FSTs are advanced solid-state processing methods that address the growing industrial demand for lightweight components with enhanced mechanical properties. These techniques, including friction stir welding and friction stir processing, are distinguished by their capability to refine microstructures and improve the quality and longevity of welds and surfaces, making them integral to modern manufacturing. Recent advancements in machine learning (ML) have facilitated the integration of data-driven approaches into FST applications, demonstrating significant potential for optimising performance. This review explores the use of ML in FSTs, highlighting how various ML models improve the prediction of mechanical properties and the optimisation of processing parameters. Findings indicate that ML provides higher accuracy in predictions for FST applications than traditional statistical methods, while hybrid ML techniques further enhance outcomes by refining process control. The review further highlights existing knowledge gaps and proposes directions for future research to enhance ML integration in FSTs. This comprehensive synthesis is drawn from academic literature primarily sourced from the Scopus and Web of Science databases, supplemented by insights from recent books published in the past 15 years.

The present study investigates ultrasonic metal welding to manufacture 10 mm2 copper (Cu) wire joints with different core diameters. The primary purpose of this study is to explore the influence of wire core diameter on the performance of ultrasonic welded joints. Wire core diameter is positively correlated with the peeling resistance of the joint. Superior mechanical properties of the joint are achieved with an increased diameter of the wire core. The peeling strength of the welded joint of two wires with a wire core diameter of 0.25 mm reaches 306.8 N. Examining the welding temperature and assessing the joint’s porosity reveals a significant impact of temperature on porosity. However, relying solely on porosity as a criterion for judging the overall forming quality of joints may be insufficient. Scanning electron microscope and energy-dispersive X-ray elemental analysis revealed that certain wires underwent plastic deformation at elevated temperatures without attaining atomic bonding. Additionally, the welded joint exhibits a compact structure externally and a more relaxed structure internally. The upper side of the joint in contact with the briquette and the lower side in contact with the welding head exhibit minimal gaps, while numerous gaps are evident in the middle of the joint. Furthermore, upon examining the fracture morphology, two distinct failure modes are identified at the joint surface of the conductor. The first involves the fracture of the wire core with a completely separated joint surface, resulting in poor mechanical properties of the joint. The second mode entails the ductile fracture of the wire core at the joint surface, indicating good mechanical properties of the joint. © IMechE 2024.

The present study unveils a comprehensive analysis of ultrasonic welding bonding mechanisms for multilayer copper foil combinations, notably Electrolytic Tough Pitch (ETP) copper, in pouch cell-based battery packs. Pouch cell-based battery packs utilize multilayer copper foils for their tabs, requiring a strong connection to the busbar to meet strict requirements for joint strength and electrical conductivity. Ultrasonic welding is employed for this purpose, specifically focusing on analyzing the bonding mechanisms of multilayer copper foil combinations. This study investigates the effects of key weld parameters like weld time, weld force, and weld energy on microstructure. Micrographs are analyzed to categorize welds as ‘under-welded’, ‘well-welded’, or ‘over-welded’. Light optical microscopy identifies various joint behaviors and weld defects such as swirls, interfacial waves, microbonds, interfacial gaps, voids, and delamination. A pattern in the distribution of certain joint features is noted, dividing the weld nugget into three regions: top, middle, and bottom. The top and bottom regions show signs of material mixing, while the middle region is characterized by microbond formation.

This article explains development of high strength and lightweight Ti6Al4V5Cr alloy by μ-plasma powder additive manufacturing (μ-PPAM) process for automotive, aerospace, military, dies and moulds, and other similar applications. Microstructure, formation of phases, porosity, microhardness, tensile properties, abrasion resistance, and fracture toughness of multi-layer deposition of Ti6Al4V5Cr alloy are studied and compared with Ti6Al4V alloy. Results reveal that the presence of chromium in Ti6Al4V5Cr alloy refined the grains of its β-Ti and α-Ti phases, increased volume % of β-Ti phase, and promoted formation of its equiaxed grains. It also increased tensile strength, microhardness, abrasion resistance, and fracture toughness of Ti6Al4V5Cr alloy. It enhanced solid solution strengthening and formed higher hardness imparting intermetallic Cr2Ti phase and changed fracture mode to mixed ductile and brittle mode with larger size dimples, cleavage facets, and micropores. But it decreased formation temperature of β-Ti phase and % elongation as compared to Ti6Al4V alloy. Chromium and vanadium content in β-Ti phase of Ti6Al4V5Cr alloy is 7 % and 2.1 % more than its α-Ti phase. This study demonstrates that inclusion of limited amount of chromium content to Ti6Al4V5Cr alloy by μ-PPAM process is very beneficial to enhance microstructure, mechanical properties, crack propagation resistance, and abrasive wear resistance of the Ti6Al4V5Cr alloy. It makes Ti6Al4V5Cr alloy very useful in many commercial applications that require higher strength than Ti6Al4V alloy along with lightweight requirement.

In present study, a wall structure of SS309L was constructed through Gas metal arc welding based Wire-arc additive manufacturing process. The wall structure of SS309L underwent investigation for microstructure and mechanical properties at three positions along the horizontal deposition direction. Mechanical assessments, including microhardness testing, impact testing, tensile testing, and fractography, were conducted at three positions of walls. Microstructure study has shown a fine granular structure in addition to colony of columnar dendrites in bottom section, a columnar dendrites in middle section, and a mix of dendritic structure with even coarser structures in top section. The mean microhardness values were observed to be 159 ± 4.21 HV, 162 ± 3.89 HV, and 168 ± 5.34 HV for the top, middle, and bottom sections, respectively. Results of impact testing for the wall structure indicated greater strength compared to wrought SS309L. The tensile strength of the built structure showed average values of yield strength, ultimate tensile strength, and elongation to be 409.33 ± 7.66 MPa, 556.66 ± 6.33 MPa, and 39.66 ± 2.33 %, respectively. In comparison, wrought 309 L steel typically exhibits tensile strengths in the range of 360–480 MPa for yield strength, 530–650 MPa for ultimate tensile strength, and 35–45 % elongation. Thus, the obtained tensile strength results for the wall structure fall within the range of tensile strength observed in wrought 309 L steel. Fractography of the tensile and impact specimens, as obtained through Scanning Electron Microscopy, revealed the superior ductility of the fabricated component. This study contributes valuable insights into the manufacturing of wall structure and their analysis regarding mechanical characteristics.

Friction stir-based techniques (FSTs), originating from friction stir welding (FSW), represent a solid-state processing method catering to the demands of various industrial sectors for lightweight components with exceptional properties. These techniques have gained much more attraction by providing an opportunity to tailor the microstructure and enhance the performance and quality of produced welds and surfaces. While significant attention has historically been directed towards the FSW process, this review delves into the working principles of FSTs, exploring their influence on mechanical properties and microstructural characteristics of various materials. Additionally, emphasis is placed on elucidating the advancement of hybrid FSW processes for both similar and dissimilar metal components, aimed at enhancing welding quality through meticulous control of grain textures, structures, precipitation, and phase transformations. Finally, the review identifies current knowledge gaps and suggests future research directions. This review paper synthesises academic literature sourced from the Web of Science (WoS) and Scopus databases, supplemented by additional sources such as books from the last 15 years. 

In this study, submerged friction stir welding (SFSW) was performed to weld 6 mm thick AZ31B Mg alloy plates, aiming to explore the impact of rotation speed on microstructure and tensile behavior. The water medium was used to submerge the samples. The SFSW was conducted at three different speeds (815, 960, and 1200 rpm), to assess the impact of rotation speed on SFSWed joint performance. As the rotation speed increased from 815 to 960 rpm, tensile strength increased plateauing over a range of the rotation speed. However, a significant drop in tensile strength occurred at 1200 rpm due to the formation of void defects. The SZ exhibits a size and width increment in the lower part with increasing rotation speed. The hardness of the stir zone (SZ) gradually rose with increasing rotation speed from 815 to 960 rpm. Fracture locations were observed in the thermal-mechanically affected zone (TMAZ) adjacent to the SZ at a rotation speed of 815 rpm, and in the heat-affected zone (HAZ) adjacent to the TMAZ at a rotation speed of 960 rpm. The joint welded at 1200 rpm fractured within the SZ. This study offers valuable insights into the welding and joining field, particularly regarding their mechanical characteristics. 

A key challenge in the production of high-grade automotive aluminum components through the High-Pressure Die Casting (HPDC) process is the imperative to minimize imperfection. In addressing this concern, this study utilizes friction stir processing (FSP), a widely recognized intense plastic deformation technique. FSP is applied to systematically alter the microstructure of HPDC Al-4Mg-2Fe, a prominent alloy extensively used in the die-casting sector. By using the pass strategy to incorporate both one-pass and two-pass approaches, the microstructure is selectively altered to establish a defect-free processed zone. The utilization of FSP demonstrates its efficacy in breaking aluminum dendrites and acicular silicon particles, leading to a uniformly dispersed arrangement of equiaxed silicon particles within the aluminum-based matrix. In addition, FSP eradicates porosity and disintegrates needle-like Fe particles, resulting in a more refined and homogeneously distributed structure. Subsequently, the material’s mechanical properties processed by FSP were assessed in the longitudinal direction concerning the processing axis and then compared with those of the original base material. The microstructural refinement and reduction in porosity induced by FSP result in a notable enhancement in hardness, with an increase of 23 % after one pass and 37 % after two passes. The substantial improvement in mechanical properties during the FSP process is predominantly attributed to modifications in the morphology, refinement, and dispersion of intermetallic particles within the matrix. This improvement is further complemented by the ultrafine dispersion of casting defects. This study underscores the efficacy of FSP as a valuable tool for modifying microstructures and improving mechanical properties in HPDC Al-4Mg-2Fe alloys. Such advancements align with the lightweighting objectives pursued by the automotive industry. 

Aluminum-based metal matrix composites have a wide range of applications in the automotive and aerospace industries due to their high strength-to-weight ratio. They are difficult to manufacture using fusion-based additive manufacturing (FBAM) processes because of solidification problems such as thermal stresses, hot cracks and porosity. Moreover, the formation of undesired phases at high temperature creates anisotropy in the composites. To overcome these problems, promising solid-state additive manufacturing (SSAM) processes such as ultrasonic AM, cold-spray AM, friction stir AM, and additive friction stir deposition have been developed. These solid-state processes introduce a novel concept for AM where material is added layer by layer in the solid state by maintaining the maximum temperature below the melting point of feedstock material. These processes have demonstrated the uniform distribution of reinforcing particles, fine-grained microstructure along with good bonding of layers which can offer improved scope for Industry 4.0 applications. This chapter summarizes progress in the SSAM of composites with an emphasis on aluminum-based composites. In addition, various challenges and future work have been briefly discussed which would be helpful to the researchers and industrialist working in the field of SSAM of composites.

Aluminium-lithium (Al-Li) 2060 alloy, a 3rd generation Al-Li alloy, is considered a structural material for aircraft components. This study employs the Friction Stir Welding (FSW) process with a kinematic 5-axis robotic arm to weld 4-mm-thick plates of 2060-T8E30 Al-Li alloy. The focus is on the impact of tool axial force and speeds on the microstructural evolution, mechanical properties, and surface integrity of the welded joints. The applied process parameters included rotational speeds ranging from 800 to 1600 rpm, traverse speeds from 2 to 4 mm/s, and axial forces from 4 to 6 kN. We utilise the Taguchi L9 orthogonal array to optimise the process parameters. The results revealed that rotational speed is paramount for affecting the welds’ quality, followed by axial force and then traverse. Defect-free samples exhibited a fine surface finish, with average roughness values of 3.05 μm and 3.536 μm. The study also showed that 5 kN of axial force, 1200 rpm of rotational speed, and 3 mm/s of traverse speed were the best FSW conditions for getting a maximum stir zone microhardness value of 128.77 HV. This study also shows how to improve the FSW parameters for Al-Li alloys, showing how important precise parameter control is for improving joint strength and weld quality in high-tech aerospace and automotive applications.