Self-healing Micro-arc Oxidation/Ternary MgLiAl-LDHs Composite Coating on Magnesium Alloys

JIAO Zuojun; WU Liang; YU Fubing; TIAN Zhenzhen; ZHOU Yan; YAO Wenhui; YUAN Yuan; XIE Zhihui; WU Guozhi

doi:10.16490/j.cnki.issn.1001-3660.2025.15.003

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Surface Technology ›› 2025, Vol. 54 ›› Issue (15) : 33-46. DOI: 10.16490/j.cnki.issn.1001-3660.2025.15.003

Technology and Application

Self-healing Micro-arc Oxidation/Ternary MgLiAl-LDHs Composite Coating on Magnesium Alloys

JIAO Zuojun^1a, WU Liang^1a,1b,*, YU Fubing^1a, TIAN Zhenzhen^1a, ZHOU Yan^1a, YAO Wenhui^1a,1b, YUAN Yuan^1a,1b, XIE Zhihui², WU Guozhi³

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Abstract

Magnesium lithium (Mg-Li) alloy is the lightest structural metal, but the alloying of Li elements improves the chemical activity, which seriously limits its application. In order to improve the corrosion protection ability of Mg-Li alloy, this study constructs a layered double hydroxide (LDHs) composite layer based on a micro-arc oxidation (MAO) coating through the one-step hydrothermal method on Mg-Li alloy, and introduces organic corrosion inhibitor molecules salicylic acid (SA) and 2-hydroxy-1,4-naphthoquinone (HNQ) through a low-temperature water bath, thereby creating a corrosion resistant and intelligent self-healing coating. With Mg-8Li alloy as the substrate, an MAO coating is prepared in an aluminate electrolyte. NO₃^- ions are introduced into the hydrothermal solution to grow MgLiAl-LDHs ternary LDHs coating in situ. Self-healing coatings (MgLiAl-LDHs-SA and MgLiAl-LDHs-HNQ) are prepared by introducing SA and HNQ through a low-temperature (50 ℃) water bath, respectively. The structure and composition of the coatings are characterized by SEM, EDS, XPS, FT-IR, and XRD. The corrosion resistance and self-healing performances of the samples are evaluated through electrochemical experiments, scratch tests, and scanning vibrating electrode technique (SVET) measurements. The results exhibit that a composite coating is successfully prepared, exhibiting LDHs structures with (003) and (006) X-ray diffraction peaks. After the introduction of corrosion inhibitors, the characteristic peaks of LDHs shift to smaller angles, indicating the successful incorporation of inhibitor molecules into the LDHs coating surface. The MAO coating displays a typical crater-like morphology, while the LDHs nanosheets effectively cover the defects of the MAO coating. The ternary MgLiAl-LDHs structure is more compact than conventional MgAl-LDHs, and the dope of corrosion inhibitors further increases the thickness and density of the composite coating. Electrochemical experiments exhibit that the corrosion current density (J_corr) of the MgLiAl-LDHs-HNQ decreases to 4.74×10^-7 A/cm², with a charge transfer resistance (R_ct) of 5.7×10⁵ Ω·cm², and a significant reduction in hydrogen evolution rate. Scratch tests reveal that the LDHs coating inhibits the expansion of scratches on the MAO coating, and the corrosion inhibitors achieve self-healing effects by complexing with metal ions and chelating to the exposed metal substrate. SVET experiments demonstrate that the self-corrosion potential at the scratched sites of the composite coating significantly decreases after immersion, further confirming the self-healing ability of the coating. According to the experimental data, it is inferred that the corrosion resistance and self-healing performance of the coating are rooted in the following aspects: The introduction of Li⁺ replaces part of Mg²⁺, and grows perpendicular to the substrate to form a more compact ternary MgLiAl LDHs coating. The compact structure can be used as the first physical barrier to prevent the invasion of corrosive media. When the LDHs coating is eroded by Cl^- ions, the intercalated NO₃^- exchanges with Cl^- ions to form a high concentration of Cl^- ion on the coating surface, thus inhibiting its contact with the metal substrate. SA and HNQ are loaded into the LDHs coating in the form of intercalation anions. When the coating is corroded and degraded, the inhibitor releases and combines with free metal cations to form stable precipitation to participate in the formation of the corrosion product film, forming a self-healing effect. In conclusion, the prepared MgLiAl-LDHs-HNQ composite coating shows the best corrosion resistance and self-healing performance. This study provides valuable insights for the study and application of corrosion-resistant and self-healing functional coatings on Mg-Li alloy.

Key words

magnesium-lithium alloy / micro-arc oxidation / layered double hydroxide / corrosion inhibitor / self-healing

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JIAO Zuojun, WU Liang, YU Fubing, TIAN Zhenzhen, ZHOU Yan, YAO Wenhui, YUAN Yuan, XIE Zhihui, WU Guozhi. Self-healing Micro-arc Oxidation/Ternary MgLiAl-LDHs Composite Coating on Magnesium Alloys[J]. Surface Technology. 2025, 54(15): 33-46 https://doi.org/10.16490/j.cnki.issn.1001-3660.2025.15.003

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Funding

National Natural Science Foundation of China (52171101); The Fundamental Research Funds for the Central Universities (2024IAIS-QN009); National Key R&D Program of China (2021YFB3701100)