IMMERSION AND ELECTROCHEMICAL TESTS STUDY ON CORROSION RESISTANCE OF CHROME-FREE CHEMICAL CONVERSION FILM ON AZ91DMgALLOY IN 5 wt%NaClSOLUTION

X. P. Zhang and G. Chen
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X. P. Zhang: Department of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, P. R. China
G. Chen: Department of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, P. R. China

Surface Review and Letters (SRL), 2005, vol. 12, issue 03, 417-424

Abstract: Immersion and electrochemical tests have been applied to study corrosion protection of AZ91DMgalloy coating with chrome-free chemical conversion (CCC) coat in 5wt%NaClsolution. The immersions tests include weight-loss measurements after full or partial immersion with whole coating and full immersion with damaged coating. The electrochemical tests include electrochemical impedance spectroscopy (EIS) and polarization curves measurement. The results of immersion and electrochemical tests show that chrome-free chemical conversion (CCC) surface treatment can significantly improve the corrosion resistance of AZ91DMgalloy in 5%NaClsolution, and that the corrosion protection effect of CCC coating is not sensitive to pores or cracks. The equivalent circuit models are fitted from Nyquist plots for the uncoated specimens and the CCC-coated specimens. The charge transfer resistance,Rct, increases from about 1.669 Ω cm2for the uncoated alloy to about 210 Ω cm2after the alloy is coated with CCC coating.

Keywords: Magnesium alloy; corrosion protection; immersion test; electrochemical test; chrome-free chemical conversion (search for similar items in EconPapers)
Date: 2005
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DOI: 10.1142/S0218625X05007244

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