Development Of Bipolar Microarc Oxidation Power Supply And Surface Modification Of Aluminum Alloy

Microarc oxidation (MAO) is a new surface modification technique developed from anodic oxidation. The technique has been paid more and more attention due to its capability to fabricate ceramic film with superior properties, such as high micro-hardness, good corrosion resistance, wear-resistance and so on. The pulse power with bipolar for MAO has been developed and used to investigate the current characteristics of flowing through plate specimen in Na₂SiO₃ solution. Meanwhile, the effect of the instrumented parameters on surface properties of the films, including treatment time, electric parameters and solution concentration is investigated in details.The bipolar pulse-bias power supply is needed to achieve better surface properties. The emphasis is paid on the design for main circuit, selection of power switch and adjustment for protection and control system. The power supply has been developed and it can achieve multiple working modes and operation flexibilities.The current behavior flowing through the plate specimen has been investigated. The results show that the oxidation current of the anode plate decreases as the distance between the cathode and the anode electrodes increases. Furthermore, oxidation current is independent on the size of cathode but much affected by surface area of anode electrode. Moreover, in baffle plate configuration, the current of the front plate is higher than that of the back plate.The effects of the experimental parameters on the properties of fabricated films are also investigated in this paper. The results indicate that the main phase consists ofγ-Al₂O₃ in the MAO surface. Mechanical properties and corrosion resistance have been substantially improved. Surface hardness increases with processing time. Besides there exist optimal parameters including current density, frequency or duty to achieve higher surface hardness with the single pulse mode. The wear-resistance increases with frequency, current density, and corrosion-resistance increases with pulse width, For the Na₂SiO₃ solution, surface hardness increases initially with solution concentration and decreases latter. With the bipolar pulse-bias, surface hardness, corrosion-resistance and friction-resistance...