Influence of electrical parameters of the micro-arc oxidation mode on the structure and properties of coatings

The influence of different power sources of the micro-arc oxidation process on the peculiarities of structure formation and properties of coatings on aluminum alloy AB formed in alkali-silicate electrolyte in the anode-cathode mode is investigated. It is shown that the pulse technology and the anode-cathode mode make it possible to form coatings containing mainly oxides of the alpha-A1(2)O(3) type (corundum) with a high growth rate. It has been established that with a small thickness of the oxide layer, the rate of heat removal both to the metal and to the electrolyte is high; this fact promotes the formation of alumina in the form of the gamma-A1(2)O(3) phase. The energy concentration in the thick oxidizing layer causes the formation of high-temperature modification of alpha-A1(2)O(3). It is shown that the mechanism of gamma-A1(2)O(3) formation is determined by two factors: the energy difference in the formation of gamma-A1(2)O(3) and alpha-A1(2)O(3) phases, and the polymorphic high-temperature transformation of gamma-A1(2)O(3) -> alpha-A1(2)O(3) in the high-temperature region of the arc discharge.