Journal of the Korean institute of surface engineering (한국표면공학회지)

The Korean Institute of Surface Engineering (한국표면공학회)
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Effect of pre-treatment in 0.5 M oxalic acid containing various NH4F concentrations on PEO Film Formation of AZ91 Mg Alloy

NH4F가 첨가된 0.5 M 옥살산 전처리가 AZ91 마그네슘 합금의 PEO 피막 형성에 미치는 영향

  • Kwon, Duyoung (Nano-Surface Materials Division, Korea Institute of Materials Science) ;
  • Song, Pung-Keun (Department of Materials Science and Engineering, Pusan National University) ;
  • Moon, Sungmo (Nano-Surface Materials Division, Korea Institute of Materials Science)
  • 권두영 (한국재료연구원 나노표면재료연구본부) ;
  • 송풍근 (부산대학교 재료공학부) ;
  • 문성모 (한국재료연구원 나노표면재료연구본부)
  • Received : 2022.02.06
  • Accepted : 2022.02.25
  • Published : 2022.02.28
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Abstract

This study investigated the effect of pre-treatment on the PEO film formation of AZ91 Mg alloy. The pre-treatment was conducted for 10 min at room temperature in 0.5 M oxalic acid (C2H2O4) solution containing various ammonium fluoride (NH4F) concentrations. The pre-treated AZ91 Mg specimens were anodized at 100 mA/cm2 of 300 Hz AC for 2 min in 0.1 M NaOH + 0.4 M Na2SiO3 solution. When AZ91 Mg alloy was pretreated in 0.5 M oxalic acid with NH4F concentration less than 0.3 M, continuous dissolution of the AZ91 Mg alloy occurred together with the formation of black smuts and arc initiation time for PEO film formation was very late. It was noticed that corrosion rate of the AZ91 Mg alloy became faster if small amount of NH4F concentration, 0.1 M, is added. The fast corrosion is attributable to fast formation of porous fluoride together with porous oxides in the reaction products. On the other hand, when AZ91 Mg alloy was pretreated in 0.5 M oxalic acid with sufficient NH4F more than 0.3 M, a thin and dense protective film was formed on the AZ91 Mg alloy surface which resulted in faster initiation of arcs and formation of PEO film.

Keywords

Acknowledgement

This study was supported financially by Fundamental Research Program of the Korean Institute of Materials Science (KIMS).

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