Journal of the Korean institute of surface engineering (한국표면공학회지)

The Korean Institute of Surface Engineering (한국표면공학회)
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Effects of Na3PO4 Concentration on the Porosity of Plasma Electrolytic Oxidation Coatings Surface on the 6061 Al Alloy, and Subsequent-NaAlO2 Sealing

6061 알루미늄 합금의 플라즈마 전해산화 피막의 표면기공율 및 부식특성에 미치는 Na3PO4 농도 및 NaAlO2 봉공처리의 영향

  • Song, Euiseok (Department of Chemistry and Chemical Engineering, Inha University) ;
  • Kim, Yong-Tae (Department of Chemistry and Chemical Engineering, Inha University) ;
  • Choi, Jinsub (Department of Chemistry and Chemical Engineering, Inha University)
  • Received : 2019.04.15
  • Accepted : 2019.05.20
  • Published : 2019.06.30
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Abstract

In this study, surface porosity and corrosion resistance of PEO coatings prepared on the 6061 Al alloy were investigated in terms of sodium phosphate ($Na_3PO_4$) concentrations in an alkaline solution and $NaAlO_2$ sealing. The surface morphologies of the PEO coatings clearly show that the coatings film formed in $9g\;L^{-1}$ had the lowest porosity. The $NaAlO_2$ sealing was found to remove micropores and cracks existing on the surface of PEO coatings. As a result, the $NaAlO_2$ sealing resulted in the movement of corrosion potential toward more positive value and lower corrosion current density.

Keywords

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Fig. 1. Voltage-time curves as a function of the concentration of Na3PO4.

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Fig. 2. Top view FE-SEM images of PEO coatings; (a) 3 g L-1, (b) 6 g L-1, (c) 9 g L-1, and (d) 12 g L-1. (e) Variation of the porosity and the conductivity in different electrolytes.

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Fig. 3. Top and cross-sectional view FE-SEM images of PEO coatings; (a), (b) before and (c), (d) after NaAlO2 sealing

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Fig. 4. XRD patterns before and after NaAlO2 sealing.

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Fig. 5. Potentiodynamic polarization curves before and after NaAlO2 sealing in 0.6 M NaCl solution.

Table 1. The parameters derived from the potentiodynamic polarization curves.

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