Abstract
The aim of the present work was to investigate the effect of the treatment time on the surface chemistry and corrosion behavior of cerium-based chemical conversion coatings on the AZ91D magnesium alloy. The conversion coating was prepared by the immersion technique from a bath consisting of 0.05 mol.L-1 Ce(NO3)3.6H2O and 0.254 mol.L-1 H2O2 (30 wt.%) for times ranging from 20 s to 120 s. The surface chemistry was examined by X-ray photoelectron spectroscopy (XPS). The corrosion behavior was assessed by electrochemical impedance spectroscopy and potentiodynamic polarization. XPS analysis detected the presence of cerium oxides (Ce2O3 and CeO2) and cerium/magnesium hydroxides. The best corrosion behavior was observed for the treatment conducted for 60 s. The results are discussed with respect to coating morphology and composition.
Highlights
Magnesium alloys are the most attractive metallic materials for technological application in lightweight structures, owing to their low density[1, 2] and high strength-to-weight ratio[3]
The aim of this work was to investigate the effect of the treatment time on the corrosion behavior of cerium-based conversion coatings developed on the AZ91D magnesium alloy
The surface chemistry was studied by X-ray photoelectron spectroscopy (XPS)
Summary
Magnesium alloys are the most attractive metallic materials for technological application in lightweight structures, owing to their low density (approximately 1,7 g/ cm3)[1, 2] and high strength-to-weight ratio[3]. One major limitation for the widespread use of magnesiumbased structural components is its intrinsic high chemical reactivity[4,5,6,7,8,9,10,11,12,13,14,15]. The corrosion resistance of magnesium alloys with cerium-based conversion coatings has been evaluated by several authors[17,18,19,20]. Protective coatings have been developed in order to overcome this limiting design feature of magnesium alloys. Different deposition methods may be employed such as electrodeposition, physical vapor deposition, anodization and chemical conversion coatings[1]. The conversion process is usually conducted by immersion at temperatures below 50°C in the presence of an oxidant, resulting in the formation of hydrated species or mixed oxides[21]
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