STUDY ON AL2O3 DUPLEX COATINGS DEPOSITED BY NEW MICRO-ARC OXIDATION (MAO) PROCESS USING NATURAL ADDITIVES OF RICE HUSHES ASH (RHA) AND PORCELANITE ROCKS OF PRE-ANODIZED 6061 AL ALLOYS

In this study, pre anodized Al 6061 alloy was coated with protective ceramic coatings using micro- arc oxidation process (MAO). MAO electrolyte was modified using natural additives of rice hushes ash (RHA) fired at 800 ͦC and porcelanite rocks fired at 700 ͦ C. The surface morphology, phase content, structure, and element distribution of the coatings were investigated by X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy, and atomic force microscopy. Results showed that the samples coatings contained γ-alumina, and their thickness and hardness increased by the increasing of deposition time. The research demonstrates that a relatively hard, thick and uniform coatings with good wear resistance, can successfully be deposited on pre anodized Al alloy using natural additives of rice hushes ash (RHA) and porcelanite rocks containing MAO electrolytes as natural additives. The results proved that the pre anodized surfaces promoted the MAO coating in providing the higher hardness in comparison to untreated surfaces