Friction Stir Welding Technology Research Articles

A Review on Friction Stir Welding of Copper: Tool Geometry, Process Parameters, and Joint Properties.

This paper comprehensively reviews friction stir welding (FSW) as applied to copper and its alloys. FSW is a solid-state joining process that offers significant advantages over traditional fusion welding methods, particularly for materials like copper that are difficult to weld conventionally due to their high thermal conductivity and oxidation issues. Over time, the FSW process has been developed for different industries. Copper structures joined through FSW are utilized for nuclear waste storage, electrical connectors, chemical and petrochemical storage, refrigeration systems, heat exchangers, and the aerospace industry. This covers recent advancements in FSW technology, the geometry of the tools used, the process parameters, and the microstructural characteristics and mechanical properties of the joints. It examines the shapes, sizes, and materials of the tools used for welding copper and its alloys, along with process parameters such as rotational speed and traverse speed, and their influence on the quality of the joints. Additionally, the paper presents syntheses of previously published results, highlighting the values of parameters that indicate the quality of the welds, including grain size, microhardness, mechanical strength, and elongation. The challenges and potential solutions in applying FSW to copper are also discussed, providing a starting point for future research and industrial applications.

Microstructure and crack propagation behavior of 2195 Al–Li alloy with different orientations in the friction stir welding nugget zone

The 2195 Al–Li alloy is widely used in the aerospace field, where using friction stir welding technology can achieve lightweight and reduced wear designs for components. Fatigue failure, as one of the main modes of damage affecting the life and reliability of structural components, is particularly significant. This paper thoroughly explores the differences in microstructure and fatigue crack propagation behavior between the advancing side and retreating side of the friction stir welded joint in different sampling directions, providing a theoretical basis for enhancing the fatigue performance of friction stir welds. Characterization of the microstructure of the samples was performed using Electron Backscatter Diffraction (EBSD) and X-Ray Diffraction (XRD), and the fatigue properties were investigated using fatigue crack propagation rate curves and crack growth rate curves. The results indicate that the longitudinal base material grains tend to a fibrous structure, while the axial base material grains are distributed in a lamellar fashion. Compared to the advancing side of weld nugget zone, the retreating side of weld nugget zone has significantly reduced grain size and texture types. The fatigue performance of the retreating side of the weld nugget zone is superior to that of the advancing side, and the circumferential welds outperform the longitudinal welds in terms of fatigue performance.

Eliminating heat-affected zone of nuclear heat-resistant steel joint via low-temperature friction stir welding

Ferritic/martensitic (F/M) heat-resistant steels are one of the most promising candidate materials applied in core fuel assemblies such as cladding and packaging in nuclear reactors, but their weldments with high performance especially the creep properties were difficult to obtain by conventional welding methods due to the formation of heat-affected zone (HAZ) and rapid dissolution of precipitates. Here we successfully averted the formation of HAZ by reducing the heat input during welding to improve the structure-property synergy of a 12Cr-F/M steel joint via a low-temperature friction stir welding (FSW) technology. Complex microstructure regions consisting of stirred zone (SZ), fine-grained HAZ and inter-critical HAZ were generated in the traditional FSW joint with a high heat input, while only SZ and thermo-mechanically affected zone were found in the low-temperature FSW joint with a peak temperature between the Ac3 and Ac1 temperature. Under dynamic recrystallization at the α+γ two-phase region, ultrafine ferrite and martensite were generated and large amounts of precipitates were retained, giving rise to the greatly improved microhardness and superior tensile strength and impact toughness on par with that of the base metal. This work recommends a feasible technique to produce high-performance heat-resistant steel joints for lengthening the service life of nuclear reactors.

Research on friction stir welding technology of urban rail transit car body

Abstract In this paper, the principle and technical characteristics of friction stir welding are introduced. According to the form of the side wall of urban rail transit vehicles, a friction-stir welding joint structure with convex is proposed. In order to verify the performance of the joint, the joint tensile strength test and the static strength test of the car body are carried out. The results show that the designed friction stir welding joint has high smoothness and excellent performance, fulfilling the requirements for the standard EN12663.

Online prediction of joint mechanical properties of FSW thick AA2219-T8 based on multi-source information fusion using 1DCNN

High strength AA2219-T8, Al-Cu alloy of 18 mm plate is welding by friction stir welding (FSW) technology and used for heavy-lift launch vehicles tank. During FSW thick AA2219-T8 plate, joint tensile strength and microhardness are affected by multiple interconnected variables including welding force, temperature, and geometric quantity of the butt face. The joint mechanical properties are difficult to predict and ensure. This paper proposed a hybrid predicting approach based on multi-source information fusion, called Down-Sampling and One-Dimensional Convolutional Neural Network (DS-1DCNN). Initially, FSW experiments were conducted to collect the axial force, welding surface temperature at advancing and retreating side, gap, and mismatch signals, which were fused through DS technology. To extract temporal information and features from signals, a 1DCNN prediction model was established, with the fused multi-source signals as input and the tensile strength and Vickers hardness as output. Subsequently, the optimal model architecture and hyper-parameters of 1DCNN were determined through experiments and grid search combined with K-fold cross-validation, and an online prediction system was developed. Finally, effective validation experiments were conducted and the experimental results agreed with the DS-1DCNN prediction results with an acceptable error of approximately 5%. Parameter sensitivity analysis revealed that the number of convolutional layers and learning rate were identified as critical parameters affecting the model performance. Additionally, time analysis showed that the calculation time of the prediction system was less than 200 ms which can meet the time requirements of real-time thick-plate FSW application. The research lays a foundation on the real-time quality monitoring in the process of FSW thick-plate butt joint.

Thermal and Mechanical Investigation of Friction Stir Welding with Disparate Materials AA6061 and AA7075

Background:: The primary objective of this study is to assess the impact of welding conditions on the mechanical properties of friction stir-welded butt joints created from two distinct aluminium alloys, namely, AA6061 and AA7075. Friction stir welding (FSW), known for its innovation and low-energy solid-state bonding technique, was employed in this research. Methods:: FSW experiments were carried out on both AA6061 and AA7075 alloys using a computer numerical control (CNC) machine. The selection and design of the tool geometry were meticulous, with an emphasis on new pin profiles that are nearly flat at the weld contact point. Precisely, four distinct tool geometries were machined from HC-HCr (High carbon, high chromium steel): Circular, Square, Tapered third, and Triangular. Critical process variables that significantly influence weld quality include rotation speed (800 rpm-1400 rpm) and traverse speed (12 to 25 mm/min). These variables were carefully optimized to achieve flawless welds. During the friction stir welding process, the nugget zone undergoes significant deformation, leading to the formation of a new microstructure that substantially impacts the mechanical properties of the joint. Results:: This study comprehensively investigates the thermal and mechanical properties of friction stir welding using aluminium alloys AA6061 and AA7075, considering various tool shapes. Among the four tool shapes employed, two were found to yield higher hardness values (referred to as BH). Notably, the square-shaped tool produced the highest temperature, reaching up to 690ºC, as determined by thermocouple readings. Based on the findings, the optimal FSW parameters for enhancing hardness involve an axial feed and spindle speed of 800 rpm combined with a feed rate of 15 mm/min. These parameters were identified as crucial for achieving the desired mechanical properties in the friction stir-welded joints. Conclusion:: This study presents new developments in FSW technology, which may have patent implications.

Active Vibration Avoidance Method for Variable Speed Welding in Robotic Friction Stir Welding Based on Constant Heat Input.

Robotic Friction Stir Welding (RFSW) technology integrates the advantages of friction stir welding and industrial robots, finding extensive applications and research in aerospace, shipbuilding, and new energy vehicles. However, the high-speed rotational process of friction stir welding combined with the low stiffness characteristics of serial industrial robots inevitably introduces vibrations during the welding process. This paper investigates the vibration patterns and impacts during the RFSW process and proposes an active vibration avoidance control method for variable speed welding based on constant heat input. This method utilizes a vibration feedback strategy that adjusts the spindle speed actively if the end-effector's vibration exceeds a threshold, thereby avoiding the modal frequencies of the robot at its current pose. Concurrently, it calculates and adjusts the welding speed of the robot according to the thermal equilibrium equation to maintain constant heat input. A simplified dynamic model of the RFSW robot was established, and the feasibility of this method was validated through simulation experiments. This study fills the gap in vibration analysis of RFSW and provides new insights into control strategies and process optimization for robotic friction stir welding.

Effect of probe length on tensile strength of dissimilar friction stir welded lap-joint between AA6061 and 316 stainless steel using marine structure

Recently, optimizing marine structure have been facing with a lot of challenges to reducing weight, increasing strength, and improving resistance corrosion. Using dissimilar joint may be one of the suitable solutions for manufacturer. In this study, dissimilar lap-joints between aluminum alloys 6061 and 316 stainless steel was produced by friction stir welding technology. The attention was put on the effect of different probe lengths on joint strength. The probe length was arranged from 2.7 mm to 2.9 mm. The experimental results show that the tensile strength of lap-joints increased with long probe length. The highest tensile strength is obtained approximately 6976 at the probe length of 2.9 mm that fracture location was found at aluminum side. The impact of interface properties on the joint strength was investigated and analyzed in this work. Key works: Dissimilar joint, FSW, probe length, tensile strength.

Optimization of Installation Position for Complex Space Curve Weldments in Robotic Friction Stir Welding Based on Dynamic Dual Particle Swarm Optimization

Robotic friction stir welding (RFSW), with its wide application range, ample working space, and task flexibility, has emerged as a vital development in friction stir welding (FSW) technology. However, the low stiffness of serial industrial robots can lead to end-effector deviations and vibrations during FSW tasks, adversely affecting the weld quality. This paper proposes a dynamic dual particle swarm optimization (DDPSO) algorithm through a new comprehensive stability index that considers both the stiffness and vibration stability of the robot to optimize the installation position of complex space curve weldments, thereby enhancing the robot’s stability during the FSW process. The algorithm employs two independent particle swarms for exploration and exploitation tasks and dynamically adjusts task allocation and particle numbers based on current results to fully utilize computational resources and enhance search efficiency. Compared to the standard particle swarm optimization (PSO) algorithm, the DDPSO approach demonstrated superior search capabilities and stability of optimization results. The maximum fitness value improved by 4.2%, the average value increased by 12.74%, and the concentration level of optimization results rose by 72.91% on average. The new optimization method pioneers fresh perspectives for optimizing the stability of RFSW, providing significant grounds for the process optimization and offline programming of complex spatial curve weldments.

Mechanical properties and corrosion resistance study of dissimilar metal thin sheet friction stir welded joints

This study employs friction stir welding (FSW) technology to achieve the butt welding of 2mm thick 1060 aluminum and T2 copper. The research investigates the macroscopic formation, tensile properties, microhardness, and electrochemical corrosion behavior of the welded joints. The results indicate that the welded joints exhibit excellent formation, with a tensile strength reaching 84.76% of that of the 1060 aluminum material. Well-formed welded joints can be obtained by controlling the rotation speed and welding speed within a certain range. However, the rotation speed has a more significant impact on the microhardness in the weld zone. The corrosion potential of T2 copper is higher than that of 1060 aluminum, forming a macroscopic galvanic couple between the two materials. The corrosion potential of the welded joint falls between that of T2 copper and 1060 aluminum.

Advancements and Applications of Friction Stir Welding: A Comprehensive Review

Friction Stir Welding (FSW) has emerged as a groundbreaking joining technique revolutionizing the field of manufacturing and engineering. This review paper provides an in-depth analysis of the evolution, principles, process parameters, advancements, challenges, and diverse applications of FSW. It discusses the fundamental mechanisms governing FSW, explores the latest developments in tool materials and designs, examines the influence of process parameters on weld quality, and highlights the innovative applications of FSW across various industries. Additionally, this paper addresses the current challenges and future prospects to further enhance the efficiency, reliability, and versatility of FSW technology. Keywords: Friction Stir Welding, Joining Techniques, Weld Quality, Process Optimization, Advanced Materials, Applications, Challenges, Future Directions.

Digital Twin Virtual Welding Approach of Robotic Friction Stir Welding Based on Co-Simulation of FEA Model and Robotic Model

Robotic friction stir welding has become an important research direction in friction stir welding technology. However, the low stiffness of serial industrial robots leads to substantial, difficult-to-measure end-effector deviations under the welding forces during the friction stir welding process, impacting the welding quality. To more effectively measure the deviations in the end-effector, this study introduces a digital twin model based on the five-dimensional digital twin theory. The model obtains the current data of the robot and six-axis force sensor and calculates the real-time end deviations using the robot model. Based on this, a virtual welding model was realized by integrating the FEA model with the digital twin model using a co-simulation approach. This model achieves pre-process simulation by iteratively cycling through the simulated force from the FEA model and the end displacement from the robot model. The virtual welding model effectively predicts the welding outcomes with a mere 6.9% error in lateral deviation compared to actual welding, demonstrating its potential in optimizing welding parameters and enhancing accuracy and quality. Employing digital twin models to monitor, simulate, and optimize the welding process can reduce risks, save costs, and improve efficiency, providing new perspectives for optimizing robotic friction stir welding processes.

Microstructure and Mechanical Properties of Friction Stir Dissimilar Welding of Pure Ti and 6061 Aluminum Alloy

Taking the advantage of its low density, high specific strength and strong corrosion resistance, titanium and aluminum alloys have high marine adaptability and can be directly used in various marine engineering equipment that will expose to seawater or directly contact with seawater. The seawater heater has to withstand 90~120°C corrosion in seawater. This unique working condition makes titanium and aluminum alloys are superior materials which can significantly lower the heater construction cost. In this study, the technology of friction stir welding was used to join the dissimilar materials of aluminum alloy 6061 and commercially pure titanium by means of butt joint. High-speed steel stir rod was used for the friction stir welding, and a 2o title was applied to the stir rod during friction stir welding. To discuss the influence of different rotating speeds and travel speed, the specimens were analyzed for their microstructure, mechanical properties, and elemental analysis was carried out followed by the friction stir welding. Experimental results showed that the best mechanical properties of the butt joint can be obtained by setting the rotational speed of 1000 rpm and the travel speed of 100 mm/min. After welding, grain refinement can be observed in the stirring zone. However, the grains in the heat-affected zone had become larger, and there had a tendency of hardness decreasing, causing failure in this area during tensile testing.

Effect of friction stir welding on microstructure and foaming mechanism of rolled-state anisotropic powder

Friction stir welding (FSW) has a significant impact on welding aluminum foam sandwich (AFS) precursor. Yet, the understanding of the microstructure and foaming process on rolled-state powder of welded precursor remains limited. This study exploited the single-pass double-sided forming welding approach to weld the AFS precursor, while the impact of different process parameters of FSW on the microstructure of rolled-state powder was evaluated. Meanwhile, the foaming process of anisotropic powder at different directions was observed in-situ using synchrotron radiation. The results display that FSW transforms gap-like voids, which were ∼20 µm in width and 100–400 µm in length, into circular voids with a diameter of ∼6 µm in the powder at the weld zone (WZ). The welding process eliminates powder agglomeration aggregation and increases the relative density (>97%) of rolled-state powder. However, the low thermal conductivity of the rolled-state powder (117 W·m−1·K−1) leads to a tunnel defect at the root of the WZ. In addition, in-situ observation experiments of the foaming process found that the bubble nucleation of rolled-state powder exhibits anisotropic characteristics, and the welding process causes a transition in the types of bubble nucleation in the WZ region. This study demonstrates the feasibility of improving the anisotropy of powders caused by processing methods to obtain an isotropic pore formation and foam expansion by FSW technology.

Microstructural Evolution and Material Flow during Friction Stir Welding of 6013 Aluminum Alloy Studied by the Stop-Action Technique

This work is part of a wide-ranging study aiming to enhance the technology of dissimilar friction-stir welding of aluminum and titanium. In the previous study, a new approach was proposed that provided an exceptionally narrow intermetallic layer. However, an essential disadvantage of this technique was the significant material softening in the aluminum part. Hence, the present work was undertaken in order to obtain insight into microstructural processes and material flow in the aluminum part. To this end, the stop-action technique was applied. It was found that the microstructural evolution included several stages. Specifically, the initial material underwent the discontinuous static recrystallization in the heat-affected zone. With the approach of the rotating tool, the recrystallized grains experienced continuous dynamic recrystallization, which resulted in grain refinement. The subsequent transportation of material around the rotating tool provided no significant alterations in microstructure. This “superplastic-like” character of material flow was attributed to a dynamic balance between grain refinement and grain coarsening. It was also found that the stirred material experienced a secondary deformation induced by the rotating tool shoulder far behind the welding tool. The concomitant microstructural changes were most pronounced at the upper weld surface and gave rise to a fine-grained layer.

Experimental investigation of friction stir welding of aluminium alloy

In this work an effort is made to review various methods by using vertical milling machine to reach special welding technology of friction stir welding (FSW) which is a solid-state fusion process. As this method of joining is achieve success daily at the level of investigate but it’s excess to workshops having lesser capital is limited because of costlier machines. Experiment work carried out on 6351 aluminium alloy on a vertical axis CNC milling machine for each testing. Increase in the feed speed the material was observed to have increased surface roughness. Increased the tensile strengths with increases in hardness.

High-cycle fatigue enhancement of dissimilar 2017A-T451/7075-T651 Al alloy joint fabricated by a single pass FSW without any post-processing

This study investigates the microstructural, mechanical, high-cycle fatigue, and fracture behaviour of a dissimilar 2017A-T451/7075-T651 Al alloy joint produced by single-pass friction stir welding (FSW) without post-processing. Residual stress analysis revealed low tensile residual stresses in the longitudinal direction on the crown side and compressive residual stress in the transverse direction and on the root side of the weld, indicating an almost zero-stress state. High-cycle fatigue tests showed the superior fatigue endurance of the FSWed sample due to the synergistic effect of expressive grain refinement and compressive residual stress in the transverse direction. Fractographic observations confirmed a brittle type II failure with low fracture toughness in the base material 7075-T651 alloy. In contrast, both the FSWed samples and the base 2017A-T451 alloy displayed a ductile transition with type I failure, resulting in higher average fracture toughness values. The direction and propagation of the fatigue crack in the FSWed sample were influenced by the microstructure, with the crack completely bypassing the stir region consisting of larger crystal grains that acted as the crack arrester. This study highlights the high potential of single-pass FSW technology for producing thick dissimilar Al alloy joints with enhanced high-cycle fatigue life without requiring post-treatment. The findings of this study can benefit industries that require high-performance lightweight structures with improved fatigue life, such as aerospace and transportation.

Computer Simulation of Heating Cycle of Aluminum Alloys Using Friction Stir Welding Technology

The paper deals with welding of aluminum alloys using Friction Stir Welding technology. This repre-sents one of the solid-state welding technologies in which the base materials are not melted. This pro-vides new possibilities for the use of special and hybrid manufacturing technologies. The article presents the current progress in the Friction Stir Welding technology, a microstructure analysis of a weld joint created by the FSW method and a heat-deformation computer simulation of an aluminium alloy speci-men in the program Ansys.

Improved mechanical properties of magnesium alloy thick plate joint via uniform microstructure by differential double-shoulder friction stir welding

The magnesium (Mg) alloy thick plates welded using traditional friction stir welding usually exhibit large temperature gradient and uneven microstructure, which seriously affect the joint quality. In this work, a new technology of differential double-shoulder friction stir welding (DDS-FSW) was innovatively proposed to weld a 20 mm AZ31 Mg alloy thick plate. The microstructure and mechanical properties of the joint were studied. The results indicated that DDS-FSW improved the grain size uniformity and texture consistency of the joint, and as a result the deformation incompatibility of the joint was weakened. The tensile strength of the joint reached 86.4 % of the base material. The crack initiation mechanism of DDS-FSW joint was basal slip caused by “orientated micro-interface”. DDS-FSW provides a new and effective strategy for the Mg alloy thick plates welding.

Research progress and prospect of friction stir welding of copper and copper alloys

Copper and copper alloys are widely used in various industries due to the excellent properties, and they are indispensable materials in modern industrial fields. At present, friction stir welding technology is the most promising welding method for copper and copper alloys, and there have been a series of studies on copper and copper alloys FSW field. This paper summarizes the research achievements in this field in the past 30 years, and aims to provide a comprehensive and systematic summary for researchers in this field. In addition, combined with the authors team’s research and experience in this field and existing relevant references, we point out the development direction of this field in the next stage.