To enhance the corrosion resistance, adhesion strength, and electrical conductivity of bipolar plates for proton exchange membrane fuel cells (PEMFCs), a duplex surface treatment comprising plasma nitriding (PN) followed by arc ion plating of a TiN coating was applied to 316L stainless steel. The duplex coating exhibited a bilayer structure with a TiN top layer (~1.3 μm) and a nitrided diffusion layer (~9.2 μm). Compared with a single TiN coating, it showed superior corrosion resistance in both cathode and anode environments, with corrosion current densities of 0.069 and 0.422 μA·cm−2, respectively, and maintained stable performance over 10,000 s of potentiostatic polarization. Its interfacial contact resistance at 140 N·cm−2 was 7.84 mΩ·cm2, below the Department of Energy (DOE) 2025 target of 10 mΩ·cm2. The water contact angle also increased, benefiting water management. The nitrided interlayer substantially enhanced the adhesion strength of the TiN coating. These findings confirm that the sequential combination of plasma nitriding and TiN coating is an effective strategy for improving the corrosion resistance, electrical conductivity, and adhesion of stainless steel bipolar plates for PEMFC applications.
The present study aims to investigate the cumulative effects of multi-pulse femtosecond laser etching at the graphene/aluminium interface. In addition, the study seeks to achieve accurate prediction of the ablation threshold and process optimisation at this interface. In this study, a 1.5 μm graphene coating was first deposited onto the surface of a pure aluminium substrate. In the ensuing experiment, the graphene/aluminum interface was subjected to femtosecond laser etching, with the laser parameters varying in both frequency and energy. The present study investigated the ablation process of the graphene/aluminum interface under the action of repeated laser pulses at different frequencies. A model of the cumulative effect of femtosecond lasers at the graphene/aluminum interface was established, and the influence of the cumulative effect on the ablation threshold of the graphene/aluminum interface was analysed. The results indicated that with increasing laser fluence and frequency, the dimensions of the ablation grooves increased significantly and the edge sharpness improved. The square of the ablation diameter showed a linear correlation with the logarithm of the laser fluence. The ablation threshold of graphene decreased gradually with an increase in the effective number of pulses, with a pronounced reduction when the effective pulse number was below 80, and a gentler decline when it exceeded 80. A fitting analysis based on the cumulative model indicates that the cumulative effect coefficient, designated as δ, which was intended to illustrate how the graphene damage threshold changes with the number of pulses, was as low as 0.16. This finding suggested that there was a significant cumulative effect. Through this investigation of the femtosecond laser cumulative effect, an accurate description of the multi-pulse ablation threshold for graphene/aluminum was achieved, providing a theoretical basis and process reference for high-precision femtosecond laser processing of graphene.
Global urbanization continues to accelerate, driving rapid growth in demand for new buildings and infrastructure, as well as further exacerbating natural resource consumption, ecological degradation, and greenhouse gas emissions [...]
Owing to their exceptional thermal insulation and protective capabilities, thermal barrier coatings (TBCs) are widely applied to critical hot-section components of aero-engines. However, under increasingly harsh service environments, internal defects such as delamination tend to form within the coatings, posing a severe threat to engine operational safety and service life. To effectively evaluate delamination defects in TBCs, this study employs the immersion ultrasonic pulse-echo technique to inspect specimens subjected to various thermal cycling treatments. Four specimens, subjected respectively to 21, 32, 43, and 54 thermal cycles at 1200 °C, were tested. Ultrasonic response data were systematically acquired via normal incidence scanning from both the superalloy substrate side and the ceramic top coat side. Combining Fast Fourier Transform (FFT), Continuous Wavelet Transform (CWT) based on the generalized Morse wavelet, Wavelet Packet Energy Entropy (WPEE), and peak-to-peak amplitude variations of the second echo, multi-dimensional features were extracted from ultrasonic signals across the frequency domain, joint time-frequency domain, and energy distribution profiles. Through comparative analysis, ultrasonic waveform and time-frequency characteristics representing defect evolution were obtained. A significant monotonically decreasing trend of WPEE with the aggravation of interfacial delamination was established, characterizing the acoustic energy confinement process induced by interfacial damage. Furthermore, a multilayer finite element (FE) model reasonably reproduced dynamic acoustic wave propagation; numerical results are in agreement with experimental data, validating the feasibility of the proposed detection method. The detection and evaluation framework established in this study provides a reference for safety monitoring and lifespan prediction of aero-engine TBCs.
The 7075-T6 aluminum alloy exhibits excellent specific strength due to the presence of precipitated η′ phase, but its surface mechanical performance under demanding conditions is often limited. In this study, a horizontal cylindrical magnetron sputtering system was used to deposit TiN coatings on the surface of 7075-T6 aluminum alloy to enhance its surface mechanical properties and structural performance. The effects of deposition temperature, substrate bias voltage, and N2/Ar flow ratio on the microstructure, surface morphology, phase composition, hardness, and residual stress of the coatings were systematically investigated. The results showed that at 80 °C, enhanced lateral atomic diffusion promoted the transformation of the coating growth mode from coarse columnar crystals to dense quasi-layered structures. The surface roughness decreased from 0.193 μm at room temperature to 0.077 μm, the (111) preferred orientation significantly increased, the hardness reached 383 HV, and the compressive stress was −2.8 GPa. However, when the temperature was raised to 120 °C, grain coarsening and TiN/7075Al interface thermal mismatch stress dominated, and the hardness decreased by approximately 19.3%. At −80 V bias, the atomic impact effect produced by ion bombardment made the coating densified optimally, with the lowest surface roughness of 0.068 μm, a hardness of 377 HV, and a compressive stress of −3.1 GPa; at −150 V, excessive bombardment led to severe re-sputtering and lattice distortion, resulting in a compressive stress of −6.8 GPa and a hardness of 351 HV. When N2/Ar = 10/25, the reaction sputtering kinetics and chemical thermodynamic conditions reached the optimal balance, achieving the highest diffraction peak signal-to-noise ratio and the narrowest full width at half maximum. These results reveal the temperature-dependent competitive relationship between thermally activated coating densification and thermal mismatch-induced structural degradation, providing insights into the optimization of TiN coating deposition parameters on aluminum alloys.
A rare carved lacquer (tixi) plate recovered from the Southern Song Dynasty Nanhai No. 1 shipwreck was examined to reconstruct its coating stratigraphy, raw materials, and manufacturing sequence. Detached fragments collected before conservation treatment were investigated by cross-sectional optical microscopy, micro-Raman spectroscopy, thermally assisted hydrolysis–methylation pyrolysis–gas chromatography/mass spectrometry (THM-Py-GC/MS), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and wood-anatomical microscopy. The polished cross-section contains nine lacquer layers with a combined thickness of 387.3 μm above a heterogeneous ground, yielding ten visually distinguishable strata. Alternating dark, red, and yellow layers establish the technological basis for the carved polychrome effect. Raman bands identify cinnabar (HgS) in the red layer and orpiment (As2S3) in the yellow layer. THM-Py-GC/MS detected homologous alkenes, alkanes, and alkylbenzenes diagnostic of Chinese lacquer derived from Toxicodendron vernicifluum. Monocarboxylic acids were present, whereas no clear dicarboxylic-acid markers of a drying oil were observed; because the object was waterlogged and degraded, this absence is treated as a lack of positive evidence rather than proof that oil was never used. The ground is enriched in Ca and P and is therefore consistent with a bone-ash-based filler, although phase-specific confirmation remains necessary. Wood anatomy identifies the substrate as Chinese fir (Cunninghamia lanceolata, Cupressaceae). Together, the results document an organic–inorganic multilayer coating system and provide material evidence for Southern Song carved-lacquer technology, while defining conservation risks associated with a waterlogged wooden core and light-sensitive pigments. The marine archaeological context and the support-to-surface, layer-resolved design distinguish this case from most previous studies of Song-dynasty lacquerware. Beyond technological reconstruction, the findings identify conservation priorities for waterlogged wood, the wood–ground–lacquer interface, and light-sensitive pigmented layers, and provide a transferable evidence framework for comparative research on archaeological lacquer.
The electrostatic rotary bell (ESRB) sprayer is widely used in the coating industry due to its ability to achieve uniform film thickness and reasonable paint transfer efficiency. However the efficiency of paint transfer and spraying coverage in ESRB systems remain highly sensitive to process parameters. Therefore, optimizing these parameters is essential to reducing paint consumption, energy use, and environmental impact. In this study, a simulation model of the ESRB spraying process was established using ANSYS/Fluent. The spraying flow field, paint deposition profile, and film thickness distribution were validated through the experiment. Based on a single-factor test and the Box–Behnken response surface method, a multi-parameter optimization framework was designed to investigate the effects of six spraying process parameters, including inner and outer shaping air flow rate, bell rotational speed, applied voltage, target distance, and paint flow rate, on coating pattern width and paint transfer efficiency. Based on the Z-score standardization, a mathematical model of the comprehensive score with six factors was established to evaluate spraying efficiency and paint transfer efficiency and predict optimal spraying process parameters. The results indicate that voltage and spray distance are significant factors affecting the comprehensive score, with the order of influence being voltage > spray distance. The optimal parameters were as follows: bell rotational speed X1, 40 kr/min; inner shaping air flow rate X2, 196 sl/min; outer shaping air flow rate X3, 298 sl/min; paint flow rate X4, 249 cc/min; applied voltage X5, 52 kV; and target distance X6, 154 mm. Validation tests showed deviation between the predicted comprehensive score and the actual value from simulation and experiment were 2.03% and 1.36%, respectively. These results demonstrate that the proposed optimization model has high reliability and can be used to optimize spraying process parameters.
Waterborne polyurethane (WPU) has emerged as one of the most promising environmentally friendly coating materials owing to its low volatile organic compound (VOC) emissions, excellent film-forming ability, good adhesion, and versatility in formulation. However, WPU suffers from several intrinsic limitations including inadequate thermal stability, modest mechanical strength, poor flame retardancy, and a lack of inherent antibacterial activity. To address these deficiencies, phosphorylated microfibrillated cellulose (PMFC), prepared from beech wood sawdust via sequential steam explosion, phosphorylation, and superfine grinding, was employed as a substrate for in situ silver nanoparticle (AgNPs) synthesis and subsequent incorporation into WPU via aqueous blending and solvent casting. PMFC functions through a combined mechanism: the hydroxyl and phosphate groups coordinate Ag+ ions, providing nucleation sites, while the nanofibrillar network provides steric stabilization against post-synthesis aggregation. The influence of AgNPs loading (1–10 wt% relative to PMFC at a fixed 1 wt% PMFC content) on the morphology, antibacterial activity, silver release behavior, thermal stability, flame retardancy, and mechanical properties of the resulting composite films was comprehensively investigated using free-standing composite films as a model system. At the optimal Ag loading of 5 wt%, the composite exhibited strong antibacterial activity against Escherichia coli with silver release below 1.15 ppb after 96 h, while tensile strength and Young’s modulus increased by 80% and 298%, respectively, relative to neat WPU. At high Ag loadings (70–80 wt%), the composites achieved conductive-level surface resistivity (~3 log Ω) through percolation network formation, demonstrating antistatic functionality. This study provides an effective strategy for fabricating WPU composite films with combined antibacterial, mechanical reinforcement, and antistatic capabilities.
Postharvest quality losses limit the storage life of strawberries, highlighting the need for environmentally friendly preservation approaches. In this study, CaO-Based nanoparticles were green-synthesized using hemp (Cannabis sativa L.) leaf extract as a reducing and stabilizing agent, characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX), and applied to Portola and Monterey strawberries at concentrations of 50, 100, 150, and 200 ppm. XRD analysis confirmed CaO as the main crystalline phase, with CaCO3 identified as a secondary crystalline phase, whereas the presence of metallic Ca could not be confirmed unambiguously. The fruit were stored at 1 ± 0.5 °C and approximately 90% relative humidity for 21 days. The effects of CaO-NP treatments varied according to cultivar, concentration, storage period, and the quality parameter evaluated. In Portola, the 100 ppm treatment resulted in the lowest weight loss, while the 50 ppm treatment maintained the highest firmness and total monomeric anthocyanin content at the end of storage. The 200 ppm treatment produced the lowest numerical decay rate, although it was statistically similar to the control and 100 ppm treatments. In Monterey, the 50 ppm treatment maintained the highest firmness and showed the lowest weight loss among the nanoparticle treatments; however, it did not reduce weight loss below the control and resulted in the highest decay rate. The 100, 150, and 200 ppm treatments maintained decay rates comparable to the control. The 150 ppm treatment maintained comparatively high soluble solids content in both cultivars, while the 200 ppm treatment resulted in the highest total phenolic content in Monterey. No sustained improvement in total antioxidant capacity was observed. Overall, no single CaO-NP concentration was consistently effective across all quality attributes or both cultivars, indicating that these coatings require cultivar- and quality-target-specific optimization.
This study addresses the unclear damage mechanisms of TiAlSiN-coated tools during high-speed milling of GH4169 by integrating milling experiments with finite element simulations, and establishes a thermo-mechanical coupled damage prediction model that accounts for the superposition effect of cyclic loads. Cutting experiments show that with increasing cutting speed, the rake face damage evolves from peeling and abrasive wear to comb-shaped thermal cracks, mechanical cracks, and large-area peeling, accompanied by a significant reduction in tool life. Simulations reveal that the superposition of residual thermal compressive stress during the idle-cutting phase with mechanical stress in the subsequent cutting cycle forms alternating loads, which is the fundamental cause of thermo-mechanical fatigue crack initiation. The XFEM-CEM coupled model indicates that at higher cutting speeds, the maximum principal stress increases, promoting easier coating crack initiation and greater interfacial debonding. The thermo-mechanical coupled damage prediction model, improved by incorporating a temperature-modified strength threshold and a thermal acceleration factor, yields predictions consistent with experimental results, providing a theoretical basis for process parameter optimization and tool life prediction.
Ti-35Nb-2Ta-3Zr (TNTZ) β-titanium alloy is attractive for biomedical applications because of its relatively low elastic modulus and composition based on nominally non-cytotoxic alloying elements; however, its surface hardness and intrinsic bioactivity remain limited. In this study, Zn nanoparticles were incorporated into the near-surface region of TNTZ by friction stir processing (FSP), followed by compression plasma flow (CPF) treatment in nitrogen. Cross-sectional scanning electron microscopy and energy-dispersive X-ray spectroscopy, X-ray diffraction, microhardness testing, and inductively coupled plasma mass spectrometry after 60 days of immersion in simulated body fluid were used to characterize the modified layers. CPF treatment produced a distinct surface-modified layer approximately 10–15 μm thick, increased the Zn signal within the upper approximately 11 μm, and generated diffraction peaks assigned to Ti2N. The fitted β-phase lattice parameter decreased with nominal X-ray penetration depth, and tensile residual stresses were calculated for all CPF-treated conditions. Sample 1 exhibited the highest microhardness at the lowest applied load. After 60 days of immersion, the mean Zn concentration was 261.87 ± 0.0031 μg/L for FSP and 102.41 ± 0.0063 μg/L for FSP + CPF, corresponding to an approximately 60.9% lower mean cumulative Zn concentration after CPF treatment. Electrochemical, tribological, and biological testing is still required to establish corrosion, wear, and biological performance.
In this work, a Fe-based amorphous coating (Fe44Cr18Mo7Ni4Cu2B20Si3C2) was fabricated via high-velocity oxygen fuel (HVOF) spraying, and the effect of annealing temperature on its microstructure, phase composition, and corrosion resistance in 3.5 wt.% NaCl solution was investigated. The as-sprayed (AS) coating exhibits an amorphous content of 85.71% and a porosity of 1.37%. Annealing at 540 °C (H540) reduces porosity to 0.98% without significant crystallization, whereas annealing at 640 °C (H640) and 740 °C (H740) triggers extensive crystallization (amorphous content drops to 24.18% and 19.20%), and porosity increases to 1.82% and 2.17%. Electrochemical tests show that corrosion resistance deteriorates progressively with increasing temperature. icorr increases from 3.56 μA/cm2 (AS) to 50.0 μA/cm2 (H740), while Rp decreases from 8472 to 669 Ω·cm2. EIS reveals that the AS coating is dominated by the inner barrier layer (Rb >> Rt), whereas annealing causes a drastic collapse of Rb (from 8.374 × 104 to 5.011 Ω·cm2). This degradation is attributed to crystallization-induced grain boundaries and reduced effective Cr content, which impair passive film integrity and accelerate corrosion.
The dust generated during coal mining poses a significant threat to miners’ health and safety. Surfactants, as effective agents for improving coal wettability, require a deeper exploration of their microscopic action mechanisms. This study systematically investigates the micro-interaction behaviors and wetting regulation mechanisms of four types of surfactants—anionic (SDBS), cationic (CTAB), zwitterionic (BS-12), and nonionic (AEO-9)—with lignite, bituminous coal, and anthracite through molecular simulations and dynamic contact angle experiments. To correlate the wettability differences with the physical and chemical properties of different coal ranks, XRD and SEM observations were employed to analyze the mineral composition and surface microstructure. The results demonstrate that SDBS has the strongest adsorption capacity on coal, with the wettability capacity ranked as follows: SDBS > CTAB > BS-12 > AEO-9. This research reveals the regulation mechanism of surfactants on coal wettability, providing a theoretical basis for optimizing dust prevention technologies and fostering the development of green mining.
With the rapid development of manufacturing, increasingly stringent requirements for material quality and inspection efficiency have promoted the widespread application of deep learning-based nondestructive testing technologies in industrial quality control. In recent years, steel surface defect detection has expanded from conventional inspection scenarios with controlled imaging conditions, such as steel strips, plates, and welds, to more challenging applications involving the inner surfaces of steel pipes, castings, and complex industrial components. This paper reviews recent advances in deep learning-based steel surface defect detection from an industrial application-oriented perspective, with particular emphasis on developments in application scenarios, datasets, methodological frameworks, and research trends. It analyzes representative reviews and their limitations, summarizes publicly available datasets covering conventional flat steel products, pipes, and castings, examines the defect characteristics of different inspection objects, and reviews the development of deep learning and its industrial applications. Furthermore, defect detection and segmentation methods are systematically organized according to practical requirements, including challenging imaging conditions, limited annotated data, small and low-contrast defects, real-time deployment, and cross-domain generalization. Finally, the key challenges, emerging trends, future research directions, and priorities for the next stage of development are discussed.
Stable tension is critical for the coating quality of lithium-ion battery electrodes. As the origin of tension control, the unwinding system’s control accuracy governs the stability of downstream processes and the final yield. To achieve the required precision, we propose a control strategy that combines reinforcement learning and fuzzy PID. We first derived a nonlinear time-varying dynamic model of the unwinding tension system based on the unwinding mechanism. Leveraging this model, we then designed a reinforcement-learning-based fuzzy PID controller. Finally, we validated the performance of the proposed control strategy through simulations and experiments. Simulations and experiments confirm that, under varying coil radius, the reinforcement-learning-based fuzzy PID controller outperforms both the conventional PID and fuzzy PID controllers in robustness, effectively accommodating the effects of time-varying tension system parameters. Moreover, this method substantially improves the dynamic performance of the unwinding system, with pronounced overshoot suppression, and demonstrates superior robustness and disturbance rejection capabilities.
Half-cell photovoltaic modules have been widely applied in distributed photovoltaic systems and building-integrated photovoltaic systems. Linear edge shading caused by buildings, guardrails, and adjacent modules is a key factor affecting their power generation performance. To address this problem, this paper establishes an equivalent prediction model for edge-shading of half-cell modules by combining the series–parallel topology of the module and the conduction behavior of bypass diodes. The genetic algorithm is employed to extract the model parameters, and the bisection method is used to solve the output current and obtain the corresponding I–V and P–V characteristics of the module under shading conditions. Simulation analysis is conducted by considering the edge-shading ratio and module installation orientation as variables, and the output characteristics and variation trends of PV modules under two configurations, namely long-edge shading with horizontal installation and short-edge shading with vertical installation, are investigated and compared. The results show that long-edge shading can cause current mismatch in cell strings and conduction of bypass diodes, leading to step features in the I–V curve, a multi-peak structure in the P–V curve, and rapid power attenuation. Short-edge shading only results in a linear decrease in photogenerated current, with smooth output curves and an approximately linear reduction in power along with the shading ratio, resulting in relatively smooth output characteristics. This study reveals the coupled effects of edge-shading and module installation orientation and provides a reference for evaluating shading-induced performance degradation and selecting suitable installation orientations for half-cell PV modules under the investigated shading conditions.
Passive daytime radiative cooling (PDRC) technology with high solar reflectance and high infrared emissivity has been increasingly applied in green buildings. However, current PDRC designs are either high-cost or require additional multi-step fabrication processes, and both factors hinder their broader industrial application. Here, we present a low-cost, easy-to-process, scalable and uncomplicated porous epoxy-based radiative cooling coating via a simple Pickering high-internal-phase-emulsion (HIPE) approach. The obtained porous epoxy-based coating has micro- and submicropores. These hierarchical porous microstructures enable a synergistic interaction between the filler and the porous microstructure, thus enhancing the radiative cooling performance. As a result, the obtained porous epoxy-base polymer with alumina as fillers (PEP-A) coating presents a high solar reflectance of 95.6% in the wavelength range of 0.3–2.5 μm and a high infrared emissivity of 96.3% in the wavelength range of 8–14 μm, as well as a maximum subambient cooling temperature of 3.4 °C and an average cooling power of 105.6 W·m−2 under solar shortwave radiation of 123.01–134.67 W·m−2. Furthermore, the PEP-A coating can be easily applied via roll-coating, blade-coating, or brush-coating, and self-cures on diverse substrates like aluminum sheets, steel plates, polypropylene sheets, bricks, and wall surfaces without any additional template-extraction process. In particular, the cost of the raw materials for the PEP-A coating is 0.2–1.3% of that of previously reported radiative cooling coatings (e.g., Poly(vinylidenefluoride-co-hexafluoropropylene) and polydimethylsiloxane). The extraction-free nature, easy processability, self-curing ability, and low cost of the PEP-A coating make it very promising for large-scale PDRC production and applications.
This study evaluated and compared four irrigation activation protocols—conventional syringe irrigation (CSI), passive ultrasonic irrigation (PUI), photon-induced photoacoustic streaming (PIPS), and shock wave-enhanced emission photoacoustic streaming (SWEEPS)—with 17% EDTA as a final irrigant, with respect to smear layer (SL) removal and push-out bond strength (PBS) of root canal sealer in the apical third of curved root canals. One hundred and twenty extracted single-rooted human premolars with oval canals and moderate curvature (20–40°, Schneider’s method) were allocated into four groups randomly (n = 30 each). Canals were prepared crown-down under 2.5% NaOCl irrigation, followed by final 17% EDTA irrigation per the assigned protocol: CSI, PUI, PIPS, and SWEEPS. 10 specimens per group underwent SEM evaluation of SL removal using Hülsmann’s criteria; remaining specimens were obturated. In 10 samples, apical sealer adaptation was assessed via SEM. PBS of ten samples were evaluated using a universal testing machine, followed by failure mode assessment. Data were statistically evaluated using two-way mixed ANOVA, followed by Tukey’s post hoc test for PBS and Kruskal–Wallis test with Dunn’s multiple-comparison test with Bonferroni correction for SL scores (p < 0.05). Minimum SL removal was exhibited by the apical third of Group 1 (CSI-EDTA) samples. PIPS-EDTA and SWEEPS-EDTA presented comparable SL elimination outcomes in the cervical and middle thirds (p > 0.05). SL elimination between these two groups was significantly different in the apical third. The cervical section of Group 4 displayed the highest bond integrity. However, the lowest bond strength was exhibited by the apical third of Group 1 (CSI-EDTA). SWEEPS combined with EDTA demonstrated superior smear layer removal throughout curved root canals, including the apical third, and yielded the highest push-out bond strength among all tested irrigation protocols.
To reveal how meniscus dynamics affect wet film uniformity during slot-die coating for perovskite solar cell manufacturing, a 2D numerical model employing the VOF method is established for perovskite precursor fluids. A photoresist is used as a qualitative substitute liquid for auxiliary experimental validation, and dry film thickness is measured to characterize the relative uniformity of wet coating. The results show that the capillary number governs the upstream meniscus shape. Inlet velocity, slot gap, and coating gap influence film thickness by altering the downstream meniscus climbing height. Optimal film thickness uniformity is achieved when the pre-coating liquid volume accounts for about 31% of the total coating volume; this empirical optimal ratio is only valid within the tested inlet flow rate range under the fixed experimental conditions adopted in this work, and further multi-parameter verification under diverse process windows will be carried out in follow-up research.
The cross-sectional microstructure, local chemical composition, and mechanical behavior of anodic oxide layers produced by oxalic acid anodizing of cast A356 aluminum alloy were investigated using digital optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and in situ nanoindentation inside the SEM chamber. The anodized specimens contained a compact oxide-side interfacial region adjacent to the substrate–oxide interface and an outer porous oxide layer. The oxide layers formed at the higher nominal charge density were generally thicker than those formed at the lower charge density. Cross-sectional nanoindentation revealed two characteristic interface-related features: localized, unusually high apparent hardness values on the oxide side of the interface and a gradual hardness increase within the adjacent substrate-side region. The highest apparent values exceeded the expected hardness range of anodic oxide layers on A356 alloy and were therefore interpreted as interface-affected responses rather than intrinsic oxide hardness values. Their repeated occurrence at a well-defined position nevertheless supported their association with the oxide-side interfacial region. The substrate-side hardness increase was characterized by the estimated width of an anodizing-affected substrate zone. EDS line scans showed that the oxide-side interfacial region retained a significant oxygen concentration, whereas the substrate-side hardness increase was not accompanied by a systematic elemental concentration gradient. The results demonstrate that the cross-sectional mechanical response of oxalic-acid-anodized A356 alloy is governed not only by the conventional barrier-layer–porous-layer structure, oxide thickness, and porosity, but also by local chemical composition, microstructural heterogeneity, and substrate/interface-related effects.
