Surface modification of the AK12MMGH aluminum alloy by micro-oxidation technique to improve operating characteristics

DOI: 10.34759/vst-2020-1-217-223

Аuthors

Sergeev S. V.^*, Al-Bdieri M. S.^**, Dubrovina N. A.^***

Belgorod State national research University, 85, Pobedy str, Belgorod, 308015, Russia

*e-mail: sergeyev72@gmail.com
**e-mail: engmahmood86@gmail.com
***e-mail: natysia2601@mail.ru

Abstract

Coatings formed by micro-arc oxidation on aluminum alloys have a unique combination of properties such as high heat resistance, wear resistance, adhesive strength and corrosion resistance. This combination of properties is largely stipulated by the nanocrystalline structure, which, according to a number of studies, is represented in the MAO-layers by small-scale pores and crystallites with sizes not more than 100 nm.

For modifications employing MAO the AK12MMGH aluminum alloy was selected. Oxidation was performed in an alkaline electrolyte with addition of liquid glass. Capacitors capacity of MAO installation, was-78 pF, except for the mode of the sample No 3, when MAO was being performed at 100 pF. This was done to significantly reduce the processing time and increase the coating thickness. The processing time т was determined by the process intensity decrease (arc discharge occurrence on the ribs).

Samples No. 1 and No. 2 have the thinnest coating. This is associated with the lower concentration of liquid glass. The thickest coating was formed on the sample No. 4, due to the increase in the electrolyte concentration. Despite this, being compared with the sample No. 5, it has a more porous technological layer. The same as samples No. 4 and No. 5, sample No. 3 has a thick coating. In this case, it is stipulated by the fact that capacitor capacitance increase of the MAO installation led to the increase of micro-arc discharges, and, as a consequence, the volume of reaction products, formed per unit time, increases.

The surface modification of the AK12MMGH aluminum alloy by micro-arc oxidation method allowed that formed coatings had a layered structure intrinsic to MAO-coatings of aluminum alloys. The installation capacitor capacitance increasing steps up the MAO process intensity, which leads, in its turn, to the number of electrochemical reaction products build-up, and, as a consequence, to the thicker coatings forming.

The cross-section study revealed that porosity is characteristic only for the outer technological layer. The MAO installation capacitors capacitance increasing helps the porosity reduction. Hardness measurement revealed heterogeneity of mechanical properties of MAO coatings in thickness depending on the phase composition and the presence of defects.

Keywords:

micro-arc oxidation, AK12MMGH aluminum alloy, coating thickness, capacitor capacitance

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