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i l St. Petersburg Polytechnic University Journal. Physics and Mathematics. 2022 Vol. 15, No. 3.1 Научно-технические ведомости СПбГПУ. Физико-математические науки. 15 (3.1) 2022
Conference materials
UDC 544.63:620.197.3
DOI: https://doi.org/10.18721/JPM.153.129
Composite triazole-containing PEO-coatings for effective corrosion protection of AlMg3 aluminum alloy
Ya. I. Kononenko 1 H, A. S. Gnedenkov \ S. L. Sinebryukhov 1
V. S. Filonina 1, I. E. Vyaliy 1, S. V. Gnedenkov 1 1 Institute of Chemistry, Far Eastern Branch of the RAS, Vladivostok, Russia H kononenko.yai@gmail.com
Abstract: The study considers composite coatings formed on the AlMg3 aluminum alloy, consisting of PEO-coatings impregnated with corrosion inhibitors, 1,2,4-triazole and benzotriazole, in various concentrations. The morphology and composition of the resulting coatings were studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The increase in the protective properties of composite coatings was studied by electrochemical impedance spectroscopy (EIS). SEM-images showed that the coatings have a self-assembled microtubular structure with a tube diameter varying from 300 to 500 nm and average tube height of 9 ^m. EIS results showed that samples with composite inhibitor-containing PEO-coatings have better protective properties compared to pure aluminum alloy and base PEO-layer. An increase in the concentration of inhibitors of the triazole group from 0.05 M to 0.1 M during impregnation into a PEO-coating leads to a decrease in the corrosion resistance of the samples with composite coatings.
Keywords: Anti-corrosion composite coating, aluminum alloy, PEO coating, micro-tubular structure, corrosion inhibitor
Funding: Inhibitor-containing bioactive composite coatings on magnesium alloys for implant surgery, no. 20-13-00130; Multifunctional biodegradable coatings of new generation for controlling the resorption of magnesium-based materials: self-healing mechanism, personalized medicine, no. 21-73-10148.
Citation: Kononenko Ya. I., Gnedenkov A. S., Sinebryukhov S. L., Filonina V. S., Vyaliy I. E., Gnedenkov S.V., Composite triazole-containing PEO-coatings for effective corrosion protection of AlMg3 aluminum alloy, St. Petersburg State Polytechnical University Journal. Physics and Mathematics. 15 (3.1) (2022) 173-178. DOI: https://doi.org/10.18721/JPM.153.129
This is an open access article under the CC BY-NC 4.0 license (https://creativecommons. org/licenses/by-nc/4.0/)
Материалы конференции
УДК 544.63:620.197.3
DOI: https://doi.org/10.18721/JPM.153.129
Композиционные триазолсодержащие ПЭО-покрытия для эффективной защиты от коррозии алюминиевого сплава AlMg3
Я. И. Кононенко 1 н, А. С. Гнеденков 1 , С. Л. Синебрюхов 1 , В. С. Филонина 1 , И. Е. Вялый 1 , С. В. Гнеденков 1 1 Институт химии Дальневосточного отделения РАН, г. Владивосток, Россия н kononenko.yai@gmail.com
Аннотация. В данной работе на алюминиевом сплаве AlMg3 сформированы композиционные покрытия, состоящие из ПЭО-покрытий, импрегнированных ингибиторами коррозии, 1,2,4- триазолом и бензотриазолом, в различных концентрациях.
© Kononenko Ya. I., Gnedenkov A. S., Sinebryukhov S. L., Filonina V. S., Vyaliy I. E., Gnedenkov S.V., 2022. Published by Peter the Great St. Petersburg Polytechnic University.
St. Petersburg Polytechnic University Journal. Physics and Mathematics. 2022 Vol. 15, No. 3.1
Морфология и состав полученных покрытий исследовались методами растровой электронной микроскопии (РЭМ) и энергодисперсионной спектроскопии (ЭДС). Увеличение защитных свойств композиционных покрытий фиксировали методом электрохимической импедансной спектроскопии (ЭИС). РЭМ-изображения показали, что покрытия имеют самоорганизованную микротрубчатую структуру с диаметром трубки варьирующимся от 300 до 500 нм, и высотой трубки, в среднем, составляющей 9 мкм. Результаты ЭИС показали, что образцы с композиционными ингибиторсодержащими ПЭО-покрытиями обладают лучшими антикоррозионными свойствами по сравнению с чистым алюминием сплавом и образцом с базовым ПЭО-покрытием. Увеличение концентрации ингибиторов группы триазолов с 0,05 М до 0,1 М при импрегнировании в ПЭО-покрытие приводит к уменьшению коррозионный стойкости алюминиевого сплава с композиционным покрытием.
Ключевые слова: Антикоррозийное композиционное покрытие, алюминиевый сплав, ПЭО-покрытие, микротрубчатая структура, ингибитор коррозии
Финансирование: Ингибиторсодержащие биоактивные композиционные покрытия на магниевых сплавах для имплантационной хирургии, № 20-13-00130; Многофункциональные биодеградируемые покрытия нового поколения для контроля процессов резорбции материалов на основе магния: механизм самозалечивания, персонализированная медицина, № 21-73-10148.
Ссылка при цитировании: Кононенко Я. И., Гнеденков А. С., Синебрюхов С. Л., Филонина В. С., Вялый И. Е., Гнеденков С. В.Композиционные триазолсодержащие пэо-покрытия для эффективной защиты от коррозии алюминиевого сплава Л1М§3 // Научно-технические ведомости СПбГПУ. Физико-математические науки. 2022. Т. 15. № 3.1. С. 173-178. БО1: https://doi.org/10.18721/JPM.153.129
Статья открытого доступа, распространяемая по лицензии СС БУ-МС 4.0 (ИМ^:// creativecommons.Org/1icenses/by-nc/4.0/)
Introduction
Aluminum is a structural material with such important properties as light weight, high strength and ductility, etc. It found application in many industries. However, during operation, aluminum may contact the aggressive environment, which results in corrosion degradation [1, 2].
One of the ways to prevent aluminum corrosion is to produce protective coatings on its surface. Plasma electrolytic oxidation (PEO) is one of the easiest and most optimal methods to protect the surface of valve metals (including aluminum and its alloys) [3—8]. In some cases, the duration of the corrosion protection of PEO-coatings may be insufficient due to high heterogeneity (including porosity) of obtained surface layers. Corrosion inhibitors are widely used for modification of coatings in order to provide autonomous self-healing properties and prolong the provision of protective ability [9—12]. The most studied metallic corrosion inhibitors are phosphates, nitrites, molybdates, tungstates, vanadates, borates, rare earth salts and the organic corrosion inhibitors including different types of triazoles [13]. For example, [14] describes the efficiency of a composite coating applied by a sol-gel method, with benzotriazole. It was established that this corrosion inhibitor, in a protective layer, is capable of starting the process of healing damage of the coating on AA7075 alloy.
This study is focused on forming composite coatings on the AlMg3 alloy introducing inhibitors of the triazole group of various concentrations in the previously formed base PEO-layer with the purpose of improving the protective properties of the material.
Materials and Methods
The experiments were carried out with samples made of the AlMg3 aluminum alloy with the size of 20x30x2 mm. The surface preparation of the samples was realized through wet grinding with SiC paper with a gradual decrease in abrasive grain size from 28—40 to 14—20 ^m, followed
© Кононенко Я. И., Гнеденков А. С., Синебрюхов С. Л., Филонина В. С., Вялый И. Е., Гнеденков С. В., 2022. Издатель: Санкт-Петербургский политехнический университет Петра Великого.
by washing in isopropyl alcohol and drying in a desiccator. PEO was carried out in a tartrate-fluoride electrolyte in a galvanostatic mode for 40 s. The current density was equal to 1.79 A-cm-2 and the duty cycle was equal to 1. To ensure the best filling of coating microtubes with inhibitor, the formed samples were subjected to vacuum impregnation in aqueous solutions of 1,2,4-triazole and benzotriazole at various concentrations (0.05 M and 0.1 M), with the following exposure to inhibitor solutions for 1 h under constant stirring, and then dried in a desiccator at a temperature of 40 °C for 24 h.
The protective properties of the formed coatings were assessed using the electrochemical techniques, including electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP) measurements. Experiments were carried out in a three-electrode cell with a silver chloride (Ag/AgCl) electrode as a reference electrode and platinum mesh as a counter electrode using the VersaSTAT MC potentiostat/galvanostat electrochemical system (Princeton Applied Research, USA). 3 wt.% NaCl solution was used as an electrolyte. The area of the surface in a contact with solution was 1 cm2.
A Sigma 300VP (Carl Zeiss, Germany) scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) was used to analyze the morphology and composition of the surface.
Results and Discussion
As a result of the study the composite inhibitor-containing coatings with high protective properties were obtained on the AlMg3 aluminum alloy. Coatings consisted of a PEO-layer with a microtubular structure (Fig. 1) and inhibitors of the triazole group.
SEM analysis of the sample surface (Fig. 1, a) showed that the PEO-coating has a well-ordered porous structure with a pore diameter ranging from 300 to 500 nm. It can be concluded from analyzing the SEM image of the sample cross-section that the coating has a self-organized microtubular structure (Fig. 1, b). The tube height averages 9 ^m.
a) b)
Fig. 1. SEM images of PEO-coating morphology: SEM-image of PEO-coating surface (a), SEM-image of a cross-section of PEO-coating (b)
Analysis of the results obtained by EDS showed that the main elements of the coating are aluminum (Fig. 2,a) and oxygen (Fig. 2, c). Magnesium is contained in a smaller amount (Fig. 2, b). The presence of Mg in the coating is explained by the composition of the original AlMg3 alloy (that is one of the alloyed elements in this alloy). Such elements as fluorine, carbon, sodium and potassium, which are presented in the composition electrolyte for oxidation of the samples, are absent in the composition of the coating.
Table 1 shows the results of EIS study for an uncoated AlMg3 aluminum alloy (A), the AlMg3 aluminum alloy immersed in 1,2,4-triazole or benzotriazole with a concentration of 0.1 M (B, C), a PEO-coated sample (D), and samples with inhibitor-containing layers (E-H) after the exposure for 1 h in a 3 wt. % NaCl solution. It should be mentioned that Table 1 presents the specific values of the impedance modulus normalized by the area of the sample (i.e., □•cm2).
The obtained results indicate higher protective properties of the AlMg3 1,2,4-tr 0.1 M and AlMg3 b-tr 0.1 M compared to AlMg3 uncoated, which suggests a high efficiency of the inhibitors selected for the AlMg3 alloy (Table 1). As can be seen from the analysis of the impedance modulus measured at the lowest frequency (IZIy=01 Hz, Table 1) after 1 h of exposure, all samples
Fig. 2. Image of element distribution in the cross-section of a sample with a PEO-layer, where (a) is the distribution of aluminum, (b) is magnesium, and (c) is oxygen
with composite inhibitor-containing coatings (E—H) have a higher corrosion resistance compared to the uncoated sample (A) and base PEO-layer (D).
The sample with a PEO-layer impregnated with 1,2,4-triazole at a concentration of 0.05 M (E) is characterized by the best protective properties. The value of IZI/=01 Hz for this composite coating is more than one order of magnitude higher than one for the sample with base PEO-layer (Table 1). An increase in the concentration of inhibitors to 0.1 M leads to a decrease in the IZI and, as a consequence, a decrease in corrosion resistance, due to the PEO-layer
degradation, which is consistent with the data presented in [14]. This result can be related with probable reaction of inhibitor with components of PEO-coating matrix with following formation of the compounds, which have higher solubility as compared to PEO-layer [15]. However all inhibitor-conatining coatings have higher protective properties as compared to base PEO-layer. Therefore, lower values of the IZI1 Hz for PEO 1,2,4-tr 0.1 M and PEO b-tr 0.1 M as compared to PEO 1,2,4-tr 0.05 M and PEO b-tr 0.05 M can be related with probable lower density of the formed inhibitor layer.
1,2,4-triazole and benzotriazole are used to retard the corrosion rate of Cu, Fe, Zn, Mg and Al materials. The mechanism of the corrosion protection is based on the adsorption on the surface of treated metal or alloy [16—19]. It should be noted that PEO-coating is suitable as a matrix for inhibitor storage due to its complex morphology. As a result of coating degradation during immersion of the sample in an aggressive environment, the inhibitor can be released from the pores of the PEO-layer to the damaged part of the surface and form an additional barrier layer, which will delay the corrosion rate of the material.
Table 1
Coating specification and electrochemical parameters of samples
according to the results of E [S test
Sample Coating type IZf=0.1 Hz' Q-Cm2
A AlMg3 uncoated 2.56-104
B AlMg3 1,2,4-tr 0.1 M 7.23-106
C AlMg3 b-tr 0.1 M 6.40-106
D PEO-coating 4.65-106
E PEO 1,2,4-tr 0.05 M 6.61-107
F PEO 1,2,4-tr 0.1 M 6.1M06
G PEO b-tr 0.05 M 1.63-107
H PEO b-tr 0.1 M 7.72-106
Conclusion
During the study, heterooxide layers with a microtubular structure were obtained on the AlMg3 aluminum alloy. Impregnation of the PEO-coating with corrosion inhibitors contributed to a significant increase in the corrosion resistance of the studied material. The sample impregnated with 1,2,4-triazole at a concentration of 0.05 M is characterized by the best protective properties.
Acknowledgments
The sample preparation, protective coating formation, and electrochemical measurements were supported by a Russian Science Foundation grant no. 21-73-10148 (https://rscf.ru/en/ project/21-73-10148/). The study of coating composition was supported by a Russian Science Foundation grant no. 20-13-00130 (https://rscf.ru/en/project/20-13-00130/).
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THE AUTHORS
KONONENKO Yana I.
kononenko.yai@gmail.com ORCID: 0000-0002-2299-9009
FILONINA Valeria S.
filonina.vs@gmail.com ORCID: 0000-0002-9544-3597
GNEDENKOV Andrey S.
asg17@mail.com
ORCID: 0000-0002-9822-7849
VYALIY Igor E.
vyaly@ich.dvo.ru
ORCID: 0000-0003-3806-1709
SINEBRYUKHOV Sergey L.
sls@ich.dvo.ru
ORCID: 0000-0002-0963-0557
GNEDENKOV Sergey V.
svg21@hotmail.com ORCID: 0000-0003-1576-8680
Received 22.05.2022. Approved after reviewing 19.07.2022. Accepted 20.07.2022.
© Peter the Great St. Petersburg Polytechnic University, 2022
