Research On Device And Processes In Scanning Micro-arc Oxidation

As a kind of surface modification technology, the micro-arc oxidation (MAO)technology has been a research focus at home and abroad，due to its capability tofabricate ceramic film fast, on the original place of the surface of aluminum,magnesium, titanium and their alloys. On the other hand, some disadvantages of theworkpiece-immersed MAO processes were exposed in its development process, justfor its high energy consumption, the limit to workpiece size, and the renovation ofthe damaged film. To solve these problems, a new method called scanningmicro-arc oxidation (SMAO) was proposed. The approach to the renovation of thedamaged film was studied in this paper.At the beginning, based on the basic principle of MAO, the similarities anddifferences on the phenomena of the workpiece-immersed MAO and SMAO wereanalyzed. According to the characteristics of voltage and current, the MAO processwas divided into four stages, and the electrochemical reaction of each stage wasdiscussed. The electric breakdown model was set up, and the characteristics of filmgrowth in each stage were explained.The device for SMAO processes was developed, which mainly consists of thepulse power supply, the hand-held cathode and the pump for cycling the solution. Inaccordance with the requirements for the pulse power supply, a unidirectional pulsepower supply based on CPLD was designed. The structure of the handle SMAOdevice was devised, as well as the structure of the tubular cathode. At the same time,the cycling style of the solution, the distance between the cathode and workpiecewere planned. On the whole, out of security, the material of the hand-held cathodewas selected.Aimed at the working time, the distance between the two poles, the electrolyteconcentration of NaOH, the overlap rate of scanning and so on, some exploratoryexperiments were conducted, using the developed SMAO device. Thecharacteristics of the films were researched and summarized, which have revealedsome rules about the effects of some parameters.At last, some experiments on renovation of the films were performed, fromwhich, the feasibility in renovating the damaged film was confirmed. On account of the studies above, a new idea was put forward, that the processes for renovatingthe damaged film can be applied to workpieces of large area. Thus, it may solvethe problems in workpiece-size-limited conventional MAO processes.