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Microstructural characteristics and corrosion property of non‐chromate surface treatments on AZ91D magnesium alloy
Author(s) -
Chen B.,
Li Q.,
Gao H.,
Fan J. M.,
Tan X.
Publication year - 2009
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.200805167
Subject(s) - chromate conversion coating , materials science , corrosion , coating , nanocrystalline material , magnesium alloy , scherrer equation , conversion coating , dielectric spectroscopy , scanning electron microscope , magnesium , metallurgy , alloy , chemical engineering , composite material , electrochemistry , nanotechnology , chemistry , electrode , engineering
Chromate conversion coatings can be successfully used for corrosion protection of magnesium alloys. However, the environmental laws have imposed severe restrictions on chromate use in many countries. In this study, a novel protective environmental‐functionally gradient coating was formed on AZ91D magnesium alloy by non‐chromate surface treatments, which consisted of pre‐etching followed by cerium‐based chemical conversion before applying the sol–gel CeO 2 film. It was determined by the analysis of X‐ray diffraction that the gradient coating was mainly composed of CeO 2 . The calculation, based on the Scherrer formula, further revealed the formation of nanocrystalline structure in the coating. Scanning electron microscopy (SEM) observations showed that the coating was homogeneous and compact, no obvious cracked structure occurred. According to the immersion tests, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) tests, the corrosion resistance of AZ91D magnesium alloy was found to be greatly improved by means of this novel environmental‐functionally gradient coating.