Effect of high temperature oxidation prefab film on formation of micro-arc oxidation coatings on 6061 aluminum alloy

Ceramic coatings were formed by micro-arc oxidation (MAO) on 6061 aluminum alloy with and without a high temperature oxidation prefab film under a constant voltage. The effect of the high temperature oxidation prefab film on the initial stage of growth process of the MAO ceramic coatings was studied in this paper. The results showed that the prefab film decreased the arc starting voltage and the arc starting time of the micro-arc oxidation, and promoted the evolution processes of the micro-discharge and the surface morphology of the coating. The prefab film and electrolyte composition, especially element P, participated in the formation of the coatings. The growth process of the micro-arc oxidation ceramic coatings on specimens with the prefab film consists of four steps. The first step is the formation of grain type of oxide lumps, the second step is the spread of the lumps like little worms along the specimen surface, the third step is the formation of many network areas with a number of linear materials like little worms, and the fourth step is the development of network areas into a continuous layer. However, at the same period, the growth process of micro-arc oxidation ceramic coatings on the specimens without the prefab film consists of two steps. The first step is the formation of a little grain type of oxide lumps, and the second step is the increase of the number of grain type of oxide lumps and the expansion of the lumps like little worms in line along the surface of specimens. (C) 2012 Elsevier B.V. All rights reserved.