Friction Stir Welding Joints Research Articles

A molecular dynamic simulation-based study on nanoscale friction stir welding between copper and aluminium

ABSTRACT The primary aim of this study is to enhance our understanding of friction stir welding (FSW) at the atomic level. To accomplish this, we utilised molecular dynamics simulations to examine the nanoscale fusion welding of dissimilar metals, i.e. aluminium and copper, through the FSW method. Our particular focus was on how the rotation speed of the tool affects structural changes and defect evolution during the nanoscale FSW process. Our research findings revealed that the region subjected to frictional stirring undergoes a phase change as a result of extensive plastic deformation during the FSW operation. Notably, stacking faults and similar defects were predominantly observed on the advancing side as the tool rotated and moved into the friction stir zone. Further, investigation of atomic shear strain snapshots indicated that higher rotational speeds resulted in a broader and more scattered friction stir zone, requiring a longer recovery time compared to slower rotational speeds. Additionally, the changes in atomic concentration during FSW have been studied using displacement vectors, concentration profiles and diffusion coefficient parameters. We also conducted simulation-based tensile and shear deformation tests, which revealed that higher tool rotational speeds led to enhanced material interlocking, consequently improving the mechanical strength of the FSW joints.

Effect of process parameters on friction stir welding of aluminium alloy AA6082–T6 with an interlayer using response surface methodology

In the present study, the effects of variation of process parameters on the mechanical properties of friction stir welded A6082–T6 aluminium alloy joints with Zinc (Zn) interlayer are experimentally investigated. Four process parameters, viz. rotational speed, welding speed, interlayer thickness and tool pin diameter are selected to fabricate the Friction Stir Welding (FSW) joints. After filling the Zn particles into the gap maintained between the plates, FSW is performed using different process parameters. Thereafter, tensile and impact strength tests are performed to evaluate the performance of the joints. It is analyzed that the tensile and impact strength of the joints vary from 121 to 197 MPa and 6 to 17 J, respectively. Subsequently, mathematical models are developed using Response Surface Methodology (RSM) to predict the effect of FSW process parameters on the tensile and impact strength of joints. Analysis of Variance (ANOVA) is used to check the level and degree of direct effect of process variables on the tensile and impact strength of the joints. It is observed from the results that tool rotational speed is the most influential process parameter, which enhances the mechanical properties of FSW joints, whereas an increase in welding speed reduces the mechanical properties of the joints.

Achieving an improved performance in double-sided friction stir weld joints by adjusting the welding conditions during the passes of AA6061-T6 aluminium alloy

The present study aims at investigating the effect of interaction between the process parameters of each weld pass (1st pass and 2nd pass) to improve the joint performance during the double-sided friction stir welded joints of AA6061-T6 aluminium alloy. Experimental designs were conducted following a design matrix developed using response surface methodology to investigate the impact on the microstructural changes and tensile properties. Pronounced interaction between the process parameters of each weld pass of the joint was observed and indicated a strong interdependency between them. The detailed microstructural study conducted through EBSD insights into the extent of homogenization, and abnormal grain refinement and reflects a vast transformation of low-angle grain boundaries into high-angle grain boundaries within the stir zone. The profound examination through scanning electron microscopy and transmission electron microscopy analysis validated the uniform homogeneous distribution of Al-Fe and Al-Si-rich precipitates. The significant improvement in the grain refinement and distribution of the strengthening precipitates within the stir zone led to a substantial enhancement in the microhardness, along with achieving a maximum ultimate tensile strength of 223 MPa and a percentage elongation of 14%. A study of the fracture morphology ensures the ductile fracture behavior of the tensile fracture specimen by observing the presence of numerous dimples within a well-bonded joint.

Study on the Properties of a 2219 Aluminum Alloy Friction Stir-Welded Joint under the Biaxial Stress State

Friction stir welding (FSW) has been considered ideal for aluminum alloy structures. The performance of FSW joints under unidirectional stress state has been widely tested, but there is still a lack of experimental data under a biaxial stress state. For accurate characterization of the mechanical properties of 2219 aluminum alloy FSW joints under a biaxial stress state, this article conducted biaxial tests. The FSW joint was tested using scanning electron microscopy (SEM) to obtain its microscopic properties and obtain the partition results of the welded joint. The stress–strain relationship and yield characteristics of welded joints under different loading ratios were studied using biaxial tensile tests of cruciform specimens combined with digital image correlation technology. By comparing it with the existing yield criteria, the yield criterion suitable for FSW joints of 2219 aluminum alloy under a biaxial tensile load was determined.

Microstructure evolution and mechanical properties of friction stir welded Fe50Mn30Co10Cr10 high-entropy alloy

Metastable Fe50Mn30Co10Cr10 HEA has a significant strength-ductility synergistic effect and a wide application prospect in nuclear power. The present work reports the microstructure evolution and tensile behavior of friction stir-welded joints for Fe50Mn30Co10Cr10 high entropy alloy (HEA) at various rotational speeds. Defect-free welds of Fe50Mn30Co10Cr10 alloy were obtained by a W-Re alloy welding tool. Significant grain refinement occurs in the nugget zone, where the most of HCP phases in the base metal transformed into FCC phase. Additionally, strain-induced Σ3 mechanical twins are generated in the FCC austenite grains. The microstructure of thermo-mechanically affected zone exhibited multiple deformation mechanisms, including stacking faults, martensite lath, martensite variants, and reverse transformation. The microhardness of the joint primarily depends on the grain size of the FCC phase and the fraction of twins and HCP phase. In the nugget zone of the joint welded at 300 rpm, a high microhardness zone ranging from 266.7 to 310 HV was detected. While the reverse transformation and fresh twinning in the joint at 600 rpm contribute to the enhancement of tensile properties, the increase in grain size and ε martensitic fraction have resulted in a noteworthy reduction in ultimate tensile strength (UTS) and elongation (EL). Conversely, the joint of 300 rpm exhibited optimum UTS and EL owing to the grain refining after FSW and the transformation induced plasticity (TRIP) effect. These insights confirm that FSW is an ideal approach for achieving superior joint performance in dual-phase HEAs.

Study on the materials flow, microstructure and mechanical properties of ultrasonic vibration-assisted friction stir weld of 1500 MPa martensitic steel

In this study, friction stir welding (FSW) was conducted on 1500 MPa martensitic steel with a thickness of 2.3 mm at 500 rpm and 60 mm/min with and without the application of ultrasonic vibration. The utilization of pure nickel as a marker material could help to visualize the material flow behavior throughout the whole FSW process. In addition, the width change of the marker material was used to distinguish the welding stages. At the same time, the microstructure was also characterized to study the effect of ultrasonic vibration on the welding process. The conventional FSW (C-FSW) joint had tunnel defects due to poor material flow, while the ultrasonic vibration-assisted FSW (U-FSW) joint was defect-free. To study the microstructure and texture evolution during the process, a fully austenitized welding zone was reconstructed from martensite to prior austenite grain (PAG) based on the Kurdjumov-Sachs orientation relationship. The strain rate increased in U-FSW compared to that in C-FSW, resulting in a reduction of the PAG size and an alteration of its shear texture components from type-A to type-B. The uniaxial tensile tests showed that the ultimate tensile strength (UTS) of the stir zone (SZ) of U-FSW was significantly increased compared with that of C-FSW.

Analysis on the performance of aluminum/steel UVeFSW joints by changing ultrasonic powers

The optimization mechanism of ultrasonic power on the performance of aluminum/steel dissimilar metal ultrasonic vibration enhanced friction stir welding (UVeFSW) joints was studied. The results indicated that ultrasonic vibration can significantly improve the surface forming quality of the weld seam, increase the width of the joint interface zone, adjust the height of the hook structure, suppress the generation of intermetallic compounds, and enhance the failure load of the joints. When the ultrasonic power was 500 W, the lap joints with the best mechanical properties were obtained, and its failure load was 5.14 kN, which was 51.2% higher than that of conventional FSW (0 W).

Experimental Investigation of Friction Stir Welding on Al 2024-T3 and Al 7075-T6 Alloy

Aluminum alloys are becoming increasingly popular due to their potential to offer superior durability while being lower in weight. Most industrial sectors, including transportation, aviation, marine, automotive, and others, have a strong interest in light-weight components, particularly in the transportation industry. Traditional joining techniques have a negative impact on the joining of these lightweight industrial materials, necessitating the development of new environmentally friendly joining methods. The lap joint of Al 2024-T3 and Al 7075-T6 alloys is done utilizing friction stir welding (FSW) with tool rotational speed (TRS) and tool travel speed (TTS) as process parameters. In addition, a tensile and microhardness test was performed to determine the mechanical characteristics of the weld joints. For FSW joints, the hardness of the stir zone at the weld center at 1000 RPM and 40 mm/min is 151.86 Hv. Carbon inclusion in the stir zone is demonstrated by EDS investigation of tool material dispersion in the weld region.

Fatigue life simulation of AA7075-T651 FSW joints using experimental data

The friction stir welding (FSW) process is a solid phase type applied in this study to connect AA7075-T651 aluminum alloy plates. This study investigates the impact of welding input quantities such as tool rotational speed, welding speed, shoulder radius, and tool geometry on welding joint quality, including strength, toughness, hardness, fractography, and fatigue behavior. Also, in this study, the fatigue life in the base material (BM) and joints obtained from the simple, threaded, and truncated triangular pyramid pins as an FSW effective input parameter was obtained by the finite element analysis (FEA). The experimental outcomes represented that the mechanical attributes of the threaded pin are higher than that of the simple and truncated triangular pyramid pins with the same input parameters. Also, the outcomes of the numerical simulation with the experimental outcomes of fatigue life for the BM were in acceptable agreement, and the error value of the validation result for σmax=0.5σy for the stress ratio R=-1 was equal to 0.4%. In addition, the FEA results indicated that the fatigue strength of FSW joints in the stir zone for the threaded, simple, and truncated triangular pyramid pins in the fatigue life of 107 cycles was 64%, 63%, and 43% of the BM, respectively.

Influence of post weld aging treatment on microstructural features and fatigue behaviour of unnotched and notched specimens of friction stir welded AA6061-T651 aluminium alloy joints under completely reversed stress cycle

A comparative investigation on rotating bending fatigue behaviour between unnotched and notched specimens of friction stir-welded (FSW) AA6061-T651aluminium alloy joints has been conducted under completely reversed cyclic loading (R = −1). Post-weld aging treatment was done for 8 h at 200°C on the welded joints. After post-weld aging treatment, the fatigue strength was significantly improved, while the grain size remained unchanged. Microstructural evolution before and after post-weld aging treatment was studied using orientation imaging microscopy (OIM) and transmission electron microscopy (TEM). It was found that post-weld aging treatment decreased dislocation density and facilitated precipitation hardening through the reprecipitation of fine β″(Mg2Si) particles. Fine particles of post-weld aged specimens of FSW joints were sheared by dislocations generated during cyclic loading, resulting in difficult crack initiation and tortuous crack propagation. Fractographic results confirmed that Post-weld aged specimens of FSW joints have better fatigue resistance than as-welded specimens, owing to the presence of significant precipitates along the grain boundary.

Precipitation Behavior and Corrosion Properties of Stirred Zone in FSWed AA5083 Al-Mg Alloy after Sensitization

This paper investigated the Mg-rich phase precipitation behavior and the corrosion performance throughout the thickness direction within the stirred zone (SZ) of friction stir welded (FSW) AA5083 alloy after 175 °C/100 h sensitization. For the as-welded SZ, the recrystallized grain size gradually decreased from the top surface (5.5 μm) to the bottom (3.7 μm). The top and bottom of the SZ maintained relatively high levels of deformed grains and accumulated strain induced by either shoulder pressing or pin stirring. After 175 °C/100 h sensitization, 100 nm thick β′-Al3Mg2 precipitates were present along the grain boundaries (GBs) in the SZ. The bottom of the SZ exhibited more continuous precipitates along GBs due to the fine grain size and the large fraction of high-angle grain boundaries (0.724%). Although the as-welded SZ exhibited excellent corrosion resistance, it became extremely vulnerable to intergranular cracking (IGC) and stress corrosion cracking (SCC) after sensitization. The large SCC susceptibility indices of the SZ samples ranged from 66.9% to 73.1%. These findings suggest that sensitization can strongly deteriorate the corrosion resistance of the Al-Mg FSW joint, which is of critical importance for the safety and reliability of marine applications.

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.