Corrosion Resistance of Bis-Silane-Modified Epoxy Coatings on an Al-Zn-Mg-Cu Alloy
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JMEPEG https://doi.org/10.1007/s11665-020-05049-5
Corrosion Resistance of Bis-Silane-Modified Epoxy Coatings on an Al-Zn-Mg-Cu Alloy Diping Zeng, Zhiyi Liu, Song Bai, Juangang Zhao, and Jian Wang (Submitted October 25, 2019; in revised form May 12, 2020) A bis-silane prepolymer-modified epoxy coating was applied to an Al-Zn-Mg-Cu alloy to improve corrosion protection. The bis-silane prepolymer was synthesized from tetraethoxysilane and c-glycidoxypropyl trimethoxysilane. To study the mechanism of protection failure by the silane–epoxy hybrid coating and to determine an appropriate coating for protection, various coatings with different silane prepolymer contents were developed. The corrosion behavior of the coatings was studied by electrochemical impedance spectroscopy in a 3.5 wt.% NaCl solution. In comparison with silane monomer-modified epoxy coatings, the bissilane-modified epoxy coating had lower coating capacitance (Cc), higher charge transfer resistance (Rdl) and lower double-layer capacitance (Cdl) during long immersion times, indicating a higher resistance to water permeation and stronger protection against substrate corrosion. The lowest Cc and Cdl values were obtained by mixing epoxy and the bis-silane prepolymer at a ratio of 1:1. Keywords
bis-silane prepolymer, corrosion behavior, EIS, water permeation
1. Introduction Al-Zn-Mg-Cu alloys are widely used in many engineering applications due to their excellent performance. However, under corrosive conditions such as in humid, acidic and alkaline environments, aluminum alloys are prone to corrosion. To protect or mitigate corrosion processes, protective coatings are typically applied to metal surfaces (Ref 1-3). In recent years, silane–epoxy hybrid coatings have attracted the attention of many researchers because of their excellent chemical properties, corrosion resistance and good substrate adhesion (Ref 4-6). Matejka et al. obtained an epoxy-silica composite coating by introducing tetraethoxysilane (TEOS) into an epoxy adhesive and found that the polyester–epoxide– TEOS system was composed of an organic network of polyester and epoxide with silicon compounds (Ref 7). Bakhshandeh et al. (Ref 8) developed organic–inorganic hybrid coatings based on bisphenol-A (DGEBA) epoxy resin and TEOS, showing that TEOS can modify the epoxy resin and effectively improve the protective properties of the metal substrate. Wei-Gang Ji et al. (Ref 9) investigated epoxy coatings successfully modified with a variety of silane monomers (such as c-aminopropyltrimethoxy silane, c-APS and 3-glycidoxypropyltrimethoxysilane, GPTMS) that could dramatically enhance the corrosion resistance of epoxy coatings
Diping Zeng, School of Materials Science and Engineering, Central South University, Changsha 410083, China; and Department of Mechanical and Energy Engineering, Shaoyang University, Shaoyang 422000, China; and Zhiyi Liu, Song Bai, Juangang Zhao, and Jian Wang, School of Materials Science and Engineering, Central South University, Changsha 410083, China. Contact e-mails: liuzhiyi@cs
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