Study On Formation And The Surface Roughness Of The Micro-arc Oxidation Coating

Micro-arc oxidation with the remarkable effect of surface modification, the environmentaly friendly technology, simple process and easy operation etc., has a very good prospect for industrial applications. With the industrial application development, the quality of coating surface is higher and higher that industrial application requestes. And the surface roughness, one of the indicators that evaluate the coating surface performance, attracts more and more attertion. During micro-arc oxidation processing, the coating surface forms that accompanies the spark discharge genertates the coating. And it is importmant to the surface roughness that spark discharge and coating formation are researched.At first, this paper has summarized the phenomenon such as coating surface morphology, current, voltage in the different spark stages. According to the sequence of a single spark discharge from gengerating to disappearing, a single spark diacharge was divided into four consecutive phases, namely the plasma soruceof the spark discharge formed, coating breakdown, the coating material generated, and the spark disappearing. The mechanism of a single spark discharge process was researched by use of the sub-timing method. Further the mechanism of coating formation and spark discharge variation were explored.According to analysis of the discharge phenomenon and coating microstructure in the stages of white spark and red spark, the mechanism of the plasma source formation is different in two stages. It causes the plasma soruce formation that the electron bombards the bubble wrapping the coating in the white spark stage. And in the red spark stage, the area of strong electric field generates the plasma source where the coating of excessive polarization turns out easily. Focusing on the two mechanism of plasma source formation the two models were established that white and red spark discharge plasma source form.During analysis of the discharge channel formation from plasma source in different locations of coating, three kinds of discharge channel models were obtained. The models successfully explain the phenomenon that the different sizes spark exist in the same moment during micro-arc oxidation process, the mechanism of the coating formation, and the mechanism of suppressing arc oxidation.The theory of a single spark discharge successfully explained the spark discharge mechanism of auto-generating and disappearing, and revealed the spark discharge mechanism of auto-evolution processed by the single-pulse output and double-pulse output.Then, the mechanisms of the coating and the surface topography formation were researched by using the theory of a single spark discharge, and were verified by the experiments performenced on LD10 and LY12. At the same time, the relationship between spark discharge and the evolution of coating formation was obtained, as follow: the coating formation of insulating amorphous→large spark turning out in cutting-edge position and phase change→large spark and phase change moving to specimen center→scan completing and a new round of discharge and coating growth→the end of the coating growth.Finally, the support vector machine regression analysis was introduced for the micro-arc oxidation process data analysis, and combined with the orthogonal experimental design. It is first created the model of the support vector machine regression analysis on orthogonal design basis for micro-arc oxidation process data analysis, and the processing parameters were successfully predict to treat LD10 and AZ91D by the model. In order to analysis influence of the process approach and substrate material on the frequency, duty ratio, time, and working solution temperature, and variation of the coating surface roughness with these parameters, the experiments were performanced according to the predictive parameters.