Study On The Load Model Of Micro Arc Oxidation Process Of Magnesium Alloy

As a surface treatment method for light metals,micro arc oxidation(MAO)technology has many advantages like environmental protection,high efficiency and simple process.So it has been widely concerned by domestic and abroad scholars.Besides,MAO has been applied in industrial manufacturing preliminarily.The study of MAO loading model is not only favorable for understanding the mechanism of MAO,but also significant to the online monitoring of the film performance and quality.In this dissertation,the loading of MAO on magnesium alloy was taken as the research object.The equivalent circuit model of MAO loading was established and analyzed bytheoretical analysis,experimental research,numerical simulation and material performance characterization.The effects of voltage and time on the performance of the coating were studied,respectively.Corresponding analysis between the performance of the coating and the load equivalent element was carried out.The specific research contents and results are shown as following:Firstly,the process of MAO was divided into several stages based on the arc and voltage current waveform.A second-order nonlinear equivalent circuit model was established using automatic control principle and circuit theory,and the transfer function of the equivalent circuit was calculated using this model,additionally.Further,according to the experimental data,the loading model in the conditions of constant voltage with different treating time and different voltage was calculated and analyzed quantitatively using the principle of automatic control and electrotechnics and obtained the evolution law of the values of each element in the equivalent circuit.Besides,it was found that the evolution trend of each element value and the growth process of MAO film was consistent with the characteristics of the electrolytic cell and then the physical significance of each element was analyzed.Finally,the quantitative calculation results were substituted into the loading equivalent circuit model for simulation analysis and the results were consistent with the measured waveform aforementioned,which indicated that the loading model and the quantitative calculation process were correct and further provided a theoretical model for the advanced research.Secondly,the analysis of the affection of voltage and time on the film performance implied that with the increasing of voltage,the film thickness upgraded,the film bonding force increased,the density became worse and the corrosion resistance decreased simultaneously.In the condition of constant voltage,the film thickness and film bonding force continued to increase with the extension of treatment time,but the corrosion resistance improved firstly and then became worse.It can be seen that the bonding strength of film base was determined by the thickness mainly,and the corrosion resistance of film was affected by the film thickness and compactness.Finally,,it was found that the load model can correspond to the actual film,the equivalent resistance can correspond to the film thickness and film bonding force,and the voltage withstand value of the zener diode could correspond to the density.Therefore,the loading model can realize the online monitoring and prediction of the film with different parameters.In conclusion,the loading equivalent circuit model established here was able to reflect the characteristics and structure of the electrolytic cell,and the load equivalent element can reflect the arc state,film thickness and compactness,indirectly.These results provided a new research method and idea for online monitoring and the prediction of MAO process and film performance of magnesium alloy.