Search Results (554)

This study presents a simple and innovative design to join a 2 mm thick steel sheet to a 5 mm thick aluminium sheet in a butt configuration. Thickness differences were addressed using support plates, while an aluminium run-on plate was employed to prevent the FSW tool from plunging into the steel. The process produced a unique S-shaped Al/St interface, the formation mechanism of which is analysed in this study. Scanning electron microscopy (SEM) observations revealed a gradient in the thickness of intermetallic compounds (IMCs) along the joint interface, decreasing from the top to the bottom. This S-shaped interface led to a 150% increase in the ultimate tensile strength (UTS) of the joint. The mechanism underlying this enhancement, attributed to the curved geometry of the interface and its alignment with the loading direction, is discussed in detail. These findings highlight the potential of this approach for improving the performance of dissimilar material joints in lightweight structural applications. Full article

In this study, FSW experiments were conducted on a 4 mm-thick A380 aluminium alloy plate and 6061 aluminium alloy using four different needle lengths (2.5 mm, 2.8 mm, 3.0 mm, and 3.5 mm) of H13 steel. The experiments were conducted at the same welding parameters (1000 rpm and 120 mm/min) to explore the effects of different stirring needle lengths on the microstructures and properties of the FSW joints. The experimental results show that FSW joints with varying lengths of needles have a significant effect on the microstructures and properties of welded joints, and the tensile strength increases and then decreases with increases in the needle length. A 2.8 mm needle length can achieve the maximum tensile strength of 203 MPa, about 85.3% of the base material. Too long or too short a needle leads to a decrease in joint performance. Furthermore, different needle lengths have a significant influence on the flowability of the weld core zone, and a suitable needle length will lead to better flowability in the weld core zone. With increases in the needle length, the heat production also increases, and the area of the RS-HAZ will increase with the heat production. When the joints achieve appropriate heat production, the weld core zone will experience grain refinement. At the same time, the grain will grow in the RS-HAZ; the hardness cloud diagram shows that, in the RS-HAZ, the material properties are weaker, and the tensile specimens are mainly fractured in the RS-HAZ. Finally, the tensile specimens exhibit mixed fracture. Full article

Despite the significant economic and environmental advantages of friction stir spot welding (FSSW) and its amazing results in welding similar and dissimilar metals and alloys, some of which were known as unweldable, it has some structural and characteristic defects such as keyhole formation, hook defects, and bond line oxidation. This has prompted researchers to focus on these defects and propose and investigate techniques to treat or compensate for their deteriorating effects on microstructural and mechanical properties under different loading conditions. In this experimental study, sheets of AA6061-T6 aluminum alloy with a thickness of 1.8 mm were employed to investigate the influence of reinforcement by graphene nanoplatelets (GNPs) with lateral sizes of 1–10 µm and thicknesses of 3–9 nm on the static and fatigue behavior of FSSW lap joints. The welding process was carried out with constant, predetermined welding parameters and a constant amount of nanofiller throughout the experiment. Cross-sections of as-welded specimens were tested by optical microscope (OM) and energy-dispersive spectroscopy (EDS) to ensure the incorporation of the nanographene into the matrix of the base alloy by measuring the weight percentage (wt.%) of carbon. Microhardness and tensile tests revealed a significant improvement in both tensile shear strength and micro-Vickers hardness due to the reinforcement process. The fatigue behavior of the GNP-reinforced FSSW specimens was evaluated under low and high cycle fatigue conditions. The reinforcement process had a detrimental effect on the fatigue life of the joints under cyclic loading conditions. The microstructural analysis and examinations conducted during this study revealed that this reduction in fatigue strength is attributed to the agglomeration of GNPs at the grain boundaries of the aluminum matrix, leading to porosity in the stir zone (SZ), the formation of continuous brittle phases, and a transition in the fracture mechanism from ductile to brittle. The experimental results, including fracture modes, are presented and thoroughly discussed. Full article

Resistance Element Soldering (RES) is one of the new methods of joining dissimilar materials by resistance heating using an element. Sn60Pb40 solder, which has been used for decades in tin smithing and the electrical industry, has already been tested for joining galvanized steel sheet with thermoplastic using RES. However, legal restrictions are currently moving towards prohibiting the use of lead in mass production. For this reason, the possibility of replacing Sn60Pb40 solder with Sn91Zn9 lead-free solder was verified. The results showed that with an appropriate choice of flux and resistance heating conditions, it is possible to replace Sn60Pb40 solder with Sn91Zn9 solder when joining galvanized steel sheet with thermoplastic using RES. With a suitable heat input during soldering, good conditions were achieved for wetting the base material with molten solder with a sufficient volume of remelted solder in the core of the Cu/Sn91Zn9 bimetallic element. The strength of the soldered joint made at a heat input of 901 J was measured at the level of 94% of the strength of Sn91Zn9 solder. Full article

Self-piercing riveting (SPR) has become a highly promising new method for connecting dissimilar materials in multi-material vehicle bodies, while the joint’s forming quality which largely affects its connection performance lacks sufficient research. This study conducted a detailed numerical investigation on the forming quality of carbon-fiber-reinforced polymer (CFRP)/aluminum alloy (Al) SPR joint and proposed a novel multi-objective optimization strategy. First, the finite element (FE) model of CFRP/Al SPR joint forming was established and then verified to monitor the forming process. Second, based on FE numerical simulation, the action laws of rivet length and die structural parameters (die depth, die gap, and die radius) on the joint’s forming quality indicators (bottom thickness and interlock value) were systematically studied to reveal the joint’s forming characteristics. Finally, taking the rivet length and die structural parameters as design variables and the above forming quality indicators as optimization objectives, a hybrid Taguchi–Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method was proposed to conduct the multi-objective optimization of the joint’s forming quality. According to the outcomes, the bottom thickness and interlock value of the joint were respectively increased by 10.18% and 34.17% compared with the baseline design, achieving a good multi-objective optimization of the joint’s forming quality, which provides an effective new method for efficiently predicting and improving the forming quality of the CFRP/Al SPR joint. Full article

This study developed a metallurgical and mechanical hybrid resistance element welding (REW) method to fabricate lightweight Al/steel joints between 2.0 mm 6061 aluminum alloy and 1.2 mm DP780 steel, addressing critical challenges of interfacial intermetallic compounds (IMC layer thickness: 4.6–8.3 μm) in dissimilar metal welding. In addition, the scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and electron probe microanalysis (EPMA) were used to observe the microstructure characteristics and element distribution. The lath martensite and solidification microstructure were observed in the steel-nugget zone and Al-nugget zone, respectively. Furthermore, the microhardness distribution, volume fraction of the α phase, tensile–shear load, and failure mode of REWed joint were studied. Process optimization demonstrated welding current’s pivotal role in joint performance, achieving a maximum tensile–shear load of 6914.1 N under 10 kA conditions with a button pull-out failure (BPF) mechanism. Full article

During use, titanium alloy structural components may experience sudden overloads or occasional loads, which can reduce their fatigue life and accelerate structural failure. To study the fatigue behavior of TC4/Ti60 joints, this paper uses electron beam welding technology to obtain TC4/Ti60 dissimilar joints. The results show that the microstructure changes during the welding process, with the weld zone being relatively uniform, primarily consisting of coarse α′ phase. The near heat-affected zone on the TC4 side consists of α′, while on the Ti60 side, in addition to the α′ phase, there is a small amount of residual α phase. Fatigue tests reveal that as the pre-deformation increases, the fatigue life gradually decreases. During the early stages of fatigue, the joint exhibits cyclic hardening, which transitions to cyclic softening as the test progresses, ultimately leading to failure. Fatigue fracture analysis reveals that all fatigue samples failed on the TC4 side, with no failure observed in the weld zone. This is likely due to the presence of martensite, which gives the weld zone higher strength than the TC4 base materials. Additionally, fatigue cracks initiated from surface or near-surface defects, with ductile fractures being predominant. Full article

Ultrasonic welding is characterized by its energy-saving and environmentally friendly nature. Compared to conventional molten welding technology, the intermetallic compounds formed by diffusion during ultrasonic welding are thinner, and material deformation is reduced. This process has become a primary welding technique for assembling lithium batteries in electric vehicles. Aluminum and copper ultrasonic welding has increasingly gained attention as a research hotspot. The research on aluminum and copper ultrasonic welding primarily focuses on the interfacial microstructure evolution, mechanical performance during the welding process, and numerical simulations to investigate macro- and micro-scale physical phenomena. Given the aluminum and copper multi-layer structures used in lithium battery packaging, numerous studies have been conducted on aluminum and copper multi-layer ultrasonic welding. For Al/Cu joints, advancements in understanding the microstructure evolution, joint performance, and finite element modeling of the welding process have been systematically reviewed and summarized. Moreover, significant progress has been made in molecular dynamics simulations of Al/Cu ultrasonic welding and hybrid welding techniques based on Al/Cu ultrasonic welding. Finally, several new research directions for Al/Cu ultrasonic welding and joining have been proposed to guide further in-depth studies. Full article

Friction surfacing (FS) is increasingly recognized as an advanced technique for coating similar and dissimilar materials, enabling superior joint quality through plastic deformation and grain refinement. This study investigates the deposition of AA6082-T651 alloy on a medium-carbon steel EN14B substrate using FS, with process parameters optimized, and the effect of axial load, rotational speed, and traverse speed on coating integrity. The optimal sample was subjected to heat treatment (HT) at 550 °C for 24, 36, and 48 h to further enhance mechanical properties. Comprehensive microstructural and mechanical analyses were performed on both heat-treated and non-heat-treated samples using optical microscopy (OM), field emission scanning electron microscopy (FESEM) with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), microhardness testing, and micro-tensile techniques. The optimized sample was processed with a 6 kN axial load, a rotational speed of 2700 rpm, and a traverse speed of 400 mm/min, and demonstrated superior bond quality and enhanced mechanical properties. The highest interfacial hardness values, 138 HV0.1 were achieved for the sample annealed for 48 h, under an axial load of 6 kN. Annealing for 48 h significantly improved atomic bonding at the aluminum–steel interface, confirmed by the formation of Fe₃Al intermetallic compounds detected via FESEM-EDS and XRD. These compounds were the primary reason for the enhancement in the mechanical properties of the FS deposit. Furthermore, the interrelationship between process and thermal parameters revealed that a peak temperature of 422 °C, heat input of 1.1 kJ/mm, and an axial load of 6 kN are critical for achieving optimal mechanical interlocking and superior coating quality. The findings highlight that optimized FS parameters and post-heat treatment are critical in achieving high-quality, durable coatings, with improved interfacial bonding and hardness, making the process suitable for structural applications. Full article

The hybridization of additive manufacturing (AM) with conventional manufacturing processes in tooling applications allows the customization of the tool. Examples include weight reduction, improving the vibration-dampening properties, or directing the coolant to the critical zones through intricate conformal cooling channels aimed at extending the tool life. In this regard, metallurgical challenges like the need for a post-processing heat treatment in the AM segment to meet the thermal and mechanical properties requirements persist. Heat treatment can destroy the dimensional accuracy of the pre-manufactured heat-treated wrought segment, on which the AM part is built. In the case of dissimilar joints, heat treatment may further impact the interface properties through the ease of diffusional reactions at elevated temperatures or buildup of residual stresses at the interface due to coefficient of thermal expansion (CTE) mismatch. In this communication, we report on the laser powder bed fusion (L-PBF) processing of MAR 60, a weldable carbon-free maraging powder, to manufacture a hybrid tool holder for general turning applications, comprising a wrought segment in 25CrMo4 low-alloy carbon-bearing tool steel. After L-PBF process optimization and manipulation, as-built (AB) MAR 60 steel was characterized with a hardness and tensile strength of ~450 HV (44–45 HRC) and >1400 MPa, respectively, matching those of pre-manufactured wrought 25CrMo4 (i.e., 42–45 HRC and 1400 MPa). The interface was defect-free with strong metallurgical bonding, showing slight microstructural and hardness variations, with a thickness of less than 400 µm. The matching strength and high Charpy V-notch impact energy (i.e., >40 J) of AB MAR 60 eliminate the necessity of any post-manufacturing heat treatment in the hybrid tool. Full article

Ceramic matrix composites (CMCs) are composite materials made by using structural ceramics as matrix and reinforcing components such as high-strength fibers, whiskers, or particles. These materials are combined in a specific way to achieve a composite structure. With their excellent properties, including high specific strength, high specific stiffness, good thermal stability, oxidation resistance, and corrosion resistance, CMCs are widely used in the aerospace, automotive, energy, defense, and bio-medical fields. However, large and complex-shaped ceramic matrix composite parts are greatly influenced by factors such as the molding process, preparation costs, and consistency of quality, which makes the joining technology for CMCs increasingly important and a key trend for future development. However, due to the anisotropic nature of CMCs, the design of structural components varies, with different properties in different directions. Additionally, the chemical compatibility and physical matching between dissimilar materials in the joining process lead to much more complex joint design and strength analysis compared to traditional materials. This paper categorizes the joining technologies for CMCs into mechanical joining, bonding, soldering joining, and hybrid joining. Based on different joining techniques, the latest research progress on the joining of CMCs with themselves or with metals is reviewed. The advantages and disadvantages of each joining technology are summarized, and the future development trends of these joining technologies are analyzed. Predicting the performance of joining structures is currently a hot topic and challenge in research. Therefore, the study systematically reviews research combining failure mechanisms of ceramic matrix composite joining structures with finite element simulation techniques. Finally, the paper highlights the breakthroughs achieved in current research, as well as existing challenges, and outlines future research and application directions for ceramic matrix composite joining. Full article

Resistance spot welding (RSW) is now the primary joining process used in the automobile and aerospace sectors. Mechanical parts, when put into service, often undergo cyclic stress. As a result, avoiding fatigue failure should be the top priority when designing these parts. Given that spot welds are a type of localised joining that results in intrinsic circumferential notches, they increase the likelihood of stress concentrations and subsequent fatigue failures of the structure. Most of the fatigue failures in automotive parts originate around a spot weld. To that end, this study seeks to examine the mechanical properties and fatigue behaviour RSW joints made of titanium (Ti) grade 2 alloy and AISI 304 austenitic stainless steel (ASS) with equal and unequal thicknesses of 0.5 and 1 mm. Based on the mechanical properties and fatigue life results, the maximum tensile shear strength and fatigue life for the RSW titanium joint were 613 MPa and 7.37 × 10⁵ cycles for the 0.5–0.5 mm case, 374.7 MPa and 1.39 × 10⁶ cycles for the 1–1 mm case, and 333.5 MPa and 7.69 × 10⁵ cycles for the 1–0.5 mm case, respectively. The maximum shear strength and fatigue life of ASS welded joints were 526.8 MPa and 4.56 × 10⁶ cycles for the 1–1 mm case, 515.2 MPa and 3.35 × 10⁶ cycles for the 0.5–0.5 mm case, and 369.5 MPa and 7.39 × 10⁵ cycles for the 1–0.5 mm case, respectively. The assessment of the shear strength and fatigue life of the dissimilar joints revealed that the maximum shear strength and fatigue life recorded were 183.9 MPa and 6.47 × 10⁵ cycles for the 1 mm Ti–0.5 mm ASS case, 115 MPa and 3.7 × 10⁵ cycles for the 1 mm Ti–1 mm ASS case, 156 MPa and 4.11 × 10⁵ cycles for the 0.5 mm Ti–0.5 mm ASS case, and 129 MPa and 4.11 × 10⁵ cycles for the 0.5 mm Ti–1 mm ASS case. The fatigue life of titanium and stainless steel welded joints is significantly affected by the thickness, particularly at maximum applied stress (0.9% UTS), meaning that similar thicknesses achieve a greater fatigue life than unequal thicknesses. Conversely, the fatigue life of the dissimilar joint reached the greatest extent when an unequal thickness combination was used. The ductile failure of similar Ti and ASS welded joints was demonstrated by the scanning electron microscopy (SEM) examination of fatigue-fractured surfaces under the high-cycle fatigue (HCF) regime, in contrast to the brittle failure noticed in the low-cycle fatigue (LCF) regime. Brittle failure was confirmed by the SEM fatigue of dissimilar joint fractured surfaces due to interfacial failure. The Ti and ASS fractured surfaces presented river-like cleavage facets. On the Ti side, tiny elongated dimples suggest ductile failure before fracture. The topography results showed that the roughness topography parameters of similar and dissimilar fractured specimens made from Ti grade 2 and AISI 304 for the HCF regime were lower than those of the fractured specimens with LCF. The current study is expected to have practical benefits for the aerospace and automotive industries, particularly the manufacturing of body components with an improved strength-to-weight ratio. Full article

Friction stir welding (FSW) is a solid-state welding method. The effects of tool structure, tool rotational speed, and welding speed in friction stir welding on the temperature, microstructure, and mechanical properties during the welding of 3 mm thick 6061-T6 aluminium alloy and T2 pure copper plates were investigated through experiments, numerical simulations, mechanical property tests, and microstructural observations, with the aim of enhancing welding strength and efficiency. The results showed that the welding heat input increased with the shoulder and pin diameters. When the shoulder diameter was in the range of 10–16 mm, proportional increases in the pin diameter resulted in an approximate increase of 30 °C in the weld centre temperature for every 2 mm increase in shoulder diameter. Compared to welding speed, rotational speed had a more significant effect on the heat input. Compared to the smooth tool, the threaded tool promoted the dispersion of copper particles within the aluminium matrix, facilitating the formation of Al₂Cu phases. This increased the tensile strength of the weld joint from 183 to 236 MPa (a 28.9% improvement), along with a 57% increase in the weld centre hardness. An energy-dispersive X-ray spectroscopy analysis indicated that welding with the threaded tool resulted in the presence of significantly hard and brittle intermetallic compounds, including AlCu and Al₂Cu_, in the stirring zone, which substantially enhanced the weld strength. Full article

Advanced high-strength steels are considered the first choice when manufacturing lighter vehicles. Quench-partitioning (QP) steels are good candidates that fulfill manufacturing and performance requirements with their outstanding strength and formability. Laser welding offers a productive solution to the challenges of liquid metal embrittlement due to a low heat input and higher welding efficiency. This study investigated the microstructural evolution and mechanical performance of dissimilar laser-welded joints between QP980 and QP1180 steels. The microstructure of the joint mainly consisted of martensite phase in the fusion zone (FZ) and super-critical heat-affected zone (HAZ). In the mid and sub-critical HAZ, the microstructure consisted of tempered martensite along with ferrite and retained austenite on both sides. Due to these microstructural evolutions, FZ and HAZ are strengthened, and thus, laser welds can be achieved without the formation of a visible soft zone. Fracture of the joints occurred in softer base metal (BM) with ductile characteristics without any considerable strength loss. However, the ductility of the joints was lower than that of BMs because of deformation localization due to microstructure, yield strength, and thickness variations in the tensile and Erichsen test specimens. These results show that laser welding can be considered an effective alternative for joining QP steels. Full article

Facing the global energy crisis and increasingly stringent environmental protection regulations, automotive lightweighting has become a core issue for the sustainable development of the automotive industry. In particular, the qualified combination of steel and aluminum alloy has become a promising development direction to achieve the aim of lightweight design. As an innovative solid-phase welding technique, magnetic pulse welding (MPW) exhibits unique advantages in joining these dissimilar metals. The 6061 Al alloy and 20# steel tubes were joined by the MPW technique in this study. The microstructure and interface morphology of the MPW steel/Al tube were characterized using optical microscopy (OM), scanning electron microscopy (SEM), and an electro-probe microanalyzer (EPMA). The microstructure in the region adjacent to the interface was similar to that of the base metals (BMs). The element transition zone could be observed at the interface. The thickness of the transition layer was approximately 6 μm. The transition layer did not possess high hardness and brittleness like the Fe–Al binary IMC layer. Therefore, the interface bonding quality and long-term stability of the MPW steel/Al joint were relatively good. The welded joint interface could be divided into three zones: the bonded zone in the center and unbonded zones on both sides. In particular, an obvious wavy interface with gradually increased amplitude was detected in the bonded zone. The interaction between the reflected wave and the welding collision point could promote the initiation of the wavy interface. In addition, the formation of the wavy interface depended on the impact velocity and angle of the MPW process. The qualified mechanical properties of the joint could be attributed to the formation of the wavy interface. The microhardness at the interface was higher than that on both sides, owing to work hardening, at approximately 226 HV. Full article