Joining Technique Research Articles

Depriving friction stir weld defects in dissimilar aluminum lap joints

The contemporary automotive industry increasingly incorporates composite materials and innovative joining techniques to meet customer demands for lightweight, high-strength alloys. This research explores the feasibility of using friction stir welding (FSW) methods to fabricate dissimilar aluminum nanocomposite lap joints, integrating Al2O3 nanoparticles into the weld nugget. Lap joints were prepared with varying tool rotation speeds (1000–1600 rpm) and the mechanical and metallurgical behaviors of AA6061–AA7075-T6/Al2O3 lap joints were examined. The inclusion of filler material in the weld joint resulted in an 18% increase in shear strength compared to joints without filler. Dynamic crystallization impeded grain boundaries and reduced grain size in the weld stir zone (SZ), with the most enhanced mechanical characteristics observed at a tool rotation speed of 1400 rpm. The shear strength at 1400 rpm was 5780 N, representing a 17% increase compared to joints prepared at 1000 rpm. Field emission scanning electron microscopic examination revealed evenly dispersed Al2O3 nanoparticles within the weld zone, supporting the lap shear test results. Notably, joints created at lower (1000 rpm) and higher tool rotational speeds (1600 rpm) exhibited brittle fracture behavior. The addition of Al2O3 significantly improved lap joint tensile strength due to its uniform dispersion in the SZ. Increasing the FSW tool rotational speed from 1000 to 1400 rpm facilitated nanoparticle dispersion, further enhancing lap joint strength.

Improving Thermal and Mechanical Properties of CuـAl Based Alloy Used for High-Temperature Applications (A Review) By IJISRT

Despite the increased usage of composite materials, high-strength aluminum alloys maintain significance in airframe construction. Aluminum's attributes of being lightweight, relatively low-cost, heat- treatable, and capable of withstanding high-stress levels contribute to its continued importance. These properties also reduce manufacturing and maintenance costs compared to other high-performance materials. Recent advancements in aluminum aircraft alloys have enabled them to compete effectively with modern composite materials. This study delves into the latest developments, focusing on improving the mechanical properties of aluminum alloys and utilizing high-performance joining techniques. Cu-Al-based alloys represent a new class of functional materials. Due to their unique thermoelastic martensite structure, their exceptional damping performance has garnered attention in materials science and engineering. However, challenges such as elastic anisotropy and larger grain sizes can lead to brittle fractures, impacting the material's mechanical properties. It is widely acknowledged that achieving a finer grain size is pivotal when creating Copper Aluminum alloys with exceptional mechanical attributes and effective damping characteristics. Smaller grain sizes allow for the combined use of fine grain strengthening and interfacial damping, resulting in alloys demonstrating exceptional overall characteristics. This paper presents several standard approaches for preparing Copper Aluminum alloys, subsequently examining research efforts dedicated to enhancing grain size through alloying and heat treatment. Moreover, nanomaterials are being investigated as potential agents for reinforcing Cu–Al-based alloys, leading to substantial improvements in their mechanical characteristics and damping capacities. The study aims to serve as a valuable reference for future research in developing structure-function integrated materials capable of simultaneously offering high strength and high damping characteristics.

Inline failure detection in laser beam welding of battery cells: Acoustic and spectral emission analysis for quality monitoring

The mobility sector is considered a major contributor to global greenhouse gas emissions and air pollution. As a result, many countries have initiated the transition from fossil fuel-powered to electrified powertrains. This transformation of the powertrain concept will lead to a rapid increase in the production of electric vehicles and, therefore, to a high demand for so-called traction batteries. As a production step of the traction batteries, a connection between the cell connector and the terminal of the battery cell has to be manufactured. For this purpose, laser beam welding is a reliable and efficient joining technique. In order to ensure continuous quality of the welding process during production and to detect defects in real time, reliable process monitoring is required. In this study, spectral and acoustic emissions during laser beam welding were recorded using a laser welding monitor and an optical microphone. For determining possible correlations between the signals and weld defects, various failure cases were generated by the systematic placement of disturbance elements. These elements included a contaminated surface, a gap between the cell connector and the battery cell, and a misalignment of the cell connector. Based on the recorded signals, statistical metrics were calculated. Finally, weld seams with and without defects were compared to assess the capability of both sensor systems for detecting the weld defects.

Optimizing Interfaces in Laser-Brazed Ceramic-Stainless Steel Joints for Hydrothermal Sensors through Finite-Element Modeling

The development of reliable joining techniques for ceramics and metals is crucial for energy applications, such as fuel cells, nuclear reactors, and high-temperature sensors, most especially for the sealing of hydrothermal sensors to study multiphase flows. However, during one-step active laser brazing it is a serious problem that a high thermal stress concentration can occur at the joint interfaces or on the ceramic side of the joint due to mismatches between the CTEs (coefficients of thermal expansion) and/or elastic constants. The uncontrolled thermal residual stress can lead to cracks and defects in the brazement. In the present work, an elastoplastic finite element method/numerical model was formulated to study the thermal residual stresses developed in the brazement between ceramics and austenitic stainless steel during cooling in active laser brazing. Calculations and comparison experiments were conducted to validate the simulated stress distribution in un-patterned ceramics. Stress analyses were conducted for planar and cylindrical specimen geometries (lab joints) relevant for miniaturized energy sensors. Laser interface patterning was employed to create micro-scale features on ceramic interfaces that reduce thermal stress concentrations. The optimization of the interface designing parameters including hatch size, structure width, pattern depth and metal/ceramic thickness ratio was performed using the Taguchi method with orthogonal arrays. The study suggests that laser interface structuring can modify thermal residual stresses in ceramic-to-metal brazements, thereby increasing the reliability of active brazing joints.

A study on the formation and failure mechanisms of CF/PPS-metal induction welding joints strengthened by micro-pins

This study proposed a novel hybrid joining technique that combines through-thickness reinforcement (TTR) and induction welding methods to address the challenges of composite-metal joining. The effects of geometrical parameters of micro-pins on the formation and bearing performance of hybrid joints were investigated by combing the experimental and numerical simulation approaches. Two simulation models which included the induction heating transfer and joint tensile failure process were established by COMSOL Multiphysics and Abaqus/Explicit. Subsequently, digital image correlation (DIC) was used to monitor the deformation process of different types of joints under tensile load, and a scanning electron microscope (SEM) was used to observe the welding interface of failed joints. By comparing the experimental and simulation results, it is found that adding pins can significantly improve the mechanical performance of welded joints, with maximum increases of 159% and 1758% in ultimate strength and energy absorption respectively compared to welded joints without interlock structures. This technique presents a potential solution for achieving high-quality metal-composite welded structures.

NiTi-Cu Bimetallic Structure Fabrication through Wire Arc Additive Manufacturing.

This study endeavors to comprehensively explore and elucidate the seamless integration of NiTi shape memory alloys (SMAs) into multifaceted applications through the utilization of novel joining techniques. The primary focus lies in the utilization of wire arc additive manufacturing (WAAM) to deposit Nitinol (NiTi) onto Copper (Cu), thereby introducing a transformative approach for their integration into electro-mechanical systems and beyond. Through a detailed examination of the NiTi/Cu bimetallic junction, using advanced analytical techniques including SEM, XRD, and DSC analyses, this research aims to unravel the intricate complexities inherent within the interface. The SEM images and X-ray patterns obtained reveal a complex and nuanced interface characterized by a broad mixed zone comprising various constituents, including Ti(Ni,Cu)2, pure Cu, Ti2(Ni,Cu)3 precipitates, and Ni-rich NiTi precipitates. The DSC results, showcasing low-intensity broad peaks during thermal cycling, underscore the inherent challenges in demonstrating functional properties within the NiTi/Cu system. Recognizing the critical importance of an enhanced martensitic transformation, this study delves into the effects of heat treatment. Calorimetric curves post-annealing at 500 °C exhibit distinct transformation peaks, shedding light on the intricate influence of NiTi layer distribution within the junction. The optimal heat treatment parameters for NiTi/Cu junction restoration are meticulously explored and determined at 500 °C for a duration of 12 h. Furthermore, the study offers valuable insights into optimizing NiTi-Cu joints, with micro-hardness values reaching 485 HV and compressive strength scaling up to 650 MPa. These significant findings not only hold promise for diverse applications across various industries but also pave the way for further research directions and explorations into the realm of SMA integration and advanced joining methodologies.

Experimental investigation of crack propagation mechanism in refill friction stir spot joints of AA6082-T6

Since many aluminum alloys preferred in structural engineering can be welded conventionally only with great effort and energy input interest in alternative joining techniques is growing, such as solid state joining processes. In this work, the effect of refill friction stir spot welding (refill FSSW) on the crack propagation behavior in AA6082-T6 is studied. To be able to identify the individual fracture mechanism, refill FSSW was performed as a blind weld, i.e. only in one sheet designed as C(T)100 specimens. The vertical distance between notch and spot weld was varied and tested in two phases. First, a cyclic pre-crack was induced and then the specimen was caused to fail in quasi-static conditions, resulting in two different fracture modes. The results showed that the cyclic crack is dominated by residual stresses but the microstructure mainly influences the quasi-static crack propagation. It was also found that a stress concentration occurs in the transition area even without a hook. Furthermore, it was found that the crack propagation is not exclusively driven by the local strength but also by the angle at which the crack hits the spot weld.

Advancements and Applications of Friction Stir Welding: A Comprehensive Review

Friction Stir Welding (FSW) has emerged as a groundbreaking joining technique revolutionizing the field of manufacturing and engineering. This review paper provides an in-depth analysis of the evolution, principles, process parameters, advancements, challenges, and diverse applications of FSW. It discusses the fundamental mechanisms governing FSW, explores the latest developments in tool materials and designs, examines the influence of process parameters on weld quality, and highlights the innovative applications of FSW across various industries. Additionally, this paper addresses the current challenges and future prospects to further enhance the efficiency, reliability, and versatility of FSW technology. Keywords: Friction Stir Welding, Joining Techniques, Weld Quality, Process Optimization, Advanced Materials, Applications, Challenges, Future Directions.

Optimisation of the processing parameters for the fabrication of high-quality joints between Y–Ba–Cu–O single grain, bulk superconductors

Abstract High-strength permanent magnets are essential for a wide range of technologies, including levitation devices, motors, generators and magnetic separators. Replacing permanent magnets with single grain, bulk superconductors will enable a step-change in the performance of these technologies by providing an order-of-magnitude increase in magnetic field. However, there remain many key challenges to the practical implementation of bulk superconductors, of which size and geometry are the most fundamental. The current limits to the size and geometry of (RE)-Ba–Cu–O single grain, bulk superconductors would be overcome substantially by the ability to fabricate high-quality joints between these technologically important materials. In this work we present new insights into the creation of superconducting joints between single grain bulk YBCO superconductors using a YBCO-Ag intermediate composition. We have investigated the effect of the joint fabrication temperature on the quality of the joint in order to begin to optimise the joint fabrication route for YBCO. We report on 35 joints produced at different joining temperatures as part of this study. The trapped field properties of the resulting joined samples were measured and the microstructure at each joint was examined. We show that this simple and rapid joining technique is robust to small changes in joint fabrication temperature and suggest routes to further optimise this potentially transformative technique.

Influence of zinc (Zn) powder on the microhardness characteristic and microstructure properties of stainless steel SS304 hybrid joint using low power microwave heating

AbstractMicrowave hybrid heating (MHH) process is a unique and novel approach of joint materials. Several lightweight materials (medium and high melting point) such as nickel, copper and aluminum have been successfully joined in the past research. However, small dimensions and low melting point of light weight materials such as zinc (Zn) metal or zinc (Zn) powder were always being a challenging mere for creating bond via any joining techniques. The sheets of stainless steel SS304 (17 mm×7.9 mm×0.2 mm) have been fabricated and joined at lap joint by using novel Microwave hybrid heating technique with mini heat chamber of 2.45 GHz of frequency and 200 W–360 W of microwave power, using pure zinc powder (99.9 %) as an interface material. Epoxy rate and exposure time have been varied from 10 % to 20 % and 2 min to 4 min, respectively. A developed heat chamber has been set in domestic microwave oven properly as proposed. To evaluate the microstructure correlation and microhardness at joint interface, the field emission scanning electron microscopy (FESEM – EDS), x‐ray diffraction (XRD) and Vickers hardness were used. For the experimental studies, it had found an excellent bonding was produced at interface layer between the upper and lower sections with good penetration rate of 360 W of microwave power, 4 min of exposure time and 20 % of epoxy rate as the 183.1 HV 0.05 of excellent microhardness and the intermetallic phase of iron‐zinc (FeZn11), nickel‐zinc (NiZn) and nickel‐zinc (NiZn3) were observed at interface layer.

A State-of-the-Art Review on Direct Welding of Polymer to Metal for Structural Applications: Part 2 — Joint Design and Property Characterization

Structural lightweighting through the effective use of multiple materials has received increasing attention for fulfilling today’s demands for environmental sustainability in transportation systems. Direct dissimilar material joining methods (versus, e.g., traditional adhesive bonding or mechanical fastening) have become increasingly desirable since they offer process simplicity, production efficiency, and hermetic sealing, among others. In Part I of this two-part article, we provided a critical assessment of the state-of-the-art research and promising direct dissimilar material joining techniques reported over the last decades, with a particular emphasis on their potential for structural applications. As such, in Part 2, recent advances in advanced joint design and modeling methods for enabling optimum joint design for joint ability and joint performance are presented along with some detailed examples for demonstrating their potential impacts on industrial applications. Finally, recommendations on future research and development directions are outlined for supporting the industry’s drive towards multi-material lightweighting.

Experimental characterisation and statistical modelling of woven carbon fibre weld conductors for electrical resistance welding of thermoplastic composites

Resistance welding of high-performance thermoplastic composites is a promising joining technique for the structural assembly of aerospace components. Knowledge of the weld conductor resistance as a function of its dimensions, as well as external boundary conditions such as contact preparation and pressure, can be used to scale welding parameters. This paper presents a comprehensive review on the weld conductor contact preparation, length, width and contact pressure dependent resistance with respect to the Toray 5HS T300JB carbon woven prepreg 281 gsm fibre architecture. The study is based on a 4-wire resistance measurement of the carbon fibre fabric weld conductors and was conducted to provide a solid basis for defining the weld conductor’s resistance, considering the dependence on length, width and contact pressure. The experimentally determined resistance values were approximated using linear and non-linear regression functions and combined into a general formulation with respect to the investigated carbon fibre fabric architecture. The least squares fit of experimental versus model data confirmed a very high model confidence. Thus, the model allows a simplified transfer of electrical properties for process pre-design and scaling considering weld conductors with the same fibre architecture.

A comprehensive review on the machining and joining characteristics of natural fiber‐reinforced polymeric composites

AbstractNatural fiber composites are gaining interest in many industries, particularly the automotive and aerospace industries. One of the critical secondary activities required to produce a near‐perfectly shaped product is machining. The majority of product components had to be assembled before they could be used. This article reviews the various conventional and non‐conventional machining processes and its influential parameters investigated by various researchers. Non‐traditional machining is now proving to be a better choice than traditional machining. Non‐traditional machining has several advantages, including the absence of thrust force, chatter or vibration, minimal tool wear, and lower frictional heat. Delamination is the major issue occurring in the conventional machining processes like drilling. Researchers are more focused on the non‐conventional machining processes like abrasive water jet machining. Joining of natural fiber reinforced composites is another aspect discussed in this article. Adhesive joining is the most preferable joining method in the natural composites. The joining technique is also influenced by the intricacy of the materials to be bonded. Microwave joining and induction joining processes are the new methods of natural composites joining. This review also covers the various joining processes in the natural reinforced composite materials.

Analysis of heat generation during friction stir welding of aluminum alloy 2024-T4 and its impact on joint characteristics

Friction stir welding (FSW) is a successful welding technique for joining of aluminium and many other materials with the required joint configurations. During this welding process, large amount of heat is generated, which influences the integrity, performance, and microstructure of the weld joints. In this study, both experimental and numerical approaches are adopted to analyse the influence of heat generation on the metallurgical and mechanical properties of friction stir-welded joints of AA2024-T4. A computational fluid dynamics (CFD) model is constructed for quantitative analysis of heat flux, heat generation, temperature distribution, strain rate and viscosity. The model is validated by experimentally measured temperature data, and both agree well. The results showed that both heat flux and strain rate are more or less symmetric about the tool axis whereas plastic material flow is asymmetric. Heat flux affects the grain size and mechanical properties of the joint.

Microwave joining of copper pipes using selective microwave hybrid heating process: Simulation and experimental study

High thermal conductivity of copper poses serious challenges in its joining in conventional welding techniques leading to development of alternate welding techniques. Microwave welding is one such newly developed joining technique that use selective microwave hybrid heating (SMHH). The joining of the copper pipes using SMHH has not been explored in existing literature. The present paper attempts the microwave joining of copper pipes using SMHH. The exposure time required for joining copper pipes using SMHH was predicted by COMSOL Multiphysics software. The joining was attempted at the predicted exposure time using a novel cavity design inside a conventional microwave oven. The copper pipes have been successfully joined at temperature and exposure period of 1080ºC and 720 s respectively and was in good agreement with the predicted values i.e., 708 s. Scanning electron microscopy (SEM) revealed good metallurgical bonding between the base metal and joint interface. The presence of columnar grains has been observed at heat affected zone (HAZ) using electron back scattered diffraction (EBSD). EBSD analysis revealed randomly arranged grains with mixed modes of planes inside the base metal. The occurrence of high angle grains (HAGs) along with high dislocation density in base metal resulted in the improvement in the mechanical properties as revealed in grain average misorientation (GAM) maps. The maximum value of microhardness has been observed at the joint region (105 ± 7 Hv) followed by base metal and HAZ i.e. (97 ± 5 Hv) and (89 ± 8 Hv) respectively owing to the existence of fine grain of copper (µm) and carbide formation.

Durability of Single Lap Friction Stir Welded Joints between S355-J0 Steel and AA5083 Aluminum Alloy–Mechanical Tests

This study aims to investigate a friction stir welded joint between steel and aluminum alloy. FSW is nowadays one of the most interesting joining techniques due to the possibility of connecting materials and thicknesses that are difficult or impossible to weld with traditional techniques. The main advantage is that materials are not affected by thermal cycle problems during solidification and cooling, and the absence of fumes and pollution during the process favors the quality of the welded joint. The life of metal joints could be greatly reduced in a corrosive environment since the less noble material will tend to increase its corrosion rate, while the nobler one will reduce its electrochemical dissolution. Accelerated aging tests (i.e., salt fog test) are used to estimate the lifetime of metal joints in highly aggressive environments. The aim of the present work is to evaluate the durability at a long aging time in the salt spray test (according to ASTM B117) of carbon steel/aluminum alloy joints, obtained by FSW. In this first part, mechanical test results are reported. A deep metallographic and chemical investigation is going to be reported in part two. The current research work investigates the welding direction and residence time in the salt spray chamber. The breakage of all tested samples, evaluated after the tensile tests were carried out, always occurs at the interface of the joint, regardless of the change of direction of the weld on the advancing or retreating side. The welding direction influences the breakage of the joint only before the aging treatment. Specifically, specimens produced in advance are characterized by increased joint strength. On the other hand, the factor that influences the performance of the joints is the exposure time where, starting from the first point of aging, i.e., after two months, there is a decrease in the maximum load of 40%, and the effect of corrosion leads to a significant deterioration of the weld which remains almost similar until the last point of aging.

Towards an efficient multi-scale numerical model of the impact behavior of woven materials with global/local approach

This paper presents the global/local approach in the multi-scale modeling of woven material impact behavior. This approach optimally considers important microscopic mechanisms to accurately predict outcomes and reduce computational time. The inspiration for this approach stems from the specific behavior exhibited by woven materials under ballistic impact:(1) Zone 1 (Local) is a small square around the impact position, requiring comprehensive microscopic modeling to describe complex physical phenomena accurately.(2) Zone 2 (Global) represents the remaining fabric outside of Zone 1, exhibiting more global behavior and modeled with a mesoscopic model.Building upon a previous work's joining technique, an interface between these two zones is implemented and validated through numerical tensile testing. The proposed approach is then compared to the complete mesoscopic model already validated in the case of a 2D Kevlar KM2 woven fabric submitted to ballistic impact. The global/local approach demonstrates slightly greater flexibility due to the presence of microscopic yarns. It successfully predicts all microscopic phenomena while significantly reducing the degrees of freedom compared to full microscopic modeling along the entire yarn length.

Advanced Analysis of the Properties of Solid-Wire Electric Contacts Produced by Ultrasonic Welding and Soldering.

The current article presents an advanced analysis of the properties of solid-wire electric contacts produced with ultrasonic welding and soldering. Soldering is generally used to join thin, solid copper wires to produce electrical contacts in small-volume production, as ultrasonic welding does not provide acceptable peel force and tensile strength due to the deformation and thinning of the wires. In this article, ultrasonic welding of thin, solid copper wires using a ring before and after a thermal shock test is discussed and compared with the standard soldering technique. The thermal shock test was carried out in the temperature range from -30 to 150 °C. Half of the samples, for both the joining techniques and the wires, were subjected to the thermal shock test; the other half were not. Investigations included electrical resistance tests, optical and SEM microscopy, XRD, microhardness measurements, peel tests, tensile tests, and fractographic analysis. The electrical resistance test, microscopy, microhardness measurements, and fracture examinations showed no differences between the thermal shock-exposed and the non-exposed samples with the same joining process. In mechanical tests, the ultrasonic joint demonstrated superior strength compared to the soldered joint.

A pragmatic approach for the fatigue life estimation of hybrid joints

The need for more environmentally sustainable ways of transportation and for a reduction in emissions and fuel consumption make lightweight structures essential. Together with the use of lightweight materials and design optimisation, the use of hybrid joints represents one way to reduce the weight of components and it is becoming increasingly popular in the transportation industry. The name ‘hybrid joint’ refers to a connection where adhesive bonding is used in conjunction with traditional joining techniques, such as spot welds and rivets with the aim of combining and exploiting the advantages of the individual joining techniques. To optimise the design of hybrid joints and minimise the risk of in-service fatigue failures, the transportation industry needs efficient, robust, and easy-to-use approaches for the modelling and fatigue life estimation of hybrid joints.This work presents two practical methodologies for estimating the fatigue life of hybrid joints that can be easily adopted by companies in the transportation industry. The first methodology neglects the life given by the mechanical joints after failure of the adhesive (the joint is considered failed when the adhesive fails), while the second methodology considers the life of both the adhesive and the mechanical joints. In the first methodology, just one configuration would need to be analysed (‘hybrid’ joint or ‘purely bonded’ joint, if this simplification is considered reasonable). In the second methodology, instead, the analysis of two configurations would be required (the previous configuration followed by a configuration where only the mechanical fasteners are considered). The second methodology would produce more realistic fatigue life estimations compared to the first methodology, but it would be more onerous both in terms of modelling and computationally. For both methodologies, FE modelling guidelines to recover the required stresses are suggested. These guidelines require limited changes to the typical FE modelling strategies currently used, especially in the automotive industry. Furthermore, the proposed modelling guidelines provide FE models that are not computationally too onerous, reasonably mesh insensitive and that do not require congruent meshes. The relevant stresses recovered from the FE model are then used as an input into nCode DesignLife to estimate the fatigue life of the hybrid joints in the analysed structure. The fatigue life estimation is carried out using standard Stress-Life (SN) based nCode DesignLife analysis engines and bespoke SN curves obtained through testing of hybrid joint specimens, representative of the joints in the production parts.

Tokamak, fusion reactor device: Welding and joining for plasma facing components

Nuclear fusion might be an unlimited, everywhere available source of energy for electrical production. Among the various machines designed and prototyped to demonstrate electricity production from nuclear fusion the tokamak is certainly the most promising. Tokamaks are complex devices, consisting of various components, which in turn are composed of many parts. This contribution reports on the joining and welding techniques used and specifically developed for the elements of a tokamak, with a focus on plasma facing components as the divertor targets.