The Effect of Sealing with Potassium Permanganate on Corrosion Resistance of Anodized AD31 Aluminum Alloy
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SUBSTANCES, MATERIALS, AND COATINGS
The Effect of Sealing with Potassium Permanganate on Corrosion Resistance of Anodized AD31 Aluminum Alloy M. A. Osipenkoa, *, D. S. Kharitonova, b, **, I. V. Makarovac, A. Wrzesińskad, and I. I. Kuriloa aBelarusian
bJerzy
State Technological University, Minsk, 220006 Belarus Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Krakow, 30-239 Poland c Lappeenranta University of Technology, Lappeenranta, FI-53850 Finland dLodz University of Technology, Lodz, 90-924 Poland *e-mail: [email protected] **e-mail: [email protected] Received November 15, 2019; revised April 14, 2020; accepted April 21, 2020
Abstract—The effect of the preparation conditions and parameters of finishing treatment of permanganateion-modified anodic oxide coatings based on AD31 aluminum alloy (AA6063) on their physicomechanical and protective properties has been determined using potentiodynamic polarization, electrochemical impedance spectroscopy, scanning electron microscopy, and Raman scattering, as well as salt-spray chamber tests. It has been shown that sealing in potassium permanganate solution over 5 min provides a more than 200-fold increase in the corrosion resistance of the anodic oxide layer. DOI: 10.1134/S2070205120050214
INTRODUCTION Aluminum and its alloys are widely employed in the building, automotive, and aircraft industries due to their unique chemical and mechanical characteristics. Aluminum is alloyed with Si and Mg in order to provide increased mechanical strength with the retention of ductility. However, the Al–Mg–Si alloys possess lower corrosion resistance as compared to pure aluminum and are susceptible to local types of corrosion and stress corrosion cracking due to the presence of intermetallic particles [1–4]. Anodizing and subsequent chemical sealing of the anodic oxide coatings with various modifying solutions is an effective approach to increasing the corrosion strength of silicon- and magnesium-containing aluminum alloys [5, 6]. Currently, oxidation in 15–20% sulfuric acid solution is widely employed in industry. A bilayer film consisting of the internal thin nonporous barrier layer and a thick (up to 3 μm) hexagonal honeycomb porous layer, which is formed perpendicular to the metal surface, is formed on the surface upon oxidation. The presence of intermetallic particles in the alloy results in defect and crack initiation upon anodizing. This necessitates subsequent treatment of anodic oxide coatings (AOCs), such as sealing in various solutions, which results in pore clogging, as well as delay of penetration of aggressive ions to substrate [7–11]. AOCs are conventionally sealed in hot distilled water or chromium(VI) solutions; however, it is promising to use the electrolytes containing less hazardous
corrosion inhibitors based on cerium(III) and zirconium(IV), which significantly increase the corrosion resistance of aluminum alloys [8, 12]. It should be noted that sealing in hot water is energy-consuming, employment of chromium(VI)-based
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