Corrosion Resistance of Bis-Silane-Modified Epoxy Coatings on an Al-Zn-Mg-Cu Alloy

Abstract

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 (C c), higher charge transfer resistance (R dl) and lower double-layer capacitance (C dl) during long immersion times, indicating a higher resistance to water permeation and stronger protection against substrate corrosion. The lowest C c and C dl values were obtained by mixing epoxy and the bis-silane prepolymer at a ratio of 1:1.

Effect of Water Uptake, Adhesion and Anti-Corrosion Performance for Silicone-Epoxy Coatings Treated with GLYMO on 2024 Al-Alloy

“…The introduced Model D (i.e., Figure 6 d) contains the diffusion impedance, which includes the diffusion capacitance ( ) and the diffusion resistance ( ). This diffusion behaviour is not the ideal Warburg impedance, resulting in dispersion coefficient n deviating from 0.5 [ 26 , 27 , 28 , 29 , 30 ].…”

“…The corrosion results in NaCl solution also show that the pore resistance of silicone-epoxy coating increased with the increase of GLYMO content because the hydrolysis and condensation of GLYMO in the matrix reduced the through-hole ratio, with the appropriate value (~1.5%) of Coating C. The impedance modulus (unit: ) of Coating C at the early and late immersion stages are respectively and . Compared with other similar silane-modified epoxy coatings [ 28 , 29 ], Coating C also has better protective performance.…”

“…Considering the system’s non-ideal capacitance characteristics, a constant phase element (CPE) is used to replace all capacitors in EECs to obtain a more accurate fitting result. The impedance of CPE is defined as follows [ 10 , 25 , 26 , 27 , 28 , 29 ]: where is the CPE-constant with the units of , the imaginary number, n the CPE-power ( ), and is the angular frequency ( , is the frequency). The CPE is a pure capacitance for n = 1, in which the derivation of n from the unit is due to the dispersion effect.…”

“…Electrochemical impedance spectroscopy (EIS) is a well-known electrochemical technique used to evaluate the performance of organic coatings. It has proven to be a powerful tool for obtaining specific parameters of coating/metal systems [ 14 , 15 , 25 , 26 , 27 , 28 , 29 , 30 ]. The coating resistance, capacitance and other parameters obtained from the equivalent circuit (EECs) can quantitatively reflect the corrosion resistance of the coating.…”

One‐step preparation of the superhydrophobic Al alloy surface with enhanced corrosion and wear resistance

“…[1,2] However, the oxide film on Al alloy surface is easily damaged by the perforation and exfoliation of chloride ions in seawater, which aggravates alloy corrosion. [3,4] It also has a great impact on its service life and engineering application.…”