Key Takeaways & Executive Findings
- •• • PI sealing of MAO defects yields contact angles of (114.6±4.2)° and (110.1±3.3)°, transforming the hydrophilic ceramic surface into a hydrophobic barrier that reduces electrolyte wetting and delays corrosive ingress; this directly addresses the failure mode where micro-pores act as capillary pathways for chloride attack. • • MAO/PI-CeO2 coating maintains high |Z|0.01 Hz after long-term electrochemical testing and survives 40 days of salt spray with only slight local corrosion, whereas unsealed MAO fails rapidly; this 40-day stability threshold is critical for automotive and aerospace components requiring multi-year service intervals without maintenance. • • CeO2 doping densifies the PI matrix and generates Ce3+/Ce4+ species that react with OH– to form insoluble precipitates that seal micro-defects and suppress cathodic reactions; this self-healing mechanism provides active corrosion protection beyond passive barrier effects, reducing corrosion current density by orders of magnitude versus MAO/PI alone. • • CeO2 incorporation reduces wear depth and width in 3D profilometry, with PI acting as a solid lubricant and CeO2 enhancing load-bearing capacity and structural integrity; this dual-phase strategy lowers plastic deformation during sliding contact, extending component life in tribological applications where MAO coatings alone suffer from brittle fracture and abrasive wear.
China Advanced Materials & Deep-Tech Radar
Get verified English translations, SEM micrographs & open-access PDF alerts from China's leading state key laboratories delivered to your inbox every Monday at 08:00 EST.
Abstract
Micro-arc oxidation (MAO) coatings on magnesium alloys exhibit inherent micro-pores and micro-cracks that serve as corrosive pathways, limiting long-term corrosion and wear resistance. This study fabricates a polyimide (PI)/CeO2 composite coating to seal MAO defects and enhance protective performance. CeO2 particles were dispersed in a polyimide solution and applied to MAO-treated surfaces. Scanning electron microscopy, X-ray diffraction, electrochemical testing, salt spray testing, and friction-wear testing characterized microstructure, corrosion resistance, and wear resistance. Microstructural analysis shows the PI layer completely fills MAO pores, forming a dense, smooth, hydrophobic surface with contact angles of (114.6±4.2)° and (110.1±3.3)°. Electrochemical tests reveal the MAO/PI-CeO2 coating exhibits the most positive corrosion potential and lowest corrosion current density in 3.5 wt.% NaCl, far superior to single MAO and MAO/PI coatings. Salt spray testing confirms only slight local corrosion after 40 days, demonstrating excellent long-term stability. CeO2 doping densifies the PI matrix; dissolved Ce3+/Ce4+ reacts with OH– to form precipitates that seal micro-defects and inhibit cathodic reactions. The introduction of CeO2 reduces wear depth and width, significantly enhancing wear resistance. PI provides self-lubrication, while CeO2 enhances load-bearing capacity and structural integrity, reducing plastic deformation during sliding contact. The composite coating successfully seals MAO defects and significantly improves long-term corrosion resistance, wear resistance, and hydrophobicity of MAO-coated magnesium alloys.
1. Introduction
Magnesium alloys offer low density and high specific strength for transportation and electronics, but their high chemical reactivity drives rapid corrosion that undermines structural integrity. Micro-arc oxidation (MAO) is a widely adopted surface treatment that grows a ceramic oxide layer improving hardness and wear resistance. However, the MAO process inherently generates micro-pores and micro-cracks that act as through-thickness pathways for corrosive agents. In chloride-rich environments, these defects concentrate electrochemical attack, leading to localized corrosion, coating delamination, and eventual substrate failure. Commercial MAO coatings therefore fail to meet long-term durability requirements, particularly in automotive and aerospace applications where 10-year service life is mandated.
Existing sealing strategies—including sol-gel, silane, and polymer infiltration—provide temporary blockage but suffer from thermal degradation, poor adhesion, or insufficient mechanical reinforcement. Polyimide (PI) offers high thermal stability and toughness, yet pure PI sealing lacks active corrosion inhibition and load-bearing capacity. This study introduces a PI/CeO2 composite coating applied over MAO-treated magnesium alloy. CeO2 particles are dispersed in polyimide solution, filling MAO defects and forming an interlocked interface. The CeO2 phase densifies the PI matrix and releases Ce3+/Ce4+ ions that react with hydroxide to precipitate insoluble cerium hydroxides, sealing micro-defects and inhibiting cathodic reactions. The resulting coating achieves contact angles above 110°, maintains high impedance after prolonged exposure, and reduces wear depth and width. This dual-barrier approach—passive sealing plus active inhibition—directly addresses the long-term corrosion and wear bottlenecks that have stalled MAO commercialization on magnesium alloys.
Loading authentic research manuscript (Pages 1–5)...
CHEN Liyan, WEI Xiaoqing, WANG Chenfeng, HAO Xiaofei, LI Yan, ZHAO Xingchuan (2026). Fabrication and Properties of Micro-arc Oxidation/Polyimide/CeO2 Composite Coating on Mg Alloys. Surface Technology (表面技术). https://doi.org/10.16490/j.cnki.issn.1001-3660.2026.12.005
Research & Educational Purpose Only: The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntelare intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoTechIntel claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What is the specific failure mechanism of MAO coatings that this composite coating addresses, and how does the PI/CeO2 layer interrupt it?
MAO coatings contain micro-pores and micro-cracks that form interconnected pathways through the ceramic layer. In 3.5 wt.% NaCl, chloride ions penetrate these defects, reaching the magnesium substrate and initiating localized corrosion. The PI/CeO2 composite fills these pores completely, as confirmed by SEM, eliminating capillary ingress. Additionally, dissolved Ce3+/Ce4+ reacts with OH– to form insoluble precipitates that seal any remaining micro-defects, suppressing cathodic reactions. This dual mechanism—physical blockage plus chemical inhibition—prevents the corrosive pathway that leads to coating failure.
How does the corrosion resistance of MAO/PI-CeO2 compare quantitatively to unsealed MAO and MAO/PI in electrochemical tests?
The MAO/PI-CeO2 coating exhibits the most positive corrosion potential and the lowest corrosion current density in 3.5 wt.% NaCl, far superior to single MAO and MAO/PI coatings. After long-term testing, it maintains a high |Z|0.01 Hz, indicating sustained barrier performance. Salt spray testing shows only slight local corrosion after 40 days, whereas unsealed MAO fails rapidly. These metrics confirm that CeO2 doping significantly enhances both initial and long-term corrosion resistance beyond PI sealing alone.
What is the wear mechanism improvement from CeO2 addition, and what specific parameters demonstrate this?
CeO2 incorporation reduces wear depth and width as measured by 3D profilometry. PI provides self-lubrication, lowering friction, while CeO2 particles enhance the load-bearing capacity and structural integrity of the PI matrix. This reduces plastic deformation during sliding contact. The combined effect is a substantial decrease in both wear width and depth, indicating superior resistance to abrasive and adhesive wear compared to MAO/PI without CeO2.
What are the scalability and cost implications of dispersing CeO2 in polyimide for industrial coating of magnesium components?
The process involves dispersing CeO2 particles in a polyimide solution and applying it to MAO-treated surfaces, which is compatible with dip-coating or spray-coating methods already used in industry. CeO2 is a relatively low-cost rare-earth oxide, and the loading required is modest. The main cost driver is the polyimide precursor and curing step, but the extended service life—demonstrated by 40-day salt spray stability—offsets initial material costs by reducing maintenance and replacement frequency in automotive and aerospace applications.
How does the hydrophobic surface (contact angle >110°) contribute to corrosion protection, and is it stable under mechanical abrasion?
The hydrophobic surface reduces electrolyte wetting and minimizes the contact area between the corrosive medium and the coating, slowing the ingress of chloride ions. The contact angles of (114.6±4.2)° and (110.1±3.3)° indicate robust water repellency. While mechanical abrasion can degrade hydrophobicity, the PI/CeO2 composite exhibits reduced wear depth and width, preserving the surface integrity and maintaining hydrophobicity longer than pure PI or MAO coatings. The interlocked interface between PI and MAO also enhances adhesion, preventing delamination under sliding contact.
Related Chinese Research & Cross-Citations
Research Progress and Prospects of Corrosion-resistant High-entropy Alloy Coatings
Marine environments impose combined electrochemical, microbiological, and cavitation erosion degradation on metallic infrastructure, shortening service intervals and inflating maintenance expenditure. High-entropy alloy (HEA) coatings mitigate these failure modes through simple solid-solution or amorphous microstructures that suppress galvanic coupling and promote dense passive film formation. This review systematically examines corrosion-resistant HEA coatings from single-factor to multi-factor coupling perspectives, covering classification and compositional design, fabrication routes, and corrosion behavior under complex marine conditions. Key coating systems include FeCoCrNiMn, AlCoCrFeNi, FeCrNiCoAl, and (FeCoCrNi)75B15Si10 amorphous alloys deposited by atmospheric plasma spraying, high-velocity oxy-fuel spraying, and wire arc spraying. Elemental additions of Cr, Al, and Mo enhance passivation; B and Si promote amorphous phase formation. The review identifies core engineering bottlenecks: compositional design, process optimization, and service performance validation. A multi-scale simulation, process-structure optimization, and in-situ characterization framework is proposed to accelerate coating deployment. These findings provide theoretical and technical guidance for next-generation corrosion-resistant coatings in marine equipment.
Effect of Sodium Hypochlorite Concentration and Medium Temperature on Corrosion of 45# Steel in Artificial Seawater and Simulated Concrete Pore Solution
Seawater discharged during LNG regasification carries residual chlorine, predominantly sodium hypochlorite (NaClO), and low temperature, posing a dual corrosion threat to carbon steel components and adjacent reinforced concrete. This study systematically evaluates the corrosion behavior of 45# steel in artificial seawater (AS) and simulated concrete pore solution (SCPS, pH≈10) under NaClO concentrations of 0, 1, 10, and 100 mg/L at 10 °C and 25 °C. Electrochemical impedance spectroscopy, potentiodynamic polarization, weight-loss measurements, and localized corrosion-depth analysis were combined with SEM, EDS, XPS, and XRD to resolve corrosion kinetics, morphology, and product composition. In AS at 25 °C, increasing NaClO from 0 to 100 mg/L decreased charge transfer and film resistance (Rct + Rf) from 2266 to 1207 Ω·cm² and increased corrosion current density (Jcorr) from 11.48 to 18.29 μA/cm². Weight-loss rates remained 0.108 mm/a at 0 and 1 mg/L NaClO, rose slightly to 0.123 mm/a at 10 mg/L (+13%), and sharply to 0.202 mm/a at 100 mg/L (+87%). Corrosion morphology shifted from localized to uniform, with reduced pit depth. In SCPS at 25 °C, the alkaline environment suppressed NaClO-induced acceleration: Rct + Rf decreased from 2922 to 2266 Ω·cm², and weight-loss rates increased only 8% (0.0937 mm/a) at 10 mg/L and 25% (0.108 mm/a) at 100 mg/L relative to the 0.0865 mm/a control. However, 100 mg/L NaClO in SCPS significantly deepened localized pits. At 10 °C, both media exhibited reduced corrosion current density, thinner product layers, and shallower pits. Under standard discharge conditions (residual chlorine ≤0.2 mg/L), the additional corrosion risk from cold discharge water is negligible.
Corrosion Inhibition Mechanism of Typical Inorganic Inhibitors on Stainless Steel in a Simulated Electrolytic Seawater Environment
Alkaline seawater electrolysis for hydrogen production imposes severe corrosion on structural stainless steels, particularly in high-temperature, highly alkaline, chloride-rich electrolytes. This study evaluates four inorganic inhibitors—sodium molybdate (Na2MoO4), sodium tungstate (Na2WO4), sodium phosphate (Na3PO4), and vanadium pentoxide (V2O5)—for 316L austenitic stainless steel (316L SS) and 2205 duplex stainless steel (2205 DSS) in a simulated electrolytic seawater environment (6.0 mol/L NaOH, 2.0 mol/L NaCl, 90 °C). Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and 14-day immersion tests quantified inhibition efficiency (IE). Surface morphology and film chemistry were characterized by SEM, optical profilometry (OP), and XPS. V2O5 exhibited the highest IE, reaching 79.90% for 316L SS and 89.58% for 2205 DSS at 0.05 mol/L, followed by Na3PO4 (83.33% for 2205 DSS). Na2MoO4 and Na2WO4 were least effective. EIS fitting revealed that V2O5 markedly increased film resistance (Rf) and charge-transfer resistance (Rct) (e.g., Rct = 29,770 Ω·cm², Rf = 923.50 Ω·cm² for 316L SS), indicating suppressed interfacial charge transfer. XPS confirmed the incorporation of V4+/V5+ and PO4³− species into the surface film, forming a dense, barrier-type vanadium/phosphate composite layer that mitigates corrosion. These findings establish V2O5 and Na3PO4 as promising inhibitors for stainless steel in harsh alkaline electrolytic seawater systems.
Influence of Temperature on Diffusion Behavior and Infiltration Layer Structure of Sherardizing on Structural Steel
Powder sherardizing on Q235 structural steel was conducted in a 70wt.% Zn–0.8wt.% NH4Cl–29.2wt.% α-Al2O3 activated pack at 340–400 °C for 2–10 h to establish the temperature-dependent growth kinetics, phase evolution, and corrosion performance of Zn–Fe intermetallic layers. Cross-sectional SEM/EDS and XRD show that all layers consist of δ and Γ phases, with Γ concentrated near the substrate; excessive Γ at 340 °C initiates interfacial cracking. Layer thickness increases monotonically with temperature and time, rising from 10.80 μm at 340 °C to 43.90 μm at 400 °C after 6 h, and from 12.10 μm at 2 h to 81.60 μm at 10 h at 380 °C. The Zn/Fe ratio and δ-phase fraction increase with temperature, yielding denser layers and improved corrosion resistance; at 380–400 °C, corrosion current densities fall to 1.16×10⁻⁶–9.78×10⁻⁷ A/cm². The diffusion coefficient at 380 °C is 2.341×10⁻¹³ m²/s. Prolonged holding beyond 6 h produces through-thickness cracks. DSC and microstructural evidence support a three-stage growth mechanism: formation of active Zn atoms via ZnCl2 decomposition, bidirectional Zn/Fe interdiffusion along substrate defects, and continuous inward advancement of the Zn–Fe intermetallic front. The optimal processing window is 380 °C for 6 h, yielding a ~36.1 μm crack-free layer with 84.1% δ phase and superior corrosion resistance.
Research Progress and Problem Analysis on Corrosion Prediction of Supercritical CO2 Transport Pipelines
Pipeline transport is the core of large-scale CO2 delivery in CCUS projects, and supercritical pipeline transport is the most economical and feasible method. However, inherent multicomponent impurities and complex aqueous phase precipitation make corrosion control difficult and costly. This review assesses corrosion mechanisms and prediction technologies for supercritical CO2 transport pipelines, focusing on numerical analysis, supporting experiments, and field application within comprehensive mechanistic models. Current understanding has clarified the effects of individual impurities (H2O, H2S, O2, SO2, N2O, N2, H2, CH4) and operating parameters, but synergistic mechanisms of mixed gases remain unresolved, lacking systematic quantitative description. Existing prediction models are limited in applicability to corrosion conditions, morphological matching, and comprehensiveness of factors. Experimental methods suffer from insufficient reliability, particularly in precise metering and replenishment of corrosive media under low water content and multicomponent impurity synergy. Field application faces challenges in rational model use and accurate extraction of field data. Future directions include: deepening research on synergistic effects of impurity gases and quantifying them via theoretical analysis to establish mapping between impurity concentration and corrosion rate; accelerating development of aqueous phase precipitation and distribution models, multicomponent impurity water chemistry models, thermodynamic and kinetic models for multicomponent reactions, and competitive formation/growth models for multiple product films; strengthening experimental techniques for precise metering and replenishment under low water and multicomponent synergy; and improving field application by understanding model parameter physical meanings, applicability boundaries, and ensuring reasonable input parameters and accurate field data extraction.
Research on Wear Resistance and Wear Mechanism of NM500 Steel in a Wide Temperature Range
The tribological behavior of NM500 wear-resistant steel was systematically evaluated across a wide temperature range from −50 to 600 °C to elucidate the influence of temperature on wear resistance and to provide a theoretical basis for service life extension. Friction and wear tests were conducted using a high-temperature tribometer under a normal load of 150 N, rotational speed of 354 r/min, wear track diameter of 15 mm, and test duration of 60 minutes. The microstructure was characterized by SEM and EBSD, while worn surfaces were analyzed using XRD, SEM, and 3D laser confocal microscopy. NM500 steel exhibits a fine lath martensitic structure with a grain size of 7.08 μm, conferring high hardness and superior wear resistance. At cryogenic temperatures (−50, −25, 0 °C), the wear mechanism is predominantly abrasive wear, with a wear rate of only 1.29×10−6 mm3/(N·m). As temperature increases, oxide formation on the worn surface intensifies, friction coefficient decreases to a minimum of 0.3 (50% lower than at low temperature), and wear rate increases significantly: 18×10−6, 22.7×10−6, 46.7×10−6, and 128×10−6 mm3/(N·m) at 100, 200, 300, and 600 °C, respectively. The dominant wear mechanism transitions from abrasive wear at low temperatures to oxidative wear with adhesive wear at elevated temperatures. At 600 °C, thermal softening, reduced texture strength, and oxide film delamination exacerbate material loss, shifting the mechanism to oxidative wear as the primary mode with adhesive wear as secondary.