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Funct. Mater. 2019; 26 (4): 752-758.

doi:https://doi.org/10.15407/fm26.04.752

Increase of the α-Al2O3 phase content in MAO-coating by optimizing the composition of oxidated aluminum alloy

V.V.Subbotina1, U.F.Al-Qawabeha2, O.V.Sobol'1, V.V.Belozerov1, V.V.Schneider1, T.A.Tabaza2, S.M.Al-Qawabah2

1National Technical University "Kharkiv Polytechnic Institute", 2 Kyrpychov Str., 61002 Kharkiv, Ukraine
2Al-Zaytoonah University, 594 Queen Alia Airport Str., 11733 Amman, Jordan

Abstract: 

By the method of microarc oxidation of technically pure aluminum and aluminum doped with copper, vanadium and zinc (in an alkali silicate electrolyte at a current density of ~ 20 A/dm2), the resulting coating is about 100 μm thick. The nonmonotonic dependence of the phase composition and hardness on the doping level of aluminum (Al + Cu, Al + Zn, and Al + V systems) is revealed. It was established that the degree of influence of alloying elements on the transformation process of γ-Al2O3 -> α-Al2O is determined by their crystal-chemical characteristics (charge, ionic radius). Therefore, the mechanism of formation of the phase composition should be associated with the stabilization and destabilization of the γ-Al2O phase. The results indicate that Cu2+ cations contribute to destabilization of the γ-Al2O3 phase, while Zn2+ and V5+ cations stabilize the γ-Al2O3 phase (with a Zn and V content of more than 3 wt.%). A model is proposed for explaining the results obtained, which is based on the formation of the γ-Al2O phase in the initial period of time and the appearance of the γ-Al2O3 phase in subsequent periods (as a result of an increase in the power of microdischarges). It is shown that the highest hardness of coatings on aluminum alloys (about 16 GPa) is achieved with a copper content in the range of 3-4 wt.%.

Keywords: 
microarc oxidation, corundum, structural engineering, anode-cathode regime, coating thickness, phase composition, properties.
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