In order to improve the corrosion resistance of magnesium alloys and gain a deeper understanding of the corrosion inhibition mechanism of corrosion inhibitors, this work explores the application of purple polyamide (PPA) as an organic corrosion inhibitor for AZ31B magnesium alloys. Magnesium alloys such as AZ31B are widely utilized in structural and transportation applications due to their low density and excellent mechanical properties. However, their inherently poor corrosion resistance in chloride-rich environments, such as marine and physiological media, remains a major barrier to their broader application. So, the development of effective, environmentally benign corrosion inhibitors is of significant scientific and industrial interest. In this work, the corrosion inhibition behavior of PPA in 3.5% NaCl solution was systematically investigated through a combination of electrochemical testing, including potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), hydrogen evolution measurements, and static weight loss experiments. At 25 ℃, the corrosion inhibition efficiency of PPA was determined to be 74.9% by weight loss measurement, 59.6% by hydrogen evolution, 73.5% by EIS, and 53.9% by potentiodynamic polarization. This discrepancy reflected the different sensitivities and evaluation principles of each technique. With the increase of temperature and immersion time, the inhibition efficiency of PPA improved significantly, indicating enhanced adsorption stability and protective film integrity under elevated conditions, reaching a maximum of 93.9% (as determined by the weight loss method) at 50 ℃ and 72 h. To understand the underlying inhibition mechanism, detailed surface characterizations were carried out. Specifically, a scanning electron microscopy (SEM) was employed to visualize changes in surface morphology before and after PPA treatment, revealing a more compact and uniform film in the presence of the inhibitor. On the contrary, a loose magnesium hydroxide layer was formed on the surface of AZ31B alloy in 3.5% NaCl solution. Energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses further confirmed the presence of a dense protective layer composed of Mg-Al layered double hydroxides (LDHs) intercalated with PPA species. These layered structures were known to offer barrier properties that physically isolated the metallic substrate from the aggressive chloride-containing environment.
Mechanistically, the inhibition effect of PPA was attributed to its ability to form a stable, compact, and adherent interfacial layer. Upon dissolution in 3.5% NaCl solution, PPA molecules ionized and released protons, thereby acidifying the environment. This proton release transformed PPA into negatively charged anionic species. During corrosion, the hydrogen evolution reaction at the cathodic sites of AZ31B alloy surface increased the local pH, which eventually stabilized at approximately pH = 10. This alkaline environment promoted the in-situ formation of Mg-Al LDH on the surface of the alloy. Simultaneously, the PPA anions became intercalated within the interlayer galleries of the LDH structure, effectively becoming an integral part of the protective film. This synergistic interaction between the inhibitor molecules and the LDH host not only reinforced the integrity of the protective LDH layer, but also enhanced its stability against dissolution and mechanical degradation. Consequently, the resulting PPA-intercalated LDH film served as a robust barrier that blocked the diffusion of corrosive species such as Cl- ions to the AZ31B surface, significantly retarding the corrosion process.
Key words
purple polyamide /
AZ31B /
corrosion inhibitor for magnesium alloy /
MgAl-LDH /
inhibition mechanism
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References
[1] WANG Y B, SUN Y Q, LIU X T, et al.Recent Progress in Mg Alloys Investigated via Synchrotron Radiation[J]. Materials Science and Technology, 2022, 38(3): 131-142.
[2] WANG M Q, YANG L H, LIU H, et al.Recent Progress on Atmospheric Corrosion of Field-Exposed Magnesium Alloys[J]. Metals, 2024, 14(9), 1000.
[3] TAN J, RAMAKRISHNA S, TAN J, et al.Applications of Magnesium and Its Alloys: A Review[J]. Applied Sciences, 2021, 11(15), 6861.
[4] XIE L L, JI H T, HUANG C M, et al.Multimodal Characterization of an in-Situ Chemical Conversion Composite-Coating on Mg-Alloys[J]. Electrochimica Acta, 2024, 498: 144652.
[5] SONG G L.“Electroless” Deposition of a Pre-Film of Electrophoresis Coating and Its Corrosion Resistance on a Mg Alloy[J]. Electrochimica Acta, 2010, 55(7): 2258-2268.
[6] HU R G, ZHANG S, BU J F, et al.Recent Progress in Corrosion Protection of Magnesium Alloys by Organic Coatings[J]. Progressin Organic Coatings, 2012, 73(2/3): 129-141.
[7] LAMAKA S V, VAGHEFINAZARI B, MEI D, et al.Comprehensive Screening of Mg Corrosion Inhibitors[J]. Corrosion Science, 2017, 128: 224-240.
[8] 陈扬. 缓蚀剂在镁合金表面的吸附行为原位观察及其缓蚀机制研究[D]. 南昌: 南昌大学, 2023: 41-46.
CHEN Y.In-situ Observation of Adsorption Behavior of Corrosion Inhibitors on Magnesium Alloy Surfaces and Study on itsCorrosion Inhibition Mechanisms[D]. Nanchang: Nanchang University, 2023: 41-46.
[9] 肖涛, 党宁, 侯利锋, 等. 木质素磺酸钠对3.5%NaCl溶液中AZ31镁合金的缓蚀作用[J]. 稀有金属材料与工程, 2016, 45(6): 1600-1604.
XIAO T, DANG N, HOU L F, et al.Corrosion Inhibition Effect of Sodium Lignosulfonate on AZ31 Magnesium Alloy in 3.5% NaCl Solution[J]. Rare Metal Materials and Engineering, 2016, 45(6): 1600-1604.
[10] 李凌杰, 姚志明, 雷惊雷, 等. 苯甲酸钠对AZ31镁合金的缓蚀作用[J]. 材料保护, 2009, 42(11): 24-26.
LI L J, YAO Z M, LEI J L, et al.Corrosion Inhibition Effect of Sodium Benzoate on AZ31 Magnesium Alloy[J]. Materials Protection, 2009, 42(11): 24-26.
[11] 翟亚如, 熊金平, 赵景茂. 3.5%NaCl溶液中硝基巴比妥酸对AZ31B与AZ91D镁合金腐蚀的缓蚀作用及机理研究[J]. 中国腐蚀与防护学报, 2025, 45(4): 916-926.
ZHAI Y R, XIONG J P, ZHAO J M.Study on the Corrosion Inhibition Effect and Mechanism of Nitrobarbituric Acid on AZ31B and AZ91D Magnesium Alloys in 3.5% NaCl Solution[J]. Chinese Journal of Corrosion and Protection, 2025, 45(4): 916-926.
[12] DINDODI N, SHETTY A N.Stearate as aGreen Corrosion Inhibitor of Magnesium Alloy ZE41 in Sulfate Medium[J]. Arabian Journal of Chemistry, 2019, 12(7): 1277-1289.
[13] HELAL N H, BADAWY W A.Environmentally Safe Corrosion Inhibition of Mg-Al-Zn Alloy in Chloride Free Neutral Solutions by Amino Acids[J]. Electrochimica Acta, 2011, 56(19): 6581-6587.
[14] GAO L, ZHANG C, ZHANG M, et al.Phytic Acid Conversion Coating on Mg-Li Alloy[J]. Journal of Alloys and Compounds, 2009, 485(1-2): 789-793.
[15] FRIGNANI A, GRASSI V, ZANOTTO F, et al.Inhibition of AZ31 Mg Alloy Corrosion by Anionic Surfactants[J]. Corrosion Science, 2012, 63: 29-39.
[16] GAO X, MA D, HUANG Q, et al.Pyrazole Ionic Liquid Corrosion Inhibitor for Magnesium Alloy: Synthesis, Performances and Theoretical Explore[J]. Journal of Molecular Liquids, 2022, 353: 118769.
[17] 王海媛, 卫英慧, 杜华云, 等. 绿色缓蚀剂SDDTC对AZ31B镁合金的缓蚀作用及吸附行为[J]. 中国腐蚀与防护学报, 2018, 38(1): 62-67.
WANG H Y, WEI Y H, DU H Y, et al.Corrosion Inhibition and Adsorption Behavior of Green Corrosion Inhibitor SDDTC on AZ31B Mg-Alloy[J]. Journal of Chinese Society for Corrosion and Protection, 2018, 38(1): 62-67.
[18] ZHANG T, LI Y, WANG F H.Roles of β Phase in the Corrosion Process of AZ91D Magnesium Alloy[J]. Corrosion Science, 2006, 48(5): 1249-1264.
[19] 黄居峰, 宋光铃. 镁合金腐蚀测试与分析研究进展[J]. 中国腐蚀与防护学报, 2024, 44(3): 519-528.
HUANG J F, SONG G L.Research Progress on Corrosion Testing and Analysis of Mg-Alloys[J]. Journal of Chinese Society for Corrosion and Protection, 2024, 44(3): 519-528.
[20] 郭金玲, 沈岳年. 用Scherrer公式计算晶粒度应注意的几个问题[J]. 内蒙古师范大学学报(自然科学汉文版), 2009, 38(3): 357-358.
GUO J L, SHEN Y N.Several Problems Needing Attention in Calculating Grain Size with Scherrer Formula[J]. Journal of Inner Mongolia Normal University (Natural Science Edition), 2009, 38(3): 357-358.
[21] CAO F Y, SHI Z M, HOFSTETTER J, et al.Corrosion of Ultra-High-Purity Mg in 3.5% NaCl Solution Saturated with Mg(OH)2[J]. Corrosion Science, 2013, 75: 78-99.
[22] XU S, DONG J, KE W.Effect of Magnesium Hydride on the Corrosion Behavior of Pure Magnesium in 0.1 M NaCl Solution[J]. International Journal of Corrosion, 2010, 2010: 1-5.
[23] SEYEUX A, LIU M, SCHMUTZ P, et al.ToF-SIMS Depth Profile of the Surface Film on Pure Magnesium Formed by Immersion in Pure Water and the Identification of Magnesium Hydride[J]. Corrosion Science, 2009, 51(9): 1883-1886.
[24] XU D, ZHUO Z, XIE Z H, et al.Preparing Corrosion- Resistant Layered Double Hydroxide Coating on Magnesium Alloy under Mild Condition[J]. Corrosion Science, 2024, 236: 112229.
[25] HUANG M, LU G, PU J, et al.Superhydrophobic and Smart MgAl-LDH Anti-Corrosion Coating on AZ31 Mg Surface[J]. Journal of Industrial and Engineering Chemistry, 2021, 103: 154-164.
[26] PILLADO B, MINGO B, DEL OLMO R, et al.LDH Conversion Films for Active Protection of AZ31 Mg alloy[J]. Journal of Magnesium and Alloys, 2023, 11(1): 201-216.
[27] ZHU Y X, SONG G L, WU P P, et al.A Protective Superhydrophobic Mg-Zn-Al LDH Film on Surface- Alloyed Magnesium[J]. Journal of Alloys and Compounds, 2021, 855: 157550.
[28] ZHANG X, YIN Z, BUHE B, et al.Effect of Temperature on Corrosion Resistance of Layered Double Hydroxides Conversion Coatings on Magnesium Alloys Based on a Closed-Cycle System[J]. Metals, 2021, 11(10): 1658.
Funding
The National Natural Science Foundation of China (52371046)
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