Search Results (193)

This study investigates the effect of SiC nanoparticle addition on the microstructure, interfacial reactions, and mechanical properties of Zn5Al3Ti active solder used for ultrasonic soldering of AlN ceramic to copper substrates. Composite solders containing 3 and 6 wt.% SiC nanoparticles were prepared and applied under flux-free ultrasonic soldering conditions. The solder alloys were evaluated by tensile testing, while the soldered joints were evaluated by shear strength testing. The solder microstructure and interfacial regions were characterized using SEM/EDS analysis. The results showed that the addition of SiC nanoparticles modified the microstructure of the Zn5Al3Ti solder and influenced the mechanical performance of the ceramic/metal joints. Among the investigated systems, the AlN/Zn5Al3Ti + 6 wt.% SiC/Cu joint exhibited the highest shear strength, reaching approximately 101 MPa. SEM/EDS observations revealed the formation of compact multilayered interfacial regions, including possible Cu–Zn intermetallic phases at the Cu/solder interface and Al–Ti–Zn-based reaction products near the solder/AlN interface. The improved joint performance may be attributed to the combined effect of SiC-induced microstructural modification, the presence of Si-containing particles, and the formation of compact metallurgical bonds. The results indicate that Zn5Al3Ti solder modified with 6 wt.% SiC nanoparticles is a promising material for producing strong AlN/Cu joints under the applied ultrasonic soldering conditions. Full article

To address the insufficient strength of friction-stir-welded (FSW) ultra-high-strength Al–Cu–Li alloy joints, the effects of post-weld heat treatment (PWHT) on microstructural evolution and mechanical properties were systematically investigated. The as-welded joint showed a “W”-shaped microhardness profile, with the minimum value located in the thermo-mechanically affected zone (TMAZ), mainly caused by the dissolution of T₁ phases and precipitation of coarse AlCu, AlCuMg, and AlCuMn phases during welding. Direct artificial aging at 155 °C for 24 h failed to improve joint strength due to solute depletion induced by pre-existing coarse secondary phases. Solution treatment re-dissolved coarse precipitates into the matrix, and subsequent aging led to uniform precipitation dominated by T₁ and θ′ phases, with a consistent microhardness of ~155 HV across all zones. By introducing pre-stretching deformation after solution treatment, T₁ became the dominant strengthening phase in all regions, accompanied by a remarkable increase in both microhardness and tensile strength. With 3% pre-stretching, the microhardness reached 185 HV, and the ultimate tensile strength of the joint reached 600 MPa, corresponding to a joint efficiency as high as 95%, which is superior to most reported values for Al–Li alloy FSW joints. This study clarifies the precipitation evolution mechanism under tailored PWHT and provides an effective strategy for property regulation of high-performance Al–Cu–Li alloy FSW structures in aerospace applications. Full article

The increasing demand for reliable and high-performance electric vehicle (EV) batteries requires precise and defect-free welding of battery components. Conventional Gaussian laser beam welding faces challenges such as keyhole instability, spattering, porosity, and brittle intermetallic compound formation, particularly in dissimilar Al-Cu joints. These issues significantly affect the electromechanical performance and durability of battery connections. Beam shaping technology has emerged as a core method for improving weld quality, process stability, and efficiency in laser welding, making laser beam welding increasingly vital for high-volume production of e-mobility components. This review systematically evaluates recent advancements in laser beam shaping for laser welding, especially static beam configurations, such as core-ring profiles, flat top, elliptical, and shaped beams; emphasis has been placed on how altering the intensity distribution influences the challenges associated with conventional welding and emerges as an effective solution to address these challenges. By tailoring the spatial energy distribution, beam shaping improves control of heat input, stabilizes melt pool dynamics, and enhances microstructural uniformity. Static beam shaping, compatible with cost-effective near-infrared continuous-wave laser systems, is already being adopted in industry, whereas dynamic beam shaping remains at an earlier stage of industrial maturity. This review highlights key welding challenges in EV battery manufacturing, evaluates beam shaping strategies as practical solutions, and identifies future research directions for large-scale industrial implementation. Full article

Aiming at the urgent heat dissipation demands of high-power, high-integration electronic devices, Cu/Al composite heat sinks combine the high thermal conductivity of copper and the lightweight advantage of aluminum, becoming a mainstream solution for advanced thermal management systems. The significant physicochemical differences between Cu and Al, however, make high-quality joining a technical bottleneck. In this study, flux-free ultrasonic brazing with a Zn-based filler metal was used to join 6061 aluminum alloy and industrial pure copper. Gradient heat treatment (55–300 °C) was subsequently applied to systematically investigate its effect on the microstructure, microhardness, and thermal properties of the joints. The results show that the as-brazed joint exhibited excellent bonding (97.3% bonding rate) and shear strength (95.24 MPa). The weld seam consisted of Zn solid solution, Cu solid solution, and Al-Cu-Zn ternary compounds. Heat treatment did not induce new phases but led to the coarsening of Zn-Al-Cu compounds and aggregation of the eutectic structure, reducing grain boundaries. Consequently, the microhardness at the weld center varied non-monotonically, and the thermal conductivity of the joint showed an overall increasing trend with rising heat treatment temperature. This enhancement is attributed to reduced phonon scattering at diminished grain boundaries. This study clarifies the heat treatment–microstructure–thermal properties relationship, providing important guidance for the thermal performance optimization of Cu/Al composite heat sinks. Full article

In this study, the microstructure and mechanical properties of ultrasonic welded joints between large-diameter aluminum wire and Cu (Ni-plated copper) terminals were systematically investigated, to reveal the underlying fracture mechanisms. The cross-sectional morphology, interfacial microstructure, and mechanical properties of the two types of welded joints are investigated. The results indicate that ultrasonic welding produces well-structured Al-Cu and Al-Ni joints. Under the same welding process parameters, the Al-Cu joint exhibits many pores, while the Al-Ni joint has no pores in its microstructure. The interfacial region of the Al-Cu joint presents various morphologies, such as flat bonding, interlocking, and eddy current patterns, whereas the Al-Ni joint interface is flat. No significant atomic diffusion phenomenon occurs between the interfaces of the two types of joints. The tensile strength of the Al-Cu joint is 53 MPa, with fracture modes including ductile fracture and brittle fracture, whereas the tensile strength of the Al-Ni joint is 50 MPa, with a failure mode of pull-out fracture. In working conditions requiring ultrasonic welding of aluminum and copper, nickel-plated copper can be used as a substitute for copper to prevent electrochemical corrosion between aluminum and copper. Full article

Four compositions of rapidly quenched ribbon brazing alloys based on Ag–Cu–Ti (Ag–26.5Cu–1.5Ti, Ag–25Cu–5Ti) and Ag–Cu–Zr (Ag–26.5Cu–1.5Zr, Ag–25Cu–5Zr) systems were produced. Initial ingots were synthesized by arc melting. Rapidly solidified ribbons, 50–100 μm thick, were then fabricated from homogenized ingots using a “Crystall-702” facility. A comparative analysis of the microstructure and phase composition of both the ingots and ribbons was conducted using scanning electron microscopy and X-ray diffraction. The analysis revealed the presence of Cu₄Ti and CuTi intermetallic compounds in the Ag–Cu–Ti alloys, and AgCu₄Zr and Zr₂Cu in the Ag–Cu–Zr alloys. Rapid quenching was found to produce metastable structures and significantly refine the intermetallic phases. Microhardness measurements of the ingot and ribbon states demonstrated a substantial influence of the processing route on the mechanical properties. The tensile strength of the ingots was also evaluated. The wetting angles of the rapidly quenched alloy melts on 99% Al₂O₃ (alumina) ceramic substrates under vacuum were determined. All produced ribbons, except for the Ag–26.5Cu–1.5Zr composition, demonstrated adequate wettability. Thus, these materials are considered promising for further research into heat-resistant metal–ceramic joints. Full article

Welding copper (Cu) and aluminum (Al) is highly demanded for lightweight and cost-effective manufacturing. However, it faces significant challenges. First, substantial differences in physical properties may lead to high residual stresses and distortion. Second, brittle intermetallic compounds (IMCs) readily form at the interface, severely compromising the joint’s mechanical properties and electrical conductivity. Third, the native oxide film on Al impedes effective wetting and bonding. Therefore, effective control over the interfacial microstructure of the welded joint is essential. This review provides a critical analysis and comparison of several typical welding techniques, including laser welding (LW), friction stir welding (FSW), ultrasonic welding (UW), brazing and soldering, and welding–brazing. These analyses focus on their process characteristics, joint microstructures, and corresponding formation mechanisms. Furthermore, this review synthesizes key strategies for enhancing joint quality, including process parameter optimization, introduction of functional interlayers, and external assistance, aimed at optimizing joint microstructure and minimizing defects. Based on the analysis, this work provides comparative insights into process selection and microstructure control, and highlights future directions: advancing novel methods such as magnetic pulse welding and transient liquid phase bonding; developing intelligent real-time process control to suppress brittle IMCs and associated defects; promoting sustainable practices and establishing standardized performance evaluation; and systematically investigating long-term reliability to support the industrial application of robust Cu/Al joints. Full article

The addition of Cu or La plays an important role in microstructure and property manipulation of 4xxx series Al-Si alloys. However, the effects of Cu-La hybrid modification on the microstructure and properties of Al-5Si alloys and welding performance remain unclear. In this paper, the influence of Cu-La addition on the strength and elongation of one commercial Al-5Si alloy and the welding joint characterization are investigated. The results show that the addition of Cu-La can refine α-(Al) and Fe-rich phase and improve the fluidity. Meanwhile, the elongation can be improved by Cu-La microalloying, which is beneficial for the manufacturing filler wire. The uniform distribution of Cu in the alloy but not segregation at grain boundaries due to La addition is the key factor to adjust the mechanical properties. Moreover, the filler materials were used to conduct metal inert gas welding on 6061 alloy. It reveals that, with Cu-La addition, the weld pool width increases and porosity defect decreases significantly. This is ascribed to Cu-La co-addition enhancing wettability and fluidity, which improves the welding performance. Our results offer an effective strategy for manufacturing and optimizing welding performance of welding wires. Full article

Thermal degradation of the interfacial microstructure critically limits the service life of Zn-Al brazed Cu/Al joints. This work elucidates the stabilizing role of trace Ni (0.3 wt.%) in retarding interfacial deterioration during 200 °C isothermal aging for up to 1000 h. Microstructural evolution and micromechanical responses were probed via SEM, EDS, and nanoindentation. In Ni-free joints, continuous Zn influx triggers the decomposition of the massive CuAl₂ phase into a defect-ridden, Zn-rich lamellar structure, precipitating a sharp decline in shear strength from 57 MPa to 37.5 MPa. Conversely, Ni doping constructs a robust fine-grained interfacial architecture. The Ni-bearing coral-like layer exhibits exceptional morphological stability, while the underlying Cu-based transition layer undergoes in situ stratification and Zn ejection, functioning as a chemical buffer to intercept Zn diffusion. This microstructural reconfiguration enables Ni-doped joints to sustain a shear strength of ~55.2 MPa after 1000 h—matching the initial strength of Ni-free counterparts. The superior durability stems from the modulus softening of the stratified transition layer and a multi-stage crack deflection mechanism, offering a viable metallurgical strategy for robust Cu/Al interconnects. Full article

The current research first investigates the flow in the fractional order of a vertical artery with atherosclerosis using a Casson-based penta-hybrid nanofluid. Gold (Au), copper (Cu), silver (Ag), magnesium oxide (MgO), and alumina (Al₂O₃) nanoparticles are dispersed in blood to make the hybrid nanofluid. It is assumed that the flow is very pulsatile. The mathematical model is constructed by using differential forms of the conservation laws of mass, momentum, energy, and irreversibility analysis. By applying the mild stenosis approximation, the governing equations are transformed into dimensionless form. To generalize the classical model to its fractional counterpart, the Caputo–Fabrizio fractional derivative (C-FFD) is employed. Closed-form solutions for the velocity and temperature fields are realized by the joint application of the Laplace and Hankel transforms. The impact of essential physical parameters on velocity, temperature, and entropy generation is displayed through figures. The physical significance of enhanced thermal characteristics is shown, emphasizing their potential relevance to thermal regulation, targeted drug delivery, and minimization of irreversible energy losses in biomedical flow systems. The velocity profile elevates with the increase in the Casson parameter, while the temperature drops as the fractional-order parameter rises. Entropy generation is observed to amplify with the increasing values of the thermodynamic parameter in question, whereas an opposite tendency is seen for the Bejan number. The Bejan number decreases as the control parameter becomes higher. The novelty of the present investigation lies in the simultaneous incorporation of Caputo–Fabrizio fractional dynamics, penta-hybrid nanoparticle suspension, and entropy generation analysis in a stenosed arterial configuration. Unlike existing fractional Casson blood flow models that primarily focus on single or hybrid nanofluids, the present framework highlights the synergistic enhancement of thermal transport and irreversibility control achieved through penta-hybrid nanoparticles, which may be relevant for advanced biomedical and targeted therapeutic applications. Full article

The long-term interfacial reliability of Cu/Al brazed joints is critical for power equipment but is often compromised by severe intermetallic compound (IMC) degradation during thermal aging. This study investigates the evolution mechanism and mechanical stability of Cu/Al joints brazed with 0.5 wt.% Ga-modified Zn-15Al filler metal, aged at 200 °C for up to 1000 h. Microstructural evolution, diffusion kinetics, and mechanical properties were systematically characterized using SEM, EDS, nanoindentation, and shear testing. Results indicate that the unmodified control interface degrades via Zn-diffusion-driven “in situ Cu depletion” of the Cu₉Al₄ layer, leading to severe embrittlement. In contrast, the addition of Ga induces a “sacrificial reconstruction” mechanism, where the outer CuAl₂ layer transforms into a dense lamellar ternary structure via cellular decomposition. This reconstructed layer acts as an effective diffusion barrier and “Zn sink,” trapping infiltrating atoms and preserving the structural integrity of the underlying Cu₉Al₄ phase. Consequently, the Ga-modified joints demonstrate superior shear strength retention and an optimized H/E ratio throughout the aging process, shifting the failure mode from brittle cleavage to a toughened lamellar peeling mechanism. This work elucidates how Ga-modulated phase reconstruction fundamentally enhances interfacial stability, offering a theoretical basis for high-reliability interconnects. Full article

In this study, the corrosion performance and near-surface residual stress state of laser-welded Ti6Al4V/AA7075 dissimilar joints produced with a silver (Ag) interlayer are investigated. Potentiodynamic polarization, cyclic polarization, and electrochemical impedance spectroscopy (EIS) were carried out on Ti6Al4V base alloy (BA), AA7075 BA, and the fusion zone (FZ) containing the Ag interlayer. The Ag interlayer FZ exhibits an intermediate but clearly improved corrosion response compared with AA7075 BA, with a corrosion potential E_corr ≈ 0.260 V, corrosion current density i_corr ≈ 4.55 × 10⁻⁶ A cm⁻², and polarization resistance Rp ≈ 7.08 kΩ cm². EIS fitting further indicates a charge-transfer resistance of R_ct ≈ 3.7 × 10⁴ Ω cm² and a moderate oxide film resistance, consistent with a more stable electrochemical interface than AA7075 BA in 3.5 wt.% NaCl. Additionally, the residual stress measurements reveal that the Ag interlayer joint develops a predominantly compressive residual stress field on both sides of the weld. This compressive state is beneficial for delaying pit-to-crack transition and enhancing durability under corrosive loading. A brief comparison with our previously published Ti6Al4V/AA7075 welds produced using a Cu interlayer under the same laser welding parameters and joint configuration as the present study shows that the Ag interlayer provides more favourable compressive residual stresses and a more noble, higher-resistance electrochemical response. Full article

Ensuring friction stir welding (FSW) joint quality typically relies on ultrasonic testing (UT) and radiographic testing (RT), but achieving complete coverage is challenging, and echo-based defect discrimination becomes difficult in dissimilar joints. Laser ultrasonics is a promising non-contact technique that remotely assesses weld quality and provides high spatial resolution at the generation and detection points. This study establishes a laser-ultrasonic method for defect detection in dissimilar Cu–Al FSW joints. Slit-like artificial defects (0.1–2.5 mm deep in 5 mm thick plates) were introduced at the Al-side interface of specimens fabricated with an Al-offset tool. Experiments and numerical simulations were used to evaluate wave modes and irradiation configurations, focusing on intensity-attenuation ratios of specific wave types, including longitudinal and Rayleigh waves. On the non-slit surface, attenuation of reflected longitudinal waves enabled detection of defects ≥0.5 mm deep. On the slit surface, Rayleigh-wave attenuation allowed identification of defects as shallow as 0.1 mm, although slit-side irradiation may be less practical during joining. These results demonstrate that defect identification in dissimilar materials can be achieved by evaluating wave-intensity attenuation rather than relying solely on the presence of reflected echoes, suggesting potential for implementing laser ultrasonics in in-process monitoring of FSW joints. Full article

Titanium alloys and copper have broad applications in aerospace, defense, and industry, but their dissimilar welding faces challenges from significant physicochemical differences and easy formation of brittle Ti-Cu intermetallic compounds, while existing methods like laser welding or friction stir welding have limitations, such as low strength or inability to weld ultra-thin plates. This study adopted cold welding to join Ti-6.5Al-1Mo-1V-2Zr alloy and 99.90% pure copper. The mechanical properties of the joint were tested, the microstructure and fracture of the weld were observed, and the phase composition of the weld was analyzed. The results show that the weld fusion zone mainly consists of Cu-based solid solution and Cu₃Ti. Low cold welding heat input reduces the Cu₃Ti content, so the joint mechanical properties do not decrease significantly. The tensile strength of the joint reaches 284 MPa, which is 83% of that of copper-based metals, and the elongation rate reaches 6.25%. Diffusion kinetics and solidification thermodynamics analyses confirm that Cu₃Ti intermetallic compounds are preferentially generated in the weld seam. Full article

Aluminum–based brazing alloys have been developed for joining 7072 high–strength aluminum alloys. However, challenges related to their high melting points and joint softening still require further exploration. This study employs a combination of first–principles calculations and experimental techniques to examine the microstructure and mechanical properties of 7072 aluminum alloy joints brazed with (Ni, Y)–modified Al–Si–Cu–Zn filler alloys. Through the virtual crystal approximation (VCA) method, it was observed that the Al–10Si–10Cu–5Zn–xNi–yY (x = 0, 1.0, 2.0, 3.0, y = 0.2, 0.4, 0.6) filler alloy exhibits excellent mechanical stability, combining both high strength and reasonable ductility. Seven brazed joint samples with varying Ni and Y contents were fabricated using melting brazing and analyzed. The findings showed that Ni reduces the liquidus temperature of the filler, narrowing the melting range. This facilitates the conversion of the brittle Al₂Cu phase into a more ductile Al₂(Cu,Ni) phase, thus enhancing joint strength. Y acts as a heterogeneous nucleation site, promoting local undercooling, increasing the nucleation rate, and refining the microstructure. When the Ni content was 2.0 wt.% and the Y content was 0.4 wt.%, the tensile strength of the brazed joint reached a peak value of 295.1 MPa. Computational predictions align with the experimental results, confirming that first–principles calculations are a reliable method for predicting the properties of aluminum alloy brazing materials. Full article