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In ceramic/metal brazing, high residual stress usually causes fracture in the ceramic substrates. Therefore, composite fillers consisting of ductile matrix featuring low yield strength and elastic modulus, as well as reinforcements featuring low coefficient of thermal expansion (CTE), are employed. However, for AgCuTi-base composite fillers, the reinforcements are likely to weaken the deformability of brazing seams (BS), i.e. increase the elastic modulus and yield stress of BS. To address this issue, we developed a new AgCu-base composite filler with "hedgehog-like" reinforcement clusters. Herein, AgCu + NbB 2 composite filler was used to braze ZrB 2 –SiC and TC4-TiB w , wherein ductile Ag(s,s) and Cu(s,s) dominated BS, thereby ensuring high deformability; in addition, a NbB layer along with limited TiB whiskers was formed at the NbB 2 /brazes interface with the orientation relationship of (-11-1) NbB //(0-1-1) TiB and [-314] NbB //[12-2] TiB , resulting in "hedgehog-like" reinforcement clusters. This structure exhibited the following advantages: (i) crystallographic misfit at the interface of reinforcement clusters/brazes and the controlled formation of TiB whiskers minimised the conventional fine grain strengthening and dispersion strengthening effects of BS; (ii) isolated reinforcement clusters decelerated the increase in the elastic property of BS; (iii) "hedgehog-like" structure absorbed fracture energy by deflecting cracks; and (iv) the formation of brittle compounds could be avoided. In other words, the designed reinforcement clusters reduced the deformability expense and compensated for the mechanical-resistance of BS. Therefore, the maximum joint strength was obtained with 2 wt% NbB 2 , which increased the shear strength of the joint six times compared to that with 0 wt% NbB 2. For the joints failing inside ceramic substrates, (i) the key factor for limiting joint strength was the residual stress inside ceramics and (ii) the remission of the trade-off between thermal expansion mismatch and deformability expense contributed to relaxing residual stress, thereby confirming the reliability of our design. [ABSTRACT FROM AUTHOR]

Recent developments in laser beam sources expand the possibilities of laser beam welding of similar and dissimilar copper joints. New methods of beam shaping and adjustable intensity profiles using two layer fibers create a center and ring spot, which is the newest state of the art in fiber laser beam sources. In this study, the influences and possibilities of adjustable intensity profiles on the weldability of steel copper dissimilar lap joints with copper on the top side will be discussed. The results show that the former problems of spattering and poor beam coupling in copper can be avoided through new beam shaping technologies and adjusted parameter settings. In the investigations joints without melt ejections on copper surfaces of state of the art fiber laser technologies are demonstrated and the influence of different intensity distributions on the weld geometry will be discussed. [ABSTRACT FROM AUTHOR]

The transportation industry has played a crucial role in advancing human society, but it has also raised concerns about carbon emissions and environmental pollution. As a result, significant research is being conducted in various areas, such as electric vehicles, powertrain energy efficiency, shared mobility, and autonomous driving. However, vehicles remain essential, and reducing their energy consumption is vital. One effective way to achieve this is by light–weighting vehicle materials. In the past, steel was the primary material used, but the transition to materials like aluminum has shown better weight-to-strength ratios. To drive change, we must explore the use of diverse materials since no single material is perfect. By combining specific materials, we can complement their weaknesses and enhance their strengths, opening up new possibilities for the future of mobility. One critical factor in advancing future mobility is the joining of dissimilar materials. This paper delves into various methods of joining dissimilar materials, their characteristics, and techniques to improve their joining performance. The joint strength for each joining method is also summarized in this study. The joining methods are primarily divided into mechanical joining, chemical joining using adhesives, and thermal fusion welding. Methods to enhance the joint include combining each joining method and improving surface interactions through surface treatments. The joint exhibiting the highest strength was the laser-welded joint of strength 312 MPa between Ti 3 Al-Nb alloy and Ni-based superalloy, while the lightest and strong joint was the friction stir-welded joint of strength 63.4 MPa in Polyamide 6 GFRP. Welded joints of polymer materials appear promising for the future mobility industry, particularly in terms of being lightweight. Additionally, there is a need to develop new methods to measure strength as the units used to represent the physical characteristics of the joints are not standardized. Some joints suffer from issues due to unclear joint area, highlighting the necessity to develop new strength measurement methods for future advancements. • The transportation industry has significantly advanced human society, but concerns over carbon emissions and environmental pollution have emerged. • Research focuses on areas such as electric vehicles, energy-efficient powertrains, shared mobility, and autonomous driving to address these concerns. • Light-weighting vehicle materials, like transitioning from steel to aluminum, is a key approach to reduce energy consumption. • Utilizing diverse materials and combining them can offset their individual weaknesses and amplify their strengths, creating new potential for future mobility. • A pivotal aspect of this evolution is the joining of dissimilar materials, with this paper exploring various joining methods, their attributes, and strategies to enhance their performance. [ABSTRACT FROM AUTHOR]

This study investigated the joining of TiBw/Ti6Al4V composites and Inconel 718 alloy with Cu interlayer using gas tungsten arc welding (GTAW) equipment in order to modify the joints strength. Microstructure analysis indicated that Ti-Cu intermetallic compounds (IMCs) and a small number of Ti-Ni-Cu compounds were generated in the reaction layer with low heat input. While the main products changed into Ti-Ni-Cu compounds, also combined with Ti-Ni compounds and a few ternary compounds with the increase of heat input. Accordingly, the shear strength of dissimilar joints firstly increased and then decreased with the increase of welding current or the decrease of welding speed. The maximum shear strength (370 MPa) was obtained with the current of 100 A and the speed of 110 mm min −1 . Moreover, the hardness of reaction layer was much higher than that of parent materials due to the formation of IMCs, and medium heat input can reduce the hardness mismatch in joints. [ABSTRACT FROM AUTHOR]

Metal 3D printing through laser powder bed fusion (L-PBF) has revolutionised the manufacturing industry. However, size limitations and production costs persist as challenges for the 3D printing of metallic alloys. Thus, joining L-PBF components to other parts becomes a vital aspect to produce composite structures for engineering applications. Among the dissimilar joining of various non-ferrous alloys, the integration of L-PBF components with difficult-to-join materials, such as aerospace-grade AA-7XXX aluminum alloys, still remains an unaddressed industrial problem. To address this problem, the current study was carried out to investigate the feasibility of joining L-PBF manufactured AlSi10Mg alloy with a traditionally rolled AA7075-T651 alloy using friction stir welding process. In this study, the influence of the base material positioning and heat input on the mechanical and metallurgical characteristics of welded joints was examined, followed by their interrelationships for more efficient adoption of this technology. The results revealed that the base material placement significantly influenced the joint strength at low heat input but showed negligible impact at high heat input. The joints fabricated at high heat input exhibited higher hardness within the nugget zone owing to the higher concentration of MgZn 2 and β-Mg 2 Si secondary-phase particles as compared to the joints fabricated at low heat input. Texture analysis of welds showed that the C {001} <110> shear component dominated the nugget zone when AA7075-T651 was placed on the retracting side. Whereas, the A 1 * / A 2 * {111} < 1 ‾ 1 2 ‾ >/{111} < 11 2 ‾ > simple shear component was prominent when AA7075-T651 was placed on the advancing side of the joint. Finer grains and high dislocation density in the nugget zone at low heat input resulted in the maximum joint efficiency of 77% with respect to the AlSi10Mg alloy. In contrast, a coarse grain structure at high heat input reduced the joint efficiency to 74%. The findings from this research suggest friction sir welding to be an efficient method for dissimilar joining of additive components with conventionally manufactured parts. [ABSTRACT FROM AUTHOR]

In this study, the fatigue properties of SPR joints in CFRP-to-AA6111 aluminum alloy in lap-shear and cross-tension specimens are presented. The test specimens were produced with two distinctive targeted rivet head heights separated by 0.3 mm. The tensile failure load and fatigue life of the lap-shear joints in particular was highly influenced by the flushness of the rivet head against the top sheet of CFRP. The lap-shear SPR joints produced with a proud head height exhibited higher tensile failure load and slightly longer fatigue life than SPR joints produced with a flush head height. In cross-tension joints, the flushness of the rivet had no significant influence on the quasi-static failure load and fatigue life of the SPR joints. Two distinctive failure modes were observed, in quasi-static loading, the lap-shear and cross-tension joints failed due to rivet pullout of the bottom aluminum sheet. In cyclic loading, the lap-shear joints failed due to kinked crack growth in the bottom aluminum sheet, while the cross-tension joints failed due to rivet pulling out of the top CFRP sheet. Finally, an analytical based, structural stress model was used to generate a master curve to predict the fatigue life of the SPR joints for both specimen types. The study shows, the flared rivet diameter as a controlling parameter in evaluating the fatigue life of the SPR joints. [ABSTRACT FROM AUTHOR]

This study presents the interface microstructure, mechanical properties and corrosion resistance of dissimilar joints between Inconel 52M overlays and 316L stainless steel during multipass laser welding for nuclear power plants. The results indicate that the microstructure at the interface beside 316L stainless steel consists of cellular with the width of 30–40 μm, which also exhibits numerous Cr and Mo - rich precipitates like flocculent structure and in chains along grain boundaries as a mixed chemical solution for etching. Many dendritic structure with local melting characteristics and Nb-rich precipitates are exhibited at the interface beside Inconel 52M overlays. Such Nb-rich precipitates at the interface beside Inconel 52M overlays deteriorate the tensile strength and toughness of dissimilar joints at room temperature. The tensile strength of 316L stainless steel at 350 °C significantly decreases with the result that dissimilar joints are fractured in 316L stainless steel. The correlation between corrosion behavior and microstructure of weld metals is also discussed. The difference in high corrosion potential between Nb-rich precipitates and the matrix could result in establishing effective galvanic couples, and thus accelerating the corrosion of weld metals. [ABSTRACT FROM AUTHOR]

In the present work, the effect of process parameters on joining of AZ91 Mg alloy and Al6063 aluminum alloy sheets during friction stir welding (FSP) was studied. A successful joint was achieved at 1100 r.p.m. tool rotational speed and 25 mm/min tool travel speed. Combination of tool rotational speed and tool travel speed has observed a profound effect on the material flow mechanisms at the nugget zone. From the microstructural studies, the joint formation was observed as mainly due to mechanical mixing of the materials. The level of metallurgical continuity at the nugget zone was observed as poor and a sharp interface at the joint was noticed. The microhardness measurements across the weld joint also revealed the lack of establishment of a perfect metallurgical bonding. X-ray diffraction analysis of weld zone showed presence of both magnesium and aluminum. Hence from the preliminary observations, it can be understood that the joining of AZ91 Mg alloy and Al6063 alloy can be achieved by FSP; however, complex issues in material mixing still need further investigations. [ABSTRACT FROM AUTHOR]

In this paper, Cu-based and Ni-based filler metals were used to obtain laser-CMT hybrid welded copper/stainless steel (Cu/SS) joints. The effect of wire compositions on the microstructure and mechanical properties of T2 Cu/304 SS dissimilar metal joint was studied. The results showed that Fe–Cu liquid phase separation occurred in the fusion zone of the Cu-based weld, and Cu penetration cracks appeared in the heat-affected zone (HAZ) on the steel side. The Cu penetration cracks formation is derived from supersaturated Cu atoms penetrating, gathering and merging at the steel side fusion line along the austenite grain boundaries. The penetration cracks can be eliminated effectively by the Ni-based filler metal, because the diffusion of Cu into the fusion zone and the HAZ on the steel side is limited significantly by the increase of Ni content. The Ni-based weld consisted of dendrite grains in the fusion zone, and Fe-rich blocks and Ni-rich islands nearby the HAZ of Cu-side. • Defect-free weld was obtained by laser-CMT hybrid welding with Ni-based wire. • Cu-based weld penetration cracks mechanism was illustrated. • The microstructures of Cu-based and Ni-based welds were compared. • The mechanism of inhibition of penetration cracks in Ni-based weld was discussed. [ABSTRACT FROM AUTHOR]

• The processing temperature plays a significant role in the joining mechanisms such as mechanical interlocking and chemical adhesion. • The joint geometry affect the amount of secondary bending moment that is generated. • Higher levels of secondary bending moment will induce more local stress that may limit the joints' mechanical performance. • The specimens exhibited three different failure mechanisms: interfacial failure; base material failure; mixed failure mode. • Chemical adhesion was observed in the interfacial transition between base materials. An engineering grade, glass fibre reinforced (GFR) polymer – Noryl™ Resin GFN2 - and an aluminum magnesium silicon alloy - AA6082-T6 - were joined by Friction Stir Welding (FSW) in overlap configuration. A systematic analysis was conducted on the effects of different process parameters, namely, vertical force, rotating speed and transverse speed, on processing temperature and mechanical performance, and how they relate with the failure mechanisms of the joints. The analysis encompassed the morphology of the joints' interfaces and generated defects associated to the joining process. The quasi-static tensile tests resulted in average tensile strengths varying between 15.9 and 37.9 MPa, representing joints' efficiencies ranging from 19.9% up to 47.4%. Both macro and micromechanical interlocking were found to be the main joining mechanisms, whilst chemical bonding played a secondary role. The development of interlocking features was found to be related with the processing temperature, and it should be comprised between the softening and melting temperature of the polymeric material. Processing temperature influences both the joints' strength, and failure mechanisms, with low strength joints' tending to exhibit interfacial failure, whereas high strength joints' failure can be associated with the failure of the weakest base material close to the joint region. This research work validates the feasibility of dissimilar polymer-to-metal joining through FSW. To this end it was studied the failure mechanisms in the Aluminum and the GFR polymer which exhibit highly dissimilar physical and thermo-mechanical properties. The mechanical performance of these joints is limited by the weakest base material and is mainly governed by macro and micro-mechanical interlocking features, which relates to the failure mechanism. The relation between macro and micro-mechanical interlocking features, failure mechanism and joint strength is crucial towards maximization of the joints' mechanical performance. [ABSTRACT FROM AUTHOR]

NiTi is an increasingly applied material in industrial applications. However, the difficulties faced when welding and joining is required, limits its broader use in the production of complex shaped components. The main weldability problems associated with NiTi are: strength reduction, formation of intermetallic compounds, modification of phase transformation and transformation temperatures, as well as, changes in both superelastic and shape memory effects. Additionally, NiTi is envisaged to be joined to other materials, in dissimilar joints with more complex problems depending on the other base material. Thus, intensive research in welding and its effects on the joints performance has been conducted since the early stages of NiTi. This paper presents a detailed review of welding and joining processes applied to NiTi, in similar and dissimilar combinations considering both fusion and solid-state processes. Since laser is the most studied and applied welding process, a special section is devoted to this technique. [ABSTRACT FROM AUTHOR]

The aim of this study was to analyze the microstructural changes of two dissimilar Ti-6Al-4V/Ti17 and Ti-6Al-4V/BT9 joints welded via electron beam welding (EBW), and establish the relationship between microstructure and properties. The results showed that the occurrence of phase transformation was mainly dependent on the peak heating temperature during EBW, and despite the same welding parameters the microstructures of two dissimilar joints were different except in the heat-affected zone (HAZ) on the Ti-6Al-4V side. Both dissimilar joints exhibited a higher strength compared with Ti-6Al-4V base metal (BM), and the strength of Ti-6Al-4V/Ti17 joint was slightly higher than that of Ti-6Al-4V/BT9 joint due to the presence of finer martensite. Fatigue life of dissimilar joints was almost the same as that of Ti-6Al-4V BM within the experimental scatter. Fatigue failure of both dissimilar joints occurred in the HAZ, and fatigue crack basically initiated from the specimen surface. [ABSTRACT FROM AUTHOR]

Dissimilar joining of copper to duplex stainless steel (DSS) is challenging at high temperatures of fusion welding owing to the large difference in physical properties of the base metals. To reduce negative effects of welding at high temperatures, solid state welding at lower temperatures has been proposed. To study different effects of welding parameters (rotation speed, travel speed and tool offset) on weld zone microstructure and mechanical properties butt joints of a copper alloy and duplex stainless steel (DSS) were produced by friction stir welding (FSW). It has been found that heat input generated by the interaction of different welding conditions has a significant effect on the formation of a brittle intermetallic at the interface and eventually the final mechanical properties. At low heat inputs, mixing of the two sides is insufficient and metallurgical bonding is weak; while at high heat inputs, the thickness of the formed intermetallic is too thick which causes stress concentration at the interface and premature failure. An optimum welding condition was found (rotation speed of 1200 rpm, travel speed of 30 mm/min and tool offset of 0.5 mm) which almost reached the mechanical properties of the Cu-alloy monolayer. [ABSTRACT FROM AUTHOR]

The mechanical performance and electrical resistance of dissimilar and multi-layered Cu-Al sheets, which represent the battery electrodes and tabs, were evaluated by ultrasonic welding (UW). Different possibilities of lap-joining configurations using sheets of Cu and Al were considered. The weld strength at each weld interface of the multi-layered joint was evaluated by 90° peel test and by heat input measured by an infrared imager (IR). The strength of each weld interface of UW joined multiple Cu-Al layers were found to be strong enough to produce a through-thickness tearing. A typical weld criterion for producing a developed nugget was achieved. Weld quality at interfaces was assessed by cross-sectioning the UW joint parts. Depending on the lap-joint configuration, weld interfaces were characterized by bonded and unbonded interfaces. Measuring the electrical resistance passing through the joints demonstrated that the unbonded weld interface produced an increase in the joint electrical resistance. The joint electrical resistance measurement is shown to be used as a criterion to validate the quality of Cu-Al battery cell joints. [ABSTRACT FROM AUTHOR]

In this study, the authors used keyhole tungsten inert gas (K-TIG) welding to weld together 12-mm-thick dissimilar TC4/TA17 titanium alloy plates without grooves. The microstructural evolution of the dissimilar joints was analyzed, to determine the relationship between their microstructure and their mechanical properties. The results showed that nine identifiable sub-zones were formed in each joint under the thermal action of welding. Significant microstructural changes occurred after welding, with the formation of the α phase, α' martensite and β phase in the heat-affected zone (HAZ), α' martensite in the fusion zone (FZ), and the α phase with a small volume of the β phase in the base metals (BMs). The textural distribution and intensity in the HAZ and FZ changed significantly compared with those in the BMs. Under the action of welding-induced heat, the distorted microstructures reverted, resulting in a marked reduction in the number of low-angle grain boundaries in the HAZs. Due to differences in their chemical composition and microstructure, the microhardness of the joint was characterized by an asymmetric distribution, that was ranked as follows: TC4 HAZ > TC4 BM > FZ > TA17 HAZ > TA17 BM. The ultimate tensile strength and yield strength of the joints were between those of the two BMs, but their elongation was smaller than that of either owing to the large difference in strength between the BMs. Because the TA17 BM had the lowest strength, the joint on its side underwent ductile fracture near the HAZ. In addition, the impact-induced energy absorbed in the FZ of the joint was between those of the BMs and was close to the average of their values. The work here provides a new method for the K-TIG welding of dissimilar titanium alloys in plates of medium thickness. • The TC4/TA17 dissimilar titanium alloy were welded via the Keyhole TIG welding. • The microstructure, texture distribution and intensity of the joint were changed. • The TC4/TA17 welded joints exhibits satisfying mechanical properties. [ABSTRACT FROM AUTHOR]

The fatigue behavior of single friction spot welded AA5754 and Ti6Al4V dissimilar joints was investigated based on experimental observations. Fatigue tests were performed in a constant amplitude load control servo-hydraulic machine with a load ratio of R = 0.1 at room temperature. Two-parameter Weibull distribution was used to analyze statistically the fatigue data for the joined overlapped sheets. Weibull graphics were plotted for each stress amplitude value. Subsequently, S–N curves were drawn for different reliability levels (10%, 50%, 90% and 99%) for the benefit of designers. A fatigue limit of 25 MPa was determined for the AA5754/Ti6Al4V joints (at survival level of 50%), corresponding to 15% of the maximum average static fracture load. Two different types of fatigue failure modes were observed for the specimens. Under high cyclic loads, the failure occurred in the upper Al sheet because of the higher stress concentration at the notch tip leading to crack initiation followed by its propagation through the thickness toward the joint surface and, subsequently, along the specimen width direction. Under low cyclic loads, “through weld” failure was observed as the crack rapidly propagated along the interfacial surface until a critical point at which the remaining cross section could no longer sustain the shear overload and failed. A fatigue crack growth mechanism based on the paths of the dominant fatigue cracks was then proposed and used to explain the fatigue fracture evolution under different loading conditions. [ABSTRACT FROM AUTHOR]

• Dissimilar joint was fabricated by DLD via adding an (Nb + Cu-10Al) interlayer. • The addition of an (Nb + Cu-10Al) could effectively inhibit the formation of Ti-Fe IMC. • The average tensile strength is 335.5 MPa. • The strength of Grade1/316L joint could be improved by using an gradient interlayer. The heterogeneous compounds of titanium and iron steel are of wide interest in additive manufacturing. To prevent the formation of brittle intermetallic compounds, a layer of Nb and Cu was used. The use of the Nb and Cu interlayer successfully prevents the mixing of Ti and Fe, thus avoiding the formation of FexTiy brittle phases. In the Ti–Nb–(Nb + Cu–10Al) transition interlayer, it was possible to achieve the interlayer without the formation of brittle phases. The static tensile strength of the Grade1/316 L compounds with Nb–(Nb + Cu–10Al) interlayer is 335.5 MPa, the compounds exhibit ductile–brittle fracture. [ABSTRACT FROM AUTHOR]

Friction stir welding (FSW) of dissimilar welds between ZG61 alloy and AZ91D alloy was investigated. Severe deformation and metal flow occur in the stir zone under high strain rates and high temperatures. No distinct reaction layer or intermetallic compounds are observed at the interface of two alloys. When AZ91D was arranged in the advancing side and ZG61 in the retreating side, the joints quality was very poor with all parameters. Microstructure and texture evolution during the FSW and relationship of microstructure, texture and mechanical properties are discussed. The tensile properties of the weld of joints are significantly influenced by the materials positions, grain size and crystallographic orientation. Materials positions and plasticity of base metals is of importance during the FSW of dissimilar alloys. It can be seen that defects cannot be avoided when the heat input were too low to make the metal flow. [ABSTRACT FROM AUTHOR]

It is essential to understand the weld interface characteristics and mechanical properties of dissimilar joints to improve its quality. This study is aimed at exploring the properties of friction welded magnesium–titanium dissimilar joint using tensile testing coupled with digital image correlation, optical and scanning electron microscopy, x-ray diffraction and microhardness measurements. Microstructurally different regions such as contact zone, dynamic recrystallized zone, thermo-mechanically affected zone, and partially deformed zone in the magnesium side were observed. No discernible regions were observed in the titanium side, as it had not undergone any significant plastic deformation. Phase analysis indicated that the aluminium from the magnesium side diffused toward the weld interface and formed a thin continuous intermetallic layer by reacting with the titanium. Microhardness mapping showed a steep hardness gradient from the titanium to magnesium side. Critical analysis is done on the tensile characteristics of the specimen and the response of the local regions to the deformation process is mapped. [ABSTRACT FROM AUTHOR]

In the present work, the effect of tool axis offset from the joint interface and geometry of the FSW tool pin on the mechanical and metallographic characteristics of dissimilar friction stir butt welded aluminum (Al) alloy, AA5052 H32 and HSLA steel, IRSM42-93 were investigated. FSW tools having fixed shoulder diameter, pin tip diameter and pin length with three different tapered cylindrical (TC) and one straight cylindrical (SC) tool pin profiles were experimented. The constant FSW parameters used were: tool rotational speed of 500 rpm, welding speed of 45 mm/min, axial load of 7 kN and tool tilt angle of 1.5°. The effect of tool axis offset was investigated by continuously changing the tool axis offset by keeping the tool traverse direction at an angle to the joint interface. The ultimate tensile strength (UTS) of the joint is considered as the main criterion of the joint performance. The results show that the TC pin profile is beneficial and for a given FSW tool geometry and parameters, the taper angle of the tool pin and volume of tool pin penetration into steel side have significant influence on the thickness and composition of the intermetallic compound (IMC) layer formed and hence the joint performance. FSW tool having TC pin with 10° taper angle has produced the best joint at a tool axis offset of 2 mm towards the Al alloy. For the experimented tool pin geometries, the IMC layer formed at the joint interface is consistent with FeAl, Fe 2 Al 5 and FeAl 3 . [ABSTRACT FROM AUTHOR]

This study investigates the effect of length scale on the tertiary creep behavior of elastically constrained ductile metal joints. Creep tests were performed in tension on Sn–Cu joints of thicknesses ranging from 1.4 mm to 170 μm. Sn being more creep compliant as compared to Cu undergoes creep deformation, whereas Cu remains in the elastic state. The overall creep rate and the amount of strain accumulated during the tertiary creep decreased with reduction in joint thickness. This was accompanied by a reduction in the extent of lateral contraction, especially near the fracture surfaces of the joints. Fractographs revealed a transition in the mode of creep failure from pure necking in thick joints to cavitation along with constrained necking in thin joints. A joint size dependent tertiary creep model incorporating necking and cavitation was developed to explain the observed transition in tertiary creep behavior and final failure. The model captures the effects of both joint size dependent triaxial stress state and a decrease in the size of the necking ligament with reduction in joint size. Overall, the decrease in strain accumulated during tertiary creep is attributed to smaller size of the neck and higher triaxiality in thin joints, which enhances the strain due to cavity growth and reduces that due to necking as the joint thickness reduces. [ABSTRACT FROM AUTHOR]

The increasing mechanical and economical demands in modern systems and structures are forcing an inevitable need for joining dissimilar materials, thus creating the challenge of establishing a process to inspect and monitor dissimilar joints. Condition monitoring is a necessity to ensure that the structures are being safely used and to extend their lifetime. Lamb waves (LWs) are ultrasonic guided waves that are widely used for structural health monitoring of mechanical, aerospace, and civil structures. This paper proposes a novel structural health monitoring approach for damage detection, localization, and assessment using a minimal LW sensor-actuator set-up. More specifically, the proposed framework provides damage detection, localization and assessment within a dissimilar-material joint by Bayesian inference of six parameters of damage extent and location. Finite element simulations are used to simulate the measured LWs and generate a dataset required to train artificial neural networks (ANN), acting as surrogate models for LW simulation with reduced computational cost. The ANN-based LW simulations are further used as forward model within an Approximate Bayesian Computation (ABC) framework to provide probabilistic inference of the damage size and position. The results show that damage of different sizes and locations can be successfully identified with a high level of resolution and with quantified uncertainty. The results also show that data fusion for ABC inference using multiple sensor measurements can be possible with improved inference results. However, a precise and robust damage inference can be achieved using a minimal sensing set-up based on one actuator and two sensing points, with consideration of certain levels of measurement noise. These findings imply a considerable reduction of complexity of LW actuator-sensor networks, and overall, they imply a significant reduction of computational resources and cost for damage detection and assessment in structures, thus providing a step forward towards online/onboard monitoring applications. • A novel framework to detect, localize, and assess damage using Lamb-waves, is proposed. • A reliable damage identification was achieved using only one actuator and two sensors. • Surrogate models for Lamb-wave propagation have been developed based on Artificial Neural Networks. • Probabilistic damage inference was performed using Approximate Bayesian Computation. • Data fusion was employed for ABC inference using multiple sensor measurements. [ABSTRACT FROM AUTHOR]

Abstract: The microstructure, hardness, tensile and fatigue properties of electron beam welded dissimilar joints between Ti–6Al–4V and BT9 (Ti–6.5Al–3.5Mo–1.5Zr–0.3Si) titanium alloys were studied. A marked microstructural change occurred after welding, with martensite in the fusion zone (FZ) and in the heat-affected zone (HAZ) of Ti–6Al–4V side, and martensite plus some retained α phase in the HAZ of BT9 side. While an asymmetrical hardness profile across the dissimilar joint was observed with significantly higher hardness values in the FZ, no soft zone was present in the HAZ of the Ti–6Al–4V/BT9 dissimilar joints. The ultimate tensile strength, monotonic and cyclic yield strength, and cyclic strain hardening exponent of the dissimilar joints lay in-between those of two base metals (BMs). The joint and BMs had almost the same monotonic and cyclic stress–strain curves and fatigue life, while the cyclic strain hardening exponent was slightly higher than the monotonic strain hardening exponent. Although cyclic softening occurred at higher strain amplitudes, cyclic stabilization appeared at lower strain amplitudes up to 0.6% for both BMs and joints. Fatigue failure of the dissimilar joints occurred in the BM of Ti–6Al–4V, with crack initiation from the specimen surface or near-surface defect and crack propagation characterized by fatigue striations along with secondary cracks. [Copyright &y& Elsevier]

In the present investigation, the microstructure evolution and mechanical properties of dissimilar materials Copper-Stainless Steel pipe joints welded by continuous drive friction welding under two different processing conditions are analyzed. The processing conditions of friction welding for copper-stainless steel joints are varied by two friction times of 10 s and 15 s while keeping other processing parameters constant. The welded specimens are analyzed for materials characterizations and mechanical testing using optical microscopy and scanning electron microscopy, electron dispersive x-ray spectroscopy, electron backscatter diffraction analysis, X-ray diffractions, tensile testing, and microhardness measurements. The results revealed that the major microstructural evolution is observed at the Cu side with dynamic recrystallized zones. Enhanced metallurgical bonding between Cu-SS materials is obtained with microstructural evolutions (such as full dynamic recrystallized zone at Cu side and quenching zone at SS side) near to Cu-SS interface, in case of weld made by friction time of 15 s. Superior interatomic diffusion leading to enhanced metallurgical bonding is evidenced for weld made by friction time of 15 s. The reaction layer thickness influences the bonding and mechanical properties of Cu-SS friction welds. The reaction layer thickness of 17.28 μm is observed for the weld made by friction time of 10 s, whereas the reaction layer thickness of 1.21 μm is observed for the weld made by friction time of 15 s. The ultimate tensile strength of 181.05 MPa is obtained for Cu-SS friction weld. [ABSTRACT FROM AUTHOR]

• Dissimilar joint was fabricated by DLD via adding an (Mo + Cu-10Al) interlayer. • The addition of an (Mo + Cu-10Al) could effectively inhibit the formation of Ti-Fe IMC. • Three Cu–Ti intermetallic compounds was formed at the Ti/ (Mo + Cu-10Al) interface. • The strength of Grade1/316L joint could be improved by using an gradient interlayer. The dissimilar joining of titanium alloys and steel is more challenging due to the formation of brittle Ti-Fe intermetallic compounds (IMCs). The use of Cu-Mo interlayer successfully prevented the mixing of Ti and Fe to avoid the formation of Fe x Ti y brittle phases. Near Ti-(Cu + Mo) interlayer boundary typical CuTi2, CuTi and Cu 3 Ti 2 phases are formed. Intermetallic stoichiometry, morphology are discussed. The tensile strength of the Grade1/316 L joints with the Cu-Mo interlayer is 175 MPa, and the joints exhibited the ductile–brittle fracture. The fracture region formed at the interlayer along the molybdenum particles. [ABSTRACT FROM AUTHOR]

Abstract: The friction stir welding (FSW) process parameters play a major role in deciding the joint characteristics. Response Surface methodology (RSM) was used to predict the ultimate tensile strength, yield strength and displacement of friction stir welded (AA6061-T6 and AA7075-T6) aluminium alloy. The experiments were conducted based on three factors namely rotational speed, welding speed and axial force. The empirical relationships were developed by response surface methodology (RSM) incorporating FSW tool parameters (rotational speed, welding speed, axial forceand process parameterstensile strength, Yield strength (YS) and Displacement (DP) by Central composite design (CCD) technique. [Copyright &y& Elsevier]

It is very important to understand the interfacial behavior for effective evaluation of welding quality. This letter reports a simple nondestructive characterization method of the interfacial strength of dissimilar metallic joints. Using a scanning Kelvin probe, the electron work function of Cu–steel joints was measured and a strong correlation between the electron work function and the interfacial tensile strength was found. [ABSTRACT FROM AUTHOR]

Abstract: A mechanical and metallurgical characterization of friction stir welded butt joints of aluminium alloy 6061-T6 with 6082-T6 was carried out. For comparison, similar material joints made from each one of the two alloys were used. The work included microstructure examination, microhardness, tensile and bending tests of all joints. An approximate finite element model of the joint, taking into account the spatial dependence of the tensile strength properties, was made, modelling a bending test of the weldments. This study shows that the friction stir welded dissimilar joint present intermediate mechanical properties when compared with each base material. In tensile tests the dissimilar joint displayed intermediate properties. For instance in the hardness profile the lowest values were obtained in the AA6082-T6 alloy plate side where rupture occurred, and in the nugget all type of joints present similar values. [Copyright &y& Elsevier]

Cracking as one of the most common weld defects for joining dissimilar metals can lead to challenges as lack of mechanical properties, lack of joint tightness, lowered electrical conductivity or can be a point of attack for corrosion. Joints between stainless steel and copper also suffer from weld metal cracking which is caused by the effect of liquid copper on the microstructure of solidifying steel matrices. The crack formation is dependent on the dilution of copper in the weld metal, the overall metal intermixing and thermal stresses while cooling down. To investigate the crack susceptibility of laser beam welds with that material combination, lap joints with stainless steel on the top side were welded with a wide range of parameter settings to create different weld metal compositions. The joints were evaluated regarding metal intermixing, cracking, micro hardness and shear tensile strength by metallographic cross sections, x-ray spectroscopy line scans, x-ray spectroscopy element mapping and shear tensile tests to create sufficient datasets for analyses. The results show a correlation between the mixing ratio of copper and the formation of hot cracks with a critical amount of approximately 10 w co.% copper in the fusion zone. Based on that, a hypothesis in order to reduce cracks by decreasing the amount of copper in Fe-rich weld metals or to create copper dominated weld metals was put forward. The crack formation has no influence on the tensile shear strength, which is dependent on the connection width reached between the sheets with a maximum shear strength of 9.6 kN at full penetration of both sheets and shows ductile fraction behavior. Consequently, the crack formation in this welding configuration at copper contents above 10 w co.% has to be weighed against the better mechanical properties at higher connection width and mixing ratios for joining stainless steel and copper. Hardness measurements of the weld metal show results mostly independent of the overall mixing ratio with median values of 170 HV0.1. [ABSTRACT FROM AUTHOR]

Abstract: Aircraft aluminium alloys generally present low weldability by traditional fusion welding process. The development of the friction stir welding has provided an alternative improved way of satisfactory producing aluminium joints, in a faster and reliable manner. In the present work dissimilar Al alloys (AA2024-T351 and AA6056-T4) were friction stir welded. Butt joints were obtained by varying process parameters, namely the rotational speed (500–1200rpm) and the welding speed (150–400mm/min), while axial force and tool geometry were kept constant. Parameter optimisation, which has been based on the results of macrographic analysis and microhardness testing, indicated that sound joints can be obtained in the parameters range of rotational speed equal to 800rpm and welding speed of 150mm/min. Light and scanning electron microscopy in several positions revealed the presence of a lamellar material flow pattern due to the differential flow, suggesting material mechanical mixing within the stirred zone. High level of strain and temperatures usually over 400°C, resulted in a dynamically recrystallised stirred zone with refined grains. Tensile testing (standard flat L-T samples) has shown that strength is up to 90% of the weakest joining partner 6056-T4. Fracture took place in the thermo-mechanically heat affected zone of the alloy 6056-T4, where annealed structure led to decrease in microhardness. This behaviour was confirmed by microflat tensile testing, which indicated the drop in tensile strength and the associated increase of strain, in the regions of microhardness drop. This study has shown that in a dissimilar friction stir weld, the weaker component dictates the performance of the joint, where failure happens in the region of the greatest strength reduction related to annealing phenomena. Microscopic investigation as well as the evaluation of local mechanical properties has suggested that mechanical mixing is the major material flow mechanism in the formation of the stirred zone. [Copyright &y& Elsevier]

Abstract: The effect of tool traverse and rotation speeds on the residual stresses are quantified for welds between non-age-hardening AA5083 and age-hardening AA6082 and compared to single alloy joints made from each of the two constituents. The residual stresses have been characterised non-destructively by neutron diffraction and synchrotron X-ray diffraction. The region around the weld line was characterised by significant tensile residual stress fields which are balanced by compressive stresses in the parent material. The rotation speed of the tool has been found to have a substantially greater influence than the transverse speed on the properties and residual stresses in the welds, particularly on the AA5083 side where the location of the peak stress moves from the stir zone to beyond the edge of the tool shoulder. The changes in residual stress are related to microstructural and hardness changes as determined in a previous study . In particular the larger stresses under the weld tool on the AA5083 side compared to the AA6082 side are related to a transient reduction in yield stress due to dissolution of the hardening precipitates during welding prior to natural aging after welding. [Copyright &y& Elsevier]

The thermal loading during the curing process of an adhesive-bonded joint induces residual stresses in the joint, thereby affecting its performance. The problem becomes worse in the case of a multi-material joint involving varying coefficients of thermal expansion (CTE) for different parts. A novel approach was developed to model the properties of automotive grade structural adhesives during the heat curing process. The material model was divided into two components: curing kinetics model and viscoelastic mechanical model. The models were calibrated using experimental data from Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) tests performed on an epoxy-based single-component adhesive. The calibrated material model parameters were fed into a finite element simulation and the prediction results were compared to a unique set of experiments utilizing two substrate combinations of adhesive-bonded single lap shear joints. An excellent agreement between the simulated and experimental results (displacement across the bond, force applied by the adhesive) was achieved. The modeling results give a better understanding of the residual stresses and agree with the experimental trend on the effect of bondline thickness on the joint. [ABSTRACT FROM AUTHOR]

Titanium alloys have been widely used in many industrial applications. Nevertheless, efforts to improve their properties are continually increasing. One of the most effective routes to improve strength, hardness and wear resistance is to create a coating layer on the substrates. In the current study, stainless steel was selected for the in-situ joining and creating a continuous layer on the Ti6Al4V alloy. The joining process was carried out at two different temperatures, 950 °C and 1050 °C, and the mechanical properties of the bonded materials were investigated employing hardness, bending strength and wear tests, while the bonding interface layer between the alloy powders was characterized by optical and scanning electron microscopes. The results showed that the higher the joining temperature, the wider the interfacial zone between the coating layer and substrate. The hardness and wear properties of the joint materials increased at 1050 °C, while the bending stress was reduced and debonding was observed after the bending test. The chemical composition at the interface zone was identified by energy dispersive X-ray analysis, and the results showed high diffusion rates between the elements. As a result, the process used in the current study can be used for many titanium alloys, and their use in industrial applications can be increased. • A new approach to joint stainless steel and titanium alloys by powder metallurgy was succesfully desgined. • A strong interface layer was obtained without adding interlayer elements. • Titanium alloy bonded with stainless steel showed enhanced wear resistance. • Increasing the temperature caused formation of the larger interface thickness. • Large interface thickness caused less strength, high brittleness, and easily debonding. [ABSTRACT FROM AUTHOR]

To combine the advantages of ductile fillers and composite fillers and alleviate residual stress in joints between ZrB 2 -SiC ceramics (ZS) and TC4-TiB w composites, a novel multi-layered joint architecture composed of a layer of clustering SiC at the center of the joint (L-C-SiC) and two ductile layers without SiC particles bordering both substrates (L-DS) was designed. To achieve this, SiC particle skeletons with continuous micro-channels (SSCC) were integrated with AgCu filler as an interlayer. The effects of SSCC porosity and brazing temperature on joint microstructure and mechanical properties were investigated. In particular, the braze/ZS and braze/SSCC interfaces were analyzed through X-ray diffractometry (XRD), transmission electron microscopy (TEM), and wavelength-dispersive spectroscopy (WDS). The residual stress was also evaluated. The results indicate that increasing the brazing temperate improved the infiltration into the SSCC and promoted the SSCC/braze interface reaction (was detrimental to the SiC particle skeleton). Reducing the SSCC porosity changed the thicknesses of the two L-DSs and enhanced the inhomogeneity of the SSCC/braze interface reaction (induced a shear stress in L-C-SiC). For brazing with an interlayer of 30% porosity at 820 °C, the joint shear strength reached a maximum of ~41.2 MPa, mainly due to the construction of the multi-layered joint architecture. Unlabelled Image • SiC particles clustered away from both substrates in joint. • Ductile layers without SiC particles bordered on both substrates. • Multi-layered joint architecture was achieved. • Multi-layered architecture mitigated residual stress in joints. • This design combined advantages of ductile fillers and composite fillers. [ABSTRACT FROM AUTHOR]

• The strength of Zr/Mo dissimilar joint was enhanced greatly through adding Ti interlayer. • The Mo 2 Zr phases in the transition layer at the Mo/FZ interface vanished after adding Ti filler. • The macro-segregation in the FZ of Zr/Mo joints was suppressed by adding Ti interlayer. • Size of grains in HAZ at the side of Mo was reduced significantly after adding Ti. Joining technology for zirconium (Zr) and molybdenum (Mo) dissimilar joints exerts significance on innovative design of nuclear power equipment. Fiber laser beam welding (LBW) of Zr-Mo dissimilar joints with and without Ti insert were welded in butt configuration with one centered pass. It was found that a transition layer containing brittle Mo 2 Zr phase with the thickness of about 2 μm formed at the interface of Mo and welded seam zone (FZ) after LBW. Transverse cracks and significant macro-segregation were observed in the FZ. Moreover, plenty of needle-like α' phases alternatively distributed in β phase matrix were found in FZ where the average microhardness was about 350 HV, which was significantly higher than those of base metals (BMs) of Mo (250 HV) and Zr (130 HV). The tensile strength of the welded joint was about 76 MPa and appeared the mixed of inter- and trans-granular fracture mode. Noting that titanium (Ti) exhibited a favorable metallurgical compatibility with both base metals (Zr and Mo), a pure Ti interlayer with width of 1 mm was inserted into the Zr/Mo interface to further conduct welding. It was found that, by adding Ti interlayer, macro-segregation in FZ was inhibited, needle-like microstructures in FZ greatly reduced and the average microhardness of FZ decreased to about 253 HV. During the tensile test, the joint with Ti addition was fractured in BM of Zr and showed the tensile strength of about 321 MPa. [ABSTRACT FROM AUTHOR]

• Fatigue life prediction of thin-walled welded structures including dissimilar joints. • Low cycle fatigue, in-phase and out-of-phase thermo-mechanical fatigue up to 750 °C. • Recommendations with guideline character and Python script for industrial use. • Fatigue assessment based on hot spot structural strains using "7-Point-Extrapolation". • Validated with exhaust components made of 1.4509 ferritic and 1.4301 austenitic steel. Widely used stress-based methods for predicting the fatigue life of welded structures are not applicable to Low Cycle Fatigue (LCF) and Thermo-Mechanical Fatigue (TMF). Hence, exhaust gas components, which often suffer LCF or TMF cannot be designed by means of these approaches. Therefore, a structural strain approach has been developed. To assess fatigue, it uses extrapolated surface strains from finite element models and corresponding structural strain-life curves resulting from tests with thin-walled welded joints. The approach is supported by guideline-like recommendations for industrial application and can be used for fatigue life prediction of LCF and TMF up to 750 °C. [ABSTRACT FROM AUTHOR]

• Dissimilar Ti-Al-V/Al-Cu-Li and Ti-Al-V/Al-Mg-Li welds were obtained by a CO 2 laser. • The optimal laser beam offset was determined to weld the high-strength joints. • The chemical composition of the aluminum alloys affected the strength of the welds. • Copper significantly increased the strength of the welds in contrast to magnesium. This paper presents the results of the studies of dissimilar Ti-Al-V/Al-Cu-Li and Ti-Al-V/Al-Mg-Li laser welds. The main variable parameter was the laser offset towards the titanium alloy. It was found that strength properties of the welds were significantly affected by alloying elements (copper or magnesium) in the aluminum alloys. The presence of copper improved kinetics and thermodynamics of the welding process due to the formation of specific phases in the fusion zone. Also, it increased the strength of the dissimilar welds by 2.5 times compared with the Ti-Al-V/Al-Mg-Li joints. [ABSTRACT FROM AUTHOR]