Corrosion resistance of a silane/ceria modified Mg--Al-layered double hydroxide on AA5005 aluminum alloy

doi:10.1007/s11706-019-0476-x

Front. Mater. Sci.

2019, Vol. 13

Issue (4) : 420-430 https://doi.org/10.1007/s11706-019-0476-x

RESEARCH ARTICLE

Corrosion resistance of a silane/ceria modified Mg--Al-layered double hydroxide on AA5005 aluminum alloy

Wei WU¹, Fen ZHANG¹(

), Yu-Chao LI², Yong-Feng ZHOU¹, Qing-Song YAO¹, Liang SONG¹(

), Rong-Chang ZENG^1,³, Sie Chin TJONG⁴, Dong-Chu CHEN⁵

¹. College of Materials Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China
². School of Materials Science and Engineering, Liaocheng University, Liaocheng 252059, China
³. School of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450002, China
⁴. Department of Physics, City University of Hong Kong, Tat Chee Avenue, Hong Kong, China
⁵. School of Materials Science and Energy Engineering, Foshan University, Foshan 528000, China

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Abstract

The present work aimed at assessing the electrochemical behavior and the corrosion inhibition performance of Mg--Al-layered double hydroxide (LDH) coatings modified with methyltrimethoxysilane (MTMS) and cerium nitrate on AA5005 aluminum alloy. The chemical compositions and surface morphologies of the coatings were investigated by XRD, FT-IR and FE-SEM, while their corrosion resistance was evaluated by electrochemical and immersion tests. An optimum corrosion resistance of the composite coatings was obtained by adding 10⁻² mol·L⁻¹ cerium nitrate. An excess addition of cerium nitrate resulted in a loose structure and poor corrosion resistance of the coating. The corrosion mechanism of the composite coatings was proposed and discussed.

Keywords aluminum alloy layered double hydroxide polymer coating cerium oxide corrosion resistance

Corresponding Author(s): Fen ZHANG,Liang SONG

Online First Date: 01 November 2019 Issue Date: 04 December 2019

Cite this article:

Wei WU,Fen ZHANG,Yu-Chao LI, et al. Corrosion resistance of a silane/ceria modified Mg--Al-layered double hydroxide on AA5005 aluminum alloy[J]. Front. Mater. Sci., 2019, 13(4): 420-430.

URL:

https://academic.hep.com.cn/foms/EN/10.1007/s11706-019-0476-x
https://academic.hep.com.cn/foms/EN/Y2019/V13/I4/420

Fig.1 SEM morphologies and selected point locations for EDS chemical analysis: (a) LDH coating; (b) LDH/PMTMS coating; (c) LDH/PMTMS-CeO₂-1 coating; (d) LDH/PMTMS-CeO₂-2 coating; (e) LDH/PMTMS-CeO₂-3 coating; (f) LDH/PMTMS-CeO₂-4 coating.

Tab.1 Elemental compositions of selected points on LDH and composite coatings as shown in Fig. 1

Fig.2 XRD patterns of alloy substrate (a), LDH coating (b), LDH/PMTMS coating (c), LDH/PMTMS-CeO₂-1 coating (d), LDH/PMTMS-CeO₂-2 coating (e), LDH/PMTMS-CeO₂-3 coating (f) and LDH/PMTMS-CeO₂-4 coating (g).

Fig.3 FT-IR spectra of LDH coating, LDH/PMTMS coating, LDH/PMTMS-CeO₂-1 coating, LDH/PMTMS-CeO₂-2 coating, LDH/PMTMS-CeO₂-3 coating and LDH/PMTMS-CeO₂-4 coating.

Fig.4 Polarization curves of alloy substrate (a), LDH coating (b), LDH/PMTMS coating (c), LDH/PMTMS-CeO₂-1 coating (d), LDH/PMTMS-CeO₂-2 coating (e), LDH/PMTMS-CeO₂-3 coating (f) and LDH/PMTMS-CeO₂-4 coating (g).

Tab.2 Electrochemical parameters determined from the polarization curves of samples as shown in Fig. 4

Fig.5 (a) Nyquist plots, (b)(c) enlarged Nyquist plots and (d) Bode plots of ?Z? vs. frequency: alloy substrate (I); LDH coating (II); LDH/PMTMS coating (III); LDH/PMTMS-CeO₂-1 coating (IV); LDH/PMTMS-CeO₂-2 coating (V); LDH/PMTMS-CeO₂-3 coating (VI); LDH/PMTMS-CeO₂-4 coating (VII).

Fig.6 SEM images of (a) LDH coating, (b) LDH/PMTMS coating, (c) LDH/PMTMS-CeO₂-1 coating, (d) LDH/PMTMS-CeO₂-2 coating, (e) LDH/PMTMS-CeO₂-3 coating and (f) LDH/PMTMS-CeO₂-4 coating after immersion in 3.5 wt.% NaCl solution for 336 h.

Fig.7 Bar graphs of LDH coating and composite coatings showing the elemental composition of coated samples after immersion in 3.5 wt.% NaCl solution for 336 h. EDS analyses were performed at Points 1, 2, 3, 4, 5 and 6 in Fig. 6.

Fig.8 XRD patterns of LDH coating and composite coatings after immersion in 3.5 wt.% NaCl solution for 336 h.

Fig.9 Water contact angle images and values of (a) alloy substrate, (b) LDH coating, (c) LDH/PMTMS coating, (d) LDH/PMTMS-CeO₂-1 coating, (e) LDH/PMTMS-CeO₂-2 coating, (f) LDH/PMTMS-CeO₂-3 coating and (g) LDH/PMTMS-CeO₂-4 coating.

Fig.10 Schematic representation and corrosion mechanism of coated samples: (a)(b)(c) LDH coatings; (d)(e)(f) LDH/PMTMS coatings; (g)(h)(i) LDH/PMTMS-CeO₂ coatings.

Tab.3 Water contact angles and i_corr of LDH/PMTMS-CeO₂ coatings on Al alloy and Mg alloy

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