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Refill friction stir spot welding (RFSSW) provides a novel method to join similar and/or dissimilar metallic materials without a key-hole in the center of the joint. Having the key-hole free characterization, the similar/dissimilar RFSSW joint exhibits remarkable and endurable characteristics, including high shear strength, long fatigue life, and strong corrosion resistance. In the meanwhile, as the key-hole free joint has different microstructures compared with conventional friction stir spot welding, thus the RFSSW joint shall possess different shear and fatigue fracture mechanisms, which needs further investigation. To explore the underlying failure mechanism, the similar/dissimilar metallic material joining parameters and pre-treatment, mechanical properties, as well as fracture mechanisms under this novel technology will be discussed. In details, the welding tool design, welding parameters setting, and the influence of processing on the lap shear and fatigue properties, as well as the corrosion resistance will be mainly discussed. Moreover, the roadmap of RFFSW is also discussed.

Magnesium alloys have a significant benefit over steel and aluminum alloys in manufacturing components for many automotive and structural applications because of their higher light-weighting potential, lowest density, and higher strength to weight ratio. However, one of the impediments to the success of multi-material integration of the above materials for automotive manufacturing is joining these materials together without any cracking or corrosion during in-service use. The present work aims to develop and demonstrate a cost-effective, novel, and versatile mechanical joining technique, named Upset Protrusion Joining (UPJ), to mechanically and rapidly join a cast magnesium component to an aluminum alloy sheet. The process involves a cylindrical protrusion emanating perpendicular to the flat surface of a cast plate that fits through a hole in an aluminum sheet. The two components are then clamped together, electrically heated, and compressed perpendicular to the protrusion axis. During compression, the protrusion expands circumferentially to fill the hole as well as the region above the hole, thus entrapping the sheet metal between the mushroomed head and the casting. The effect of different UPJ process parameters such as applied current, current duration, compression loading rate, and compression distance were studied through experimentation on die-cast magnesium alloy, with protrusion of 11 mm diameter and 14 mm height. Material-specific process window was identified to achieve a satisfactory joint quality in terms of post-UPJ joint strength with appearance. UPJ method shows a great promise to implement in automotive and other industrial manufacturing environments for fastening cast components to a similar or dissimilar wrought sheet component. Graphical abstract

Critical aspects of innovative design in engineering disciplines like infrastructure, transportation, and medical applications require the joining of dissimilar materials. This study investigates the literature on solid-state bonding techniques, with a particular focus on diffusion bonding, as an effective method for establishing engineering bonds. Welding and brazing, while widely used, may pose challenges when joining materials with large differences in melting temperature and can lead to mechanical property degradation. In contrast, diffusion bonding offers a lower temperature process that relies on solid-state interactions to develop bond strength. The joining of tungsten and steel, especially for fusion reactors, presents a unique challenge due to the significant disparity in melting temperatures and the propensity to form brittle intermetallics. Here, diffusion characteristics of tungsten–steel interfaces are examined and the influence of bonding parameters on mechanical properties are investigated. Additionally, CALPHAD modeling is employed to explore joining parameters, thermal stability, and diffusion kinetics. The insights from this research can be extended to join numerous dissimilar materials for specific applications such as aerospace, automobile industry, power plants, etc., enabling advanced and robust design with high efficiency.

Magnesium alloys have a significant benefit over the steel and aluminum alloys in manufacturing of components for many automotive and structural applications because of their extreme lightweight, low density, and high strength to weight ratio. However, one of the glaring impediments to the success of steels, aluminum, and magnesium-based multi-material integration for automotive industries is the ability to join these materials together without any cracking and corrosive damages during a performance. The present work aims to demonstrate a cost-effective, novel, and versatile joining technique, named Upset Protrusion Joining (UPJ), to mechanically and rapidly (1–2 s) join die-cast AM60 alloy to aluminum alloy sheet and evaluate its UPJ characteristics. Cast Mg plate has a cylindrical protrusion (11 mm diameter and 14 mm height) emanated perpendicular to its flat surface, and an aluminum sheet has a hole that accommodates the protrusion. Mg and Al alloy components are then clamped together, electrically heated, and compressed perpendicular to the protrusion axis. During compression, the protrusion expanded circumferentially to fill the hole as well as the region above the hole, and entrapped the Al sheet between the deformed (in a mushroom shape) head and the Mg plate. The effect of different UPJ process parameters such as applied current, current duration, compression loading rate, and compression distance is studied. The process demonstrated repeatability at given process conditions, and optimum process parameters were identified that produce visibly good joints (defect-free) and sufficient joint strengths when tested in the lap-shear mode under uniaxial tension. AM60 alloy showed a great promise as a candidate alloy to suit the UPJ method to adapt to automotive and other industrial manufacturing units to join with dissimilar wrought Al alloy sheets.

Lightweighting of vehicles and portable structures is an important undertaking. Multimaterial design is required to achieve conflicting design targets such as cost, stiffness, and weight. Friction stir welding (FSW) variants, such as friction stir dovetailing and friction stir scribe, are enabling technologies for joining of dissimilar metals. This article discusses how FSW variants are capable of joining aluminum to steel in particular. The characteristics of metallurgical bonding at the dissimilar materials interface are strongly affected by weld temperature. Control of FSW process temperature enables metallurgical bonding with suppressed formation of intermetallics at the dissimilar materials interface, resulting in improved mechanical properties relative to competing techniques. Temperature control is thus a powerful tool for process development and ensuring weld quality of dissimilar materials welds.

Effects of the surface-treated A5052 aluminum alloy on the adhesiveness of joining dissimilar materials, such as A5052 aluminum alloy sheet and polyamide resin sheet, was examined to manufacture a multi-material. Various surface treatments for the A5052 sheet were performed. The hot melt adhesive sheet comprising polyamide resin was used as the adhesive. The shear strength of adhered specimens was measured via tensile testing, and the shear strength was made to be the joining strength. Using various surface treatment techniques, oxidation films with different hole sizes and surface roughness were formed on the A5052 aluminum sheets. The joining strength of the surface-treated specimens was the lowest, whereas those joined via anode electrolysis exhibited the highest joining strength. These differences in joining strengths were owing to the anchor effect and chemical interfacial bonding force.

Joining dissimilar materials such as plastics and metals in engineered structures remains a challenge 1 . Mechanical fastening, conventional welding and adhesive bonding are examples of techniques currently used for this purpose, but each of these methods presents its own set of problems 2 such as formation of stress concentrators or degradation under environmental exposure, reducing strength and causing premature failure. In the biological tissues of numerous animal and plant species, efficient strategies have evolved to synthesize, construct and integrate composites that have exceptional mechanical properties 3 . One impressive example is found in the exoskeletal forewings (elytra) of the diabolical ironclad beetle, Phloeodes diabolicus . Lacking the ability to fly away from predators, this desert insect has extremely impact-resistant and crush-resistant elytra, produced by complex and graded interfaces. Here, using advanced microscopy, spectroscopy and in situ mechanical testing, we identify multiscale architectural designs within the exoskeleton of this beetle, and examine the resulting mechanical response and toughening mechanisms. We highlight a series of interdigitated sutures, the ellipsoidal geometry and laminated microstructure of which provide mechanical interlocking and toughening at critical strains, while avoiding catastrophic failure. These observations could be applied in developing tough, impact- and crush-resistant materials for joining dissimilar materials. We demonstrate this by creating interlocking sutures from biomimetic composites that show a considerable increase in toughness compared with a frequently used engineering joint. A jigsaw-style configuration of interlocking structures identified in the elytra of the remarkably tough diabolical ironclad beetle, Phloeodes diabolicus , is used to inspire crush-resistant multilayer composites for engineering joints.

Hot pressing has been increasingly applied as a joining technology for dissimilar materials because of its simple setup. However, various process parameters must be clearly defined here in order to obtain an optimum joint. In this study, an experimental hot pressing for joining an aluminium alloy sheet grade A5052 with a polybutylene terephthalate (PBT) plate was carried out. Different surface treatment on the aluminium samples were firstly employed by using both mechanical and chemical processes. Then, surface topographies of the treated samples were characterized by scanning electron microscope. The Fourier transform infrared spectroscopy analysis was carried out to examine the C=O in the carbonyl group of thermo-plastic at the joint. During the hot pressing, joining force and temperature were varied. Afterwards, tension shear tests were performed for the aluminium-PBT specimens to evaluate the resulted joint strength. It was found that the pressing force of 1-ton and a pressing temperature of 270°C were the optimum parameters for joining these investigated materials. The maximum joining strength was obtained by specimens subjected to sandblasting combined with chemical surface treatment, in which the surface roughness of aluminium sheet samples was in the range of 4-9 μm. The specimens after shear tests exhibited a cohesive failure. The depth of mechanical interlocking between surfaces of both materials was approximately 33 μm. No change of the molecular structure of PBT was observed by the direct bonding between aluminium and PBT using hot pressing.

Modern structural engineering is impossible without the use of materials and structures with high strength and low specific weight. This work carries out a quantitative and qualitative analysis of articles for 2016–2021 on the topic of welding of dissimilar alloys. It is found that laser welding is most widely used for such metal pairs as Al/Fe, Al/Ti, and Al/Cu. The paper analyzes the influence of the basic techniques, methods, and means of laser welding of Al/Fe, Al/Ti, and Al/Cu on the mechanical properties and thickness of the intermetallic compound (IMC). When welding the lap joint or spike T-joint configuration of Al/Fe, it is preferable to melt the steel, which will be heated or melted, by the laser beam, and through thermal conduction, it will heat the aluminum. When welding the butt-welded joint of Al/Fe, the most preferable is to melt the aluminum by the laser beam (150–160 MPa). When welding the butt-welded joint of Al/Ti, it is possible to obtain the minimum IMC and maximum mechanical properties by offsetting the laser beam to aluminum. Whereas when the laser beam is offset to a titanium alloy, the mechanical properties are 40–50% lower than when the laser beam is offset to an aluminum alloy. When lap welding the Al/Cu joint, under the impact of the laser beam on the aluminum, using defocusing or wobbling (oscillation) of a laser beam, it is possible to increase the contact area of electrical conductivity with the tensile shear strength of 95–128 MPa.

The progress of materials has never stopped, and the joining process of dissimilar materials is still a serious challenge. Vacuum brazing technology is a joining process developed in the 1940s and still meets the challenges of advanced dissimilar material joining. The choice of filler metal directly determines the performance of the brazing joint. Titanium-based filler metal is widely used because of its excellent properties. Titanium-based fillers of different compositions and contents are used to address various joining challenges and facilitate material advancements. In recent decades, dozens of types of titanium-based fillers have been developed, mainly focusing on the continuous optimization of the element types and composition content in the fillers. This paper reviews the development of titanium-based filler metal in recent years. The unique roles of common Ti, Zr, Co, Be, Mo, V, Nb, RE, and other elements in the components of titanium-based filler metal are summarized. The melting point of the filler metal with different element combinations and different content combinations and the mechanical strength of the experimental joints were compared. In addition, the characteristics, classification, and production methods of titanium-based filler metal are introduced, and the main application fields and brazing materials of titanium-based filler metal are discussed. Finally, the future development and challenges of titanium-based filler metal are proposed, and the prospect is made in order to provide reference for the future research on dissimilar material connection.