In plastic Injection Molding (IM), dimensional deviations such as shrinkage and warpage are common causes of product malfunction. Product quality is strongly governed by both geometric design and injection process parameters (IPPs). This study presents a systematic approach to address the warpage problem of a thick-walled, tubular-shaped housing cap used to regulate water intake and discharge between filters in a water purifier. The study had two objectives. First, the leakage problem of the component was resolved through a systematic design method in which candidate conceptual designs were evaluated against defined criteria. In evaluation, Analytic Hierarchy Process (AHP) was applied to make the aggregation fully objective. Second, the optimum IPP values yielding the lowest warpage for the selected design concept were identified using the Taguchi experimental design method. The results demonstrate that the leakage problem was eliminated by reducing warpage by 70%. The proposed approach shows promise for corresponding warpage problems in the IM of geometrically complex, thick-walled components; since it was validated on a single POM housing-cap geometry, its generalizability to other materials and part geometries may be approved through further case studies.
Friction Stir Surface Composite (FSSC) processing has emerged as an effective solid-state surface-modification technique for enhancing the mechanical and tribological performance of aluminium alloys and aluminium-based surface composites. It is a derivative of friction stir welding in which a rotating pinned tool severely plastically deforms the surface, refines the grain structure, and disperses hard reinforcement particles into the surface matrix. This focused review presents a critical, methodologically transparent assessment of recent developments in aluminium-based FSSCs reported between 2010 and 2026, with particular emphasis on studies published during 2020–2026. Following a PRISMA-style search protocol, the influence of matrix alloys, reinforcement strategies, process parameters and multi-pass processing on hardness, tensile strength, ductility, and wear behaviour is analysed. The roles of the major strengthening mechanisms — Hall–Petch grain refinement, Orowan strengthening, load transfer, dislocation strengthening and tribofilm formation — are examined together with the conditions under which each dominates and their approximate quantitative contributions. FSP/FSSC is also compared with competing surface-modification and fabrication routes, and its limitations, the hybrid ceramic–lubricant trade-off, and open research gaps are discussed. Hybrid, nano and sustainable reinforcement systems are highlighted as the principal current trends.
In order to reduce the weight of car bodies in the automotive industry, the demand for new materials and innovative methods to achieve this goal is increasing. However, passive vehicle safety remains a central consideration in lightweight vehicle design and must be guaranteed. Therefore, aluminium alloys, particularly those of the 7000 series, have become highly attractive for lightweight manufacturing due to their high strength. This, however, presents a significant challenge for forming and mechanical joining technologies such as semi-tubular self-piercing riveting, which are well established in the automotive industry. To extend the joining suitability of EN AW-7075 in the T6 temper at room temperature, heat treatment can be applied. While heat treatment can improve formability by dissolving precipitates and reducing flow stress, the resulting mechanical properties deteriorate. In this study, different heat treatment strategies for aluminium alloy 7075-T6 are investigated to lay the foundation for crack-free joining using semi-tubular self-piercing riveting (SPR). Therefore, the temperature, quenching rate, and re-aging strategies were varied. Additionally, the short-term heat treatment has been conducted using a diode laser type LDM 3000–100 to identify the correlation between process parameters (e.g., temperature, quenching rate, cold aging, and warm aging) and their impact on the specimen's hardness. It has been shown that the applied short-term heat treatment enables crack-free joining of die-sided EN AW-7075 with punch-sided HCT590X but simultaneously reduces the hardness of EN AW-7075. However, the reduction in hardness after short-term retrogression can be compensated for, to a certain extent, by applying different re-aging strategies.
To improve film–substrate adhesion and the tribological performance of hard coatings on Si 3 N 4 ceramics, Ti/TiN–Cu multilayer films were deposited on Si 3 N 4 substrates by magnetron sputtering. Multilayers were produced with a fixed number of deposition cycles while varying the ratio of Ti to TiN–Cu deposition times. The multilayer architecture substantially enhanced film–substrate bonding. Among the tested time ratios, Among the tested time ratios, sample F2 (Ti:TiN-Cu deposition-time ratio = 1:2) exhibited the highest second critical load (Lc2) of 27.8 N, representing a 58% increase over TiN.This sample also displayed the lowest coefficient of friction (COF) = 0.12, the narrowest wear scar width, 307.4 μm, and a reduced wear rate of 2.64 × 10 −6 mm 3 /(N·m). These results indicate that strengthening film adhesion concurrently lowers both friction and wear.
This study examines the use of untreated chloride-contaminated saline sand in coarse-aggregate-free fine-grained concrete with a ternary binder comprising Portland cement, fly ash (FA), and ground granulated blast-furnace slag (GGBS). Four mixtures were tested: a conventional concrete benchmark (S0) and saline-sand mixtures with 20%, 30%, or 40% GGBS replacement (S20, S30, and S40, respectively). The fine-grained mixtures reached 68.1–71.6 MPa at 180 days. Relative to S0, S30 showed 22.8% lower water absorption and S40 showed a 71.4% lower chloride migration coefficient; these were system-level differences. After 180 days in a 5% sodium sulfate (Na 2 SO 4 ) solution, S20–S40 retained 98.2–107.8% of their standard-cured strengths and exhibited expansion strains of 0.042–0.048%. The value above 100% for S30 was treated as an apparent response. Within S20–S40, increasing GGBS replacement reduced the chloride migration coefficient from 4.77 to 3.75 × 10 −12 m 2 /s and increased corrosion-induced cracking time from 35 to 63 days. This response does not isolate natural corrosion caused solely by saline-sand chlorides. Scenario-based modeling preserved the S20 < S30 < S40 ranking under standardized assumptions. S40 reduced embodied carbon dioxide (CO 2 ) emissions by 34.2%. S30 provided the most balanced profile, whereas S40 led the chloride-related and carbon-efficiency indicators.
The cyclic compressive response of expanded polystyrene foams exhibits stress softening, hysteresis, and progressive cycle-to-cycle degradation of peak stress. This work presents a sequential framework for parameter estimation of an interpretable constitutive model: an Ogden–hyperfoam potential coupled with an Ogden–Roxburgh pseudo-elastic Mullins damage function and a cumulative degradation factor driven by the accumulated stretch path. The eight parameters are estimated with an Unscented Kalman Filter under a phase-gating scheme: the hyperelastic parameters are updated exclusively on the virgin loading branch and the damage parameters exclusively during unloading and reloading. The damage internal variables are purely kinematic, so the identified model generates the full stress sequence from the stretch history alone. Evaluated in this replay mode against uniaxial cyclic compression experiments on two foam densities (24.0 and 8.5 kg/m 3 ), with identical settings and initialization, the identified models attained R 2 = 0.956 and R 2 = 0.990 over ten loading–unloading cycles, reaching 98.5 % and 99.4 % of the accuracy of the best nonlinear least-squares fit of the same model. In a walk-forward test, parameters frozen at the end of each cycle predicted the next, unseen cycle with R 2 ≥ 0.96 from the second cycle onward. The shear moduli estimated by nonlinear least squares scale with density as μ ∝ ρ 1.85 and those estimated sequentially as μ ∝ ρ 1.43 , both within the interval spanned by the classical Gibson–Ashby laws, and the compressibility exponent converges toward zero, consistent with the near-zero Poisson ratio of expanded polystyrene. The framework combines the interpretability of classical pseudo-elasticity with the efficiency of sequential estimation.
The development of metastable β-type Ti alloys containing non-toxic elements and exhibiting low elastic modulus is desirable for biomedical implant applications. The design of Ti–11Nb–9.96Mo and Ti–14.8Nb–8.72Mo alloys in the current study utilised a mixed strategy in terms of electronic parameters (Bo–Md), electron-to-atom ratio (e/a), and molybdenum equivalence (MoE) to position the alloys in the marginal β-region with lower elastic modulus. Both alloys had a β + α″ microstructure, and Rietveld refinement of X-ray diffraction patterns showed a β-dominant structure with a higher α″ fraction in Ti–11Nb–9.96Mo than in Ti–14.8Nb–8.72Mo, demonstrating marginal β-phase stability. Optical microscopy revealed finer grains in Ti–11Nb–9.96Mo and coarser grains in Ti–14.8Nb–8.72Mo, whereas scanning electron microscopy revealed fine intragranular acicular structures, providing morphological evidence of α″ martensite in both alloys. Ti–11Nb–9.96Mo possessed greater yield strength (625.59 ± 8.56 MPa) and ultimate tensile strength (709.6 ± 11.15) MPa, whereas Ti–14.8Nb–8.72Mo was more ductile with a lower elastic modulus (57.72 ± 1.38 GPa). Electrochemical testing in phosphate-buffered saline indicated that both alloys had better corrosion resistance than commercially pure Ti and Ti–6Al–4 V, and Ti–14.8Nb–8.72Mo had the lowest corrosion current density of (8.21 ± 0.07) × 10 −8 A/cm 2 and the noblest corrosion potential (−0.1748 ± 0.0170 V). Overall, designing Ti–Nb–Mo alloys in the marginal β-stability regime enabled reduced elastic modulus, while the alloys exhibited favourable strength and corrosion resistance, supporting their potential for biomedical implant applications.
Magnetically responsive shape-memory polymer composites enable the development of advanced sensing and switching systems that can detect thermal, magnetic, and electrical changes. In this study, multifunctional shape-memory PETG/Fe 3 O 4 nanocomposites containing 0.5–4 wt.% Fe 3 O 4 were fabricated by injection molding. The magnetic, electrical, and thermal shape-memory effects of the developed nanocomposites were systematically characterized by vibrating sample magnetometry (VSM), voltage-current (V–I) measurements, and shape recovery tests under hot-water and hot-air conditions. The saturation magnetization (M s ) increased from 0.041 to 0.158 emu/g with increasing Fe 3 O 4 content, confirming successful magnetic functionalization. The composites also exhibited an incremental increase in electrical response with increasing Fe 3 O 4 loading, while remaining electrically insulating. The shape recovery performance was improved by adding Fe 3 O 4 , and the 4 wt.% composite exhibited the shortest recovery time of 41 s and a recovery ratio of 97% in hot water. Finally, a proof-of-concept thermally triggered shape-memory switch was successfully demonstrated, showing the potential of the developed PETG/Fe 3 O 4 nanocomposites for simple thermal switching and smart sensing applications.
This paper proposes a performance prediction and design method for carbon fiber mortise-tenon structures, integrating finite element simulation, experiment, and machine learning, to address the issues of experiment dependency and low design efficiency of such structures in composite materials. Through parametric finite element analysis, a dataset of 120 samples containing six key geometric parameters—tenon angle (a), tenon height (h), tenon root length (m), tenon neck width (n), specimen width (w), and thickness (T)—was established, and the prediction performance of nine machine learning regression models was systematically compared. The GradientBoostingRegressor model, after multi-stage hyperparameter optimization, achieved the best prediction performance, with a nested cross-validation R 2 of 0.76 ± 0.11 and MAPE of 4.10% ± 0.54%. To verify model reliability, seven groups of T300 carbon fiber mortise-tenon specimens with different geometric configurations were fabricated for uniaxial tensile testing, and full-field strain was obtained using Digital Image Correlation (DIC) technology. The results indicate that the mean absolute percentage error between machine learning predictions and experimental measurements is 9.99%, while the error between finite element simulation and experiments is 4.72%, demonstrating acceptable engineering accuracy. SHAP (SHapley Additive exPlanations) analysis reveals that tenon angle (a) is the dominant feature (mean |SHAP| = 1.296), followed by neck width (n, 0.539) and specimen width (w, 0.406), providing physically interpretable insights into the data-driven predictions. DIC strain contours confirm that high-strain bands concentrate at the tenon-neck/mortise-shoulder transition zone, consistent with the failure mechanisms captured by the model. This study confirms the effectiveness of machine learning in rapid performance prediction and key parameter identification for carbon fiber mortise-tenon structures, providing a new approach for the intelligent design of composite material connections.
Mechanical metamaterials enable control of macroscopic properties, such as stiffness, through the careful design of their internal architecture. The primary objective of this research is to develop a unit cell consisting of a polymeric metamaterial with embedded pins that provides tunable mechanical behavior through a non-contact interaction mechanism. The unit cells are arranged within a housing, allowing the overall stiffness of the structure to be adjusted under external loads. Tunability is governed by the orientation of the embedded pins, which is controlled using an external neodymium magnet, enabling real-time reconfiguration and adjustment of the effective stiffness. The use of a magnetic field to manipulate the internal components without disassembling the structure represents a key advantage of the proposed approach. Numerical results from finite element simulations are compared with experimental results from 3D-printed specimens fabricated with K + polymer to validate the system's performance. The results show that shaft rotation can increase stiffness by more than 30.91% and improve energy absorption by approximately 16%, while the simulations demonstrate good agreement with the experimental observations. The structure is also examined under alternative loading conditions to evaluate its adaptability and to confirm that the tunable stiffness behavior is consistently maintained. Overall, the proposed design exhibits a stable and predictable tunable response, indicating its potential for adaptive mechanical systems.
Piston rings operate under severe sliding conditions, high temperatures, and corrosive environments, making surface degradation a critical factor affecting engine durability. This study presents a comparative evaluation of cathodic-arc physical vapor deposition (CA-PVD) TiAlN and AlCrN coatings on SR34 martensitic stainless-steel piston-ring material using structural, mechanical, tribological, thermal, and tribocorrosion assessments. FTIR, XRD, XPS, and SEM–EDAX analyses indicated that the TiAlN and AlCrN coatings had thicknesses of approximately 3.98 µm and 3.78 µm, respectively, and were continuous. AlCrN exhibited the lowest thermal-mismatch stress (12.47 MPa), a thermal expansion coefficient that closely matched that of SR34, and the smoothest surface (Ra = 0.0783 µm). In contrast, TiAlN exhibited superior mechanical properties, with an average Vickers hardness of 2626.46 HV and a nanoindentation hardness of 28.02 GPa. During lubricated sliding tests under 10 kg and 15 kg loads, TiAlN displayed the lowest COF, weight loss, and specific wear rate. Additionally, the critical failure loads determined through scratch testing were higher for TiAlN. Tribocorrosion tests revealed that TiAlN possessed the noblest corrosion potential, the lowest corrosion current density, the highest charge-transfer resistance, and the most stable friction response. Overall, TiAlN is recommended for applications where wear and tribocorrosion resistance are paramount. In contrast, AlCrN is preferable for applications prioritizing surface smoothness and thermal compatibility in piston-ring design and selection.
This study presents a comprehensive mechanical characterisation of a novel, transparent, amorphous thermoplastic hot-melt adhesive (HMA) film, based on a cyclo olefin polymer, engineered for applications in the automotive, electronics and semi-structural bonding sectors. Quasi-static tensile tests reveal typical thermoplastic behaviour, cold drawing followed by strain hardening, with a Young's modulus of 230 MPa, a tensile strength of 11 MPa and an exceptional elongation at break of 1000%. Thick adherend shear tests (TAST) yield a shear strength of 5 MPa. Fracture behaviour was investigated under Mode I and Mode II loading. Double cantilever beam (DCB) tests on CFRP substrates provide an apparent Mode I fracture energy of 0.43 N/mm. Despite minor substrate rotation and stretching effects, the results indicate a predominantly ductile response of the adhesive layer. End-notched flexure (ENF) tests reveal more complex Mode II behaviour: an initial peak fracture energy of 2.6 N/mm is obtained after a sustained plateau near 0.5 N/mm, interpreted as the onset of permanent plastic damage. This plateau, uncommon in comparable thermoplastic adhesives, suggests a progressive transition from brittle to ductile failure and consistently coincides with adhesive failure at the interface. Dynamic mechanical analysis (DMA) identifies a glass transition temperature of 88°C. Collectively, these results demonstrate that the material offers strong potential for applications requiring thermal resistance and pressure-tolerant bonding, though enhancements in interfacial adhesion are needed to fully optimize performance.
This study investigates the mechanical behavior of a novel tubular auxetic metamaterial combining chiral (rotation-dominated) and reentrant (hinging) mechanisms in a hybrid “Circle-I” design. The sole design variable was the internal extrusion thickness (the difference between external and internal diameters), varied across five configurations from 1 mm to 9 mm in odd increments. Finite element simulations under quasi-static axial compression were used to evaluate load-displacement response, stiffness, energy absorption (EA), specific energy absorption (SEA), and structural negative Poisson's ratio (NPR). Results showed strong thickness dependence: increasing internal thickness significantly enhanced conventional mechanical properties, with peak force reaching 917 N in the 9 mm configuration at smaller displacements, stiffness rising from 18 N/mm to 598 N/mm, and energy absorption increasing from 50 J for the thinnest configuration to 1496 J for the thickest. In contrast, NPR exhibited a non-monotonic trend, becoming more negative (from −1.5 to a peak of −1.8) as thickness increased from 1 mm to 5 mm, before dropping to −1.0 at 9 mm. This non-monotonic behavior highlights an optimal intermediate thickness for maximum auxeticity via efficient chiral-reentrant coupling. Experimental validation confirmed the numerical predictions. The findings demonstrate that internal thickness is an effective single-parameter control for tailoring multifunctional performance in tubular chiral-reentrant metamaterials, with potential applications in impact protection, biomedical devices, and lightweight structures.
The current study investigates the effect of friction stir processing (FSP) and subsequent thermomechanical treatments on the microstructural evolution and corrosion behavior of AA7075 alloy. Four conditions were examined: base AA7075 alloy (BM), friction stir processed AA7075 (FSP), FSP followed by hot rolling (FSP-HR), and FSP followed by shot peening (FSP-SP). Optical microscopy results showed significant grain refinement from 52 ± 8 µm in the base alloy to 5.2 ± 1.1 µm after FSP, with further reductions to 3.1 ± 0.7 µm and 1.6 ± 0.4 µm after hot rolling and shot peening, respectively. X-ray diffraction confirmed the presence of a dominant α-Al matrix along with MgZn 2 , Al 2 CuMg, and Al 13 Fe 4 phases, with no formation of new phases after processing. Electrochemical studies demonstrated considerable enhancement in corrosion resistance after thermomechanical treatments. Tafel polarization results exhibited a decrease in corrosion current density from 4.1 µA/cm 2 for the base alloy to 2.6 µA/cm 2 for FSP, 1.9 µA/cm 2 for FSP-HR, and 1.3 µA/cm 2 for FSP-SP. Correspondingly, the corrosion rate decreased from 1.70 mpy for the base alloy to 0.54 mpy for the shot-peened sample. Electrochemical impedance spectroscopy revealed a significant increase in charge-transfer resistance from 950 Ω·cm 2 in the base alloy to 5200 Ω·cm 2 under FSP-SP conditions, indicating enhanced corrosion resistance. SEM analysis of corroded surfaces confirmed reduced pitting and more compact corrosion products in processed samples. Overall, the combination of FSP with hot rolling and shot peening effectively enhances microstructural refinement and corrosion resistance of AA7075 alloy.
Sandwich composites are widely used in civil, transportation, aerospace, and defense applications due to their lightweight facesheet-core architectures, which minimize blast-induced deformation while maintaining high energy absorption capacity. Conventional metallic and synthetic protective systems provide high strength but often increase structural weight and environmental burden. This systematic literature review synthesizes studies indexed in Scopus and Web of Science published from 2016 to 2025 on blast-resistant sandwich composites, focusing on design strategies, parametric studies, and the potential of natural fibers. The review employed the PRISMA framework for study screening and bibliometric mapping to identify dominant research clusters and design trends. The synthesis shows that blast mitigation is governed not by material strength alone, but by the coupled effects of core collapse, facesheet integrity, and energy dissipation. Core geometry, graded configurations, foam filling, hybrid laminates, and topology-optimized designs can improve back-face deflection control and damage tolerance when matched to the relevant blast regime. Natural fiber-based composites offer potential for sustainable protective systems, particularly in hybrid or secondary facesheet configurations under low-to-moderate impulse conditions. However, their application remains limited by material variability, insufficient high strain rate data, and inconsistent test metrics. Standardized benchmarks, normalized performance indicators, and regime-aware design strategies are needed.
Adhesively bonded joints are increasingly employed in structural applications due to their advantages in weight reduction and efficient load transfer. However, impact fatigue represents one of the most severe and practically relevant loading conditions, as such joints are frequently subjected to repeated impacts in service. Despite its importance, the performance and failure behaviour of adhesive joints under impact fatigue loading remains poorly understood. This review examines the existing body of work on this topic (covering approximately 40 studies published between 1970 and 2026), identified through Web of Science, Scopus, and Google Scholar. While the studies vary in scope, methodology, and testing configurations, they collectively reveal a significant knowledge gap. Compared with standard fatigue, impact fatigue imposes more severe damage conditions, yet, its underlying mechanisms and design implications remain underexplored. By consolidation of the current knowledge, this review highlights critical gaps and aims to stimulate further research and industry attention toward the development of more reliable and durable design strategies for adhesively bonded joints under impact fatigue loading.
Bi-material systems are increasingly vital in aerospace, automotive, microelectronics, and biomedical engineering due to their capacity to integrate complementary material properties, such as high strength-to-weight ratios, customized thermal insulation, and targeted biocompatibility, that monolithic materials cannot achieve. Despite these advantages, the operational integrity of bi-layer architectures is frequently compromised by interfacial failure modes driven by mismatched elastic moduli, coefficients of thermal expansion (CTE), and processing-induced residual stresses. These vulnerabilities often manifest as delamination, fatigue cracking, or environmental degradation, leading to premature structural failure. While recent research has explored isolated material pairs or specific mechanisms, a holistic synthesis that bridges fundamental mechanics across diverse sectors is currently absent. This review addresses this critical gap by providing a comprehensive, multi-disciplinary examination of bi-material interfaces. We categorize prevalent failure origins, from thermo-mechanical stress concentrations to hygrothermal aging, and provide an evaluative framework for mechanical predictive methodologies, including Linear Elastic Fracture Mechanics (LEFM), Cohesive Zone Modeling (CZM), and Phase-Field Modeling (PFM). Furthermore, we assess state-of-the-art mitigation strategies, such as functionally graded interlayers, bio-inspired interlocking geometries, and advanced surface functionalization. By unifying experimental observations with computational frameworks, this work establishes a strategic roadmap for optimizing interfacial performance, offering researchers and practitioners a definitive guide to designing resilient, next-generation bi-material systems for high-performance applications.
Soft robots have emerged as a research hotspot in the field of robotics due to their flexibility and adaptability. Magnetically driven systems have found widespread application owing to their penetrability and controllability. This paper presents an in-depth investigation into both permanent magnet and electromagnetic drive mechanisms, comparing their characteristics and applicable application scenarios. It also provides a detailed overview of magnetic soft materials, which are classified into three types (soft magnetic, hard magnetic, and superparamagnetic) based on their intrinsic properties, along with their practical applications. Emphasis is laid on the design and implementation of four novel materials. Furthermore, a critical evaluation is conducted on the applications of magnetically driven soft robotics in the medical field, accompanied by specific case studies in minimally invasive surgery and targeted drug delivery. To ensure objectivity, the paper also incorporates a dedicated section on bias risk and study characterization, presenting both advantageous performance and unintended outcomes. Finally, it outlines future development directions, providing theoretical references and practical guidance for the research, development, and application of magnetic-driven soft robots.
High-entropy bulk metallic glass (HE-BMG) alloys have recently gained significant attention owing to their unique structural characteristics, outstanding mechanical performance, and potential for advanced engineering applications. In this work, we report the design and development of a Ti 20 Zr 20 Fe 20 Co 20 Ni 20 HE-BMG alloy synthesized via vacuum arc melting. The alloy was systematically characterized to evaluate its phase evolution, microstructure, thermal stability, and mechanical properties. Thermophysical parameters, including ΔH mix (mixing enthalpy), δ (atomic size difference) and ΔS mix (mixing entropy), were employed to predict the formation of a glassy phase. X-ray diffraction confirmed an amorphous structure in the as-cast state, while annealed samples revealed intermetallic phase formation. Differential scanning calorimetry measurements indicated a distinct glass transition temperature (T g ), onset crystallization temperature (T x ), and a wide supercooled liquid region (ΔT), signifying excellent thermal stability and high glass-forming ability. Scanning electron microscopy revealed a dual-phase microstructure consisting of dendritic and interdendritic regions, with energy-dispersive spectroscopy confirming elemental segregation. The potentiodynamic polarization results confirm that the HE-BMG combines excellent corrosion resistance, favorable surface wettability, and structural stability. The Ti 20 Zr 20 Fe 20 Co 20 Ni 20 HE-BMG demonstrates a unique balance of hardness, wear resistance, and tribological stability, surpassing many traditional alloys.
This study investigates the influence of Zn and Sn interlayers on the microstructure and mechanical properties of dissimilar friction stir welds between AA7075-T651 aluminum alloy and AZ31B magnesium alloy. Joints produced without an interlayer exhibited poor material mixing, interfacial cracking, and root defects. The use of a Sn interlayer produced a homogeneous lamellar stir zone with fine, discontinuous Mg2Sn intermetallic layer (thickness <1.2 mu m), effectively suppressing continuous brittle Al-Mg intermetallic phases. This resulted in the highest tensile strength (76.4 MPa, similar to 29.6% joint efficiency), highest peak hardness (154.4 HV), and improved ductility, with fracture shifting to the stir zone (SZ) / thermomechanically affected zone (TMAZ) interface region on the Mg side. In contrast, the Zn interlayer offered only limited improvement (53.81 MPa) due to incomplete dispersion, residual defects, and localized MgZn2 formation. No continuous intermetallic layers were observed in any joints, and fracture surfaces predominantly showed brittle morphology associated with intermixing defects and localized intermetallics. The findings demonstrate that interlayer effectiveness in Al-Mg dissimilar friction stir welding (FSW) is governed primarily by material flow compatibility rather than chemical barrier effects, providing new directions for interlayer selection and design in dissimilar friction stir welding.
