Effect of Asynchronous Microarc Oxidation on Microstructure of Coatings

Large-scale workpiece can be anodized by microarc oxidation (MAO) with asynchronous mode. Pure aluminum was treated by MAO in electrolyte containing Na2SiO3 and KOH using asynchronous mode. The influence of oxidation time during asynchronous MAO process on the anodizing current, coating thickness and microstructure was investigated. Results show that, at the beginning of MAO treatment, the MAO current of the naked sample is larger than that of asynchronous MAO sample significantly, and the difference decreases with increasing the processing time. Correspondingly, a long oxidation time is utilized, and the different regions of the samples tend to be the same in thickness. A longer treatment time also leads to more identical surface morphology and phase composition of MAO coatings. It is concluded that asynchronous MAO mode can effectively reduce anodizing current and a larger workpiece may be treated using a small power supply commercially achieved. This may enable wider applications of MAO in practical industries.