Journal of the Korean institute of surface engineering (한국표면공학회지)

The Korean Institute of Surface Engineering (한국표면공학회)
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Formation Behavior of Anodic Oxide Films on Al 6061 Alloy in Sulfuric Acid Solution

황산 용액에서 Al6061 합금의 아노다이징 피막 형성거동

  • Moon, Sungmo (Surface Technology Division, Korea Institute of Materials Science) ;
  • Jeong, Kihun (Gyeongsang National University) ;
  • Lim, Sugun (Gyeongsang National University)
  • 문성모 (재료연구소 표면기술연구본부 전기화학 연구실) ;
  • 정기훈 (경상대학교 재료공정융합공학과) ;
  • 임수근 (경상대학교 재료공정융합공학과)
  • Received : 2018.11.06
  • Accepted : 2018.12.10
  • Published : 2018.12.31
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Abstract

Formation behavior of aluminum anodic oxide (AAO) films on Al6061 alloy was studied in view of thickness, morphology and defects in the anodic films in 20 vol.% sulfuric acid solution at a constant current density of $40mA/cm^2$, using voltage-time curve, observation of anodized specimen colors and surface and cross-sectional morphologies of anodic films with anodization time. With increasing anodizing time, voltage for film formation increased exponentially after about 12 min and its increasing rate decreased after 25 min, followed by a rapid decrease of the voltage after about 28 min. Surface color of anodized specimen became darker with increasing anodizing time up to about 20 min, while it appeared to be brighter with increasing anodizing time after 20 min. The darkened and brightened surfaces with anodizing time are attributed to an increase in thickness of porous anodic oxide film and a chemical damage of the films due to heat generated by increased resistance of the film, respectively. Cross-sectional observation of AAO films revealed the formation of defects of crack shape at the metal/oxide interface after 15 min which prevents the growth of AAO films. Width and length of the crack-like defect increased with anodizing time up to 25 min of anodizing, and finally the outer part of AAO films was partly dissolved or detached after 30 min of anodizing, resulting in non-uniform surface structures of the AAO films.

Keywords

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Fig. 1. V-t curves of Al6061 at 40 mA/cm2 in 20% sulfuric acid solution containing 20 g/l of dissolved Al.

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Fig. 2. Slope of V-t curves obtained during anodizing of Al6061 alloy at 40 mA/cm2 in 20% sulfuric acid solution containing 20 g/l of dissolved Al.

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Fig. 3. Averaged slope of V-t curves obtained during anodizing of Al6061 alloy at 40 mA/cm2 in 20% sulfuric acid solution containing 20 g/l of dissolved Al.

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Fig. 4. Digital photographs of Al6061 alloy anodized for (a) 5, (b) 10, (c) 15, (d) 20, (e) 25 and (f) 30 min at 40 mA/cm2 in 20 % sulfuric acid solution containing 20 g/l of dissolved aluminum.

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Fig. 5. Thickness of anodic oxide films on Al6081 alloy with anodizing time at 40 mA/cm2 in 20% sulfuric acid solution containing 20 g/l of dissolved Al.

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Fig. 6. SEM surface images of anodic oxide films on Al6061 alloy formed for (a) 15 min, (b) 20 min, (c) 25 min and (d) 30 min at 40 mA/cm2 in 20 vol.% sulfuric acid solution containing 20 g/l of dissolved aluminum.

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Fig. 7. Cross-sectional SEM images of anodic oxide films on Al6061 alloy formed for (a) 5 min , (b) 10 min, (c) 15 min, (d) 20 min, (e) 25 min and (f) 30 min at 40 mA/cm2 in 20 Vol.% sulfuric acid solution containing 20 g/L of dissolved aluminum.

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Fig. 8. Cross-sectional SEM images of anodic oxide films on Al6061 alloy formed for (a) 25 min and (b) 30 min at 40 mA/cm2 in 20 Vol.% sulfuric acid solution containing 20 g/L of dissolved aluminum.

References

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