Research On Key Technology Of Ultrasound-Assisted Micro Arc Oxidation Of AZ31B Magnesium Alloy

As lightweight material,magnesium alloys have been widely used in many fields because of their good mechanical properties.Among them,AZ31B wrought magnesium alloys are widely used in transportation,electronic communications and equipment casings because of its good processing performance and excellent heat dissipation performance.However,the poor corrosion resistance slows down the development of magnesium alloys.In order to improve this defect,micro-arc oxidation treatment of magnesium alloy surface is a simple and environmentally friendly method,which can effectively improve the corrosion resistance of magnesium alloy,and the effect after processing is obvious.It has been widely used in surface processing of magnesium,aluminum alloy and so on.In order to improve the corrosion resistance and comprehensive properties of micro-arc oxidation coatings on magnesium alloys,pretreatment,post-sealing and other composite treatment methods are also the hot research directions,including grinding,sandblasting,soaking and so on.In this paper,the AZ31B magnesium alloy was pretreated by ultrasonic peening combined with cerium nitrate impregnation.The Magnesium alloy samples were placed in a self-made ultrasonic impregnation device,and cerium nitrate solution was added to the composite pretreatment.The effects of the composite treatment method on the voltage change,micro-morphology,element content and corrosion resistance of AZ31B magnesium alloy during micro-arc oxidation were studied.Orthogonal experimental method was used to analyze the effect of the setting of electrical parameters on the preparation of coating on magnesium alloys.The optimum concentration of KF was determined by optimizing the micro-arc oxidation electrolyte through conventional film-making process.The film pretreated by ultrasonic peening cerium nitrate impregnation was compared by electrochemical experiment and salt spray test,and the results were as follows:?1?Using L₉?3⁴?orthogonal test results and range analysis table,the thickness,hardness and roughness of the prepared films were used to measure the quality of AZ31B magnesium alloy oxide film.Finally,the comprehensive analysis of the properties of the surface film layer of each sample showed that when the current density was 8A/dm²,the duty cycle was 25%and the pulse frequency was 800Hz,the corrosion resistance and surface quality of the films were the best.It is concluded that among the three electrical parameters,current density has the greatest effect on the surface morphology of the films,followed by pulse frequency and duty cycle,which have relatively little effect on the early stage of film formation.?2?The composition of the electrolyte was determined by analyzing the micro-morphology,film roughness and thickness of the prepared samples.Na₂SiO₃ was used as the main component of the electrolyte,KOH was used as the regulator of the acidity and basicity of the electrolyte,glycerol and KF were used as auxiliary additives.By adjusting the concentration of KF,the effects of KF on the physical properties,corrosion resistance and voltage of the film were analyzed,and the optimum ratio of KF was obtained.?3?The composite pretreatment of AZ31B magnesium alloy was carried out by using the self-made ultrasonic impregnation device and the combination of ultrasonic and rare earth cerium nitrate impregnation.The effects of the composite pretreatment method on the film forming process and the properties of various indicators of magnesium alloy were studied.It is concluded that this method is helpful to reduce the voltage and speed up the breakdown of the film in all stages of the film-making process;the surface roughness of the film treated by this composite method is reduced,the discharge through hole is reduced,and the micro-quality is improved;the corrosion resistance of the oxide film pretreated by ultrasonic peening cerium nitrate impregnation is obtained by electrochemical experiments and neutral salt spray experiments.Corrosion performance is better.