Study On The Forming Mechanism Of Cracks And Holes During Micro-arc Oxidation And The Effects Of Ultrasonic Waves

In this paper,aluminum alloy specimen were treated by a home-made WH-1A micro-arc oxidation device,and the Micro-arc oxidation coatings were detached from the aluminum alloy by a self-developed electrochemical method.The electrochemical test was used to research the performance and structure of the Micro-arc oxidation coatings.By using the different oxidation adsorption capacity of different metals in 6061aluminum alloy,the different production methods of cracks and poles were studied.In addition,by introducing ultrasonic method,the growth state of the film layer in the process of micro-arc oxidation was changed,and the influence of the external ultrasonic on the micro-arc oxidation process was studied.The results show that the content of Mg element in the prefab oxide film of 6061aluminum alloy samples is much higher than that of substrate samples.Because of that,the Mg element can be used as the tracer element to distinguish the different phases in the micro-arc oxidation process.It was found that there were different contents of Mg element around the crack and pore on the sample surface with different micro-arc oxidation time.Thus the way of the generation of cracks and holes is not only the micro-arc discharge membrane layer damaged in the process,also may be the membrane layer in different phase melt flow piled up together caused by micro-arc oxidation process of high temperature,form composite cracks and composite holes.In order to refine the phenomenon of uneven discharge in the middle and late stage of micro-arc oxidation and improve the performance of film layer,ultrasonic wave was introduced in the process of micro-arc oxidation.By comparing SEM and EDS analysis of the two kinds of membrane surface and cross section,the study found that the ultrasonic homogenizes discharge distribution points,refines the discharge passage,and inhibits the breakdown of the ceramic layer impedance of inhomogeneous evolution.The ultrasonic wave can improve the micro-arc oxidation ceramic layer's surface roughness and reduce breakdown of micro-arc oxidation ceramic layer under the size of holes and cracks accordingly to improve the distribution density of holes and cracks in the same micro-arc oxidation time.According to the XRD comparison analysis of different time samples,it was found that the addition of ultrasonic can promote the transformation of the?-Al₂O₃ in the ceramic layer of micro-arc oxidization to?-Al₂O₃.Through the corresponding electrochemical performance test analysis,it was found that adding ultrasonic can improve the corrosion resistance of ceramic layer of micro-arc oxidation.