Microstructure characteristics and enhanced corrosion protection properties of nanocomposite Ni-Co-TiO_2 electrodeposit formed on AZ91D magnesium alloy

摘要

In this paper, Ni-Co-TiO_2 composite electrodeposits were successfully prepared on AZ91D magnesium alloy for protecting the alloy from corrosion. Scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy were employed to investigate the surface morphologies, microstructure and chemical compositions of the composite coatings respectively. The electrochemical corrosion behaviours of the coatings in neutral 3.5 wt-%NaCl, 0.6 mol L~(-1) Na_2SO_4 and 0.6 mol L~(-1) NaOH solutions were evaluated by electrochemical impedance spectroscopy and potentiodynamic polarisation techniques, and the results indicate good protection for AZ91D magnesium alloy. Long term immersion tests were carried out in neutral 3.5 wt-%NaCl solution using electrochemical impedance spectroscopy, showing that Ni-Co-TiO_2 composite coating could provide long term protection in neutral 3.5 wt-%NaCl solution for AZ91D magnesium alloy.