Characterization of Pitting Corrosion Behavior of AZ91 Mg-alloy without and with MAO Coating

doi:10.11902/1005.4537.2021.320

Journal of Chinese Society for Corrosion and protection

2022, Vol. 42

Issue (6): 1034-1042 DOI: 10.11902/1005.4537.2021.320

Current Issue | Archive | Adv Search

Characterization of Pitting Corrosion Behavior of AZ91 Mg-alloy without and with MAO Coating

LIU Yuxiang(

), XU Anyang

National Key Laboratory for Remanufacturing of China, Academy of Army Armored Force, Beijing 100072, China

Cite this article:

LIU Yuxiang, XU Anyang. Characterization of Pitting Corrosion Behavior of AZ91 Mg-alloy without and with MAO Coating. Journal of Chinese Society for Corrosion and protection, 2022, 42(6): 1034-1042.

Download:

HTML

PDF(6385KB)
Export: BibTeX | EndNote (RIS)

Abstract

The use of micro-arc oxidation (MAO) coating is a promising approach for controlling corrosion for Mg alloys. However, MAO coating and the underneath Mg-alloy substrate are constantly threatened by pitting corrosion. In order to reveal the relevant mechanism, the pitting corrosion behavior of AZ91 Mg alloy without and with MAO coating was studied via cyclic potentiodynamic polarization (CPDP) test. Meanwhile, the pitting corrosion morphology and corrosion products at different CPDP stages were characterized by means of optical microscope (OM), scanning electron microscope (SEM) and energy dispersive X-ray (EDS) spectroscope. Results show that pits initiate on α-Mg phase rather than on β phase for AZ91 Mg alloy, however, they initiate around pores and cracks on MAO-coating. The initial pits show a volcano-like morphology for both the alloy and the coating. Moreover, inside the pits on the alloy there is a corrosion products film, which act as protective barrier for the substrate, as a result, pits on the alloy widened with time. By comparison, corrosion products of poor protectiveness exfoliate and dissolve inside the pits on the MAO coating, thus, where pits grow deeper with time. The morphology evolution of pits validates the positive hysteresis loops that exist on CPDP curves for both the alloy and coating, and can also explain the larger area of the positive hysteresis loop on the MAO coating. Overall, the MAO-coated alloy might fail without proper post-treatments due to the severe pitting corrosion, therefore, it is necessary to conduct pore sealing treatment for MAO coating to provide a promising corrosion protectiveness for Mg alloys.

Key words: AZ91 Mg-alloy MAO coating cyclic potentiodynamic polarization corrosion morphology and products pits initiation and propagation

Received: 09 November 2021

ZTFLH:

TG174.41

Fund: National Key Laboratory for Remanufacturing of China(614005180101)

About author: LIU Yuxiang, E-mail: liuyuxiang0715@gmail.com

	Service

	E-mail this article
	Add to citation manager
	E-mail Alert
	RSS
	（）
	Articles by authors
	Yuxiang LIU
	Anyang XU

URL:

https://www.jcscp.org/EN/10.11902/1005.4537.2021.320 OR https://www.jcscp.org/EN/Y2022/V42/I6/1034

Fig.1 SEM surface (a) and cross-sectional (b) images (b), and EDS mapping results (c) of MAO coating

Fig.2 XRD patterns of AZ91 Mg-alloy and MAO coating

Fig.3 Open circuit potential curves of AZ91 Mg-alloy and MAO coating immersed in 3.5%NaCl solution for 30 min

Fig.4 Cyclic polarization curves of AZ91 Mg-alloy (a) and MAO coating (b) after OCP test in 3.5%NaCl solution

Table 1 Potentials and current densities at the points A, B and C of cyclic polarization curves of AZ91 Mg-alloy and MAO coating in Fig.4

Fig.5 OM corrosion morphologies of AZ91 Mg-alloy (a-c) and MAO coating (d-f) at the points A (a, d), B (b,e) and C (c, f) on CPDP curves (the inserted images presents the hydrogen evolution)

Fig.6 SEM corrosion morphologies of AZ91 Mg-alloy (a-c) and MAO coating (d-f) at the points A (a, d), B (b, e) and C (c, f) on CPDP curves in Fig.4

Fig.7 SEM cross-sectional images of AZ91 Mg-alloy (a-c) and MAO coating (d-f) at the points A (a, d), B (b, e) and C (c, f) on CPDP curves in Fig.4

Fig.8 SEM images of corrosion morphology and EDS mapping analysis for AZ91 Mg-alloy (a) and MAO coating (b) at points B on CPDP curves in Fig.4

Fig.9 XRD patterns of AZ91 Mg-alloy and MAO coating at the points B on CPDP curves in Fig.4

[1]	Chen Z N, Yong X Y, Chen X C. Micro-defects in micro-arc oxidation coatings on Mg-alloys [J]. J. Chin. Soc. Corros. Prot., 2022, 42: 1
	(陈振宁, 雍兴跃, 陈晓春. 镁合金微弧氧化膜中微缺陷问题研究进展 [J]. 中国腐蚀与防护学报, 2022, 42: 1)
[2]	Wang Z Q, Xu C X, Yang L J, et al. Microstructure and corrosion resistance of medical degradable Mg-2Y-1Zn-xZr alloy [J]. J. Chin. Soc. Corros. Prot., 2022, 42: 113
	(王中琪, 许春香, 杨丽景等. 医用可降解Mg-2Y-1Zn-xZr合金微观组织和耐蚀性能研究 [J]. 中国腐蚀与防护学报, 2022, 42: 113)
[3]	Liu Y X, Zhu S, Han B Y. Research progress in anodic hydrogen evolution of magnesium electrochemistry corrosion [J]. J. Mater. Eng., 2020, 48(10): 17
	(刘玉项, 朱胜, 韩冰源. 金属镁电化学腐蚀阳极析氢行为研究进展 [J]. 材料工程, 2020, 48(10): 17)
[4]	Esmaily M, Svensson J E, Fajardo S, et al. Fundamentals and advances in magnesium alloy corrosion [J]. Prog. Mater. Sci., 2017, 89: 92 doi: 10.1016/j.pmatsci.2017.04.011
[5]	Yang J, Yim C D, You B S. Characteristics of surface films formed on Mg-Sn alloys in NaCl solution [J]. J. Electrochem. Soc., 2016, 163: C395 doi: 10.1149/2.0161608jes
[6]	Fan Z M, Yu J, Song Y W, et al. Research progress of pitting corrosion of magnesium alloys [J]. J. Chin. Soc. Corros. Prot., 2018, 38: 317
	(樊志民, 于锦, 宋影伟等. 镁合金点蚀的研究进展 [J]. 中国腐蚀与防护学报, 2018, 38: 317)
[7]	Ding Z Y, Cui L Y, Zeng R C, et al. Exfoliation corrosion of extruded Mg-Li-Ca alloy [J]. J. Mater. Sci. Technol., 2018, 34: 1550 doi: 10.1016/j.jmst.2018.05.014
[8]	Neil W C, Forsyth M, Howlett P C, et al. Corrosion of magnesium alloy ZE41-The role of microstructural features [J]. Corros. Sci., 2009, 51: 387 doi: 10.1016/j.corsci.2008.11.005
[9]	Song Y W, Shan D Y, Han E H. Pitting corrosion of a rare earth Mg alloy GW93 [J]. J. Mater. Sci. Technol., 2017, 33: 954 doi: 10.1016/j.jmst.2017.01.014
[10]	Liu J H, Song Y W, Chen J C, et al. The special role of anodic second phases in the micro-galvanic corrosion of EW75 Mg alloy [J]. Electrochim. Acta, 2016, 189: 190 doi: 10.1016/j.electacta.2015.12.075
[11]	Dong C F, An Y H, Li X G, et al. Electrochemical performance of initial corrosion of 7A04 aluminium alloy in marine atmosphere [J]. Chin. J. Nonferrous Met., 2009, 19: 346
	(董超芳, 安英辉, 李晓刚等. 7A04铝合金在海洋大气环境中初期腐蚀的电化学特性 [J]. 中国有色金属学报, 2009, 19: 346)
[12]	Chen L, Chen J, Su Y. Study on pitting and corrosion inhibition of AZ63 magnesium alloy in sodium chloride solution [J]. Surf. Technol., 2013, 42(5): 24
	(陈琳, 陈静, 苏洋. AZ63镁合金在氯化钠溶液中的孔蚀及缓蚀研究 [J]. 表面技术, 2013, 42(5): 24)
[13]	Martin H J, Horstemeyer M F, Wang P T. Comparison of corrosion pitting under immersion and salt-spray environments on an as-cast AE44 magnesium alloy [J]. Corros. Sci., 2010, 52: 3624 doi: 10.1016/j.corsci.2010.07.009
[14]	Martin H J, Horstemeyer M F, Wang P T. Structure-property quantification of corrosion pitting under immersion and salt-spray environments on an extruded AZ61 magnesium alloy [J]. Corros. Sci., 2011, 53: 1348 doi: 10.1016/j.corsci.2010.12.025
[15]	Song G L, Atrens A. Corrosion mechanisms of magnesium alloys [J]. Adv. Eng. Mater., 1999, 1: 11 doi: 10.1002/(SICI)1527-2648(199909)1:1<11::AID-ADEM11>3.0.CO;2-N
[16]	Gobara M, Shamekh M, Akid R. Improving the corrosion resistance of AZ91D magnesium alloy through reinforcement with titanium carbides and borides [J]. J. Magne. Alloy., 2015, 3: 112
[17]	Williams G, Grace R. Chloride-induced filiform corrosion of organic-coated magnesium [J]. Electrochim. Acta, 2011, 56: 1894 doi: 10.1016/j.electacta.2010.09.005
[18]	Li T, Zhang H, He Y, et al. Comparison of corrosion behavior of Mg-1.5Zn-0.6Zr and AZ91D alloys in a NaCl solution [J]. Mater. Corros., 2015, 66: 7
[19]	Esmailzadeh S, Aliofkhazraei M, Sarlak H. Interpretation of cyclic potentiodynamic polarization test results for study of corrosion behavior of metals: A review [J]. Prot. Met. Phys. Chem. Surf., 2018, 54: 976 doi: 10.1134/S207020511805026X
[20]	Liu Y X, Liu Z, Xu A Y, et al. Understanding pitting corrosion behavior of AZ91 alloy and its MAO coating in 3.5%NaCl solution by cyclic potentiodynamic polarization [J]. J. Magnes. Alloy., 2022, 10: 1368 doi: 10.1016/j.jma.2020.12.005
[21]	He J G, Wen J B, Sun L M, et al. Characterization of pitting behavior of pure Al and Al-7Zn-0.1Sn-0.015Ga alloy by cyclic polarization technique [J]. Corros. Sci. Prot. Technol., 2015, 27: 449
	(贺俊光, 文九巴, 孙乐民等. 用循环极化曲线研究Al和铝合金的点蚀行为 [J]. 腐蚀科学与防护技术, 2015, 27: 449)
[22]	Sherif E S M. Corrosion behavior of magnesium in naturally aerated stagnant seawater and 3.5% sodium chloride solutions [J]. Int. J. Electrochem. Sci., 2012, 7: 4235
[23]	Song G L, Atrens A, Stjohn D, et al. The electrochemical corrosion of pure magnesium in 1 N NaCl [J]. Corros. Sci., 1997, 39: 855 doi: 10.1016/S0010-938X(96)00172-2
[24]	Brunner J G, May J, Höppel H W, et al. Localized corrosion of ultrafine-grained Al-Mg model alloys [J]. Electrochim. Acta, 2010, 55: 1966 doi: 10.1016/j.electacta.2009.11.016
[25]	Hou R Q, Ye C Q, Chen C D, et al. Localized corrosion of binary Mg-Ca alloy in 0.9 wt% sodium chloride solution [J]. Acta Metall. Sin. (Engl. Lett.), 2016, 29: 46 doi: 10.1007/s40195-015-0361-2
[26]	Ascencio M, Pekguleryuz M, Omanovic S. An investigation of the corrosion mechanisms of WE43 Mg alloy in a modified simulated body fluid solution: The influence of immersion time [J]. Corros. Sci., 2014, 87: 489 doi: 10.1016/j.corsci.2014.07.015
[27]	Taheri M, Phillips R C, Kish J R, et al. Analysis of the surface film formed on Mg by exposure to water using a FIB cross-section and STEM-EDS [J]. Corros. Sci., 2012, 59: 222 doi: 10.1016/j.corsci.2012.03.001
[28]	Vermilyea D A, Kirk C F. Studies of inhibition of magnesium corrosion [J]. J. Electrochem. Soc., 1969, 116: 1487 doi: 10.1149/1.2411579
[29]	Jamesh M I, Wu G S, Zhao Y, et al. Electrochemical corrosion behavior of biodegradable Mg-Y-RE and Mg-Zn-Zr alloys in Ringer's solution and simulated body fluid [J]. Corros. Sci., 2015, 91: 160 doi: 10.1016/j.corsci.2014.11.015
[30]	Wang L, Shinohara T, Zhang B P. Influence of chloride, sulfate and bicarbonate anions on the corrosion behavior of AZ31 magnesium alloy [J]. J. Alloy. Compd., 2010, 496: 500 doi: 10.1016/j.jallcom.2010.02.088
[31]	Cao C N. Principles of Electrochemistry of Corrosion [M]. 3rd ed. Beijing: Chemical Industry Press, 2008: 36
	(曹楚南. 腐蚀电化学原理 [M]. 第3版. 北京: 化学工业出版社, 2008: 36)
[32]	Südholz A D, Kirkland N T, Buchheit R G, et al. Electrochemical properties of intermetallic phases and common impurity elements in magnesium alloys [J]. Electrochem. Solid-State Lett., 2011, 14: C5 doi: 10.1149/1.3523229
[33]	Williams G, Birbilis N, McMurray H N. The source of hydrogen evolved from a magnesium anode [J]. Electrochem. Commun., 2013, 36: 1 doi: 10.1016/j.elecom.2013.08.023
[34]	Salleh S H, Thomas S, Yuwono J A, et al. Enhanced hydrogen evolution on Mg(OH)₂ covered Mg surfaces [J]. Electrochim. Acta, 2015, 161: 144 doi: 10.1016/j.electacta.2015.02.079
[35]	Birbilis N, King A D, Thomas S, et al. Evidence for enhanced catalytic activity of magnesium arising from anodic dissolution [J]. Electrochim. Acta, 2014, 132: 277 doi: 10.1016/j.electacta.2014.03.133

[1]	LV Xin, DENG Kunkun, WANG Cuiju, NIE Kaibo, SHI Quanxin, LIANG Wei. Effect of SiC_p Size on Microstructure and Corrosion Properties of Cast AZ91 Mg-alloys[J]. 中国腐蚀与防护学报, 2023, 43(1): 135-142.
[2]	Lin Changjian(State Key Lab jor Physical Chemistry of Solid Surface;Xiamen University)Tinh Nguyen(National Institute of Standards and Technology USA). AN EVXLUATION OF CORROSION RESISTANCE OF ORCANIC COAT/STEEL SYSTEM BY MCPDP TECHNIQUE[J]. 中国腐蚀与防护学报, 1994, 14(4): 315-320.

No Suggested Reading articles found!

Viewed

Full text

Abstract

Cited

Shared

Discussed