Acta Phys. -Chim. Sin. ›› 2012, Vol. 28 ›› Issue (01): 127-136.doi: 10.3866/PKU.WHXB201111112

• ELECTROCHEMISTRY AND NEW ENERGY • Previous Articles     Next Articles

Polarization Behavior of Magnesium Alloy AZ91D with Micro-Arc Oxidation Coating in NaCl Solution

CHANG Lin-Rong1, CAO Fa-He1, CAI Jing-Shun1, LIU Wen-Juan1, ZHENG Jun-Jun1, ZHANG Jian-Qing1,2, CAO Chu-Nan1,2   

  1. 1. Department of Chemistry, Zhejiang University, Hangzhou 310027, P. R. China;
    2. State Key Laboratory for Corrosion and Protection, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, P. R. China
  • Received:2011-09-21 Revised:2011-11-09 Published:2011-12-29
  • Contact: CAO Fa-He E-mail:nelson_cao@zju.edu.cn
  • Supported by:

    The project was supported by the National Natural Science Foundation of China (51131005, 51171172, 50801056) and Natural Science Foundation of Zhejiang Province, China (Y4110074).

Abstract: The polarization curves of magnesium alloy AZ91D with a micro-arc oxidation (MAO) coating showed several typical patterns caused by differences in the composition and structure of the coating. The pattern of the polarization curve of magnesium alloy AZ91D with a MAO coating depends on the primary composition and structure of the MAO coating and many experimental factors, such as the concentration of chloride ions, pH of the electrolyte, degree of cathodic polarization, and the exposed area of the specimen. These factors change the pattern of polarization curve of magnesium alloy AZ91D with MAO coating by affecting the main composition and structure of the MAO coating because of its instability in aqueous solution. Compositional and structural changes in the MAO coating on magnesium alloy AZ91D were investigated by Fourier transform infrared microscopic mapping and the corresponding optical photographs, respectively. A model was proposed to describe the transformation of the MAO coating in aqueous NaCl solution. For magnesium alloy AZ91D with a MAO coating immersed in NaCl solution, the rate determining steps of the anodic and cathodic reactions are the mass diffusion and charge transfer steps, respectively. As a result, the corrosion current density fitted from the polarization curve is not an accurate corrosion rate.

Key words: AZ91D, Micro-arc oxidaton coating, Polarization curve, Fourier transform infrared spectroscopy microscopic mapping, Electrochemical impedance spectroscopy

MSC2000: 

  • O646