Corrosion Science and Technology

The Corrosion Science Society of Korea (한국부식방식학회)
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Development of Hybrid Sol-Gel Coating to Prevent Corrosion of Magnesium Alloys

마그네슘 합금의 방청을 위한 하이브리드 졸-겔 코팅제의 개발

  • Lee, Dong Uk (Department of Industrial Chemistry, Pukyong National University) ;
  • Kim, Young Hoon (Department of Industrial Chemistry, Pukyong National University) ;
  • Moon, Myung Jun (Department of Industrial Chemistry, Pukyong National University)
  • Received : 2018.01.13
  • Accepted : 2018.02.14
  • Published : 2018.02.28
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Abstract

The high rate of corrosion of magnesium alloys makes it limited for industrial applications. Therefore, surface treatment is required to enhance their corrosion resistance. In our study, a chemical conversion coating for protecting the corrosion of the magnesium alloy, AZ31B, was prepared by using a phosphate-permanganate solution. The chemical conversion coating had a limited protection ability due to defects arising from cracks and pores in the coating layer. The sol-gel coating was prepared by using trimethoxymethylsilane (MTMS) and 3-glycidoxypropyltrimethoxysilane (GPTMS) as precursors, and aluminum acetyl acetonate as a ring opening agent. The corrosion protection properties of sol-gel and conversion coatings in 0.35wt% NaCl solution were measured by the electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization test. The EIS results indicated that the resistance of the chemical conversion coating with the sol-gel coating was significantly improved through the sol-gel sealed phosphate-permanganate conversion coating. The results of the potentiodynamic polarization test revealed that the sol-gel coating decreased the corrosion current density ($I_{corr}$). The SEM image showed that the sol-gel coating sealed conversion coating and improved corrosion protection.

Keywords

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Fig. 1 Diagram of procedure for preparation of conversioncoating and sol-gel coating specimens.

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Fig. 2 Thickness of multi-layer measured by optical microscopy(magnification x600).

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Fig. 3 Synthesis of aluminum acetyl acetonate and sol-gelcoating.

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Fig. 4 FT-IR spectra of sol-gel coating.(a-coating solution, b-cured film).

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Fig. 5 Electrical equivalent circuit of specimens. (a-chemicalconversion coating (MC specimen), b-sol-gel coated on chemicalconversion coating layer(MCS specimen)).

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Fig. 6 EIS spectra, during immersion in NaCl soluiton, of chemical conversion coating on AZ31B (a-bode plot, b-nyquist plot).

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Fig. 7 EIS spectra, during immersion in NaCl soluiton, of chemical conversion coating after sealed with sol-gel coating on AZ31B(a-bode plot, b-nyquist plot).

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Fig. 8 potentiodynamic polarization curve with specimenimmersed in NaCl solution.

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Fig. 9 SEM image of surface morphologies of chemical conversion coating and sol-gel coating (magnification of 3000x).

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Fig. 10 Sol-gel coating sealed with chemical conversion coatinggmeasured by SEM(magnification x3000).

Table 1 Composition of AZ31B magnesium alloy measured by EDS

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Table 2 Calculated values of the electrical equivalent circuit components of conversion coating　＆ sol-gel coating double layer

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Table 3 Potentiodynamic polarization parameters with various specimen

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