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铁道科学与工程学报

JOURNAL OF RAILWAY SCIENCE AND ENGINEERING

Vol. 19    No. 4    August 2009

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Influence of potassium pyrophosphate in electrolyte on coated layer of AZ91 Mg alloy formed by plasma electrolytic oxidation
Jin-Young CHO, Duck-Young HWANG, Dong-Heon LEE, Bongyoung YOO, Dong-Hyuk SHIN

Department of Metallurgy and Materials Science, Hanyang University, Ansan, 426-791, Korea

Abstract:The effect of potassium pyrophosphate in the electrolyte on plasma electrolytic oxidation (PEO) process for AZ91 Mg alloy was investigated. The morphologies and chemical compositions of the coating layer on the AZ91 Mg alloy were evaluated and corrosion resistance was also estimated by potentiodynamic polarization analysis. The coating layer on AZ91 Mg alloy coated from the Bath 2 containing 0.03 mol/L of potassium pyrophosphate for 360 s exhibited considerably dense structure and contained 11%−18% (mass fraction) of phosphorous. The higher content of phosphorous of coating layer coated from Bath 2 could be detected at the bottom of oxide layer, which strongly implied that the phosphorous ion might be concentrated at the barrier layer. Corrosion potential of coating layer of AZ91 Mg alloy increased and corrosion current density decreased with increasing the concentration of potassium pyrophosphate. The polarization resistance (Rp) of coating layer of AZ91 Mg alloy coated from Bath 2 was 4.65×107 Ω/cm2, which was higher than that (Rp=3.56×104 Ω/cm2) of the sample coated from electrolyte without potassium pyrophosphate. The coating layer coated from Bath 2 containing 0.03 mol/L potassium pyrophosphate exhibited the best corrosion resistance.

 

Key words: plasma electrolytic oxidation; magnesium alloy; phosphorous; corrosion resistance

ISSN 1672-7029
CN 43-1423/U

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