Micro-arc Oxidation Technology To Replace Hard Chrome Plating Applications

The growth process of MAO Coating made by the MAO power station designed by ourselves is studied in this paper. And the effect of the conductance and the current density on the growth process of MAO Coating is analyzed. We have got the MAO Coating which is over 250μm. The results show that increasing the conductance of MAO electrolyte can decrease the coating' s roughness and accelerate the growing speed of the coating. The relationship between the current density and the growing speed of coating is a linear relationship. Increasing current density can improve the growing speed of the coating. This paper has studied the effect of MAO parameter on the wearing action of MAO coating. If the coating' s roughness is low the wearing resistance of the coating will be good. When the coating has good surface status thicker coating has better wearing action. The current density pulse frequency and form affects the wearing action of MAO coating. Decreasing the current density can improve the coating' s wearing capability. The effect of pulse frequency on wearing resistance is not the simple linear relationship. The paper shows that the coating' s wearing capability is best when the pulse frequency is 500Hz. The wearing resistance of the coating made with triangular wave is better than that one made with rectangular wave. Compared the wearing action of MAO Coating to the chromium plating coating' s, the wear resistance of MAO Coating is better than that one of the chromium plating coating. So the MAO technics can take the place of the chromium plating technics. We observe and study the micro-form of the face and the cross section of the MAO Coating by SEM and metallography microscope and analyze the micro structure by X-ray diffraction. There are many holes in the surface of the MAO coating. If the thickness and the roughness increase the diameter of the holes will increase too. Increasing the current density the surface form of the MAO coating is look like the coral reefwhich is loosen rather than the volcano. When the coating is very thick there are metallic granules in the coating. X-ray diffraction shows that most of the coating' s structure is y-A1203. The wave' s form affects the structure of the coating. The coating made with triangular wave have a -AI2O3. But the pulse frequency has very small effect on the structure of the coating.