Effect of electrolysis regimes on the structure and properties of coatings on aluminum alloys formed by anode­cathode micro arc oxidation

• Main Authors: Valery Belozerov, Oleg Sоbоl, Anna Mahatilova, Valeria Subbotinа, Taha A. Tabaza, Ubeidulla F. Al-Qawabeha, Safwan M. Al-Qawabah
• Format: Article
• Language: English
• Published: PC Technology Center 2018-01-01
• Series: Eastern-European Journal of Enterprise Technologies
• Subjects: structural engineering; anode-cathode regime; coating thickness; phase composition; corundum; properties
• Online Access: http://journals.uran.ua/eejet/article/view/121744
• ISSN: 1729-3774; 1729-4061

The study provides research findings on the effect of current regimes in microplasma oxidation on the phase composition and the properties of oxide coatings on an aluminum alloy. To obtain oxide coatings, micro arc (microplasma) oxidation is carried out in an alkaline-silicate electrolyte with an alternating sinusoidal current and in a pulsed current mode. It has been shown that an increased density of microdischarges in the case of the pulse technology increases the total energy released in them. This produces an increase in the growth rate of the oxide coating and the probability of formation of the α-Al2O3 phase. A linear dependence of the thickness of the coating on the duration of the process time and, accordingly, on the amount of transmitted electricity has been established. It has been found that for a small thickness of the oxide layer, the high rate of heat transfer both to the metal and to the electrolyte promotes the formation of aluminum oxide in the form of the γ-Al2O3 phase. The energy concentration in a thick oxide layer causes the formation of a high-temperature modification of α-Al2O3. It has been shown that the mechanism for the formation of α-Al2O3 is determined by the action of two facts: the difference in the energies of the γ-Al2O3 and α-Al2O3 phases as well as the polymorphic high-temperature transformation of γ-Al2O3→α-Al2O3 in the high-temperature region of a micro arc discharge. The coatings obtained by microplasma oxidation in the pulsed current mode have high hardness (23 GPa) and electrical strength (20 V/μm)