Improvement Of Joint Strength Research Articles

Improvement of Joint Strength of TC4/AZ91D Bimetal in Solid-liquid Compound Casting Process Using Cu-Ni Composite Interlayer

Improvement of Joint Strength of TC4/AZ91D Bimetal in Solid-liquid Compound Casting Process Using Cu-Ni Composite Interlayer

Effect of the Ni plating on Al–Cu dissimilar metal laser welded joint

In this study, the joint strength and interfacial microstructure of Al–Cu laser welded joints are investigated to understand the effect of Ni plating. Cu without plating and Cu plated with 1 μm and 4 μm of Ni were laser welded with Al, respectively, and their differences in joint strength and microstructure were comparatively analyzed. Macrostructure observations showed that the plating had no effect on the change of weld pool shape. Lap shear tests revealed that there was a distinctive improvement in joint strength with the Ni plating. Under a 1.4 kW laser power condition, it was noted that the sample with 4 μm Ni plating showed a 49% increase in load and a 100% increase in elongation compared to the sample without plating. Fracture surface observations revealed that Ni addition has changed the crack propagation path resulting in the increased joint strength. Microstructural analysis showed that the Ni is occupied in intermetallic compounds (IMCs) such as Al3Cu2, AlCu, and Al2Cu3 developed at the interface between Cu and Al2Cu which were known as the primary crack propagation phase in Al–Cu laser welded joint. Additionally, increases in their thickness and changes in their shapes to irregular wavy forms were observed, potentially reducing load concentration and increasing joint surface area, facilitating stable joint formation. Density functional theory calculations showed that the IMCs with Ni undergo contraction in the cell volume suggesting solid solution strengthening of IMCs by Ni addition.

Atmospheric-pressure plasma jet texturing of C/C composites for improved joint strength

This study explores the use of air-fed atmospheric pressure plasma jets (APPJs) as a pre-joining treatment for 3D carbon fiber-reinforced carbon matrix composites (C/C) with the aim of both creating a textured surface that resembles a brush structure and improving the joint strength.The effects of various treatment time lengths on the mass loss, etching depth, and surface texture were investigated using SEM and confocal microscopy. An optimal process time of 30 s was selected, while keeping the other process parameters fixed (air flow of 1750 l/h and nozzle-sample distance of 5 mm). Wetting tests were conducted at 1000 °C, on both untreated and pre-treated C/C surfaces by means of liquid TiCuNi brazing alloy, and low contact angles of about 20° were measured. C/C–TiCuNi–C/C and C/C–TiCuNi–Cu joints were then produced, and their interfacial reactivity was evaluated. The apparent shear strength measured for the APPJ-treated C/C–Cu joints was 140 % higher than the value recorded for the untreated joints, thus confirming the effectiveness of the treatment.Even though a further investigation is needed in which an optimization of the process parameters should be included, this preliminary study has revealed the viability of APPJ as a promising technique to enhance the bonding of C/C composites in dissimilar assemblies and to improve the joint quality.

Shear mechanism of RCS joints with whole column-section diaphragm

The authors proposed a new precast RC column-steel beam (RCS) joint with whole column-section diaphragm, aiming to address the shortcomings including bearing failure and difficulty in prefabrication of the RCS joint details available in the existing literature. Due to its unique details, the proposed RCS joint may have a dissimilar force-transferring mechanism from the conventional beam-through type RCS joint. Moreover, the effect of various parameters on this novel joint was still unclear by limited test results. The objective of this study was to clarify the shear mechanism of the proposed joint and the impact of critical parameters. Specimens with different axial load ratios and thickness of parallel FBPs were tested under cyclic loading. The results showed that the increase in axial load ratio and thickness of parallel FBPs improved joint strength in this test. A detailed three-dimensional finite element (FE) model was developed and verified using the experimental results. The difference in the force transferring between the proposed joint and conventional beam-through RCS joints was explained in detail based on the numerical results. The dowel action of longitudinal column bars were evident in the proposed joint and the orthogonal FBPs were ineffective in activating the inner concrete strut. A parametric study was further conducted. The impacts of width of parallel FBPs, thickness of orthogonal FBPs, and axial load ratio were investigated. The joint strength linearly increased with the width of parallel FBPs. A parabolic distribution of shear stress in the parallel FBP section was obtained, while the yield zone was concentrated in the central area of the parallel FBP. The ductility could be improved with the thickness of orthogonal FBPs when the thickness was less than 10 mm. Further increasing the thickness of orthogonal FBP beyond 10 mm did not significantly affect the overall joint behavior. The joint may attain the optimal shear strength when the axial load ratio is between 0.3 and 0.4. The modeling approach in this study could be adopted as an effective tool to assess joint behavior. Moreover, the conclusions obtained by numerical study potentially promoted the application of the proposed joint.

Ultrasonic welding of Cu cables bonding: Tensile, porosity and evolution of microstructure

Tensile strength, porosity and microstructure evolution of ultrasonic bonding for BVR2.5 Cu cables at different welding energies were investigated. By X-ray computed tomography and modification of the Johnson-Cook model, the predictive model of porosity was developed for the first time to assess joint strength. When the porosity was lower than 19%, the joint formed a good bond and reached the tensile strength of 585.7 ± 17.9 N. The maximum joint tensile strength was achieved at about 10% porosity. The Cu grains at the interface underwent plastic deformation, discontinuous dynamic recrystallisation and dynamic recovery to form a good bond. Interfacial grains are refined by ultrasonic vibrations, but the reduction of the porosity is the critical factor in improving joint strength.

Optimization of process parameters for improvement of joint strength of dissimilar aluminum alloys by friction stir welding with an activated flux of titanium diboride

Optimization of process parameters for improvement of joint strength of dissimilar aluminum alloys by friction stir welding with an activated flux of titanium diboride

Control of the Weld Heterogeneity by Using a Novel Counter Variable Pin Shoulder Rotation Friction Stir Welding: A Simulation and Experimental Study

Abstract Friction stir welding (FSW) produces inhomogeneous mechanical and metallurgical properties in the weld, which further require post-weld processing to control the heterogeneity. In the present study, the heterogeneity in the weld is reduced through counter-variable rotation friction stir welding (CVRFSW). The material flow and temperature distribution significantly affect the inhomogeneity of the FSWed properties which has been studied by developing a three-dimensional Lagrangian method-based viscoplastic model. The material flow, strain rate, and temperature distribution in conventional FSW (CFSW) and CVRFSW are studied quantitatively. The study revealed that CVRFSW improved joint strength and reduced the inhomogeneity of temperature, strain, and hardness. At a 10% lower shoulder speed than a pin, the weld strength improved by 16%. The simulation predicted that the temperature difference between the advancing side (AS) and the retreating side (RS) was 36 °C in CFSW, which was reduced to 8 °C in CVRFSW. Material deformation in CVRFSW occurred at a strain rate more than twice that of CFSW, and the asymmetry of strain rate between AS and RS reduced to one-fifth. Microstructures and their orientations of the welds were studied in detail. These findings contribute to the understanding of CVRFSW processes for enhanced weld quality and mechanical performance for industrial applications.

Temperature field calculation of rail flash welding

The forging stage of rail flash welding has a decisive influence on joint strength, and the study of the temperature distribution in the process has an important role in further improving joint strength. In this paper, three calculation methods for the temperature field are given. First, the finite element model of the temperature field before forging rail flash welding is established by using the transient heat module of Ansys software and verified by infrared temperature measurement. Second, the temperature distribution of different parts of the rail before flash welding is obtained by using infrared thermal imaging equipment. Third, Matlab software is used to calculate the temperature of the non-measured part. Finally, the temperature distribution function along the rail axis is fitted through the temperature measurement data. The temperature distribution before the top forging of the rail flash welding can be used to analyze the joint and heat-affected zone organization and properties effectively and to guide the parameter setting and industrial production.

Effect of material position and tool offset on the microstructure and mechanical properties of friction stir welded AA7075/AZ31B with ultrasonic assistance

The primary focus of this study is to analyze how changes in material position and tool offset affect the microstructure and mechanical properties of dissimilar alloys (AA7075/AZ31B) joints. The study specifically examines these effects in normal and ultrasonic-assisted friction stir welded (UVaFSW) aluminum and magnesium-based joints. The experiment showed that the sound weld was achieved only when the AA7075 plate was placed on the advancing side (AS). The metallographic analysis showed that the use of ultrasonic vibration increased the flow of material in the nugget zone (NZ) and improved the length of interpenetration at the interface. Moreover, the intermetallic compound (IMC) layer thickness decreased throughout the interface during UVaFSW, improving joint strength. The maximum ultimate tensile strength was obtained at 1 mm tool-off condition for UVaFSW, i.e., 112.40 ± 7.24 MPa. Ultrasonic vibrations reduced the IMC thickness by up to 78 % at the middle of the joint interface. The fracture surface showed the ductile fracture mode in the case of UVaFSW compared to the FSW process. The current study establishes the framework for optimizing and controlling the welding process of dissimilar AA7075/AZ31B alloys, which possess considerable potential for use in the aviation industry.

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.

Metallurgical characteristics of AA6061 aluminium and AZ31B magnesium dissimilar joints by fusion welding technique.

Aluminium (Al) and magnesium (Mg) alloys are extensively used in the automobile sector because of their high strength-to-weight ratio, excellent castability low density and simplicity of recycling. Al-Mg structures used in the automotive sector can potentially reduce their weight. Although there is a significant opportunity for substantial cost reduction, the use of magnesium in aluminium structures remains restricted. This study aims to weld 3 mm-thick rolled sheets of AA6061 Al and AZ31B Mg alloy using the cold metal transfer (CMT) arc welding process. Three different filler wires (ER1100, ER4043, and ER5356) were used in the experiment. In this article, the mechanical and microstructure characteristics of Al/Mg dissimilar joints manufactured by CMT are evaluated and discussed in detail. Optical microscope (OM), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), and x-ray diffraction (XRD) were used to analyze the CMT-welded Al/Mg dissimilar joints. Of the three filler wires used, ER4043 (Al-5%Si) filler wire yielded defect-free sound joints due to the presence of Si, which improves the flow ability of molten filler during welding. The presence of Mg-rich intermetallics-Al12Mg17)and Al-rich intermetallics-Al3Mg2 were observed. The fractured area of the CMT-welded Al/Mg dissimilar joints revealed the presence of the Mg-rich intermetallics (Al12Mg17), which is responsible for the decrease in tensile strength. The reduction of intermetallics, particularly of Mg-rich intermetallics (Al12Mg17) is important for improving joint strength. RESEARCH HIGHLIGHTS: Cold metal transfer (CMT) arc welding was used to control the Al-Mg-rich intermetallics in the Al/Mg dissimilar joints. The microstructure, morphology and phase composition of the welded joints were studied by OM, SEM, TEM, EDS and XRD. The weld metal and AL substrate bonded with a strong interface, while weld metal and Mg substrate were joined at the epitaxial solidification area where the intermetallic compounds of Mg2Al3, Mg17Al12 and Mg2Si are generated. The weld metal on the Mg side experienced brittle fracture, with a continuous distribution of Mg2Al3, Mg17Al12 and Mg2Si.

Optimization of the active element and reinforcement proportion for improving joint strength of brazed Si3N4/42CrMo

Micron-TiN particles and Ti powder were introduced into the AgCu powder filler to design a particle-reinforced composite filler. This TiN particle (TiNp) modified brazing material was adopted to reliably braze Si3N4 ceramics onto 42CrMo steel, and the ratio of active element Ti to TiNp reinforcement was optimized for joint strength improvement. The reaction layer’s thickness (TiN+Ti5Si3) adjacent to the ceramic decreased by introducing TiNp. Nevertheless, the reaction layer’s thickness (TiC) at the 42CrMo side did not vary too much. TiNp showed excellent wettability with Ag-Cu-Ti braze, and there was no obvious reaction at the interface. Cu-Ti intermetallic compounds were formed and randomly distributed in the brazing seam. When the TiNp content did not exceed 8 vol.%, the joints’ mechanical properties first sharply decreased and then remained basically unchanged when Ti increased. Raising the TiNp content to 10 vol.%, the joint strength showed the changing trends of first increasing and then dropping by increasing Ti content. The bending strength reached the maximum value of 396 MPa when 8 vol.% TiNp and 4 wt.% Ti were adopted.

Interface behavior and pore distribution of Ti6Al4V/CFRTP joints affected by groove profile

This study investigated the effect of groove profile on interface behavior, pore distribution, and bonding mechanism between Ti6Al4V (TC4) and carbon fiber reinforced thermoplastic (CFRTP). Using an ultraviolet picosecond laser system, grooves with varying depth-width ratios (R) and distances between adjacent grooves (T) were precisely etched on the TC4 surface. Experiment results revealed that grooves effectively impede bubble coalescence and growth, reduce pore defects at the grooves’ outer interface, and promote closer bonding between TC4 and CFRTP, thereby enhancing joint strength. In this study, grooves significantly improved joint strength by 40.2 % to 147.5 %, primarily due to increased mechanical interlocking and bonding area. Differences in joint strength among grooved joints are mainly attributed to variations in interface behavior and pore distribution caused by R and T. Appropriate R and T are crucial for inhibiting large-volume pores and reducing pores at the grooves’ outer. When R = 1/5 and T = 360 μm, the joint with small-volume pores, no pores at the grooves' outer, and the lowest porosity exhibits the highest strength (2830.3 N). Grooves showed no significant impact on chemical bonding (CTi0.42V1.58 carburization phase and TiOS). Furthermore, no significant effect of grooves on the chemical bonding (CTi0.42V1.58 carburization phase and TiOS).

Optimizing joint structure and performance in friction spot joining of aluminum alloy AA6061 and poly-ether-ether-ketone (PEEK)

This study investigated the challenge of joining poly-ether-ether-ketone (PEEK) to aluminum alloy AA6061 through friction spot joining (FSpJ), by examining the impact of surface treatment of AA6061 sheets and analyzing various process parameters' effects on joint interface morphology, tensile-shear strength, and failure. Results indicated a peak interface temperature may reach 400 °C during FSpJ, with a 0.5–0.9 mm molten PEEK layer containing sealed bubbles. Notably, Boehmite treatment significantly improved joint strength, although the primary failure occurred in the PEEK base material. An optimization through response surface method (RSM) analysis identified plunging depth as the most influential factor in joint strength, and a peak load of 4576 N with an optimized combination of pin rotation speed, plunging depth, and dwell time was achieved. Using optimized process parameters, strong PEEK-AA6061 joints can be formed, and the approach is extendable to joining other metallic and polymeric materials.

Enhanced interfacial structure of (HfZrTiTaNb)C high-entropy ceramic joint brazed using FeCoCrNiTi0.2 alloy filler

To fabricate large-sized and complex-shaped ceramic components for service at elevated temperatures, (HfZrTiTaNb)C high-entropy ceramic (HEC) joints with the improved joint strength of 292 MPa were successfully realized by using a FeCoCrNiTi0.2 high-entropy alloy (HEA) filler at 1430 °C. The reliable joint relied on a direct metallurgical bonding with semi-coherent interfaces between HEC' carbides and HEA' alloy, independent of compounds. The high-entropy interface was confirmed by the habit planes of (020)HEC' // (020)HEA' and the calculated lattice misfit of 1.58%, which represented small internal stresses at bonding interfaces in the joints. The formation of HEC and HEA phases originated from the direct phase transition of HEC induced by active Ti and the residual of liquid HEA, respectively, and they maintained their original lattice structures, nanohardness, and elastic modulus. The joints possessed undiminished strength values when tested at 1000 °C, benefiting from high-entropy microstructures throughout the interfacial region. The failure location migrated from the HEC near the HEC' to the HEA'. In addition, the interfacial formation strategy was investigated by altering HEA thicknesses and bonding times. The HEC' was invariably present in the joint, while preventing phase separation of liquid HEA upon cooling to form HEC'/HEA'/HEC' structure required the HEA thickness of at least 300 µm and the resulting abundant liquid filling. With extended bonding times of up to 60 min, the depletion of the HEA' layer would decrease joint strength by 140 MPa. This work provides a new perspective on joint design toward ∼1000 °C high-temperature applications.

Mechanism of toughness enhancement of brittle fracture by intermittent η-intermetallic in Al/Cu joint made by FSW

It is well documented that the mechanical failure mechanism of various compounds of aluminum 1050 and commercial pure copper (Al/Cu) involves a combination of brittle and ductile fracture processes. Brittle fracture occurs through the intermetallic compounds (IMCs), while ductile fracture occurs through the base materials, either in the stir zone or the heat-affected zone. In this study, a clean and uniform Al/Cu interface was created using the Friction Stir Welding (FSW) technique, which allowed the investigation of the mechanism of pure brittle fracture in Al–Cu IMCs, using a notched tensile specimen. Fracture surfaces were analyzed in detail using scanning electron microscopy (SEM) and microstructural characterization techniques. SEM analysis of the Al/Cu interface revealed the presence of continuous Al2Cu, intermittent AlCu (η), and continuous Al4Cu9. Fractography results showed that the brittle fracture was multilayered and multi-faceted, with an intergranular fracture observed between the Al2Cu and Al4Cu9 IMCs. This crack was stopped by the intermittent AlCu IMC, resulting in transgranular fracture through AlCu. Cracks in the AlCu phase were deflected toward the Al/Al2Cu interface, resulting in delamination of the Al/Al2Cu interface. It was found that this multilayer fracture, induced by the intermittent AlCu between Al2Cu/Al4Cu9, provided the high tensile strength of the compound (173 MPa) compared to the values reported in the literature. A comparison of the Al/Cu joints with Al/steel joints also confirmed the contribution of this fracture deflection to the improved joint strength.

Mechanical behavior of hybrid joint with bearing-type and slip-critical bolted connections

In recent years, high-strength bolts with slip-critical joints have been lengthened owing to the impact of increased traffic loads and the need to rationalize steel members. However, as the length of the joint increased, the force that the bolted joint could resist decreased, because the distribution of the bolts inside the joint became uneven. Moreover, owing to the presence of secondary members in the vicinity of the joint, the length of the splice plates was limited. Therefore, it is necessary to shorten the joint length while maintaining its design strength. This study presents a method that uses a Interference body bolt arrangement at both ends of a long-bolted joint (hybrid joint) to improve joint strength. Finite-element (FE) analysis was conducted to investigate the load-sharing mechanism and slip strength of the hybrid joint. The numerical analysis results showed that 12-row hybrid joints could improve the slip load by approximately 20% compared with 12-row friction-bolted joints. We found that a hybrid joint with Interference body bolts can effectively improve its slip strength and shorten the length of the slip-critical bolted joint. Furthermore, we defined the serviceability limit state of the hybrid joint as the bolt shear yield of the bolt shank or the net cross-sectional yield of the plate. Additionally, we presented an equation to evaluate the bolt shear yield strength of a hybrid joint. Both the errors in the analysis results and the calculated values were less than 5%.

Analysis of laser welding on dissimilar materials with the influence of adding interlayer

The laser welding of dissimilar materials poses several challenges in practical applications, such as molten pool instability, the formation of intermetallic compounds (IMCs), and cracking caused by differential thermal stresses. In this study, we investigated the impact of incorporating a nickel (Ni) foil as an intermediate layer on lap joints of dissimilar materials (SS304 and Al6061) welded using the continuous laser welding (CLW) technique. The thermomechanical simulation accurately predicted the width and depth of SS304–Ni–Al6061 joints, with deviations of merely 3.92% and 19.04% from experimental results, respectively. Residual stress analysis revealed that the addition of a nickel foil reduced residual stress in the heat-affected zone (HAZ) and improved joint fatigue life. Furthermore, the incorporation of 0.1 and 0.2 mm Ni foils enhanced joint strength and effectively suppressed the formation of brittle intermetallic compounds, resulting in a remarkable maximum lap shear force of up to 1026 N. The simulation results for the shear load-displacement curve displayed excellent agreement with experimental data, with a deviation of only 6%. Notably, joints with the Ni foil demonstrated a greater ability to prevent crack formation caused by thermal expansion mismatch compared to joints without the Ni foil. The Ni interlayer served as a diffusion barrier and stress buffer, promoting a more uniform microstructure and reducing the likelihood of crack formation in bonded materials. Overall, this study comprehensively investigates the impact of incorporating a nickel interlayer on laser-welded lap joints of dissimilar materials. The findings offer valuable insights for practical applications, enabling improved joint strength, reliability, and crack resistance in laser welding dissimilar materials.

Vacuum brazing SiC to Mo using Nb0.74CoCrFeNi2 eutectic high-entropy alloy filler

Joining ceramics and metals is important to expand their application scope in the nuclear industry. The brazing of SiC and Mo was conducted using a Nb0.74CoCrFeNi2 eutectic high-entropy alloy filler. The microstructure and mechanical properties of the joints were examined at different brazing temperatures. As the temperature increased, the eutectic structure gradually disappeared, and a layered structure was formed at the brazed joint. An increase in the MoNi phase content can improve joint strength owing to differences in the thermal expansion coefficient and lattice mismatch between phases. The joints exhibited a maximum shear strength of 62 MPa at 1300 °C. Finite element analysis results demonstrated that the presence of a Cr0.46Mo0.4Si0.14 phase causes the concentration of residual stress. Brittle fracture occurred mainly in the Cr0.46Mo0.4Si0.14 phase, causing the rupture of the joint. This study provides valuable insights into the use of eutectic high-entropy alloys as fillers to establish a strong and reliable connection between ceramics and metals.

接着接合を併用した一面せん断高力ボルト接合部の耐力評価

Adhesive bonding has been increasingly used for seismic retrofit and repair recently. However, the interaction between bolt and bonding joints is not clear in detail. This study focuses on the hybrid joint method using adhesive bonding and high-strength bolts for the single-shear lapped joint to improve joint strength. Three experimental parameters, with or without adhesive, bonding area, and bolt tension, were adopted. The results show that the connection strength can be effectively increased by adhesive. Moreover, the effective adhesive area and strength evaluation formulas are proposed through the cohesion failure behavior.