（3）The ultrasonic auxiliary parameters of the process of adding Al₂O₃powder and graphite powder at the same time were found to be inconsistent with the ultrasonic auxiliary parameters when only adding Al₂O₃ powder.When the ultrasonic frequency is 45 kHz and the power is 45%,the sample has the best resistance corrosion performance and wear resistance,the corrosion rate is0.00121 g/m²h,the wear resistance of the sample is also greatly improved compared with the substrate and other processes,the friction coefficient is about0.15.The solution conductivity measured under this process is 9.32 ms/cm.