Study of gadolinium based protective coating for magnesium alloys

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Abstract
Gadolinium based conversion coating, a new chemical protective coating for magnesium alloys, was prepared and its microstructure and corrosion resistance were investigated. The micromorphology, composition and elemental chemical states were observed by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometer (EDS) respectively. The corrosion resistance was evaluated by a potentiodynamic polarisation curve and electrochemical impedance spectroscopy. Nanomechanics integrated test system was used to represent the nanomechanical property and residual stress. The results indicate that the morphology of the coating is a cracked mud structure. The EDS and XPS results reveal that the coating is primarily made of magnesium and gadolinium oxides. Gadolinium coating forming mechanism can be generally divided into two periods: the dissolution of the substrate, the codeposition of Gd(OH)3 and Mg(OH)2. The potentiodynamic polarisation curve and electrochemical impedance spectroscopy (EIS) show that the coating can improve the corrosion resistance of magnesium alloys.

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