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Dissimilar micro-friction stir welding (dissimilar μFSW) can be a preferred choice for joining dissimilar materials having thickness ≤ 1000 μm. The technique's potential applications are in miniaturized components, where the inherent benefits of the process, such as low temperature, low distortion, and clean joining, are advantageous compared to fusion welding. However, the challenges associated with dissimilar μFSW hinder its full potential applications in the relevant industries. The challenges are particularly a combination of two different characteristics of the process (i) the complexities of simultaneously fulfilling the dissimilar materials' demands due to the vast differences in the two materials' mechanical and thermal properties and (ii) the problems due to reduced sheet thickness. In this regard, the present work is a comprehensive and timely review of the research works done on dissimilar μFSW targeted at easily acquainting the research community about the know-how and the state of the art of the process. The review is broadly divided into three crucial parts: the process inputs/requisites, process mechanics, and process performance. The details about the μFSW tool, process parameters, and relative sheet positioning are discussed under the heading process inputs/requisites. Concerning the process mechanics, the intermetallic compound formation, defect generation, and material mixing are discussed. The joints' resulting performance is shown by detailing the essential properties such as formability, residual stresses, fatigue, hardness, and tensile strength. Additionally, several future research directions are presented at the end of this critical review to motivate further improvements in this joining technique and instigate its utility in relevant industries.

A simple mechanical fixture is proposed to overcome the fixturing issues present in joining of thin sheets. The fixture is similar to a lever type clamp and unlike some common FSW fixtures can hold the thin sheets close to the weld line with precision and uniform pressure. To reduce heat loss, asbestos were used as cover plate. The feasibility of the fixture was confirmed by successfully welding 0.5 mm thin aluminium alloy 6061-T6 sheets at five different tool travel speeds. A joint efficiency (UTS FSW /UTS Basemetal ) of 74% and ductility of 8% in terms of percentage elongation were obtained corresponding to 150 mm/min of tool travel speed in which case the weld also withstood 180° bending test. The welds had a distorted shape similar to that of a saddle. The macrostructure indicated that TMAZ area decreased with tool travel speed.

Triple-spiral micro-grooves on the tool-shoulder end-surface is a feature recently being used for improving material flow during micro-friction stir welding (μFSW). However, its effect on process responses in comparison to the plain tool-shoulder end-surface lacks recognition, which has been targeted in the present work. An additional contribution to the knowledge base of μFSW tools having such features is also made by investigating the effect of imparting different cross-sections (rectangular, circular, right-trapezoidal type I and right-trapezoidal type II) to the micro-grooves, on the process responses. Forces, temperature, and material flow pattern were mainly the process responses analyzed through experiment and FEA simulation of μFSW in 0.5 mm thick AA6061-T6 sheets at a tool rotation of 1900 rpm and welding speed 500 mm/min. Furthermore, the welds’ quality was assessed by its surface topography, microstructure, and tensile property. The physics of the interaction between shoulder end-surface and plasticized sheet material showed that besides the triple-spiral shape, it was the cross-section of micro-grooves (mainly the orientation angle and shape of micro-grooves’ wall) that crucially determined the mechanical, thermal, and flow characteristics of the plasticized sheet material, ultimately affecting the process responses. The possibility of low-temperature welding with enhanced material mixing had been achieved with the micro-grooved tools. A higher amount of plastic deformation was also seen, with these tools, through X-ray tomographic images of the deformed copper foils placed transverse to the welding direction. Moreover, a remarkable improvement in the weld surface finish was obtained using the micro-grooved tools. Among the four micro-grooved tools, the right-trapezoidal type II cross-section showed the best performance by yielding moderate process loads along with the best weld surface finish and tensile property.

Background Previous case series report that neuroendocrine tumors (NETs) of the ampulla of Vater have worse overall survival (OS) than NETs in the duodenum. We aimed to compare the OS of patients with ampullary NETs to patients with duodenal NETs.