Joining Process Research Articles

Abnormal rapidly homogenized joining of aluminum alloys through a cross-scale diffusion

Rapidly homogenized joining has been a longstanding pursuit in the forming manufacturing of lightweight alloys structures. In this study, ultrasound energy was introduced into the joining process to accelerate cross-scale diffusion (direct grain migration rather than atomic-scale diffusion), and a homogeneous 6063Al joint was fabricated using a Zn-40Sn alloy at 360 °C in air. The network architecture joint composed entirely of α-Al grains was formed with a sandwich structure consisting of Sn@Al2O3/MgO as the grain boundary. The tensile strength of the joints was higher than that of the base metal in only a very short diffusion time (180 s). Physical effects of ultrasound in the Sn-Zn molten metal induced violent intergranular penetration, resulting in the decohesion and migration of the α-Al grains from the base metals and realizing a rapidly homogenized joining. This provides a foundation for full-strength joining of high-strength aluminum alloys with low thermal damage.

Simulating chemical mixing and molten pool shape in dissimilar welds using thermal fluid dynamics

Estimating the properties of dissimilar metal welded joints made using modern high-energy beam techniques presents significant challenges due to the complex nature of the process. These complexities arise from the different thermal and mechanical properties of the materials involved. The properties of a welded joint are primarily determined by the element mixing and final chemical composition when two dissimilar metals are fused together, or when a dissimilar filler material is used. Hence, a representative model capable of tracking elemental distribution and temperature is essential for accurately estimating the micro-scale and macro-scale mechanical properties of the joint, thus optimising the joining process. In this work, a high-fidelity thermal fluid flow model in the multiComponentlaserbeamFoam computational fluid dynamics (CFD) solver is used to simulate the process of laser beam welding. For this purpose, the joining process of AISI 304 stainless steel with a low alloy steel filler material (G3Si1) is simulated. This framework is rigorously validated with experimental results showing the capabilities of such modelling approach. Different strategies to model the filler and material properties are explored: a stationary filler model, applied through the parent material's thickness, was found to accurately mirror experimental results. This model is then used to study the flow properties, thermocapillary effect, and diffusion on the intermixing of composition, aspects that have not been previously examined in depth. The thermocapillary forces were concluded to be the most significant, dictating the peak composition value, the shape and topology of the molten pool. Diffusion fluxes were found to be negligible and not responsible for the majority of the mixing.

Understanding the formation mechanism of SiC/Al joints by U-TLP bonding with the inactive Zn interlayer

The ultrasonic-assisted transient liquid phase (U-TLP) bonding process is extremely fast, which is a great challenge to reveal the inherent mechanisms. Understanding the joint formation mechanism of U-TLP is essential for the joining process design. In this study, the SiC ceramics and 6063Al alloys were joined by U-TLP using a Zn interlayer. The process of removing the oxide film on the base metal involved cracking, flaking off, suspending, and fragmenting. The migration of the eutectic liquid phases frontier was very fast (within 1 s). The relationship between the thickness of the liquid layer and the ultrasonic action time was a power function. The typical microstructure of the SiC/6063Al joints was SiC/amorphous Al2O3/Zn-Al eutectic/ Zn-Al eutectoid/6063Al. The shear strength of SiC/6063Al joints increased with the interfacial bonding ratio and reached up to 27 MPa for the ultrasonic action time of 5 s. The metallurgical bonding at the SiC/bond metal interface was formed through the amorphous Al2O3 transition layer. The formation mechanism of the Al2O3 reaction layer was revealed based on the thermodynamics, kinetics, and acoustics cavitation theory. This will provide a guideline for the future U-TLP process design.

The Energy Consumption of the Process of Joining Steel Sheets with the Use of Clinching With and Without an Additional Rivet, and Analysis of Sheet Deformation and Mechanical Strength of Joints

This paper presents the results of research on the impact of the use of different tools and the shape of the additional rivet, on the geometric quality of the joint, the energy consumption of the forming process, the distortion of the steel samples, and the load capacity of the joints. The tests were carried out for DX51D steel sheets with a thickness of 1.5 [mm] joined by using three different sets of tools. A steel rivet with a hardness of 400HV1 and various shapes was used for the tests. In addition to the full rivet, two types of rivet were used, the first with a through hole and the second with a depth of hole of 3 [mm]. The holes in the rivet had different diameters: 1.0, 1.5, 2.0 and 2.5 [mm]. The influence of changing the shape of the rivet (hole and its diameter) on the change in forming force and energy consumption of the joining process was analyzed. The lowest forming force was achieved for a rivet with a through hole and a hole diameter of 2.5 [mm]. The lowest joint forming force was obtained for the die with movable segments. For joints made with three tool arrangements and a series with a modified rivet, the amount of sheet metal deviation was analyzed. Of the three cases of arrangement of tools used to form the joint, the largest deviation of the sheets occurred at the clinch joint formed with a solid round die. In the case of a series of clinch-rivet joints with a modified rivet, the greatest deviation of the sheets occurred for the rivet with a hole of 1.5 [mm]. Changes in the geometric structure of the joint were also studied, and changes in the surface of the sheets in the joint area were observed. The highest value of the interlock in the joint was obtained when a solid rivet was used in the clinch-riveting technology. The strength of the joints was also identified in the lap shear test and the energy consumption at failure was determined. The use of a rivet increased the maximum load capacity to almost twice that of the clinch joint.Graphical abstract

Steel Sheet Deformation in Clinch-Riveting Joining Process

This paper presents the deformation of a joined sheet after the clinch riveting process. The DX51D steel sheet with zinc coating was used. The samples to be joined with clinch riveting technology had a thickness of 1 ± 0.05 mm and 1.5 ± 0.1 mm. The sheet deformation was measured before and after the joining process. The rivet was pressed in the sheets with the same dimension between the rivet axis and three sheet edges: 20, 30, and 40 mm. For fixed segments of the die, from the rivet side close to the rivet, the sheet deformation was greater than that of the area with movable segments. The movement of the die’s sliding element caused more sheet material to flow in the space between the fixed part of the die and movable segments. Hence, the sheet deformation in these places was smaller than for the die’s fixed element—the sheet material was less compressed. For sheet thickness values of 1.5 mm and a width value of 20 mm, the bulk of the sheet was observed. For a sheet width of 20 mm, it was observed that the deformation of the upper and lower sheets in the area of the rivet was greater than for sheet width values of 30 or 40 mm.

Evolution of interfacial microstructure and oxides of CLAM steel by hot compression bonding

The development of the joining process is essential for the application of China low activation martensitic (CLAM) steel as the structural material for fusion reactors. In the present study, the hot compression bonding (HCB) for CLAM steel was carried out under different parameters. The effects of different strain rates, temperatures, strains and holding time on the evolution of interfacial microstructure and oxides were investigated. Compressed at 1000 °C with 5% deformation, some micron-size continuous oxides distributed along the flat interface. The interfacial oxides were broken and decomposed as the deformation increased to 20%, their average size was reduced to 400 nm. With the bonding temperature increasing, more interfacial grain boundaries (IGBs) could cross the original bonding interface and flat interface became wavy. Compressed at 1000 °C/20%, the interfacial oxides consisted of fcc-structured spinel MnCr2O4 and enriched in Si and Ta oxides. The MnCr2O4 oxides would decompose preferentially after 0.5 h holding treatment at 1100 °C. Only a small number of oxides rich in Si and Ta elements remained at the original bonding area after 2 h holding treatment. Compressed at 1100 °C/20%, the bonding interface was completely replaced by the migrated grains after 2 h holding treatment and no large-size oxides could be observed. Moreover, the tensile strength and elongation at room temperature of the joint were comparable to those of the base material.

Investigations on the multiple-sector hard-copper X-band accelerating structures

The development of advanced, high gradient accelerating structures is one of the leading activity of the particle accelerator community. In the technological research of new construction methods for these devices, high-power testing is a critical step for the verification of their viability.Recent experiments showed that accelerating cavities made out of hard copper, fabricated without high-temperature processes, can achieve better performance as compared with soft copper ones. Recently, we have built cavities using Tungsten Inert Gas welding and the high-power experiments confirmed that this joining process is a robust and low-cost alternative to brazing or diffusion bonding. This is a good solution for high-gradient operation, with a gradient of about 150 MV/m in X-band, at a breakdown rate of 10−3/pulse/meter using a shaped RF pulse with a 150 ns flat part.We continue the design, construction and high power tests of three-cells standing-wave X-band accelerating cavities fabricated with a split-open geometry, made of hard copper and vacuum-sealed by welding. Our aim is the fabrication of accelerating structures made out of hard copper alloys by using innovative cost-effective technologies. Moreover, our method of multiple-sector structures opens the way to new technological approaches and design methods, for example providing the possibility of placing dampers of the parasitic higher-order modes. Such structures with dampers allow for acceleration of multi-bunch beams, both in standing and in travelling-wave accelerating modality.This paper describes the design of two cavities made of multiple sectors that were fabricated at the Italian Institute for Nuclear Physics in Frascati, Italy (INFN-LNF), assembled by means of clamping and then joined with the Tungsten Inert Gas welding in order to preserve the hardness of the metal. These are three-cell standing-wave X-band accelerating cavities, to be operated in the π-mode. We report the low-power RF tests of the first one, made of two halves, and the RF design of the second one, made of four quadrants. Both structures were built for high-gradient tests at SLAC National Accelerator Laboratory.

Effects of a nickel-based alloy interlayer on electrically assisted pressure joining of pure titanium and stainless steel 304

This study focuses on the solid-state joining of commercially pure titanium (CP-Ti) and stainless steel 304 (SUS304) using electrically assisted pressure joining. A nickel-based alloy foil acting as an intermediate layer (Ni interlayer) is inserted between two base materials during joining to avoid the formation of a detrimental TiFe intermetallic due to direct contact of the CP-Ti and SUS304. The solid-state joining process can be completed within 2 s. The effectiveness of incorporating the Ni interlayer on joint quality is systematically investigated by comparing joints made with and without the use of a Ni interlayer. Microstructure analysis reveals that the Ni interlayer plays a critical role in improving joint quality by forming a nanocrystal structure and preventing the formation of TiFe intermetallic. Furthermore, the joint with a Ni interlayer increases the joint shear strength by at least 50% more than a joint without a Ni interlayer in the same joining period and exhibits tensile ductile fracture at the heat-affected zone in the CP-Ti side during tension. The present study provides valuable insights into the benefits of Ni interlayers in the rapid and reliable creation of solid-state joints between CP-Ti and SUS304 using electrically assisted pressure joining.

High-Precision Integration of Optical Sensors into Metallic Tubes Using Rotary Swaging: Process Phenomena in Joint Formation

A novel process design for the damage-free and highly accurate positional integration of an optical multi-axial force sensor into a hollow tube by means of rotary swaging is introduced. Numerical simulations reveal the relevant process phenomena of thin disc joining inside a pre-toothed hollow tube and help us to find an optimal process design. Experimental trials show the significant effect of the axial material flow and the number of tools on the rotary swaging process. By taking these effects into account, successful form- and force-fit joining of the sensor carrying discs into the tube can be achieved. Successful joining of an optical sensor for bending force and torque measurement shows hysteresis-free sensory behavior and thus backlash-free joining of the sensor carrier discs. The paper concludes with a presentation of the results of a numerical study on a potential closed-loop approach to the joining process.

Manufacturing high-strength and corrosion-resistant 6063Al joints by an ultrasonic-assisted liquid and solid phase diffusion technology

High corrosion-resistance aluminum alloy joint obtained by filler metal containing Sn at relatively low temperatures is a longstanding goal for electronic products. In this research, 6063Al alloys was joined by a novel ultrasonic-assisted diffusion bonding via liquid phase and solid phase synergistic diffusion. It was performed via a hypereutectic interlayer of Zn-30Sn at 360 ℃ to joining 6063Al, obtaining a Zn-Al eutectoid structures joint. By the ultrasonic vibrating, the breaking of oxide film, the diffusing of liquid and solid state had been occurring in sequence during the joining process. It resulted in a series of diffusing phase transitions from “η-Zn phases + Sn-Zn eutectic structures” to “Zn-Al eutectoid structures + η-Zn phases”, and finally to “full Zn-Al eutectoid structures”, which were driven by the grain boundary penetration and chemical potential, respectively. The joints possessed a higher strength than the base metal. The joints with Zn-Al eutectoids have a better corrosion resistance that the tensile strength reduced 37.3% after a corroding of 72 h in 3.5 wt% NaCl solution in comparison with the soldered joints. Finally, the mechanism of ultrasonic accelerated diffusion, joint formation process and mechanism of improving corrosion resistance were discussed in detail.

A novel combined rivet and its effect on mechanical properties and failure behavior in double-sided self-pierce riveting

Double-sided self-pierce riveting (DSSPR) has great application potential in joining the same or dissimilar sheets due to its simplified die structure, high joining efficiency, and smooth joint surface. Previous studies have shown that changing rivet parameters, such as chamfered angle position, can improve joining strength, but the improvement effect is still relatively limited. In this paper, to significantly enhance the joining strength, a novel combined rivet structure was proposed and used in the DSSPR process of Al5052 sheets, and its effect on strength improvement and the underlying mechanism were investigated. Morphological change, strain, and stress distribution of the combined rivets during the joining process were investigated through experiments and numerical simulations. Tensile shear tests were conducted to compare the shear strength of the combined rivets and conventional rivets. Moreover, the failure behaviors of joints including macroscopic failure mode and microscopic surface morphology were analyzed, and the mechanism for combined rivets to enhance the joining strength was illustrated. Results showed that adopting the new combined rivets can significantly improve joint strength. Compared with a single conventional tubular rivet, the tensile shear strength and energy absorption of combined rivets can increase by up to 91% and 261%, respectively. Two types of failure modes were discovered according to the failure behaviors of sheets, which were characterized by the detachment of rivets and the tearing characteristics of the sheet. This paper provides a new approach for the rivet design and joining strength improvement strategy for the DSSPR process.

Detecting malicious proxy nodes during IoT network joining phase

During the joining phase of an IoT network, when a node plays the role of a proxy node, it becomes responsible for forwarding Join Requests and Join Responses between the joining node and the network coordinator. If a proxy node is malicious, it has the potential to prevent new nodes from joining the network or direct them towards another entity impersonating the coordinator. Therefore, the joining phase is a critical stage for ensuring network security.In this paper, a robust system for detecting malicious proxy nodes during the joining phase is presented. This solution involves the coordinator maintaining a log table that records the participation frequency of each node as a proxy node. Following each joining phase, the coordinator receives a lightweight end-to-end encrypted packet from the joining node, containing information about any malicious proxy nodes encountered during the joining process. Having these data, the system calculates the number of legitimate proxy node participation for each node. The detection system utilizes these factors, along with a range of tunable parameters, to categorize nodes as either malicious or honest. Furthermore, this solution takes into account various potential attacks on the detection process, originating from both proxy nodes and joining nodes.This solution was integrated with a previously proposed consensus-based authentication mechanism for the 6TiSCH protocol. The evaluation includes both theoretical analysis and simulations, taking into consideration diverse parameters and attack scenarios. The results from the theoretical analysis align with the simulation outcomes, confirming the efficacy of our detection system in identifying malicious nodes and its resilience against potential attacks.

The role of interlayers in the flash joining of Y2O3 transparent ceramic to titanium alloy

The application of soft metal interlayers in the joining process is an efficient strategy for enhancing the joint strength. In this study, we select the Ni interlayer from among three soft metals, meticulously adjusting various parameters to achieve optimal joint performance. These parameters include the interlayer thickness, temperature, current density and joining time. When the thickness of the Ni interlayer is 600 nm, the Y2O3/Ni/Ti–6Al–4V joint strength reaches a maximum of 65 ± 4 MPa at 900 °C with a current density of 1.5 mA/mm2 for 30 s, improved by 81.6% than Y2O3/Ti–6Al–4V direct flash joining. During the flash joining process, the presence of a threshold electric field induces the formation of oxygen vacancies. These vacancies tend to accumulate at the interface, thereby facilitating rapid material transfer and reaction. Notably, the role of interlayers here is not for traditional stress relieving, but to enhance the metallurgical bonding and promote the defect reaction. Wherein, the latter includes an increase in oxygen vacancies and acceleration of atomic diffusion. Hence, it is anticipated that a wider variety of interlayers will be explored for application in flash joining technologies.

The effect of heat input on tensile strength, Vickers hardness, and microstructure on DMW of AISI 1015 and 304L SS through the GMAW process

This experiment was to evaluate the effect of heat input on tensile strength, Vickers hardness, and microstructural observations.The materials welded are AISI 1015 and 304L SS, and the joining process is Gas Metal Arc Welding (GMAW). The filler electrode used is ER70S-6 with a diameter of 1.2 mm, and the workpiece size is 300 x 125 x 3 mm with a butt-joint connection. The variations in welding current applied are 120, 130, and 140 A. Meanwhile, the voltage and welding speed in the experiment were kept constant.The maximum tensile test index was 380.08 MPa, and the Vickers hardness index was 376.85 HV, with the maximum heat input being 0.5943 kJ/mm. The macro- and microstructure, as well as structural inspection of the welded joints, were observed in the experiment. The best heat input effect for the DMW technique between 304L SS and AISI 1015 is 0.5943 kJ/mm at a plate thickness of 3 mm.Dissimilar Metal Welding (DMW) is widely applied in the power generation industry. Materials generally joined using the DMW technique are austenitic stainless steel (304L SS) and low carbon steel (AISI 1015).Using the proposed heat input approach is important for the dissimilar welding industry application to obtain the right product for its expected use.This paper presents the differences in heat input to reveal the weld properties by dissimilar welding processes, where the properties will be adapted for a particular use. Particularly in the application of dissimilar joints between 304L SS and AISI 1015 with a thickness of 3 mm, which requires an average tensile strength of around 380.08 MPa and an average yield strength of about 320.16 MPa, the heat input parameter can be recommended as 0.5943 kJ/mm.

A new deformable self-clinching fastener

This work proposes a novel deformable self-clinching fastener for producing hidden lap joints suitable for both structural and electric power distribution applications. The fastener, characterized by an axisymmetric concave shape, is employed to fabricate hybrid busbar joints between electrically conductive strips of different materials and thicknesses. The self-clinching process with the new deformable fastener involves machining dovetail holes in both conductors and applying a squeezing force to the fastener to create a form-closed mechanical joint. The work encompasses both experimental investigations and numerical modeling using finite element analysis and is carried out on unit cells made from aluminum and copper conductors, which are representative of the joining process. The investigation evaluates force requirements, conducts destructive testing, and performs thermo-electric characterization of the new joints to conclude on the suitability of the new deformable self-clinching fastener for electric power distribution applications. Results indicate that while copper fasteners necessitate greater squeezing forces, they offer superior mechanical and thermo-electrical performance compared to aluminum fasteners in hybrid busbar joints.

Effect of thermal-mechanical conditions on strength of silanized Al alloy/CFRTP hybrid joint made by thinning-controlled hot pressing

The strength of thermal-assisted joined metal and carbon fiber-reinforced thermoplastics (CFRTP) is dependent on physical and chemical interactions at the joining interface, which are strongly influenced by heat and pressure. Currently, there is a lack in deep research on effect mechanism of changeable pressure on the joining quality, limiting the joining condition optimization of the thermal-assisted joining process. In this study, an improved hot-pressing joining process with added thinning displacement control was adopted to study the effect of the joining pressure on the structure and strength of the interface between a silane-treated Al alloy and three CF-Polyamide-6 (CF/PA6). A high-strength, thinning-controlled lapped joint of Al and CF/PA6 could be realized by the proposed process, regardless of the fiber volume fractions in CF/PA6. At temperatures above the melting point of PA6, higher pressure typically resulted in higher interface strength. However, as the temperature approached the decomposition temperature, the joints under higher pressure tended to exhibit lower strength. The underlying mechanism of the interface strength variation with pressure was investigated by analyzing the effects of the joining conditions on the chemical reaction conditions, the resolidified-resin structure near the interlayer, and the existence of defects. These findings lay the foundational groundwork for future endeavors in metal/composite joining, offering potential benefits for industrial applications and environmental sustainability in the automotive sector.

Force reduction of friction stir welding and processing of steel

Friction stir welding and processing (FSW&P) is considered as a new fabrication method for canisters and repair of existing dry cask storage system canisters (generally made of austenitic stainless steel). Low heat input compared to fusion joining processes and grain refinement associated with low-temperature FSW&P result in a material with improved mechanical properties and equivalent generalized corrosion performance relative to the base metal. But FSW&P of austenitic stainless steel requires significant tool forge axis force to produce a weld (or a run). Exploratory runs utilizing forge axis force control were conducted to investigate the minimum force required to achieve defect-free runs. The correlation between forge axis force and resultant plunge depth was also investigated. Furthermore, detailed microstructural characterization was conducted to display the microstructural variation within the nugget zone.

Brazing Temperature Effects on the Microstructure and Mechanical Properties of Ti-45Al-8Nb Joints Using TiZrCuNi Amorphous Interlayer

Ti-45Al-8Nb alloy is widely utilized in the lightweight design of the aerospace field because of its excellent properties. In order to make full use of this alloy, it is important to carry out relevant research, such as into the joining process of Ti-45Al-8Nb alloy. In this work, Ti-45Al-8Nb alloys were successfully connected by a TiZrCuNi amorphous interlayer, which was fabricated using the rapid solidification method. Ti-45Al-8Nb joints were composed of two zones. The typical microstructure of a Ti-45Al-8Nb joint was Ti-45Al-8Nb/AlCuTi + Ti3Al/(Ti, Zr)(Cu, Ni) + (Ti, Zr)2(Cu, Ni)/Ti3Al + AlCuTi/Ti-45Al-8Nb. The diffusion of elements between the interlayer and the substrate was enhanced by increasing the brazing temperature, which resulted in an increase in the thickness of the interfacial reaction layer. The maximum shear strength was 171.2 MPa, which was obtained at 930 °C. The typical cleavage fracture was found in all of the Ti-45Al-8Nb joints. The mechanical properties of the joint were compromised at high brazing temperature due to the presence of excessive (Ti, Zr)2(Cu, Ni) phase and coarse Ti3Al phase, both of which are inherently brittle and harmful to the shear strength of the obtained joint.

Achievement of high-strength Al/CFRP hybrid joint via high-speed friction stir lap joining and laser texturing pretreatment parameters variation

This paper presents the achievement of a high-strength Al/CFRP hybrid joint through a high-speed friction stir lap joining process, combined with variations in laser surface texturing pretreatment parameters. The study examined the impact of laser surface texturing parameters by varying the depth, interval distance and width of the laser texture. By adjusting laser texturing parameters, the softened PA66 was fully infused into the textured grooves on the aluminum surface, leading to a significant reduction in interfacial voids and cracks in Al/CFRP. The preliminary tensile shear test showed that the hybrid joint broke at the CFRP base material, indicating that the laser texturing exhibited excellent Al/CFRP interface strengthening ability. Further compression shear tests were applied to reveal the actual interfacial load-carrying performance for comparison. The maximum shear strength of 25.5−1.34+0.7 MPa was achieved at a joining speed of 3000 mm/min. Additionally, a mathematical model was proposed to assess the strengthening impact of laser texturing parameters, considering micro-texture geometry and interfacial defects. The tearing of PA66, detachment of carbon fibers, and the breakage of carbon fibers were the three primary types of fracture modes identified at the Al/CFRP interface. The joining mechanism revealed that both mechanical interlocking and the chemical bonding of Al-O-C contributed to the increase in joint shear strength. This study presents a credible method for producing high-strength Al/CFRP lightweight structures.

Single-step self-punching lockbolt process for aluminum sheets without pre-hole

For the mechanical joining of aviation-grade aluminum alloys, the study introduces an innovative approach using self-punching lockbolts. This method involves the utilization of a profiled collar and a specially designed bolt to seamlessly join EN AW-2024 T42 aluminum sheets, up to a thickness of 8.0 mm, without the need for pre-holes. In this process, when the aluminum sheets are punched, the collar undergoes slight deformation, effectively functioning as a die. Subsequently, the collar is systematically formed by applying increased force. By fine-tuning the design of the bolt ring groove, it becomes feasible to create a joint with a bolt length that accommodates sheet thickness variations of up to 1.6 mm. To facilitate this development, the joining process was meticulously designed and the auxiliary part was optimized with the aid of numeric simulation tools. The process simulation enabled the identification of deformation mechanisms within the collar, accounting for both geometry and material properties. The important factors influencing collar deformation include collar thickness, shoulder height, and shoulder diameter. Furthermore, experimental investigations were conducted to assess the mechanical properties of the joint and evaluate how material-specific factors influence joint failure behavior. It can be seen that the formation of the mechanical fit is influenced by the ring groove depth and the fitting position. The joints failed under shear tensile load exclusively at the bolt head.