The Electrochemical Corrosion Behavior of Plasma Electrolytic Oxidation Coatings Fabricated on Aluminum in Silicate Elec
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The Electrochemical Corrosion Behavior of Plasma Electrolytic Oxidation Coatings Fabricated on Aluminum in Silicate Electrolyte Zhong Yang, Rui-qiang Wang, Chen Liu, Ye-kang Wu, Dong-dong Wang, Xin-tong Liu, Xu-zhen Zhang, Guo-rui Wu, and De-jiu Shen (Submitted May 23, 2018; in revised form March 19, 2019; published online May 15, 2019) Plasma electrolytic oxidation (PEO) coatings were fabricated on the aluminum in silicate electrolyte. Microstructures and elemental compositions of these PEO coatings were examined by scanning electron microscopy (SEM) equipped with an energy-dispersive x-ray spectroscopy (EDS). Corrosion resistances of the coated samples were evaluated using the measurements of open-circuit potential (OCP), repetitive polarization and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl solution. The results indicated that the PEO coatings not only act as a physical shield limiting the penetration of corrosive solution, but also establish an anodic location with high concentration of H+ ions and other product ions as pitting corrosion begins. With the development of pitting corrosion, the accumulation of corrosion products inside the pits and pores of the coatings decreases the corrosion process effectively. Keywords
aluminum, coatings, EIS, inorganic, interface, pitting corrosion, plasma electrolytic oxidation
1. Introduction A various coating technologies have been developed to improve the corrosion and wear resistance of pure aluminum and its alloys. Among them, plasma electrolytic oxidation (PEO) has recently attracted enormous attention as a relatively new surface modification technique, in which a thick ceramiclike oxide coating could be developed in situ on valve metals (magnesium, aluminum, titanium, etc.). And as a conversion coating involving a mass of electrolyte elements, the PEO coating provides a considerable corrosion resistance (Ref 1-4). On the other hand, the thickness and the hardness of PEO coatings are much greater than those of conventional anodic films, and the PEO coatings also show a good adhesion to the substrates due to the complex hybrid reactions, involving an intricate combination of electrochemical, thermochemical, plasma-chemical and metallurgical reactions, and these interactions mainly occur on the interfaces, resulting in the PEO coatings on the metal surface composed of both the elements from the electrolyte and the substrate material (Ref 5-8). However, due to the existence of plasma discharge, gas liberation and energy generation, there are usually numerous
Zhong Yang, Rui-qiang Wang, Chen Liu, Ye-kang Wu, Dongdong Wang, Xin-tong Liu, Xu-zhen Zhang, and De-jiu Shen, State Key Laboratory of Metastable Materials Science and Technology, College of Materials Science and Engineering, Yanshan University, Qinhuangdao 066004, P. R. China; Guo-rui Wu, State Key Laboratory of Metastable Materials Science and Technology, College of Materials Science and Engineering, Yanshan University, Qinhuangdao 066004, P. R. China; and CITIC
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