Abstract
Layered double hydroxide (LDHs) coatings were developed for the corrosion protection of AZ31 Mg alloy. AZ31 is widely used in the transport industry due to its low mass density and good mechanical properties. LDH coatings were fabricated under co-precipitation conditions and applied under hydrothermal conditions. Two different systems Zn-Al LDH and Li-Al LDH were studied. Specimens were post-treated via immersion for 2 h at 45 °C in inhibitor aqueous baths. Na2WO4·H2O and LiNO3 inorganic inhibitors were used, respectively, to produce inhibitor-loaded systems: Zn-Al LDH(W) and Li-Al LDH(Li). The characterization of the coatings was carried out by field-emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The corrosion process was studied by electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET). The surface was also evaluated via the determination of water drop contact angle and the performance of a paint adhesion test using an epoxy primer. The characterization of the coating revealed two-layered coatings with a denser inner layer and a flaky outer layer. Both coatings improved the corrosion resistance of the AZ31 alloy. Loading with inhibitor further increased the corrosion resistance by one order of magnitude (bare substrate, Z10mHz~102 Ω cm2; LDH, Z10mHz~103–4 Ω cm2; LDH-inhibitor, Z10mHz~105 Ω cm2).
Supplementary Materials
The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/CMDWC2021-10041/s1.
Funding
The authors gratefully acknowledge the support of the RTI2018-096391-B-C33 FEDER/Ministerio de Ciencia e Innovación−Agencia Estatal de Investigación, S2018/NMT−4411 Regional Government of Madrid and EU Structural and Social Funds. M. Mohedano is grateful for the support of RYC-2017 21843, Ministerio de Ciencia e Innovación. B. Mingo is supported by the Royal Academy of Engineering through the RAEng Research Fellowship and by EPSRC (EP/V026097/1).
Acknowledgments
The authors are grateful to Y. Gonzalez-Garcia and A.M. Kooijman from Delft University of Technology for the support with the SVET measurements.
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