The Research On The Effect Of Micro-arc Oxidation Area Of Magnesium Alloy On Load Characteristics And Film Properties

In order to increase the surface area of a single treatment of magnesium alloy micro-arc oxidation and accelerate the promotion and transformation of technology,further development of the production process is needed.However,it was found in the experiment that the surface area of the workpiece in industrial production is much larger than that of small samples for scientific research,the load characteristics of the two are significantly different,so the load adaptability requirements are different.In order to clarify the difference between the load characteristics of the two,this paper studies the variation of load characteristics,arc conditions,film properties,and film thickness by changing the surface area of the sample,and determines the problem of matching different load characteristics with the power mode.The LCR tester and oscilloscope are used to collect the equivalent resistance,equivalent capacitance,voltage,and current waveforms of the four different areas of the sample at different stages,and simultaneously use the high-speed camera to take pictures of the arc states at different stages.Then comparing and observing its change rules to analyze the effect of different arc states on the surface structure of the film layer.The rising edge of the recorded load voltage waveform is analyzed,and the falling edge waveform is fitted by MATLAB software to analyze the discharge time constant of the capacitive load.After analyzing the voltage waveform,a load equivalent circuit is established,and it is simulated and verified by Simulink.The thickness of the film was measured with a thickness gauge,the cross-section and surface microstructure of the film were analyzed by SEM,and the corrosion resistance of the film was tested,and the effects of load characteristics and arc conditions on the performance of the film were compared and analyzed.The test results show that the two-stage load circuit model of magnesium alloy micro-arc oxidation is established by analyzing the process of micro-arc oxidation and the voltage waveform.The model of the first stage consists of inductance L,resistance R and capacitor C in series.The model of the second stage is composed of resistance R1 and capacitor C in parallel and then in series with resistor R0 and inductance L,in which R?R0 and R1 reflect the equivalent resistance and C reflects the equivalent capacitance.Simulink software was used to simulate the model,and it was found that the response of the model to pulse voltage is highly consistent with the measured current and voltage waveform,so the model could be used to characterize the load characteristics of magnesium alloy micro-arc oxidation.In the load model,with the increase of the treatment voltage,the equivalent capacitance of allsamples in the load model continues to decrease,the equivalent resistance continues to increase,and the discharge time constant of the load continues to increase.The increase of the equivalent resistance indicates that the film layer continues to grow with the increase of the treatment voltage;With the increase of the treatment area,the equivalent resistance in the load model decreases continuously under the same voltage,the load capacitance increases continuously,and the discharge time constant of the load decreases continuously,which indicates that the growth of the film slows down with the increase of the area and the larger area of the sample,the load waveform is closer to the square wave.Comparing the results of the arc state and microscopic characterization,it can be seen that with the increase of the treatment area,the number of arcs on the surface of the sample changes from less to more,and the arc spots from larger to smaller,and the change in the size of the arc is the same as that of the micropore diameter of the obtained film,At the same time,the film structure becomes more and more dense,the micropore size and surface porosity become smaller,and the film thickness also decreases.As the thickness of the film layer becomes thinner and the microstructure of the film layer is different,the corrosion resistance of the film layer is also reduced.Due to the strong resistance and longer discharge time of small-area samples in the load model,it is easy to produce continuous arc and damage the film under unipolarity,while large-area samples have strong capacitive characteristics and are easy to produce large impact current.Moreover,due to the dispersion of arc,the film is thinner under the same treatment time and corrosion resistance is poor.Therefore,it is necessary to carry out targeted process development to match its load adaptability requirements.Finally,through the correspondence between the resistance value of the equivalent resistance and the performance of the film layer,the film thickness can be predicted by the resistance value,which provides an idea for the online quality monitoring of film thickness in the future industrial promotion.