Effect of boric acid addition to an alkaline–silicate electrolyte on the structure and properties of plasma electrolytic decorative two-color coatings formed on AD31 aluminum alloy

• A.G. Rakoch¹, E.P. Monakhova², P.N. Grishin¹, O.O. Voropaeva¹ and X. Lu³

¹ Department of Metallurgy of Steel, New Production Technologies & Protection of Metals, College of Environmentally Sound Technologies & Engineering, National University of Science and Technology MISIS, Leninsky prospect, 4, 119049 Moscow, Russia
² Certification Center LLC, Amurskaya st., 9/6, 10749, Moscow, Russia
³ School of Materials Science and Engineering, Northeastern University, 3-11 Wenhua Road, 110819 Shenyang, China

Abstract: A two-stage technological process for the preparation of two-color decorative plasma electrolytic coatings on the AD31 aluminum alloy has been developed. At the first stage, plasma electrolytic treatment of the aluminum alloy should be carried out in a silicate electrolyte with addition of boric acid. At this stage, a coating with low through porosity is formed due to isomorphic substitution of silicon by boron in its oxide and, as a result, a decrease in its melting temperature. Evidence for the latter effect after the formation of the plasma electrolytic coating in a silicate–borate electrolyte includes: the formation of denser coating layers with a fused surface morphology; higher values of anodic and cathodic voltage amplitudes in plasma electrolytic treatment; the appearance of a small amount of crystalline phases in the coating based on amorphous silicon oxide; a decrease in the number of anodic plasma microdischarges per unit area of the treated aluminum alloy surface accompanied by an increase in the power released in these discharges; a decrease in anodic current density upon polarization of AD31 alloy samples with a plasma electrolytic coating. At the second stage, incorporation of a coloring component into the silicate–borate electrolyte ensures the formation of decorative two-color coatings upon plasma electrolytic treatment of the aluminum alloy.

Keywords: plasma electrolytic treatment, AD31 aluminum alloy, borate–silicate electrolyte, decorative coatings, cohesive strength

Int. J. Corros. Scale Inhib., 2026, 15, no. 2, 171-188
doi: 10.17675/2305-6894-2026-15-2-11

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