Self-reacting Friction Stir Welding Research Articles

Dissimilar welding of AA5083/AA7039 by self-reacting friction stir welding

To evaluate the potential of similar and dissimilar welding, 3 mm thick plates of 5083 and 7039 aluminum alloys were joined by using the self-reactive friction stir welding technique. The bobbin tool was manufactured from H13 tool steel. The effect of several process parameters such as shoulder pinching gap, transverse speed, and tool rotation speed was investigated in order to design a defect-free joint. Tensile testing indicated that the joint efficiency for connections 5083–5083, 7039–7039, and 7039–5083, respectively, is 94.5, 80.4, and 97.4%. Which are much superior to the joint efficiency of fusion welding procedures and at least as good as, if not slightly better than, conventional friction stir welding. Microscopic investigation of the fracture surface of welded specimens indicated that ductile fracture is the primary failure mechanism for similar joints, whereas minor areas of brittle fracture can be seen for dissimilar joints. The hardness profile of the welded components’ cross-sections near the upper and lower shoulders was investigated, and it was revealed that the higher hardness at the lower shoulder is due to the lower temperature of the workpiece in this area.

Computational investigation on void defects formation and periodic tool-workpiece sliding-to-sticking transition in self-reacting friction stir welding

Computational investigation on void defects formation and periodic tool-workpiece sliding-to-sticking transition in self-reacting friction stir welding

Self-Reacting Friction Stir Welding of Al–Zn–Mg Aluminum Alloy

Self-Reacting Friction Stir Welding of Al–Zn–Mg Aluminum Alloy

Prediction of friction stir welding in aluminium 6061 – T6 using ANN

Neural networks are algorithms in series, which is like a human brain to identify the relationships between data. It is utilized for implementing ANN and ML for better prediction techniques for self-reacting friction stir welding (FSW) in Aluminium 6061-T6. It has an input, which gathers the data from outer sources and hidden layers that runs the data, and an output layer that provides data points based on the network function. Welding of different alloys like Mg (AZ91D) and Ti (Grade 2) during FSW is significantly challenging to study. ANN was used to explore the impact of Rotation speed (RPM), Bottom Diameter Tool Pins (mm), Travel Speed (mm/min) and Tool Profiles of Ti and Mg alloy during FSW, and ANOVA was used to determine the most optimal travel speed and feed rate affecting the responses. The primary and cooperative effects of information elements are investigated.

Influence of Welding Speed on Microstructure and Mechanical Properties of 5251 Aluminum Alloy Joints Fabricated by Self-Reacting Friction Stir Welding.

In the present study, 8 mm-thick 5251 aluminum alloy was self-reacting friction stir welded (SRFSW) employing an optimized friction stir tool to analyze the effect of welding speed from 150 to 450 mm/min on the microstructure and mechanical properties at a constant rotation speed of 400 rpm. The results indicated that high-quality surface finish and defect-free joints were successfully obtained under suitable process parameters. The microhardness distribution profiles on the transverse section of joint exhibited a typical “W” pattern. The lowest hardness values located at the heat-affected zone (HAZ) and the width of the softened region decreased with increasing welding speed. The tensile strength significantly decreased due to the void defect, which showed mixed fracture characteristics induced by the decreasing welding speed. The average tensile strength and elongation achieved by the SRFSW process were 242.61 MPa and 8.3% with optimal welding conditions, and the fracture surface exhibited a typical toughness fracture mode.

An alternative pressure-dependent velocity boundary condition for modeling self-reacting friction stir welding

A pressure-dependent velocity boundary condition is developed based on wear theory for modeling self-reacting friction stir welding using computational fluid dynamics approach, which provides a new perspective in understanding the physics of sliding/sticking transition condition. The importance of shear layer in weld formation is emphasized. Effects of welding speed on the weld cross-section geometry can be robustly captured with this newly developed boundary condition. Computational results show that at higher welding speed, the TMAZ boundary moves towards the pin periphery at the advancing side, which corresponds to the experimental observations. This tendency could serve as a numerical criterion to predict void defect formation.

Hybrid Self-Reacting Friction Stir Welding of AA 6061-T6 Aluminium Alloy with Cooling Assisted Approach

In the present work, self-reacting friction stir welding of 6 mm thick Al 6061-T6 was processed considering two novel approaches as different temperatures of the water (1 °C and 30 °C), and methods of use (spraying and enveloping top surface) using water as cooling media. The four experiments as natural air cooling (NAC), spraying with room temperature water mist (S-RM), spraying with ice water mist (S-IM), and cooling with room temperature water jet (C-RJ) were performed. The thermal profile, microstructure, microhardness, and tensile properties were investigated for all the joints. The lowest hardness location was heat affected zone in NAC and it was the boundary of the thermo-mechanically affected zone and weld nugget zone in all cooling assisted joints. The C-RJ cooling assisted joint resulted in the highest tensile strength of 189.16 MPa which is 8.17% higher than the conventional self-reacting friction stir welded joint.

Computational Analysis on Weld Formation Mechanism during Self-Reacting Friction Stir Welding

Abstract Three-dimensional computational fluid dynamics models are developed to understand physical principles of self-reacting friction stir welding process. A novel approach of predicting the weld microstructure based on plastic strain distribution at cross-section behind the tool is proposed and verified with experimental results. Limitations and credibility of shear stress and velocity tool/workpiece boundary condition are evaluated from the perspective of the weld formation mechanism. The importance of the shear layer and its sticking/sliding transition state in weld formation mechanism is emphasized. From modeling perspective, shear stress boundary, which only represents a sliding condition, neglects the movement and effects of this shear layer. When shear layer is formed, due to the velocity discontinuity which could not be captured in fluid model, velocity boundary condition, which represents an averaging effect of sticking/sliding transition between tool and shear layer, is needed.

Influence of Traverse Speed in Self-Reacting FSW of AA6061-T6

Influence of Traverse Speed in Self-Reacting FSW of AA6061-T6

Effect of self-reacting friction stir welding on microstructure and mechanical properties of Mg-Al-Zn alloy joints

The 5 mm-thick Mg-6Al-1Zn alloy was self-reacting friction stir welded (SR-FSW) at various welding speeds. Sound joints were achieved with welding speed ranging from 300 to 400 mm/min. At lower welding speed, pore defect formed in the weld nugget zone (WNZ) due to the inadequate mixing of the plastic materials. The thermo-mechanically affected zone (TMAZ) consisted of fine equiaxed dynamic recrystallized grains instead of the elongated and rotated grains formed in the TMAZs of FSWed Mg alloys and SR-FSWed Al alloys. Finer grains were obtained in the WNZ, TMAZ and heat affected zone (HAZ) at higher welding speed due to the lower heat input. Both the TMAZ and WNZ have grains with a high density of dislocations due to the straining exerted by the tool. Hardness profiles show slight variation throughout the weld with the hardness values fluctuated between 50 to 68 HV. Results of tensile tests revealed that the tensile strength increased with increasing welding speed with the maximal strength efficiency reached 77%. Fracture elongations were lower than that of the base metal due to the inhomogeneous microstructure throughout the joint. The impact energy of both the WNZ and HAZ increased with increasing welding speed.

Process optimization in the self-reacting friction stir welding of aluminum 6061-T6

Self-reacting friction stir welding (SR-FSW), also called bobbin-tool friction stir welding (BT-FSW), is a solid state welding process similar to friction stir welding (FSW) except that the tool has two opposing shoulders instead of the shoulder and a backing plate found in FSW. The tool configuration results in greater heat input and a symmetrical weld macrostructure. A significant amount of information has been published in the literature concerning traditional FSW while little has been published about SR-FSW. An optimization experiment was performed using a factorial design to evaluate the effect of process parameters on the weld temperature, surface and internal quality, and mechanical properties of self-reacting friction stir welded aluminum alloy 6061-T6 butt joints. The parameters evaluated were tool rotational speed, traverse speed, and tool plunge force. A correlation between weld temperature, defect formation (specifically galling and void formation), and mechanical properties was found. Optimum parameters were determined for the welding of 8-mm-thick 6061-T6 plate.

A three-dimensional fully coupled thermo-mechanical model for Self-reacting Friction Stir Welding of Aluminium AA6061 sheets

In the present work a three dimensional model of self-reacting friction stir welding in aluminium alloy AA6061 has been developed based on the Computational Fluid Dynamics (CFD) approach using COMSOL Multiphysics software. The temperature dependent material properties have been incorporated in the model from available literature. A slip-stick contact between the workpiece and tool surface has been considered with the slip factor varying linearly with distance. The methodology adopted has been validated with experimental results available in the literature. The temperature distribution observed has been found to be asymmetric about the weld centre line. The maximum temperature has been observed on the advancing side of the weld. However, the temperature distribution across the thickness has been found to be almost symmetric about the mid thickness plane. An hourglass shaped temperature distribution has been observed across the cross-section of the weld. The material flow velocity distribution shows that the deformation zone is limited to a very small region around the tool.

Effect of rotation speed on microstructure and mechanical properties of self-reacting friction stir welded Al-Mg-Si alloy

The effect of tool rotation speed on microstructure and mechanical properties of self-reacting friction stir welded joints was investigated for Al-Mg-Si alloy. Joints were produced by a newly designed pin tool with rotation speeds ranging from 300 to 600 rpm at a constant welding speed of 350 mm/min. Cavity defect was observed in the weld obtained at the lowest rotation speed, and defect-free joints were formed with increasing of rotation speed. Self-reacting friction stir welding produced much refined microstructure accompanied by dispersion and dissolution of precipitated phases. There was little change of grain size in the weld nugget zone with increasing rotation speed, but more coarse microstructure was found in the thermomechanically affected zone and heat affected zone. The hardness of the weld was obviously lower than that of the base metal, and the lowest hardness location was in the heat affected zone. Results of transverse tensile tests indicated that the defective joint fractured in the weld nugget zone with the lowest tensile strength, while the fracture location of the defect-free joints changed to the heat affected zone.

Influences of rotation speed on microstructures and mechanical properties of 6061-T6 aluminum alloy joints fabricated by self-reacting friction stir welding tool

A 6061-T6 aluminum alloy was self-reacting friction stir welded by using the specially designed tool with unequal shoulder diameters at a constant welding speed of 150 mm/min to investigate the effect of rotation speed on microstructure and mechanical properties of the joints. Excessive flash on the bottom surface of the joint and groove defects on both surfaces of the joint were formed when the lower shoulder diameter was much smaller. The suitable shoulder sizes were determined as 16 and 18 mm in lower shoulder diameter and upper shoulder diameter, respectively. The grain size and the dislocation density in the weld nugget zone (WNZ) increased with increasing rotation speed. The tensile strength of joints first increased with increasing rotating speed and then decreased remarkably as a result of the formation of void defect. The joints welded at lower rotation speeds were fractured in the thermal mechanically affected zone (TMAZ). However, the fracture locations of the defect-free joints were changed to the heat affected zone (HAZ) at higher rotation speeds.

Metallographic Preparation of Self-Reacting Friction Stir Welded 2195/2219 Aluminum Alloys For Electron Backscatter Diffraction

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Conventional and bobbin friction stir welding of 12% chromium alloy steel using composite refractory tool materials

The use of matching tapers to provide a hot friction drive coupling for composite refractory tools for conventional and bobbin friction stir welding of 12% chromium alloy steel is described. The feasibility of using self-reacting (Bobbin) friction stir welding for steel has been demonstrated and the resulting microstructures have been evaluated.