405 ISSN 0020-1685, Inorganic Materials, 2016, Vol. 52, No. 4, pp. 405–411. © Pleiades Publishing, Ltd., 2016. Original Russian Text © V.S. Egorkin, I.E. Vyaliy, S.L. Sinebryukhov, S.V. Gnedenkov, V.M. Bouznik, 2016, published in Neorganicheskie Materialy, 2016, Vol. 52, No. 4, pp. 450–456. Effect of Polarizing Signal Duty Cycle on the Composition, Morphology, and Protective Properties of PEO Coatings on AMg3 Aluminum Alloy V. S. Egorkin, I. E. Vyaliy, S. L. Sinebryukhov, S. V. Gnedenkov, and V. M. Bouznik Institute of Chemistry, Far East Branch, Russian Academy of Sciences, pr. Stoletiya Vladivostoka 159, Vladivostok, 690022 Russia e-mail: egorkin@ich.dvo.ru Received September 8, 2015 Abstract—This paper presents a study aimed at assessing the effect of polarizing signal duty cycle D in the plasma electrolytic oxidation (PEO) process on the composition, morphology, and protective properties of coatings produced on AMg3 aluminum alloy in a tartrate-containing electrolyte. It is shown that increasing the duty cycle of a short-pulse (τ = 5 μs) polarizing signal leads to a decrease in the porosity of the growing PEO layers. This, in turn, improves the protective properties and surface strength of the alloy. The pulse duty cycle influences the chemical composition and thickness of the growing oxide coatings. Keywords: plasma electrolytic oxidation, protective coatings, chemical composition, aluminum, duty cycle, microhardness DOI: 10.1134/S002016851604004X INTRODUCTION Plasma electrolytic oxidation (PEO) is one of the most effective surface processing methods, which allows one to produce multifunctional coatings for protecting metals and alloys from the attack of aggres- sive media. Such coatings are successfully employed for processing aluminum [1], titanium [2–4], magne- sium [5], and even steel [6, 7]. PEO layers result from the action of plasma microdischarges on the surface of materials and typically consist of oxidized species of the constituent elements of the metal/alloy and the components of the electrolyte [8, 9]. PEO layers are also used as a basic layer of composite coatings on a variety of metals [10–23]. Analysis of data in the literature [9, 24–28] and experimental data obtained in our previous studies [8, 29] demonstrate that polarizing signal parameters have a significant effect on the coating quality. As pointed out by Gnedenkov et al. [8] and Hussein et al. [27], the polarizing signal duty cycle (D) used in pro- ducing oxide coatings has an advantageous effect on their morphology and chemical composition and the distribution of chemical elements over the surface being processed. As shown earlier [8, 29], a rectangular shape of polarizing pulses during the oxidation of commercially pure titanium ensures a decrease in the overall energy consumption in the plasma electrolytic oxidation pro- cess by up to a factor of 2 relative to nonrectangular pulses. Coatings thus grown possessed a higher corro- sion resistance in comparison with coatings produced using nonrectangular pulses owing to the higher den- sity of the oxide layers. In this paper, we present results of a study aimed at assessing the effect of polarizing signal duty cycle on the energy consumption in a PEO process with the use of microsecond rectangular current pulses on AMg3 aluminum alloy and on the composition, morphology, and protective properties of the PEO coatings thus produced. EXPERIMENTAL AMg3 aluminum alloy samples were 20 × 20 × 1.5 mm in dimensions. Their surface was ground with abrasive papers of different grit sizes in four steps (320–400, 600, 800, and 1000). The electrolyte used contained the following com- ponents: 0.6 g/L of NaF, 5 g/L of C 4 H 4 O 6 K 2 · 0.5H 2 O, 10 g/L of Na 2 MoO 4 · 2H 2 O, 10 g/L of Na 2 B 4 O 7 · 10H 2 O, and 10 g/L of Na 3 PO 4 · 12H 2 O. As a solvent, we used deionized water. The temperature of the elec- trolyte was maintained in the range 8–10°C and its pH value did not exceed 10. Plasma electrolytic oxidation was performed using a transistor current source [8, 29], which generated 5-μs