Power Supply And Process Control System For Micro-arc Oxidation On Magnesium Alloy Whells

With the increasing application of magnesium alloy, improvement of its surface properties is urgent. As a great potential surface treatment technology, the micro-arc oxidation (MAO) has been widely concerned. However, since it relates to materials science, electrochemistry, arc physics, power electronics and control systems and other disciplines and technical fields, it is a highly complex process affected by many factors. Therefore, many problems still did not give a definite conclusion.This paper aimed to the micro-arc oxidation technology. proposed micro-arc discharge mechanism and models. By studying micro-arc discharge phenomenon in the MAO process, the electrical signal waveforms and the oxide coatings morphology, the basic requirements of MAO power were made clear, and accordingly a high-power industrial applications for micro-arc oxidation power was developed. With this power controlled the MAO process, automatic control, efficiency of filming and the quality of coating surface were improved, offering a guidance for industrial production. The paper mainly includes the following:For industrial production, the main circuit design of the new type high-power pulse power supply of MAO, with IGBT parallel and protection measures, solves the problems of the impact load current and leads to reliable operation of power electronic devices. Taking the 16-bit high performance microcontroller 80C196KB as the core, the hardware of power supply control system has been developed. The development of system control software has been finished with the output pulse shape and voltage characteristics adjusting algorithms as the key. Taking AT89C52 microcontroller as the core to develop the process control system, human interface has been designed, guarantying the ease use of device, flexibility and maneuverability. With the designed communication protocol, the two MCU systems exchange data via serial asynchronous communication, and connect with the host computer through the RS-232C communication interface to provide support for MAO processing centers in the future. The equipment has been tested to achieve the expected technological goal, and has passed the preliminary assessment of practical application.4-courses control scheme was proposed based on the characters of micro-arc oxidation in different periods of the process. In each course, using the power we developed, micro-arc oxidation parameters such as current / voltage, frequency, duty cycle, form of pulse output and working hours were controlled individually in accordance with the preset parameters. It was found that the program above can achieve repeatable, stable and reliable quality film and high power efficiency.The influence of power loading and the parameters in MAO process was significant. Two ways can be selected to load: voltage increment and constant current. The reasonable range of control parameters of each ways of loading were established based on a large number of experiments, which is meaningful for production guide.