Study On The Properties Of Micro-arc Oxidation Coating On Pure Aluminum

Micro-arc oxidation is a new surface technology producing ceramic coating on valvemetals. It is a complex reaction process, involving plasma chemical and electrochemical,thermal chemical reactions. With this method, ceramic coatings can be directly formed onthe surface of Al alloys, and the surface properties can be improved considerably.In this paper, the effects of electrolyte composition on surface morphologies, thickness,bonding strength and corrosion resistance property of coatings were investigated.Meanwhile, the effects of cathodic current density and cathodic duty ratio on the form offilm were analyzed, due to the seldom research of mechanism of cathodic electricparameters. On the basis of original parameters, the coatings exhibit lower porosity andbetter surface appearance by the process composed of4.5mL/L C3H8O3in the electrolyte,conductivity16.5mS/cm, cathodic current density9A/dm2and cathodic duty ratio30%. Inaddition, the better bonding strength and corrosion resistance can be received.The mechanism of solute ions on the formation and growth of the ceramic coating wasstudied in the meantime. The function of solute ions is to form the unstable blocking layeron the surface of the aluminum alloy during the initial stage of film formation. In the sametime, the blocking layer provide precondition. In the ceramic’s later growth, solute ionsprovide the indispensable elements such as oxygen. Then the complete film with ceramicsstructure can be formed.