Acta Phys. -Chim. Sin. ›› 2008, Vol. 24 ›› Issue (03): 481-486.doi: 10.3866/PKU.WHXB20080323

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Effect of (NaPO3)6 on Electrochemical Corrosion Characteristic of Micro-arc Oxidation Ceramic Coatings Formed on AZ91DMg Alloy

LUO Hai-He; CAI Qi-Zhou; WEI Bo-Kang; YU Bo; HE Jian; LI Ding-Jun   

  1. State Key Laboratory of Material Processing and Die &Mould Technology, Huazhong University of Science and Technology, Wuhan 430074, P. R. China
  • Received:2007-09-17 Revised:2007-11-25 Published:2008-03-10
  • Contact: CAI Qi-Zhou

Abstract: (NaPO3)6 was added to Na2SiO3-KOH electrolyte system, and in-situ ceramic coatings were prepared on AZ91D magnesium alloy by micro-arc oxidation technique. Room temperature electrochemical behavior of the ceramic coatings, formed in electrolyte with and without (NaPO3)6, in NaCl (w=3.5%) solution was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results showed that the ceramic coating formed in electrolyte containing (NaPO3)6 indicated a considerable increase in corrosion potential and a remarkable decrease in corrosion current density compared to the bare AZ91D magnesium alloy. The main cause was that the addition of (NaPO3)6 increased oxygen vacancies on the Mg substrate surface and the content of PO3-4 in the electrolyte. As a result, the (NaPO3)6-addition speeded up the formation of Mg oxide at the interface between metal and ceramic film(coating) (M/F), and increased the thickness and compactness of the ceramic coating. Based on the studied electrochemical reaction system and the special structure of the ceramic coating, a reasonable equivalent circuit was established. Combining with the EIS data, the effect mechanismof (NaPO3)6-addition on improving the electrochemical corrosion resistance of the ceramic coatings was investigated.

Key words: AZ91D magnesiumalloy, Micro-arc oxidation, Ceramic coatings, (NaPO3)6, Mechanism of corrosion resistance, Electrochemical impedance spectroscopy


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