Effect Of High Temperature Oxidation Flim On Formation Of Micro-arc Oxidation Coatings On6061Aluminum Alloy

This paper adopted high temperature oxidation prefab film formed on6061aluminum alloy and the investigation used self-manufactured WH-1A micro-arc oxidationsurface treatment equipment. The effect of high temperature oxidation prefab film onformation of micro-arc oxidation coatings on6061aluminum alloy was studied, such as,the micro-structure, thickness, elementary composition, phase composition andcorrosion-resistance. The growth of the formation and the mechanism of micro-arcoxidation ceramic coatings were investigated.The results showed that the high temperature oxidation prefab film formed on thespecimen surface increased the growth rate of the MAO coatings, decreased the arcstarting voltage and the arc starting time of the micro-arc oxidation, Less energy wasconsumed on specimens with the high temperature oxidation prefab film than that ofwithout the high temperature oxidation prefab film to obtain the same layer thickness.Under a constant current and voltage, the high temperature oxidation prefab film promotedthe evolution processes of the micro-discharges and the surface morphologies of MAOcoating. Close relations exist among the arc starting voltage and the arc starting time, theevolution processes of micro-discharge appearance, surface morphology and thecurrent-time response. The prefab film and electrolyte composition, especially element P,Si, participated in the formation of the coatings.For a constant voltage, the initial stage of growth process of the micro-arc oxidationceramic coatings on the specimens with the prefab film consists of four steps. The firststep is the formation of grain type of oxide lumps, the second step is the spread of thelumps like little worms along the specimen surface, the third step is the formation of manynetwork areas with a number of linear materials like little worms, and the fourth step is thedevelopment of network areas into a continuous layer. However, at the same period, thegrowth process of micro-arc oxidation ceramic coatings on the specimens without theprefab film consists of two steps. The first step is the formation of a little grain type ofoxide lumps, and the second step is the increase of the number of grain type of oxidelumps and the expansion of the lumps like little worms in line along the surface ofspecimens. For a constant current, the growth process of the micro-arc oxidation ceramic coatingon specimens with the prefab film consists of three steps. The first step is the formation ofspherical objects and little worm-like objects, the second step is a number of linearmaterials like little worms and the development of network areas into a continuous layer,the third step is the formation of the discharge pores and cracks on the surface of coatings.However, at the same period, the growth process of the micro-arc oxidation ceramiccoatings on the specimens without the prefab film consists of three steps. The first step isthe extending of the discharge micro-pores on the surface of specimen, the second step isthe grain type of melted lumps areas into a continuous layer, the third step is the formationof the discharge pores, ablation and cracks on the surface of coatings. The formed ceramiccoatings on the specimens surface with and without the high temperature oxidation prefabfilm contain α-A12O3, γ-Al₂O₃phases mainly and MgSiO₄, MgO and mullite（3Al₂O₃·2SiO₂） phases lightly. The high temperature oxidation prefab film formed on thesample surface can increased the α-A12O3phases. With oxidation time going on, residualdischarge channel size in the ceramic coating increased, the surface of ceramic coatingbecame rougher while corrosion resistance turned weaker.