Hydrophobic epoxy resin coating with ionic liquid conversion pretreatment on magnesium alloy for promoting corrosion resistance

doi:10.1016/j.jmst.2019.06.024

Abstract

Abstract:

A hydrophobic epoxy resin coating with an environmental-friendly deep eutectic solvent (DES)-based conversion pretreatment was proposed to enhance the corrosion resistance of magnesium alloys. The hydrophobic epoxy resin coatings on the AZ31B magnesium alloy with and without the DES-based conversion pretreatment were thoroughly compared. It is found that the DES-based conversion film on the AZ31B magnesium alloy is mainly composed of MgH₂, MgO and MgCO₃. Furthermore, the conversion film possesses porous structure, which provides more anchor points for the following epoxy resin coating. However, without the DES-conversion pretreatment, the epoxy resin is difficult to be attached on the substrate during the dip-coating process. The double layered hybrid coating system promotes the corrosion resistance of the magnesium alloys significantly, which can be ascribed to the unique architecture and component including the hydrophobicity of the surface layer, the dense and interlocked epoxy resin, and the corrosion resistant DES-based conversion pretreatment.

Key words: Mg alloy, Deep eutectic solvent, Corrosion resistance, Double layered hybrid coating

Liting Guo, Changdong Gu, Jie Feng, Yongbin Guo, Yuan Jin, Jiangping Tu. Hydrophobic epoxy resin coating with ionic liquid conversion pretreatment on magnesium alloy for promoting corrosion resistance[J]. J. Mater. Sci. Technol., 2020, 37: 9-18.

Figures/Tables 14

Fig. 1. Schematics of preparation of the double layered hybrid coating on magnesium alloy.

Fig. 2. Reaction time dependent surface morphologies of the AZ31B substrates during the DES-based conversion pretreatment: (a) DES-10?min; (b) DES-20?min; (c) DES-30?min; (d) DES-60?min. Insets are the corresponding magnified images.

Fig. 3. Typical cross-sectional SEM image merged with EDS linear analysis of the DES-based conversion film with a reaction time of 60?min: (a) cross-sectional SEM image; (b) EDS linear analysis.

Fig. 4. XRD patterns of (a) the bare AZ31B magnesium alloy substrate and (b) the DES-based conversion film with a reaction time of 60?min. Hexagonal magnesium phase (JCPDS 35-0821) and tetragonal MgH2 phase (JCPDS 12-0697) are detected in the DES-pretreatment sample.

Fig. 5. XPS core-level spectra of the DES-based conversion film with a reaction time of 60 min: (a) survey XPS spectra; (b) Mg 2p; (c) C 1s; (d) O 1s; (e) Al 2p; (f) Zn 2p. A deconvolution procedure including Gaussian profile and a Shirley background is utilized to understand the bonding state of the elements.

Fig. 6. Mass change of the AZ31B magnesium alloy sample with and without DES-pretreatment during the dip-coating cycles.

Fig. 7. Surface morphologies of the AZ31B magnesium alloy sample with and without DES-pretreatment by dip-coating method for one cycle: (a) the bare AZ31B magnesium alloy substrate; (b) DES-based conversion film; (c) simple epoxy resin coating; (d) double layered hybrid coating.

Fig. 8. (a, b) Contact angles (CA) corresponding to the bare AZ31B magnesium alloy substrate and the DES-based conversion film, respectively and CA changes of the epoxy resin coatings on the AZ31B magnesium alloy substrate with (c) and without (d) the DES-based conversion film as a function of dip-coating cycles.

Fig. 9. FTIR spectra of the surfaces of the bare AZ31B magnesium alloy substrate, the DES-based conversion film, and the double layered hybrid coating, respectively.

Fig. 10. Potentiodynamic polarization curves of samples measured in 3.5?wt% NaCl solution at room temperature: (a) the DES-based conversion films with different reaction times; (b) different coating systems in this study. Potentiodynamic polarization curve of the bare AZ31B magnesium alloy substrate was given in the figures for comparison.

Table 1 Corrosion parameters of various samples, which were derived from Fig. 10.

Samples	E_corr (V vs. Ag/AgCl)	i_corr (μA/cm²)	Tafel slope (mV/dec)
Substrate	-1.52	725	β_a: 222 β_c: -159
DES-10?min	-1.50	219	β_a: 205 β_c: -64
DES-20?min	-1.48	192	β_a: 189 β_c: -90
DES-30?min	-1.50	147	β_a: 176 β_c: -125
DES-60?min (Conversion film)	-1.47	92	β_a: 167 β_c: -149
Simple epoxy resin coating	-1.45	1.14	β_a: 131 β_c: -100
Double layered hybrid coating	-1.42	0.19	β_a: 125 β_c: -115

Fig. 11. EIS and fitting results for the AZ31B magnesium alloy substrate, the DES-based conversion film, the epoxy resin coating with and without the DES-based conversion film: (a) Nyquist plots; (b) Bode plots of |Z| vs. frequency; (c) bode plots of phase angle vs. frequency; equivalent circuits of the EIS plots for (d) the bare AZ31B magnesium alloy substrate and the DES-based conversion film and (e) epoxy resin coating samples.

Table 2 Fitting results of the various samples, which were derived from Fig. 11.

Samples	R_s (Ω?cm²)	CPE1 (Sⁿ Ω^-1?cm^-2)	n	R₁ (Ω?cm²)	CPE2 (Sⁿ Ω^-1?cm^-2)	n	R_2m (Ω cm²)	L (H?cm^-2)	R_L (Ω cm²)	Errors (%)
Substrate	9	1.35?×?10^-5	0.99	191.2	-	-	-	107.7	68.01	<10
Conversion film	4.9	1.85?×?10^-5	0.94	255.3	-	-	-	217.2	225	<6.47
Simple epoxy resin coating	3.8	8.26?×?10^-8	0.81	329.6	2.17?×?10^-7	0.949	1.60?×?10⁴	1.39?×?10⁴	1.64?×?10⁴	<5.74
Double layered hybrid coating	1	5.57?×?10^-8	0.80	390.3	1.97?×?10^-7	0.9197	4.04?×?10⁴	3.07?×?10⁴	3.48?×?10⁴	<5.46

Table 3 Summary of the corroded surfaces in a 3.5?wt% NaCl solution for various exposure times.

Sample	0?min	10?min	2?h	4?h	32?h	120?h
Substrate
Conversion film
Simple epoxy resin coating
Double layered hybrid coating

References

[1]	G.L. Song, A. Atrens, Adv. Eng. Mater. 1(1999) 11-33.
[2]	Q.H. Yuan, X.S. Zeng, Y. Liu, L. Luo, J.B. Wu, Y.C. Wang, G.H. Zhou, Carbon 96 (2016) 843-855.
[3]	W.Q. Xu, N. Birbilis, G. Sha, Y. Wang, J.E. Daniels, Y. Xiao, M. Ferry, Nat. Mater. 14(2015) 1229-1235.
[4]	X.B. Chen, N. Birbilis, T.B. Abbott, Corrosion 67 (2011) 1-16.
[5]	L. Mao, L. Shen, J.H. Chen, Y. Wu, M. Kwak, Y. Lu, Q. Xue, J. Pei, L. Zhang, G.Y. Yuan, R. Fan, J.B. Ge, W.J. Ding, ACS Appl. Mater. Interf. 7(2015) 5320-5330.
[6]	G.S. Frankel, Nat. Mater. 14(2015) 1189-1190.
[7]	L.P. Wu, C.G. Wang, D.B. Pokharel, I.I.N. Etim, L. Zhao, J.H. Dong, W. Ke, N. Chen, J. Mater. Sci. Technol. 34(2018) 2084-2090.
[8]	M. Esmaily, J.E. Svensson, S. Fajardo, N. Birbilis, G.S. Frankel, S. Virtanen, R. Arrabal, S. Thomas, L.G. Johansson, Prog. Mater. Sci. 89(2017) 92-193.
[9]	F.Y. Cao, G.L. Song, A. Atrens, Corros. Sci. 111(2016) 835-845.
[10]	S. Heise, S. Virtanen, A.R. Boccaccini, J. Biomed. Mater. Res. Part B Appl.Biomater. 104(2016) 2628-2641.
[11]	H.K. Singh, K.V. Yeole, S.T. Mhaske, Chem. Eng. J. 295(2016) 414-426.
[12]	C.G. Wang, L.P. Wu, F. Xue, R.Y. Ma, I.I.N. Etim, X.H. Hao, J.H. Dong, W. Ke, J.Mater. Sci. Technol. 34(2018) 1876-1884.
[13]	X.P. Lu, Y. Li, P.F. Ju, Y. Chen, J.S. Yang, K. Qian, T. Zhang, F.H. Wang, Corros. Sci. 148(2019) 264-271.
[14]	A. Bakkar, V. Neubert, Electrochem. commun. 9(2007) 2428-2435.
[15]	J. Zhang, Z.H. Xie, H. Chen, C. Hu, L.X. Li, B.N. Hu, Z.W. Song, D.L. Yan, G. Yu, Surf. Coat. Technol. 342(2018) 178-189.
[16]	L.P. Wu, Z.D. Yang, G.W. Qin, J. Alloys. Compd. 694(2017) 1133-1139.
[17]	G.L. Song, Z.M. Shi, Corros. Sci. 85(2014) 126-140.
[18]	C. Blawert, W. Dietzel, E. Ghali, G. Song, Adv. Eng. Mater. 8(2006) 511-533.
[19]	X.P. Lu, C. Blawert, D. Tolnai, T. Subroto, K.U. Kainer, T. Zhang, F.H. Wang, M.L. Zheludkevich, Corros. Sci. 139(2018) 395-402.
[20]	X.P. Lu, C. Blawert, Y.D. Huang, H. Ovri, M.L. Zheludkevich, K.U. Kainer, Electrochim. Acta 187 (2016) 20-33.
[21]	G.L. Song, Adv. Eng. Mater. 7(2005) 563-586.
[22]	G. Song, A. Atrens, Adv. Eng. Mater. 9(2007) 177-183.
[23]	M. Dabala, K. Brunelli, E. Napolitani, M. Magrini, Surf. Coat. Technol. 172(2003) 227-232.
[24]	F. Zhang, C.L. Zhang, L. Song, R.C. Zeng, S.Q. Li, H.Z. Cui, J. Mater. Sci. Technol. 31(2015) 1139-1143.
[25]	Q.J. Meng, G.S. Frankel, Surf. Interface Anal. 36(2004) 30-42.
[26]	L. Anicai, R. Masi, M. Santamaria, F. Di Quarto, Corros. Sci. 47(2005) 2883-2900.
[27]	C.S. Lin, H.C. Lin, K.M. Lin, W.C. Lai, Corros. Sci. 48(2006) 93-109.
[28]	H.H. Elsentriecy, K. Azumi, H. Konno, Electrochim. Acta 53 (2007) 1006-1012.
[29]	T. Takenaka, Y. Narazaki, N. Uesaka, M. Kawakami, Mater. Trans. 49(2008) 1071-1076.
[30]	X. Jiang, R.G. Guo, S.Q. Jiang, Appl. Surf. Sci. 341(2015) 166-174.
[31]	M. Zhao, S.S. Wu, J.R. Luo, Y. Fukuda, H. Nakae, Surf. Coat. Technol. 200(2006) 5407-5412.
[32]	J.A. Latham, P.C. Howlett, D.R. MacFarlane, M. Forsyth, Electrochem.commun. 19(2012) 90-92.
[33]	P.C. Howlett, J. Efthimiadis, P. Hale, G.A. van Riessen, D.R. MacFarlane, M. Forsyth, J. Electrochem. Soc. 157(2010) C392-C398.
[34]	P.C. Howlett, W. Neil, T. Khoo, J.Z. Sun, M. Forsyth, D.R. MacFarlane, Isr. J.Chem. 48(2008) 313-318.
[35]	M. Forsyth, P.C. Howlett, S.K. Tan, D.R. MacFarlane, N. Birbilis, Electrochem. Solid State Lett. 9(2006) B52-B55.
[36]	E.L. Smith, A.P. Abbott, K.S. Ryder, Chem. Rev. 114(2014) 11060-11082.
[37]	X. Ge, C.D. Gu, X.L. Wang, J.P. Tu, J. Mater. Chem. A Mater. Energy Sustain. 5(2017) 8209-8229.
[38]	D.E. Crawford, L.A. Wright, S.L. James, A.P. Abbott, Chem. Commun. (Camb.) 52(2016) 4215-4218.
[39]	L.T. Guo, C. Gu, J. Tu, Subsurf. Sens. Technol. Appl. 48(2019) 10-18.
[40]	C.D. Gu, W. Yan, J.L. Zhang, J.P. Tu, Corros. Sci. 106(2016) 108-116.
[41]	C.D. Gu, X.J. Xu, J.P. Tu, J. Phys. Chem. C 114 (2010) 13614-13619.
[42]	L.T. Guo, C. Gu, J. Zhang, X. Wang, K. Wang, Y. Jin, J. Tu, Surf. Coat. Technol. 357(2019) 833-840.
[43]	X.J. Cui, X.Z. Lin, C.H. Liu, R.S. Yang, X.W. Zheng, M. Gong, Corros. Sci. 90(2015) 402-412.
[44]	I.A. Kartsonakis, A.C. Balaskas, E.P. Koumoulos, C.A. Charitidis, G. Kordas, Prog. Org. Coat. 76(2013) 459-470.
[45]	J.Y. Hu, Q. Li, X.K. Zhong, L. Zhang, B. Chen, Prog. Org. Coat. 66(2009) 199-205.
[46]	A. Adhikari, R. Karpoormath, S. Radha, S.K. Singh, R. Mutthukannan, G. Bharate, M. Vijayan, High Perform. Polym. 30(2018) 181-191.
[47]	J.C. Cabanelas, S.G. Prolongo, B. Serrano, J. Bravo, J. Baselga, J. Mater. Process. Technol. 143(2003) 311-315.
[48]	M. Shon, H. Kwon, Corros. Sci. 49(2007) 4259-4275.
[49]	J. Zhang, W.C. Zhang, J.J. Lu, C.X. Zhu, W.Q. Lin, J. Feng, Prog. Org. Coat. 121(2018) 201-208.
[50]	M.L. Yang, J.H. Wu, D.Q. Fang, B. Li, Y. Yang, J. Mater. Sci. Technol. 34(2018) 2464-2471.
[51]	D.K. Aswal, K.P. Muthe, S. Tawde, S. Chodhury, N. Bagkar, A. Singh, S.K. Gupta, J.V. Yakhmi, J. Cryst. Growth 236 (2002) 661-666.
[52]	K. Nakamura, M. Tsunakawa, Y. Shimada, A. Serizawa, T. Ishizaki, Surf. Coat. Technol. 328(2017) 436-443.
[53]	X. Xiang, X.T. Zu, S. Zhu, C.F. Zhang, L.M. Wang, Nucl. Instrum. Methods Phys. Res. Sect. B 250 (2006) 192-195.
[54]	W. Wysocka, A. Przybyl, G. Wojciechowski, B. Brzezinski, J. Mol.Struct. 516(2000) 157-160.
[55]	T. Jin, Y.Q. Han, R.Q. Bai, X. Liu, J. Nanosci. Nanotechnol. 18(2018) 4971-4981.
[56]	W.G. Ji, J.M. Hu, J.Q. Zhang, C.N. Cao, Corrosion Sci. 48(2006) 3731-3739.
[57]	C.N. Cao, J.Q. Zhang, An Introduction of Electrochemical Impedance Spectroscopy, Science Press, Beijing, 2002 (in Chinese).
[58]	Z.B. Wang, H.X. Hu, C.B. Liu, Y.G. Zheng, Electrochim. Acta 135 (2014)526-535.
[59]	M. Hatami, M. Yeganeh, A. Keyvani, M. Saremi, R. Naderi, J. Solid State Electrochem. 21(2017) 777-785.
[60]	Z.W. Wang, Q. Li, Z.X. She, F.N. Chen, L.Q. Li, X.X. Zhang, P. Zhang, Appl. Surf. Sci. 271(2013) 182-192.