Possibilities of phase-structural engineering and properties of microarc oxide coatings on the AMг3 alloy


  • V. V. Subbotina
  • O. V. Sobol
  • V. V. Bilozerov




microarc oxidation, electrolyte composition, coating, growth kinetics, phase composition, polymorphic transformation, hardness


Purposeof the work: to establish the regularities of the alkali-silicate electrolyte composition influence and the conditions of electrolysis during microarc oxidation of the AMг3 aluminum alloy on the kinetics of the oxide coating formation, its structure and the conditions for the formation of the α-Al2O3 phase. Results. The possibility of forming high-density MAO coatings on the AMг3 aluminium alloy during electrolysis in alkali-silicate electrolytes has been  determined. The regularities of the kinetics of MAO coatings growth at different electrolyte composition and oxidation time were revealed. It was found that the phase composition of MAO coatings consists of the following phases − α-Al2O3, γ-Al2O3, and mullite (3Al2O3•2SiO2), the ratio of which changes with a change in the amount of sodium silicate (Na2SiO3). It was found that addition of an inorganic soluble salt dopant to the electrolyte, which contains oxygen (K2Cr2O7), leads to a qualitative change in the phase composition − an increase in the amount of
α-Al2O3 phase in the coating composition and an increase in hardness. In this case, it becomes possible to obtain MAO coatings of small thickness (up to 90 μm) with a high content of the α-Al2O3 phase (up to 40 %), which cannot be carried out in an alkali-silicate electrolyte. Analysis of the effect of high-temperature annealing of MAO coatings on the shape of the diffraction spectrum made it possible to revealthe appearance of tetragonality in the crystal lattice of the
γ-А12О3 phase. The structural state with a tetragonally distorted lattice is a stage of γ-А12О3 → α-А12О3 transformation. Scientific novelty. It was found that when using an alkaline-silicate electrolyte for electrolysis, the addition of liquid glass (Na2SiO3) leads to an increase in the growth rate of the coating, but at the same time it stimulates the formation of mullite (3Al2O3 × 2SiO2) as a phase component. An increase in the alkaline (KOH) component leads to a decrease in the growth rate (to 0,6…0,7 μm/min) and stimulates the formation of the γ-Al2O3 phase. The formation of the α-Al2O3 (corundum) phase is stimulated with a long process duration, when the thickness of the dielectric layer and the breakdown power increase. An increase in the amount of α-Al2O3 leads to an increase in the hardness of the coatings. Isothermal annealing at temperatures exceeding 1 000 °C stimulates the γ-Al2O3 → α-Al2O3 polymorphic transformation. The initial stage of such a transformation is the appearance of tetragonality in the crystal lattice of the γ-Al2O3 phase. Practical value. This study allows us to propose an additive to the alkali-silicate electrolyte in the form of a K2Cr2O7 salt, which increases the rate of formation of MAO coatings to 1,4 μm/min and, at the same time, qualitatively and quantitatively changes the phase composition of the coatings, increasing its hardness.


Cui S. H., Han J.M., Du Y.P. and Li W. Corrosion resistance and wear resistance of plasma electrolytic oxidation coatings on metal matrix composites. Surface and Coatings Technology. 2007, vol. 201, iss. 9–11, pp. 5306–5309. URL : https://pdfslide.net/documents/corrosion-resistance-and-wear-resistance-of-plasma-electrolytic-oxidation-coatings.html

Chen J., Wang Z. and Lu S. Effects of electric parameters on microstructure and properties of MAO coating fabricated on ZK60 Mg alloy in dual electrolyte. Rare Metals. 2012, vol. 31, pp. 172–177.

Clyne T.W. and Troughton S.C. A review of recent work on discharge characteristics during plasma electrolytic oxidation of various metals. International materials reviews. 2019, vol. 64, iss. 3, pp. 127–162. URL : https://www.tandfonline.com/doi/full/10.1080/09506608.2018.1466492

Lu X., Blawert C., Kainer K.U. and Zheludkevich M.L. Investigation of the formation mechanisms of plasma electrolytic oxidation coatings on Mg alloy AM50 using particles. Electrochimica Acta. 2016, vol. 196, pp. 680–691.

Martin J., Leone P., Nomine A., Veys-Renaux D., Henriona G. and Belmonte T. Influence of electrolyte ageing on the plasma electrolytic oxidation of aluminium. Surface and Coatings Technology. 2015, vol. 269, pp. 36–46.

Matykina E., Arrabal R., Pardo A., Mohedano M., Mingo B., Rodríguez I. and González J. Energy-efficient PEO process of aluminium alloys. Materials letters. 2014, vol. 127, pp. 13–16.

Tseng C. C., Lee J. L., KuoT. H., Kuo S. -N. and Tseng K. -H. The influence of sodium tungstate concentration and anodizing conditions on microarc oxidation (MAO) coatings for aluminum alloy. Surface and Coatings Technology. 2012, vol. 206, iss. 16, pp. 3437–3443.

Belozerov V., Sobol O., Mahatilova A., Subbotina V., Tabaza T.A., Al-Qawabeha U.F. and Al-Qawabah S.M. Effect of electrolysis regimes on the structure and properties of coatings on aluminum alloys formed by anode-cathode micro arc oxidation. Eastern-european journal of enterprise technologies. 2018, vol. 1, iss. 12 (91), pp. 43–47.

URL : http://journals.uran.ua/eejet/article/view/121744/119351

Subbotina V.V., Al-Qawabeha U.F., Sobol' O.V., Belozerov V.V., Schneider V.V., Tabaza T.A. and

Al-Qawabah S.M.Increase of the α-Al2О3 phase content in MAO-coating by optimizing the composition of oxidated aluminum alloy. Functional materials. 2019, vоl. 26, iss. 4, pp. 752–758. URL : http://functmaterials.org.ua/ contents/26-4/fm264-752.pdf

Asadi S. and Kazeminezhad M. Multi directional forging of 2024 al alloy after different heat treatments: microstructural and mechanical behavior. Transactions of the indian institute of metals. 2017, vol. 70 (7), pp. 1707–1719.

Wen L., Wang Y., Jin Y., Liu B., Zhou Y. and Sun D. Microarc oxidation of 2024 Al alloy using spraying polar and its influence on microstructure and corrosion behavior. Surface and Coatings Technology. 2013, vol. 228,

pp. 92–99.

Xue W., Chao W., Hua T. and Yongchun L. Corrosion behaviors and galvanic studies of microarc oxidation films on Al-Zn-Mg-Cu alloy. Surface and Coatings Technology. 2007, vol. 201, iss. 21, pp. 8695–8701.

Melhem A., Henrion G., Czerwiec T., Briançon J.L., Duchanoy T., Brochard F. and Belmonte T. Changes induced by process parameters in oxide layers grown by the PEO process on Al alloys. Surface and Coatings Technology. 2011, vol. 205, supplement 2, pp. S133–S1S6.

Javidi M. and Fadaee H. Plasma electrolytic oxidation of 2024-T3 aluminum alloy and investigation on microstructure and wear behavior. Applied surface science. 2013, vol. 286, pp. 212–219.

Lv P.X., Chi G. X., Wei D.B. and Di S.C. Design of scanning micro-arc oxidation forming ceramic coatings on 2024 aluminium alloy. Advanced materials research. 2011, vol. 189–193, pp. 1296–1300.

Sobol' O.V. and Shovkoplyas O.A. On advantages of X-ray schemes with orthogonal diffraction vectors for studying the structural state of ion-plasma coatings. Technical physics letters. 2013, vol. 39 (6), p. 536–539.

URL : https://link.springer.com/content/pdf/10.1134/S1063785013060126.pdf

Klopotov A.A., Abzaev Yu.A., Potekaev A.I. and Volokitin O.G. Osnovy rentgenostrukturnogo analiza v materialovedenii [Fundamentals of X-ray structural analysis in materials science]. Tomsk : TGASU, 2012, 275 p. URL : https://www.twirpx.com/file/1251095/ (in Russian).

Reshetnyak M.V., Sobol O.V. Rasshirenie vozmozhnostey analiza strukturyi i substrukturnyih harakteristik nanokristallicheskih kondensirovannyih i massivnyih materialov kvazibinarnoy sistemyi W2B5 − TiB2 pri ispolzovanii programmyi obrabotki rentgendifraktsionnyih dannyih “new_profile” [Expanding the possibilities of analyzing the structure and substructural characteristics of nanocrystalline condensed and bulk materials of a quasi-binary system

W2B5 − TiB2 when using the X-ray diffraction data processing program "new_profile"]. FIzichna inzheneriya poverhni [Physical Surface Engineering]. 2008, vol. 6, no. 3–4, pp. 180–188. URL : http://dspace.nbuv.gov.ua/ bitstream/handle/123456789/7885/09-Reshetnyak.pdf?sequence=1 (in Ukrainian).

Curran J. A. and Clyne T.W. Thermo-physical properties of plasma electrolytic oxide coatings on aluminium. Surface and Coatings Technology. 2005, vol. 199, pp. 168–176. URL : https://citeseerx.ist.psu.edu/viewdoc/download?doi=

Trueba M. and Trasatti S.P. γ-Alumina as a support for catalysts : a review of fundamental aspects. European journal of inorganic chemistry. 2005, iss. 17, pp. 3393–3403. URL : https://www.researchgate.net/profile/Pradip_ Pachfule/post/Is_alumina_as_a_support_in_heterogenous_acid_catalysis/attachment/59d61dd779197b807797aa74/AS%3A273664275091456%401442258055060/download/Alumina+as+a+Support+for+Catalysts+A+Review+of+Fundamental+Aspects.pdf

Prins R. Location of the spinel vacancies in γ-Al2O3. Angewandte chemie. 2019, vol. 131, iss. 43, pp. 15694–15698.

Paglia G., Buckley C.E., Rohl A.L., Hart, R.D., Winter K., Studer A. J., Hunter B.A. and Hanna J.V. Boehmite derived γ-alumina system. P. 1. Structural evolution with temperature, with the identification and structural determination of a new transition phase, γ′-alumina. Chemistry of materials. 2004, vol. 16, iss. 2, pp. 220–236.

Zhou R.S. and Snyder R. Structures and transformation mechanisms of the η, γ and θ transition aluminas. Acta crystallographica section B. 1991, vol. 47, iss. 5, pp. 617–630.

Odynets L.L. and Orlov V.M. Anodnыe oksydnыe plenky [Anodic oxide films]. Leningrad : Nauka Publ., 1990, 200 р. (in Russian).

Grosed M. Study of the source of oxygen in the anodic oxidation. Journal of the electrochemical society. 1971, vol. 118, no. 5, pp. 717–727.