Preparation and Corrosion Resistance of Micro-arc Oxidation/Microcapsule Epoxy Composite Self-healing Coatings on AZ31B Magnesium Alloy

JI Fengyan; TIAN Mengzhen; LI Tao; GUO Quanzhong; WANG Chuan; WANG Yong; WU Lei; CAO Gongwang; LIU Yuwei; JIA Zhigang

doi:10.16490/j.cnki.issn.1001-3660.2025.15.009

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Surface Technology ›› 2025, Vol. 54 ›› Issue (15) : 96-107. DOI: 10.16490/j.cnki.issn.1001-3660.2025.15.009

Preparation and Corrosion Resistance of Micro-arc Oxidation/Microcapsule Epoxy Composite Self-healing Coatings on AZ31B Magnesium Alloy

JI Fengyan¹, TIAN Mengzhen², LI Tao², GUO Quanzhong^{3, *}, WANG Chuan^{3, *}, WANG Yong³, WU Lei³, CAO Gongwang³, LIU Yuwei³, JIA Zhigang³

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Abstract

In order to inhibit the rapid corrosion of magnesium alloy coatings after damage, micro-arc oxidation composite self-healing coatings are prepared by combining microcapsule self-healing coatings with micro-arc oxide films to study their corrosion properties. Microcapsules encapsulating tung oil is synthesized via in situ polymerization using a melamine-urea- formaldehyde (MUF) prepolymer. By precisely adjusting the reaction process conditions, microcapsules exhibiting a homogeneous particle size distribution and elevated encapsulation efficiency are successfully synthesized. The as-prepared microcapsules are subsequently incorporated into epoxy resin at varying mass fractions (0%, 2%, 5%, 10%, and 15%) to fabricate self-healing coatings. Concurrently, a ceramic layer with superior corrosion resistance is generated on magnesium alloy substrates through micro-arc oxidation (MAO) treatment. The chemical structure and thermal stability of microcapsules are analyzed by infrared spectroscopy and thermogravimetric analyzer. A Scanning Electron Microscope (SEM) is employed to characterize the morphological features of the microcapsules, the surface topography of the coating, and the morphological changes observed post-repair. On this basis, the distribution of microcapsules in the coating system is deeply analyzed, and the actual effect of microcapsules on coating damage repair is evaluated. Simultaneously, electrochemical testing techniques and salt spray testing methodologies are employed to assess the corrosion resistance of the coating. Furthermore, the influence mechanism of the doping amount of microcapsules on the impedance characteristics of the coating is investigated. A comparative analysis between conventional self-healing coatings and MAO-integrated self-healing coatings is performed to elucidate the reinforcement mechanisms introduced by the MAO layer on the overall coating performance. The repair capacity at scratch sites is progressively improved with increasing microcapsule content. At lower microcapsule loadings, the insufficient release of healing agent during crack propagation hinders complete damage mitigation, resulting in reduced repair efficiency. Upon increasing the microcapsule content to 10%, crack-induced release of healing agent becomes substantially enhanced, enabling polymerization-driven formation of a dense protective layer at the crack interface. This layer effectively blocks corrosive media infiltration. Combined with the coating adhesion test, the degree of adhesion between the coating and the substrate is determined. Electrochemical impedance spectroscopy (EIS) reveals that coatings with 10% microcapsule content exhibits a resistivity of 1.12×10⁵ Ω·cm², marking a two-order-of-magnitude improvement compared with the pristine state, which confirms significantly enhanced corrosion protection. Salt spray testing further validates the long-term durability, as no visible corrosion-induced delamination occurs at scratch sites after 1 000 h exposure. In contrast to conventional self-healing coatings, MAO-integrated self-healing coatings exhibit superior corrosion resistance. The MAO layer functions as a foundational barrier, enhancing the coating's mechanical integrity while significantly mitigating corrosive media penetration toward the substrate. SEM cross-sectional analysis reveals well-defined interfacial bonding between the MAO layer and the self-healing topcoat, further augmenting the system's overall performance. Electrochemical impedance spectroscopy (EIS) data show that the composite coatings display notably higher impedance magnitudes compared with standalone self-healing counterparts, with post-healing values increasing further. These findings underscore a synergistic effect between the MAO layer's barrier properties and the self-healing mechanism, cumulatively elevating the coating's protective efficacy. Electrochemical impedance spectroscopy (EIS) measurements reveal that the MAO-integrated self-healing coatings exhibit a significantly enhanced corrosion resistance compared with bare MAO layers, as evidenced by a substantial increase in low-frequency impedance modulus. Post-healing evaluation further demonstrates that the composite coatings achieve higher impedance values and extend the salt spray resistance duration relative to uncoated magnesium alloy substrates. Notably, the MAO-integrated self-healing systems outperform standalone self-healing coatings in corrosion protection efficacy. The MAO layer effectively suppresses filiform corrosion on the magnesium substrate, significantly retarding corrosion propagation kinetics and thereby extending the coating's operational lifespan.

Key words

magnesium alloy / microcapsule / micro-arc oxidation / self-healing / composite coating / corrosion mechanism

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JI Fengyan, TIAN Mengzhen, LI Tao, GUO Quanzhong, WANG Chuan, WANG Yong, WU Lei, CAO Gongwang, LIU Yuwei, JIA Zhigang. Preparation and Corrosion Resistance of Micro-arc Oxidation/Microcapsule Epoxy Composite Self-healing Coatings on AZ31B Magnesium Alloy[J]. Surface Technology. 2025, 54(15): 96-107 https://doi.org/10.16490/j.cnki.issn.1001-3660.2025.15.009

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Funding

Guangzhou Key Research and Development Program (2024B01J0037); Liaoning Province Applied Basic Research Program Project (2022JH2/101300007); Bintech-IMR R@D Program (GYY-JSBU-2022-006); Shenyang Natural Science Foundation Special Project (23503605)