Friction Stir Welding Joints Research Articles

Texture-Induced Corrosion Resistance of Dissimilar AA7204/AA6082 Friction Stir Welded Joints.

The quasi in situ EBSD test was applied to study the effect of grain orientation on corrosion behaviors of the thermomechanically affected zone I (TMAZ I) of dissimilar AA6082/AA7204 friction stir welding (FSW) joints in this work. The results show that the structure with grain orientation close to the brass texture ({110}<112>) has excellent corrosion resistance, which contributes to the better corrosion performance of the TMAZ I of the 7204-AS joint than the 7204-RS joint. Furthermore, the brass texture around by S texture ({213}<364>) in the TMAZ I of the 7204-AS joint is slightly corroded, and the orientation of the remaining structure is closer to the ({110}<112>) than before, which indicates that the corrosion, like deformation, is carried out alongside the {110} plane for the structure with grain orientation near {110}<112>. Those findings could provide new insight into the designed FSW joints and improve the corrosion resistance of the wrought aluminum alloy.

Thermal Cycling, Microstructure, and Mechanical Properties of Al-Mg-Si-Cu Alloy Bobbin Tool Friction Stir Welded Joints Based on Thermal Index

The two main process parameters of Bobbin tool friction stir welding (BT-FSW) are ω (rotational speed) and v (traverse speed). Both of these factors have a significant effect on heat input, microstructure, and mechanical properties. At present, most studies on friction stir welding adopt the control variable method to study the thermal cycling during the welding process and the mechanical properties of joints, and there are few studies on changing the two process parameters at the same time, because it can be difficult to assess the correlation between heat input and mechanical properties when changing both factors at the same time. In this study, the w/v ratio is defined as the thermal index, which is a characteristic value of heat input. The study uses ABAQUS 6.5 software to establish a BT-FSW CEL (coupled Eulerian–Lagrangian) thermal coupling model. This model explores the relationship between joint thermal cycles, microstructure, and mechanical properties for different w and v values with the same w/v ratio. The results show that increasing rotational and traverse speeds under the same w/v ratio leads to an increase in the peak temperature of the nugget zone (NZ). However, the peak temperature of the thermo-mechanically affected zone (TMAZ) and heat-affected zone (HAZ) remained almost constant. Joint strength was highest at a rotational speed of 750 r/min and a traverse speed of 650 mm/min, with a yield strength of 227 MPa. As rotational and traverse speeds increased, the recrystallized grain content of the NZ showed an increasing trend followed by a decreasing trend. The recrystallized grain content of the advancing side thermo-mechanically affected zone (AS-TMAZ) and retreating side thermo-mechanically affected zone (RS-TMAZ) showed a decreasing trend. Joint hardness had a “W” shaped distribution, with the highest average hardness value found in the NZ.

A review towards Friction Stir Welding technique: working principle and process parameters

Friction Stir Welding (FSW) is a solid-state bonding process that employes tools that are not used up and can function to connect two opposite workpieces without melting the workpiece material. The friction force has been micro-structurally tested to reformat or transform the inner state of the structure properties (atomic formation) form in metal since the kinetic energy of friction has been utilised in one of the welding techniques. Right afterwards, the studies reported that the mechanical properties also underwent a significant deformation. The aim is to determine the effect of Welding Procedure Specification (WPS) product quality. As it develops through research and applied experiments, the branch of friction-based welding discipline can be classified depending on how the friction mechanism can produce the finest solid-state joint, which is suitable to the typical property of metal and can be maximised by joint configuration. Friction Stir Welding is a friction-based welding technique that uses the stirring tool to generate friction while the workpieces are stuck on the line of the FSW joint configuration. The relevant correlations amongst process parameters and inside its respective adjustable variables are constructed to the finest principles that produced top-grades empirical reports of the weld properties. In this review, the explanation of the working principle and clarification of process parameters are presented. The cited references are selected from creditable and verifiable articles and books in the last ten years. Expectedly, it will be able to pioneer a new face of simple and understandable review articles.

Study on stress corrosion properties of aviation aluminum alloy friction stir welded joint at the different strain rate

Aviation aluminum alloy welded structures are subjected to stresses at different strain rates in corrosive environments such as the ocean. Studying the stress corrosion properties of aviation aluminum alloy Friction Stir Welding (FSW) structures is essential. Therefore, this paper focuses on the study of 12 mm thick 7085-T7452 high-strength aviation aluminum alloy FSW joints under different strain rates of stress corrosion properties changes and the impact of welding process parameters. The main conclusions of this thesis are as follows: For the base material (BM) and the aluminum alloy FSW joints, when the strain rate increased from 10−7 s−1 to 10−5 s−1, the stress corrosion strength increased, and the stress corrosion cracking (SCC) sensitivity index ISSRT decreases. The SCC sensitivity at the same strain rate: SS-400-120 > SS-300-60 > SS-300-120 > BM. After the Slow strain rate tensile (SSRT) test, the FSW joint fracture in the air is a transgranular ductile fracture. Meanwhile, the fracture is a ductile-brittle hybrid fracture in 3.5% NaCl solution, and the number of secondary cracks along the grain boundary increased significantly, showing obvious SCC sensitivity. The BM fracture after SSRT is ductile, showing lower SCC sensitivity.

Mechanical Properties and Microstructure of Dissimilar S355/AA6061-T6 FSW Butt Joints.

The aim of this paper is to analyse the mechanical properties of butt joints between S355 steel and 6061-T6 aluminium alloy, as well as their relationship to changes in the structure of the material caused by welding. The effect of the tool offset was analysed in particular. For the analysis, tensile tests were carried out using macro- and mini-specimens taken from S355/AA6061-T6 joints and base materials. In addition, the macro- and microstructure of the joints was determined, the hardness profiles in the joints were analysed, and fractographic analysis of the fractures of the specimens was carried out. Based on the results of the macro- and microstructure examinations, typical friction stir welding (FSW) joint zones were characterised. The microstructure was observed in the interface line of the materials on the root side, the negative effect of which on the quality of the joint was confirmed by digital image correlation (DIC) strain analysis during the monotonic tensile test. The highest average value of su = 141 MPa for the entire joint was obtained for a 0.4 mm tool offset. The highest average value of su = 185 MPa for the selected joint layer was obtained for a 0.3 mm tool offset. Fracturing of the joint in the selected layer for the tool offset values of 0.3 mm and 0.4 mm occurred in the weld nugget zone (WNZ) where the lowest hardness was recorded.

A review on fracture and fatigue behaviour of FSW joints of Al alloys

Friction stir welding (FSW) is solid state welding process. In this process two similar or dissimilar metallic plates are join using appropriate heat and mechanical forces with the help of rotating tool. Due to mechanical advantages like high strength to weight ratio, aluminium (Al) alloys commonly used in several engineering prospective. Recently, FSW has gained consideration in the automobile, aerospace and marine industries owing various advantages, like high weld strength, low distortion and good fatigue behaviour. This study concentrates on the fracture and fatigue characteristics of Al alloy FSW joints and importance of optimizing FSW process characteristics such as tool rotational speed, travel speed and tool offset, to obtain best joints with improved mechanical properties. This review also highlights the effect of microstructure and residual stresses on the fracture and fatigue behaviour of FSW joints as well as it provides an overall understanding of the fracture and fatigue behaviour of FSW joints of Al alloys.

Evolution mechanism of intermetallic compounds and the mechanical properties of dissimilar friction stir welded QP980 steel and 6061 aluminum alloy

Intermetallic compounds (IMCs) play an important role in the welding quality of steel and aluminum (Al) alloys by friction stir welding (FSW). However, the evolution mechanism of IMCs and their effects on the mechanical properties of FSW joints are still unclear and need to be further elucidated. In this work, QP980 steel and 6061 Al alloy are successfully welded by FSW. The microstructure and mechanical properties of joints are characterized. The results show that an IMC layer composed of Al3Fe, Al5Fe2, Al2Fe, and Al6Mn phases is generated at the weld interface. The joint efficiency is about 70.1%. The formation sequence of IMCs in the same binary system is affected by the effective enthalpy of formation, while it is related to the element concentration in different binary systems. Furthermore, the formation sequence is Al3Fe, Al5Fe2, Al2Fe, and Al6Mn phases. The interfacial bonding strength is enhanced by the low lattice mismatch between IMCs and matrix. The interfacial bonding strength of IMCs with Fe and Al matrices in the joint is in ascending order: Al2Fe and Fe, Al2Fe and Al, Al5Fe2 and Fe, Al5Fe2 and Al, Al6Mn and Fe, Al3Fe and Fe, Al6Mn and Al, as well as Al3Fe and Al. It is noted that the bonding strength between the Al2Fe and Fe is lowest, indicating that Al2Fe phase is responsible for the joint fracture during tensile test.

Mechanism of suppressing HAZ softening in friction stir welded martensitic steel through hardening phenomenon initiated by adding vanadium

In this study, heat-affected zone (HAZ) softening occurred in friction stir welding (FSW) joints of martensitic steels is suppressed through the short-time secondary hardening phenomenon initiated by adding V. Adding V significantly suppresses the HAZ softening owing to the precipitation of the extremely fine and high-density V carbides in HAZ. Vickers hardness (HV) profiles of the FSW joints were measured to evaluate the degree of HAZ softening. The degree of inhibition in HAZ softening was found to be related to the amount of V present and the Ac1 temperature of the steels, which can be controlled by the quantity of Mn. These relationships were elucidated quantitatively via transmission electron microscope (TEM) and 3D atom probe-tomography (3DAPT) together with hardening theory after investigating multiple areas of the V carbides in FSW joints containing different V and Mn contents.

Exit-hole repairing in 7475 aluminium alloy welded joints based on refill friction stir processing

In this study, the refill friction stir processing (RFSP) method was utilised to repair a exit-hole defect located at the end of the friction stir welding (FSW) joints in 7475 aluminium alloy plate. The morphology, macroscopic defects, and mechanical properties of the repaired joints were investigated. The results demonstrate that the exit-hole was successfully refilled after RFSP. Material flow caused the refill voids, annular grooves, and un-stirred material defects. The maximum strength reached 415 Mpa, equal to 105% of the base defect-free weld. The mechanical properties of repaired joint were largely influenced by the stir zone (SZ) boundary and un-stirred material defects.

The Correlation of Kissing Bond, Microstructure and Mechanical Properties of the 2195 Al-Li Alloy Friction Stir Welding Joints at Different Welding Speeds

Reasonable welding speeds are a prerequisite for obtaining high-quality joints by friction stir welding (FSW). In this paper, 2195-T8 Al-Li alloy FSW joints were successfully fabricated at different welding speeds (100–600 mm/min) with a constant rotation speed. The effect of welding speed on the microstructure and mechanical properties was analyzed under different experimental methods. Microstructural characterization was conducted using optical microscopy (OM), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). Mechanical properties were measured by a hardness test and a tensile test. The results showed that the original T1 precipitates disappeared in the nugget zone (NZ), generating many dislocations. With welding speeds increasing, joints obtained at lower welding speeds developed coarser T1 precipitates in the heat-affected zone. Also, the equiaxed grains with a bigger size and a higher fraction of high angle boundaries (HABs) were detected in the NZ of these joints. As the welding speed increased, the area of hardness value changes gradually shrunk, which was consistent with the trend of the cross-section morphology. A kissing bond and macroscopic cracking were observed in the joints that were fabricated at the higher welding speeds. The appearance of those defects significantly reduced the ultimate tensile strength and elongation of the joints at high welding speeds. Fracture morphologies of the different joints were all characterized in quasi-cleavage fractures.

Investigation of the Microstructure and Mechanical Properties in Friction Stir Welded Dissimilar Aluminium Alloy Joints via Sampling Direction

This research study investigates the influence of sampling direction on the microstructure and mechanical properties of dissimilar joints formed by friction stir welding (FSW). The specimens were cut in two directions: perpendicular (transverse) and parallel (longitudinal) to the FSW joint. The tests conducted included X-ray diffraction (XRD), macrostructure, microstructure, tensile, microhardness, and fractography analysis. Different phases were noted in the XRD patterns and explained, with the aluminum phase being the dominating one. The results further showed that the transverse dissimilar joint exhibited higher microhardness compared to the longitudinal dissimilar joint, which is consistent with the respective grain sizes. Moreover, the ultimate tensile strength of the longitudinal joint exceeded that of the transverse joints, showing a substantial 47% increase. Similarly, the elongation of the joints followed a similar trend, with the longitudinal joint displaying a significant 41% increase in elongation compared to the transverse joint. Fractographic analysis revealed ductile fracture behaviour in all joints.

Research of Friction Stir Welding (FSW) and Electron Beam Welding (EBW) Process for 6082-T6 Aluminum Alloy.

The paper presents the results of the joining tests of the EN AW-6082 T6 alloy. The materials were joined using the EBW high-energy (electron beam welding) and friction stir welding (FSW) methods. In the case of FSW welding, the following parameters were used: the linear speed was 355 mm/min, and the rotational speed of the welding tool was 710. In the case of EBW welding, the following parameters were used: accelerating voltage U = 120 kV, beam intensity I = 18.7 mA, welding speed v = 1600 mm/min and, in the case of a smoothing weld, U = 80 kV, beam intensity I = 17 mA, and welding speed v = 700 mm/min. Comprehensive microstructural tests of all welded joints (MO, SEM and TEM) and mechanical property tests (tensile and hardness tests) were carried out. The topographies of the fractures after the tensile test were also examined. Based on the results, it was found that the strength properties of the EBW joint were reduced by 23% and the FSW joint by 38% compared to the base material. A decrease in elongation was also noted, with an FSW elongation of 7.2% and an elongation of 2.7% for EBW. In the case of the EBW joint, magnesium evaporation was found in the weld during welding, while in the FSW joint, the dissolution of the Mg2Si particles responsible for strengthening the material during heat treatment to the T6 state was observed.

Effect of assisted heating on microstructure, material flow and intermetallic formation during friction stir welding of copper alloy and AA 6063

The friction stir welding (FSW) is a newly developed solid-state welding technique, which addresses a number of practical issues such as reducing melt related defects by reducing welding temperature. This provides an opportunity for dissimilar metal welding and provides high quality joints. In the present study friction stir welding was performed on AA6063 and copper alloys by conventional FSW method and with the aid of external flame heating during the FSW process. The concept behind the experimentation is to perform the welding at low RPM to improve the material mixing and joint properties. The microstructure, phase constituents and mechanical properties of FSW joints were studied through optical metallography, SEM, X-ray diffraction, micro hardness, and tensile tests. Al2Cu and Al4Cu9 intermetallic were formed during the conventional and assisted flame heating FSW process which were distributed in the nugget zone. Due to the flame heating, copper and aluminum alloys get softer and leads to distribution of intermetallic as lamellar structure. The values of tensile strength for conventional friction stir welding, and assisted flame heating FSW are 69 MPa, and 102 MPa respectively.

Prediction of ultimate tensile strength of friction stir welding joint using deep learning-based-multilayer perceptron and long short term memory networks

Friction stir welding (FSW) is a solid-state joining technique where the joint strength is mainly influenced by three process parameters, namely, spindle speed (N), welding speed (V), and plunge force (Fz). The modelling of complex relationships between the process parameters and joint strength requires many experiments, which is a challenging, time-consuming, and non-economical affair. To tackle this problem, computational mathematical models such as deep learning (DL) can be employed to predict the joint strength reliably. In this paper, DL techniques, namely, deep multilayer perceptron (DMLP) and long short-term memory (LSTM) networks have been proposed for such a purpose. The DL networks were first trained with the FSW experimental data and then, the pre-trained models were used for predicting the weld strength. It was found that the DMLP and LSTM models provided lower prediction errors, which are RMSE of 3.30 and 7.63, respectively, and can be effectively utilized for determining weld quality. The proposed DL-based techniques were further compared with the traditional models – the shallow artificial neural network (SANN) model having an RMSE of 27.11 and the ANFIS model having an RMSE of 5.31. DMLP was found to be superior in determining the weld strength most accurately.

Microstructural evolution and deformation behavior of friction stir welded twin-induced plasticity steel

The weldability of twin-induced plasticity (TWIP) steel with ultra-high strength via friction stir welding (FSW) technique was investigated, and microstructural evolution and deformation behavior of whole and micro-zones of FSW TWIP joint were studied for the first time. The results showed that the content of recrystallized grains in the stir zone (SZ) increased from 10.5% of basal material (BM) to 14.2%, and that of heat affected zone (HAZ) increased to 78.6%. The percentage of annealing twins decreased from 26.8% in BM to 11% in SZ, while increased to 35% in HAZ. Compared with the BM, the ultimate tensile strength and yield strength of the FSW joint increased to 1036 and 550 MPa, respectively, reaching 106.7% and 110.9% of BM, respectively. The elongation of the entire joint was 50.5%, which was lower than that of BM due to the nonuniform deformation during the tensile test. The engineering strain was mainly concentrated in BM and SZ and transferred to each other during the tensile test, while the engineering strain in HAZ was always the lowest. Finally, the tensile fracture occurred in the SZ. The order of ultimate tensile strength of micro-zones in the FSW joint was as follows: HAZ > BM ≈ SZ. The order of yield strength was as follows: HAZ > BM > SZ.

Feasibility of orbital friction stir welding on clad pipes of API X65 steel and Inconel 625

Orbital friction stir welding (FSW) has been applied to clad pipes, which is certainly of interest to the oil and gas industry. In this context, an FSW system capable of performing sound joints in one pass with full tool penetration was developed. Orbital FSW was executed in 6 mm thick API X65 PSL2 steel clad pipes with 3 mm thick Inconel 625 using a polycrystalline cubic boron nitride (pcBN) tool. The metallurgical and mechanical properties of the joints were investigated. Sound joints with axial forces of 45–50 kN, tool rotational speeds of 400–500 rpm, and a welding speed of 2 mm/s were obtained, illustrating that the developed system can perform FSW joints without volumetric defects.

Quasi-in-situ characterization of microstructure evolution in friction stir welding of aluminum alloy

The in-situ investigation of microstructure evolution during friction stir welding (FSW) can provide very important theoretical guidance to control the microstructure and mechanical properties of the FSW joint. In this study, a quasi-in-situ investigation method of the microstructure evolution in friction stir welding of AA1050 aluminum alloy was developed. The microstructure along the material flow path was characterized and analyzed by taking the strain, strain rate, and temperature into account simultaneously. The results show that the microstructure evolution during the FSW of aluminum alloy can be divided into four stages according to the material flow state and thermal history. Firstly, grain coarsening by static recovery and static recrystallization occurs at the static preparatory stage (or called the preheating stage). Secondly, grain refining by continuous dynamic recrystallization occurs at the acceleration stage, where the temperature gradually increases to nearly a constant. The grain size is mainly controlled by the accumulative total strain. The strain rate only affects the rate of dislocation generation and the type of β-fiber simple shear texture components. Thirdly, at the high-velocity flow stage, a dynamic equilibrium between plastic deformation and dynamic recrystallization is maintained, and the grain size only fluctuates within a small range. Finally, a second grain-coarsening process occurs through normal grain growth due to thermal activation at the deceleration stage. This process is inevitable because it occurs under the cover of the tool shoulder. The grain coarsening during the normal cooling stage was avoided in this study due to the rapid cooling used, which has been widely reported by published documents.

Evaluation of nickel shot peening process on strength of friction stir welded AA2014-T6 aluminum alloy joints

Abstract The best aluminum alloys for construction are those that incorporate copper. However, welding engineers find it difficult to join aluminium and its alloys as a result of cracking. One of the popular methods for joining nonferrous materials, especially aluminum alloys, is friction stir welding (FSW). A tensile strength of 75 % to 85 % of the basic material strength is produced by FSW joints. The majority of studies have documented a reduction in strength as a result of incomplete melting, creating a soft region at the boundary between the thermo – mechanically influenced zone and the stir zone. The current effort has focused on using the shot peening method to reduce the softness at the interface. According to the test findings, the nickel shot-peened joint produced a stronger joint than the traditional FSW joint. The shot-peened joint has gained 7 % additional strength compared to untreated joint.

Investigation of mechanical, metallurgical and corrosion characteristics of friction stir welded dissimilar AA 5052-H32 and AA 6061-T6 joints

ABSTRACT Welding is used for fabricating various components to increase the application of aluminum alloys. When compared to fusion welding, friction stir welding (FSW) is used to join non-ferrous and ferrous with similar and dissimilar materials with fewer defects. In the present work, FSW was carried out between 5 mm thick plates of solid solution-strengthened AA 5052-H32 and precipitate-strengthened AA 6061-T6 alloys. The plates were welded at tool rotational speeds (TRS) of 800, 950, and 1100 rpm. Furthermore, a salt spray test was conducted on both base metals and FSW joints. The scanning electron microscope was accustomed to examining the microstructure of the base metals and different zones. Mechanical characterization was performed to determine the welds’ strength and hardness. The phase examination was then performed on the weld nugget zone using X-Ray Diffraction (XRD). To determine the mode of failure, the tensile fracture surfaces of the welded samples were inspected. The study found that the joint prepared at 950 rpm yielded maximum tensile strength of 174.3 MPa, % elongation of 13.8% and a higher hardness of 72 HV related to other joints. The corrosion test results exposed an enhancement in corrosion resistance of maximum tensile strength obtained from the welded joint

Stress-level dependency of creep ageing behavior for the nugget zone in a friction stir welded Al–Cu–Li alloy

In this study, the creep response and microstructure evolution for the nugget zone (NZ) of a friction stir welded Al–Cu–Li alloy under different stress levels are systematically investigated. Compared to the base material (BM), the creep strain and steady creep strain rate of the NZ increase rapidly with enhancing the applied stress. The total creep strain of NZ is noticeably higher than that of BM under the same stress. The creep mechanism of NZ changes from diffusion creep to dislocation climbing creep with the increase of stress. After creep ageing, both NZ and BM samples have a significant enhancement in the strength. However, the elongation at fracture of creep-aged NZ sample falls sharply for higher creep aging stress. The fracture mechanism of creep-aged NZ sample transforms from the mixed fracture to brittle intergranular fracture with the increase of the stress. The average length of T1 precipitates of creep-aged NZ sample gradually increases with rising the stress. Meanwhile, the average length of T1 precipitates of NZ is significantly larger than that of BM under the same stress. It has been demonstrated that, during the creep-ageing process, high external stress could cause the formation of wide PFZ and lower the ductility of NZ. These results provide important theoretical support for the creep aging forming of large-size Al–Cu–Li alloy components contained the friction stir welding joint.