INVESTIGATION ON CHROMIUM-FREE CONVERSIONCOATING ON AZ91D MAGNESIUM ALLOY

J Chin Soc Corr Pro

2007, Vol. 27

Issue (1): 17-22 DOI:

Research Report

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INVESTIGATION ON CHROMIUM-FREE CONVERSIONCOATING ON AZ91D MAGNESIUM ALLOY

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华中科技大学

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;. INVESTIGATION ON CHROMIUM-FREE CONVERSIONCOATING ON AZ91D MAGNESIUM ALLOY. J Chin Soc Corr Pro, 2007, 27(1): 17-22 .

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Abstract A chromium-free conversion coating treatment whose solution contains phosphate acid、 nitrate compound and accelerator was developed for magnesium alloy.The morphology of conversion was observed using AFM and SEM.The AFM results showed the surface of coating is smooth and slightly wavy.The structure and the composition were analyzed by using EDS and XRD.The EDX results indicated that the compositions of the coating were mainly compounds of Mg,Al,Mn，P，Ca and O.XRD result showed that coating layer contains amorphous materials and a small quantity of Ca0.965Mg2Al6O27,Mn5.64P3,ZnAl2O4 and (Mg0.66Al0.34)(Al0.83Mg0.17)2O4 crystalline compounds.Electrochemical impedance spectroscopy (EIS) and electrochemical polarisation was utilized to study the coating immersion in NaCl slution.The EIS and electrochemical polarisation results demonstrated that the reason for pitting corrosion of conversion coating is that dissolution at the chlorine anion absorbed area is higher than that of non-absorbed area.

Key words: AZ91D Mg alloys chromium-free conversion coating impedance spectroscopy pitting corrosion

Received: 08 August 2005

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TG174.44

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