Joining Pressure Research Articles

Comparative study on the performance of butt fusion-welding processes for nuclear safety class large-diameter thick-walled PE pipes

New technologies in polymer synthesis and pipe extrusion equipment have led to the commercialization of high-performance, large-diameter, thick-wall high density polyethylene (HDPE) pipes. They have been used in the field of seawater transport and cooling to replace metal pipes, due to their advantages of high corrosion resistance and extensibility. Connection of HDPE pipe is important as it determines the safety of the entire piping system. Butt fusion welding is commonly used for HDPE pipe connection but may cause the formation of weak points in the welded joints, interfering the reliability of the pipeline system in the application of nuclear power plants. At present, there is a lack of research on evaluating the performance of welded joint for large-diameter thick-wall HDPE pipes made by butt fusion-welding. The purpose of this study is to investigate the influence of three different butt fusion-welding processes, i.e., single low pressure (SLP), single high pressure (SHP) and dual low pressure (DLP), by evaluating the performance of their welded joints, including characterizing tensile strength, extensibility, crystallinity and hardness. In specific, a thick-wall HDPE pipe with OD of 812.8 mm and wall thickness of 74 mm which is certified for nuclear safety class was used for study. Representative specimen from the outer, middle and inner part across the wall of the main pipe body and welded joints were taken for testing. Different test methods and specimens were designed to assess the feasibility of evaluating the welding performance from different welding process. The results showed that the mechanical properties of different locations of the welded joints were different, and the tensile strength and fracture energy of the middle part of the joint were lower than that of the inner and outer parts, which could be caused by the difference in the crystallinity and thickness of the melting zone influenced by welding processes, as can be seen from the analysis of DSC test and morphology observation. Hardness testing was conducted on the section of the welded joints, and it revealed that the micromechanical properties of the welded joints in the region of the heat-affected zone were enhanced significantly, which may be due to the annealing effect caused by welding process. In summary, The DLP process resulted in the best extensibility of the welded joints among three processes, suggesting that the joining pressure from welding process plays an important role in affecting the extensibility of the welded joints.

Influence of Metal Surface Structures on Composite Formation during Polymer–Metal Joining Based on Reactive Al/Ni Multilayer Foil

Progressive developments in the field of lightweight construction and engineering demand continuous substitution of metals with suitable polymers. However, the combination of dissimilar materials results in a multitude of challenges based on different chemical and physical material properties. Reactive multilayer systems offer a promising joining method for flexible and low‐distortion joining of dissimilar joining partners with an energy source introduced directly into the joining zone. Within this publication, hybrid lap joints between semicrystalline polyamide 6 and surface‐structured austenitic steel X5CrNi18–10 (EN 1.4301) are joined using reactive Al/Ni multilayer foils of the type Indium–NanoFoil. The main objective is to examine possibilities of influencing crack initiation in the foil plane by variation of joining pressure and different metal surface structures with regard to geometry, density, and orientation. Thus, the position of foil cracks is superimposed onto the metal structure and associated filling with molten plastic is improved. Consequently, characterization of occurring crack positions as a function of joining pressure and metal structure, analysis of the composite in terms of structural filling and joint strength, as well as possible causes of crack initiation are evaluated.

Effects of different heating strategies on the joint properties during infrared welding of glass fiber reinforced polyamide 6

In infrared welding, the heating phase is the phase offering the highest flexibility of choice regarding the process parameters. In this phase, the process parameters such as the heating time, emitter power, and emitter-component distance can be individually selected and combined with each other. The defined heating phases have a different influence on the joining components. In this work, the effects of four heating strategies and their influence on the resulting temperature distribution over the joining surface, the possible thermal material degradation, the morphology of the joining zone, and the short-term tensile strength of the welded samples are investigated. In order to investigate the morphology, microsections are prepared which enable transmitted light microscopy of the black PA6 GF50 used. In summary, it can be concluded that different heating strategies have a different influence on the material even if the generated melt layer thickness is kept the same. Three of the four strategies result in material degradation on the joining surface. However, this has almost no effect on the resulting short-term strength of the weld. The results allow the interpretation that a high joining pressure compensates for the influence of the material damage by pressing the damaged material into the bead.

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.

Fabrication of High-Temperature Solder by Zn Plating Films Containing Al Particles

This study investigated the microstructure and melting point of the Zn–Al composite electroplating film. The cross-sectional microstructure and shear strength of the joints made from the plating films were also evaluated. Zn and Al were confirmed in the plating films from initial microstructure observation. The plating film prepared by a plating bath without cationic surfactant melted near the melting point of Zn and the eutectic point of Zn–Al. When jointed at a joining temperature of 443°C, joining pressure of 5 MPa, and holding time of 5 min, multiple intermetallic compounds, Zn–Al eutectic layers, and unreacted Al particles were observed in the joint layer. From quantitative analysis, the multiple intermetallic compounds were estimated to be Zn–Ni and Zn–Al–Ni intermetallic compounds. The shear strength of the joints increased with increasing joining pressure but was lower than that of Sn–5Sb solder. Fracture after the shear test was observed at the interface between unreacted Al particles and Zn–Al–Ni intermetallic compounds, and inside unreacted Al particles.

Optimization of the Direct Diffusion Bonding Process Using Cu Stabilizing Layers of the REBCO Coated Conductors

Low resistivity joint technique for high-temperature superconducting tapes is one of the most indispensable techniques for practical applications. In the present study, we propose solid phase joining technique to make direct joint of REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> (REBCO, RE:rare earth elements) tapes, as an alternative to conventional solder joining technique. In this solid phase joining technique, we directly join the copper stabilizing layer and get rid of the soldering material, so that we can expect reduction of joint resistivity. The important points for direct joining technique are to remove the oxide layer on the metal surface and to make the joint surface adhere to each other. It means that, after removing the oxide film on the surface, it is necessary to have an optimum pressure so that sufficient adhesion can be obtained while maintaining a clean surface. First, we examined the type and concentration of the acid used to remove the oxide film. Next, the joining pressure, joining atmosphere, and joining time were optimized, while the joining temperature was fixed at 200°C. Finally, we have succeeded in joining REBCO tape with this technique. The measured resistivity at liquid nitrogen temperature was about 50-80 nΩcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Fatigue behavior analysis and life prediction of all-composite joint

In this study, we join the thermoplastic composite using thermoplastic composite fastener (TPCF), and a physics-guided neural network is designed to predict the fatigue life of the all-composite joint. The experimental results show that TPCF is only 19.0% of the weight of the titanium rivet. Under a proper joining pressure of 1.50 MPa, the all-composite joint is well connected by an ‘S-shape’ interlayer, the fatigue resistance is improved. After hot-press joining, the lower cooling rate of 1 °C/min prolongs the crystallization process of TPCF and composite hole wall, thus enhancing the fatigue life to 105.8 cycles. The experimental results are summarized as physics constraints guiding the neural network. Similar fatigue data are migrated by producing a significant constraint. The loss function is the negative logarithm of the likelihood, which can predict both mean and deviation of fatigue life. The predicted results agree well with the experiments.

Investigation of Shear Strength and Microstructure Formation of Joined Ni Superalloys Using Ni Nanopastes.

By using Ni nanoparticles, the bonding of Ni base superalloys can be achieved with shear strengths well above 200 MPa in a joining process at comparatively low temperatures between 675 °C and 975 °C. This is enabled due to the high surface-to-volume ratio of nanoparticles, which leads to distinctly lower melting and sintering temperatures than those of the corresponding bulk material. The nanoparticles in this study are employed in high-metal nanopastes, whereby different chemical compositions of the pastes and different sizes of Ni nanoparticles were investigated. The results for the joining of Ni base superalloys showed that both size and composition had a significant influence on the achievable strengths. In addition, an extensive examination was conducted to reveal the influence of the process parameters joining temperature, holding time and joining pressure on the shear strengths as well as microstructure. It was shown that the temperature exerted the most influence on the strengths and the microstructure. The joining pressure also had a significant influence. The holding time, on the other hand, did not have a major influence on the strengths and in some cases even showed an unexpected behavior, as the values decreased for some combinations with longer holding time.

Process Improvement of Continuous Induction Welding of Carbon Fiber-Reinforced Polymer Composites

Continuous induction welding is particularly suitable for joining carbon fiber-reinforced polymer composites (CFRPC) with thermoplastic matrix, as the energy required for melting the thermoplastic matrix is introduced without contact and leads to intrinsic volumetric heating of the adherends. However, the great potential of fast heating cannot be fully exploited. Therefore, a process improvement of continuous induction welding was carried out, which follows three complementary approaches. The first approach provides for the development of an adapted laminate structure. Compared to a conventional CFRPC laminate, the adapted laminate shows a heating in the joining zone that is approx. 16 K/s faster. The second approach intends to improve the currently used cooling system to cool the induction coil faced laminate surface. Spray cooling proved to be the most suitable method. Compared to pressurized air cooling, it was possible to achieve a temperature difference between the joining zone and the inductor faced laminate surface that was approximately twice as large. The third approach aims at the simulation-based improvement of the consolidation phase. This model can be used to determine the joining pressure and pressure time required to achieve intimate contact.

Laser-induced combustion joining of Cf/Al composites and TC4 alloy

The Cf/Al composites were joined to the TC4 alloy via the laser-induced combustion joining method. The exothermic reaction of the interlayer provided the required energy for the joining process. By combining the theoretical calculation and experiment, the chemical composition of the Ni–Al–Zr interlayer was designed. The microstructure and mechanical properties of the joint were investigated. The results show that the addition of Zr slightly weakened the combustion reaction of exothermic interlayer but played a key role in the successful joining. Ni–Al–Zr interlayer reacted with substrates, forming a TiAl3 layer adjacent to TC4 alloy and NiAl3, Ni2Al3 layers adjacent to the Cf/Al composites. Zr content dominated the microstructure and shear strength of the joint. When the Zr content was 5 wt.% under the joining pressure of 2 MPa, the joint had a maximum shear strength of 19.8 MPa.

Dissimilar joining mechanism, microstructure and properties of Ni to 316 stainless steel via Ni-Al thermal explosion reaction

Abstract To meet the requirements of energy-efficiency and high quality joining in the emerging industries field, a novel thermal explosion (TE) joining method was developed. The dissimilar Ni/316SS joint was first obtained by the TE reaction technology. The Ni-Al mixed powder was selected as TE reaction system, and the reaction product was used as interlayer. The effect of temperature (800, 850 and 900 °C), hold time (5, 10, 15 and 20 min) and joining pressure (0, 10, 20 and 30 MPa) on interfacial microstructure, diffusion behavior and mechanical properties of Ni/316SS joint were investigated. The maximum combustion temperature of Ni-Al interlayer during heating process was 1655 °C and a significant exothermic phenomenon was lasted for 2 s. 316SS(Al), Fe2Al5(Ni, Cr) and serration-like Ni5Al3 and Ni3Al were detected at the interface containing a reaction layer because of element diffusion. The maximum shear strength of the Ni/316SS joint was 65.2 MPa, and the failure is characterized by typical brittleness fracture. The fracture mode is the combination of partial spalling and fracture of the interlayer. The post heat-treatment assisted TE joining technique significantly shortened the bonding process of the dissimilar Ni/316SS joint at moderate temperatures, realizing the low energy and efficient joining between Ni and 316SS.

Highly mechanical and high-temperature properties of Cu–Cu joints using citrate-coated nanosized Ag paste in air

Today, a growing number of third-generation semiconductor-based power devices are used in products that can continuously operate at high temperatures for extended periods of time. Hence, traditional tin-lead and lead-free solders are no longer suitable for modern electronic packaging. A common method is to apply Ag paste for bare Cu–Cu joints under an inert or reductive atmosphere. In this study, the citrate-coated nanosized Ag paste was utilized to generate robust bare Cu–Cu joints under atmospheric conditions. The average size of citrate-coated Ag particles was approximately 4.76 ​nm after being cleaned by deionized water and acetone. The effects of process parameters, such as cleaning, joining temperature, holding time, and joining pressure, on the mechanical properties of the bare Cu–Cu joints were thoroughly investigated. Increasing washing and joining temperatures resulted in a shear strength increase of up to 28.2 ​MPa ​at a joining temperature of 260 ​°C after seven washes. In addition, a holding time of 30 ​min and a joining pressure of 1 ​MPa were selected as optimal process conditions for the application of citrate-coated nanosized Ag paste onto bare Cu–Cu joints. The newly developed Cu–Cu joints showed excellent thermal stability at 150 ​°C using the citrate-coated nanosized Ag paste. After long-term aging, the joints exhibited stability at 250 ​°C for 144 ​h, indicating a good high-temperature reliability for three-dimensional integrated circuits (3D ICs) fabricated under atmospheric conditions.

A tailored heating element for resistance welding of complex shaped joining surfaces

To obtain a larger freedom of design for structural components, a single wire heating element which is capable of welding large and complex shaped surfaces has been developed. The processing window for welds of endless-carbon-fiber-reinforced polyamide 6 (CF-PA6) using the developed heating element is investigated, varying the main process parameters electrical power, electrical energy and joining pressure. The influence of these process parameters on the quality of the welded joints is judged by single and double lap shear tests and by the analysis of micrographs. As a result, recommendations for the processing parameters are derived. The climate conditions of the specimens are varied to analyze the impact of moisture on the shear-transmitting joints whereby an accelerated method for conditioning of PA6 specimens is used. Furthermore, a sensor-free method for monitoring the temperature of the welding process is presented and compared with a classical measuring method.

Self-propagating synthesis joining of Cf/Al composites and TC4 alloy using AgCu filler with Ni–Al–Zr interlayer

The successful joining of carbon fiber-reinforced aluminum matrix (Cf/Al) composites and TC4 alloy can produce composite structure and meet the demands of lightweight in aerospace field. Up to now, few experimental researches have been reported on the joining of Cf/Al composites and TC4 alloy. In this study, the AgCu foils and Ni–Al–Zr compact were designed for the self-propagating high-temperature synthesis joining of these two materials. Cf/Al composites were joined with a reactive Ti plated on its joining surface. The typical microstructure of TC4/(AgCu/Ni–Al–Zr/AgCu)/Ti/Cf/Al joint was analyzed, and the effects of joining condition on microstructural evolution of the SHS joint were investigated. A thin reaction layer of Ni–Al–Ti intermetallic compounds was formed adjacent to the TC4 alloy. As a result, AgCu foils could reduce the effect of reaction heat on the substrates and improve the joint shear strength. When the thickness of AgCu foils reaches 150 μm, the Ni–Al–Zr interlayer mainly acts as auxiliary heat source. High joining pressure caused the active elements to diffuse into Cf/Al composites and weakened the shear strength of the joint. Finally, the joint shear strength could reach 36.4 MPa when the AgCu foils were 50 μm and the joining pressure was 2 MPa.

Effects of the joining process on the microstructure and properties of liquid-phase-sintered SiC-SiC joints formed with Ti foil

The joining of liquid-phase sintered SiC (LPS-SiC) ceramics was conducted using spark plasma sintering (SPS), through solid state diffusion bonding, with Ti-metal foil as a joining interlayer. Samples were joined at 1400 °C, under applied pressures of either 10 or 30 MPa, and with different atmospheres (argon, Ar, vs. vacuum). It was demonstrated that the shear strength of the joints increased with an increase in the applied joining pressure. The joining atmosphere also affected on both the microstructure and shear strength of the SiC joints. The composition and microstructure of the interlayer were examined to understand the mechanism. As a result, a SiC-SiC joining with a good mechanical performance could be achieved under an Ar environment, which in turn could provide a cost-effective approach and greatly widen the applications of SiC ceramic components with complex shape.

An investigation of the ultrasonic joining process parameters effect on the mechanical properties of metal-composite hybrid joints

The ultrasonic joining process was recently introduced as an alternative concept to join through-the-thickness reinforced metal-composite hybrid structures. In this work, the investigation of joining process parameters effect on the joint mechanical performance of Ti-6Al-4V-glass-fiber-reinforced polyetherimide overlap joints was carried out by Box-Behnken design of experiments. The individual and combined effects of joining energy, sonotrode oscillation amplitude, and joining pressure on the ultimate lap shear force were elucidated by response surfaces method and analysis of variance. As a result of this study, a set of optimized joining parameters were obtained to produce joints with high ultimate lap shear force. The obtained reliable reduced model (R2 = 82%) displays a major influence of joining energy (25.3%) and sonotrode oscillation amplitude (21.2%) on the joint mechanical performance. Two-way interaction response surfaces were used to support strategies to optimize the maximum ultimate lap shear force. By comparing the optimized joint condition produced in this work with previously published results an improvement of 79% in ultimate lap shear force was attained, thereby, proving the potential of the proposed process optimization procedure.

Dissimilar Joining of Pure Aluminum to SiCp/Al-MMCs Using an AlMgGaLi Active Interlayer Foil

To broaden the application of advanced metal matrix composites in the electronic packaging industry, a lead-free AlMgGaLi interlayer was developed for active soldering of aluminum to aluminum metal matrix composites. The effect of joining pressure on the microstructure evolution, interfacial wettability and mechanical properties of the dissimilar joints was investigated. The experimental results indicated that as the joining pressure increased, the mean thickness of the bond seam was 46.02 μm, and solidification of a solid solution occurred (detected by SEM/XRD analysis). The composition of the Al-based solid solution (in atom%) was 86.52% Al, 9.32% Mg, 2.56% O, 1.5% Ga and 0.1% Si. The pressure improved the interfacial wettability by enhancing the atom diffusion between the interlayer and parent materials. The joint shear strength initially increased and then decreased, and a sound joint with a maximum shear strength of ~ 45 MPa was produced at 450 °C and 0.75 MPa. The fracture crack initially occurred at the interfaces of the Al/filler metal and then propagated mainly along the Al2O3 layer on the Al side. A novel model describing the pressure-induced microstructure changes within the joint and the formation of an Al2O3 diffusion barrier layer at the Al/filler metal interface is proposed.

Application of AlMgGaLi foil for joining copper to SiCp/Al-MMCs for high-temperature and high-power electronics

A novel lead-free foil (AlMgGaLi) with a melting point of 398.3 ~ 414.8 °C was developed for active soldering of copper to aluminum matrix composite. The effect of joining pressure on the microstructure, interface wetting and shear strength of the dissimilar joints was analyzed. When the joining pressure increased to 1 MPa, an Al-based solid solution with an atomic composition of 89.62% Al, 6.5% Mg, 3.1% O, 0.46% Cu, 0.23% Ga and 0.09% Si was formed within the bond seam and the thickness of the transition layer with copper dissolution was approximately 4.9 μm. The joining pressure improved the interfacial wettability of the dissimilar joint by enhancing mutual diffusion with a shortened interface layer, tailored the runout and the formation of bond seam, and controlled an appropriate thickness of the copper dissolution transition layer. Sound joint with a maximum shear strength of 94 MPa (~ 80% of parent composites) is achievable at 450 °C using the joining pressure of 1 MPa. The failure mechanism of the joints with the AlMgGaLi foil under shear stress has been revealed from the analysis on the interface layers of the joints with SEM/EDX/XRD. Our studies provide an important guideline for using an AlMgGaLi and other similar fillers for a successfully joining of copper to Al-MMCs for high-temperature and high-power electronic devices.

Effectiveness of electrically assisted solid-state pressure joining using an additive manufactured porous interlayer

A solid-state pressure joining using resistance heating as a heat source and adopting an additive manufactured metal porous interlayer between joining specimens is demonstrated. During the joining of 316L stainless steel cylindrical specimens, an electric current is directly applied to the joint under continuous axial compression. Defect-free joints are successfully fabricated with a lower joining pressure when applying the porous interlayer with a lower compressive strength and higher electric resistivity. The microstructural analysis confirms that the porosity is eliminated as a result of the compressive deformation during joining, and recrystallization takes place in the interlayer.

Laser transmission welding of automotive headlamps without a clamping tool

A car’s front headlamps represent an important design element in the automotive industry. In order to protect them from external influences, the complex lighting technology is inserted into a stable plastic housing, which is then sealed with a transparent plastic lens. The combination of the transparent lens and the black housing is eminently suitable for laser transmission welding (LTW); the numerous advantages of this technique can be exploited here, especially with regard to design. Due to tolerance compensation, it is state of the art to join automotive headlamps by adhesive bonding. In the investigations of the KTP, a prototype with a special geometry of the joining area was evolved and analyzed. Because of segmental snap-fits, which apply the necessary joining pressure, gaps can be eliminated during the welding process as a result of the setting of the lens. With this special geometry of the joining area, a clamping tool is not necessary anymore. The two parts are welded quasi-simultaneously by a laser scan system with a fast z-axis. Also, the typical material combinations (PBT+ASA GF20, PC) of automotive headlamps were analyzed by using rectangular overlap specimens and American Welding Society specimens.