The Research On Influence Of Discharge-time And Cooling-time In Micro-arc Oxidation For Ceramic Film Growth And Film Properities

Micro-arc oxidation is a new technology for surface modification of magnesium alloy,which is improved on the basis of traditional anodic oxidation technology.Because of its simple process,green environmental protection,less procedures,and micro-arc oxidation film is not only good wear resistance,but also closely combined with the matrix,high hardness.So it is one of the most popular surface modification processes.In the process of micro-arc oxidation,an arc appears on the surface when the loading voltage is above the starting voltage.When the voltage drops below the arcing voltage,the arc disappears.In order to study the effects of arc initiation time and arc blowout time on the growth and performance of micro-arc oxidation film,the characteristics of pulse high level retention time(discharge time)equal to arc initiation time and pulse low level retention time(cooling time)equal to arc blowout time in the mode of discharge loop were discussed.In this paper,the discharge time and cooling time are innovatively regarded as two independent electrical parameters,and the other is fixed while changing the discharge time or cooling time.Experiments with different discharge time and cooling time are designed with magnesium alloy as the sample,and the corresponding frequency and duty cycle are calculated in reverse according to the discharge time and cooling time.At the same time,for the comparability of experiments,the total discharge time of each experiment scheme is set to be equal to 100 s,and according to this condition,the micro-arc oxidation processing time corresponding to each experiment scheme is inverse calculated.After the preparation of the film,the thickness and corrosion resistance of the film were detected,and the surface cross section of the film was observed by SEM.Then,the surface porosity and micropores of the film were counted according to the surface SEM photos.Finally,the film forming efficiency of each experimental scheme was calculated and compared.The effects of discharge time and cooling time on the growth and properties of micro-arc oxidation coatings were summarized and analyzed.The results show that when the total discharge time is the same,the thickness of the film increases first and then stays the same with the increase of cooling time,and the corrosion resistance of the film is better.Therefore,considering the thickness and corrosion resistance of the film,the cooling time should be increased appropriately.When the fixed cooling time is constant,the thickness of the film decreases and the corrosion resistance of the film becomes worse with the increase of the discharge time.Therefore,the discharge time should be reduced comprehensively.When the discharge time and cooling time are equal and increase synchronously,the thickness of the film gradually becomes thinner,and the corrosion resistance of the film becomes better.Considering the discharge time and cooling time,the smaller value should be taken.