Ceria/stannate multilayer coatings on AZ91D Mg alloy |
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Authors: | P. Bagalà ,F.R. Lamastra,S. Kaciulis,A. Mezzi,G. Montesperelli |
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Affiliation: | 1. Dipartimento di Ingegneria Industriale, Università di Roma — Tor Vergata, Rome, Italy;2. Consorzio INSTM — Unità di Ricerca di Roma — Tor Vergata, Italy;3. ISMN — CNR, Monterotondo Stazione, Rome, Italy |
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Abstract: | In this work, CeO2/stannate multilayer coatings on AZ91D magnesium alloy were successfully obtained by chemical conversion and sol–gel dip coating. The stannate conversion coatings were prepared from a stannate aqueous bath containing Na2SnO3, CH3COONa, Na3PO4 and NaOH at different temperatures and immersion times. Ceria films were produced on stannate/AZ91D starting from Ce(III) nitrate solutions in H2O. In some cases, the PVA was added as chelating agent. Ceria top coatings were fired at 200 °C for 1 h. Coating microstructure was examined by FE-SEM. Finally, the corrosion resistance features of the coatings were tested by the electrochemical impedance spectroscopy (EIS) in 3 wt.% NaCl solution. The effect of PVA addition was evaluated in terms of microstructure and corrosion resistance features. CeO2/stannate multilayer films, 3 μm thick, uniform, well adherent and nearly crack free were obtained. The formation of CeO2 phase was confirmed by XRD and XPS analyses. The XPS depth profiles showed a limited diffusion of Mg towards the ceramic film. The EIS tests showed a significant improvement of corrosion resistance of the multilayer coatings (~ 16.6 kΩ after 48 h in NaCl solution) with respect to the blank alloy (~ 2.4 kΩ after 48 h in NaCl solution). |
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Keywords: | Mg alloys Multilayer coatings Ceria Stannate Corrosion resistance |
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