Journal of the Korean institute of surface engineering (한국표면공학회지)

The Korean Institute of Surface Engineering (한국표면공학회)
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Adhesion and Corrosion Resistance of Electrophoretic Paint on "Electroless" Paint Coated AZ31 Mg Alloy

  • Received : 2018.11.14
  • Accepted : 2018.12.20
  • Published : 2018.12.31
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Abstract

The present study investigated the adhesion and corrosion resistance of subsequent electrophoretic paint (E-paint) on "electroless" paint coated AZ31 Mg alloy, which was formed by immersion of AZ31 Mg alloy in E-painting solution. It was found that with increasing immersion time of AZ31 in E-painting solution, the amount of paint deposited by electroless process increased but it decreased the electrochemical equivalent of E-painting process and the adhesion of the subsequent E-paint layer. The E-paint on electroless paint coated AZ31 contained pores with the highest pore density and the largest pore size was obtained on the samples with electroless times of 2 and 5 minutes, respectively. Results of the salt-spray test showed an accelerated growth of blisters over the entire surface of the sample immersed for less than 5 minutes whereas blisters were observed only in the vicinity of the scratch in case of samples treated for 15 and 30 minutes. The E-paint on AZ31 with shorter electroless immersion time in E-painting solution was found to have good adhesion and better corrosion resistance.

Keywords

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Fig. 2. Optical microscopy images of AZ31 Mg alloy after different immersion times in E-painting solution.

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Fig. 1. Open circuit potential of AZ31 Mg alloy with immersion time in E-painting solution.

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Fig. 3. Change in weight of AZ31 samples after different immersion times in E-painting solution.

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Fig. 5. Optical microscopy images of uncured E-paint on electroless painted AZ31 Mg alloy with different electroless immersion times.

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Fig. 6. Optical microscopy images of cured E-paint on electroless painted AZ31 Mg alloy with different electroless immersion times.

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Fig. 7. Pore size and pore density of cured E-paint on electroless painted AZ31 Mg alloy with different electroless immersion times.

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Fig. 8. Optical microscopy images at (a) low and (b) high magnifications after tape test of E-paint on electroless painted AZ31 with different electroless immersion times.

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Fig. 9. Surface appearance of scratched E-paint on electroless painted AZ31 Mg alloy with different testing times from 0 to 500 h SST according to ASTM B117.

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Fig. 10. Schematics illustration of (a) blister formation adjacent to scratched line and the delamination of paint, and (b) blister formation on porous E-paint layer.

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Fig. 4. (a) Total amount of paint deposited on AZ31 by both electroless painting process and E-painting process, or only E-painting process and (b) ratio of Epaint weight/electrical charge of E-painting process on electroless painted AZ31 Mg alloy with different electroless immersion times.

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