Tool Friction Stir Research Articles

Microstructural characteristics and mechanical properties of bobbin tool friction stir welded 2A14-T6 aluminum alloy

2A14-T6 aluminum alloy was bobbin tool friction stir welded (BT-FSW) at various welding speeds. The microstructural analysis indicates that in the weld nugget the grains of the upper layer are smaller than those of the lower layer, which should be attributed to the larger extent of heat dissipation through the top shoulder. An ellipse-shaped region and a triangle-shaped region characterized by large elongated grain structures are found in the middle layer of the weld nugget of BT-FSW joints. The insufficient material plastic deformation caused by the flat feature of tool pin is believed to be the reason for the formation of the both regions. The insufficiently stirred regions can significantly affect the fracture features of joints during tensile test. At low welding speeds, the joints are all fractured along the border of the ellipse-shaped region. While at high welding speeds, the fracture path is just through the triangle-shaped region. With increasing welding speed, the joint strength is firstly increased to a peak and then shows a sharp decrease due to the occurrence of void defects. A maximum strength efficiency of 75% is achieved in this study.

Development of novel heating tool friction stir spot welding (HT-FSSW) for AZ31 magnesium alloy

In this work, a new heating tool friction stir spot welding (HT-FSSW) process was developed, and its impacts on the microstructure and mechanical properties of the welded AZ31 magnesium alloy joints were investigated by microstructure observation, tensile tests and microhardness tests. An increase in the heating tool temperature resulted in a decrease in the grain size of the stir zone (SZ) and an increase in the grain size of the thermomechanically affected zone (TMAZ). The rising heating tool temperature also aggrandised the bonded zone width and enhanced the tensile shear load strength per unit area of the HT-FSSW welded joints. With an increase in the heating tool temperature, the microhardness of SZ increased while that of the TMAZ decreased. Moreover, the slope of the Hall–Petch relationship between microhardness and grain size of the TMAZ is larger than that of the SZ.

Finite Element Analysis for Bobbin Tool Friction Stir Welding

With DEFORM-3D finite element software, by thermo-mechanical coupling method, the physical modle for bobbin tool friction stir welding was set up. By this model, the temperature field and flow field of AA 2014 aluminium alloy work plate of 6mm was analyzed, which provides useful information for the investigation of this new process. Simulation results show that the temperature field of the cross section presents symmetry approximately about the mid thickness of the work plate. The high temperature zone has large radius at bottom and top surfaces near the shoulders while small radius at the mid thickness, like a waist, which is verified by the experiments. The relativey highest steady temperature keeps about 360℃. Groove defects are easy to be found in the simulation.

Influences of Tool Geometry on Metallurgical and Mechanical Properties of Friction Stir Welded Dissimilar AA 2024 and AA 5052

The present work investigates on the characterization of friction stir welded dissimilar aluminium alloys AA2024 and AA5052. Performance of commonly used tool profiles were compared against the newly developed stepped pin profile. H13 tool steel was used as friction stir tool with various pin profiles which includes cylindrical, cylindrical-threaded, squared, tapered and stepped types. Tensile and hardness studies were done to analyze mechanical behaviour. Macrographs of cylindrical and tapered pins showed minute discontinuities whereas other profiles did not. Microstructure and SEM/EDAX analysis were done to examine the metallurgical changes for every trial. The optimized process parameters of speed and feed were identified to be lOOOrpm and 40mm/min respectively. Extensive studies revealed that sound welds were produced in the plates that were welded with new stepped pin tool.

Simulation on the Temperature Field of Bobbin Tool Friction Stir Welding of AA 2014 Aluminium Alloy

Bobbin tool friction stir welding is a new type of friction stir welding. In the study, the thermo-mechanical model of the bobbin tool friction stir welding was set up. By this model, the temperature field of AA 2014 aluminium alloy work plate of 6mm was simulated, which provides useful information for the investigation of this new process. Simulation results show that the temperature field of the cross section presents symmetry approximately about the mid thickness of the work plate. The high temperature zone has large radius at bottom and top surfaces near the shoulders while small radius at the mid thickness, like a waist. The max temperature for the point at retreating side is about 40°C higher than advancing side.

Atom probe tomographic study of a friction-stir-processed Al–Mg–Sc alloy

The microstructure of a twin-roll-cast Al–4.5Mg–0.28Sc at.% alloy after friction-stir processing, performed at two tool rotational rates, was investigated by atom probe tomography. Outside the stir zone, the peak-aged alloy contains a high number density (∼8.0×1023m−3) of ∼1.5nm radius Al3Sc (L12) precipitates with a minor Mg content, providing an increase of ∼600MPa in the Vickers microhardness. In the stir zone of the sample processed at 400rpm rotational rate, the microhardness increase is mainly due to grain refinement, rather than precipitate strengthening, because the Al3Sc precipitates, with spherical lobed cuboids and platelet-like morphology, grow and coarsen to a 10–20nm radius. The Sc supersaturation across the stir-processed zone has a concentration gradient, which is higher on the retreating side and lower on the advancing side of the friction-stir tool. Hence, after aging at 290°C for 22h, the microhardness increase within the stir zone also displays a gradient due to precipitate strengthening with varying precipitate volume fractions. In the stir zone for the sample processed at 325rpm rotational rate, the microhardness increase is also predominantly due to grain refinement, as coarse Al3Sc precipitates form heterogeneously at grain boundaries with a platelet-like morphology. The hardness remains unchanged after a 290°C aging treatment. This is because the Al3Sc precipitates are highly heterogeneously distributed due to a combination of a small Sc supersaturation (0.05at.%) in the matrix, the existence of dislocations, and a large area per unit volume of grain boundaries (∼4–6×106m−1).

Shear layer modelling for bobbin tool friction stir welding

This study presents an approach to model the shear layer in bobbin tool friction stir welding. The proposed CFD model treats the material in the weld zone as a highly viscous non-Newtonian shear thinning liquid. A customised parametric solver is used to solve the highly non-linear Navier–Stokes equations. The contact state between tool and workpiece is determined by coupling the torque within the CFD model to a thermal pseudomechanical model. An existing analytic shear layer model is calibrated using artificial neural networks trained with the predictions of the CFD model. Validation experiments have been carried out using 4 mm thick sheets of AA 2024. The results show that the predicted torque and the shear layer shape are accurate. The combination of numerical and analytical modelling can reduce the computational effort significantly. It allows use of the calibrated analytic model inside an iterative process optimisation procedure.

Influences of Tool pin Profile and Tool Shoulder Curvature on the Formation of Friction Stir Welding Zone in AA6061 Aluminium Alloy

Friction stir welding (FSW) process is an emerging solid state joining process in which the material that is being welded does not melt and recast. This process uses a non-consumable tool to generate frictional heat in the abutting surfaces. The welding parameters such as tool rotational speed, welding speed, axial force, etc., and tool pin profile play a major role in deciding the weld quality. Friction stir tool plays a major role in friction stir welding process. In this investigation, it is tried to evaluate the effect of tool pin thread and tool shoulder curvature on FSW zone formation in AA6061 aluminium alloy. In this regard, six different tool pin geometries (threadless triangular pin with/without conical shoulder, threaded triangular pin with conical shoulder, threadless square pin with/without conical shoulder, threaded square pin with conical shoulder) are used to fabricate the joints. The formation of FSP zones are analyzed macroscopically. Tensile properties of the joints are evaluated and correlated with the FSP zone formation. Consequently, it is obtained that welding creates a higher quality compared to other tool pin profiles using the square tool with curved shoulder and having threaded pin.

Weld Quality Improvement with Hybrid FSW Technology Assisted by Preheating for Copper T2/Aluminium 5A06 Dissimilar Materials

Copper and aluminium alloy could be welded by friction stir welding (FSW) but it is quite difficult to achieve a defect-free welding joint for welding dissimilar materials because of the enormous difference of their thermo-physical performances. In this paper, another friction stir tool was applied as a heating source to preheat the copper side to 150~200°C in the welding direction. Preheating temperature can make up the lost heat, improve the temperature of copper plate before the FSW process, achieve the refining grains, and then obtain a high quality welding joint. We concentrated on hybrid heat-source equipments design and procedure optimization in our studies. The microstructure, mechanical properties and phase constituents of FSW joints were studied through mechanical test and metallographic analysis. The results indicated that the hybrid FSW technology with preheating for copper T2/aluminium 5A06 dissimilar materials can not only improve the welding efficiency, but also obtain the high quality welding joint. This special welding technology could solve the welding problems of Al-Cu dissimilar materials and had a good potential for application in aerospace manufacturing.

Modeling of friction stir welding process for tools design

A three-dimensional friction stir welding (FSW) process model has been developed based on fluid mechanics. The material transport in the welding process has been regarded as a laminar, viscous, and non-Newtonian liquid that flows past a rotating pin. A criterion to divide the weld zone has been given on the basis of cooperation of velocity field and viscosity field. That is, the η0-easy-flow zone that existed near the tool pin corresponded to the weld nugget zone; the area between the η0-easy-flow zone and η1-viscosity band is corresponded to the thermal-mechanical affected zone (TMAZ). The model gives some useful information to improve the understanding of material flow in FSW through the simulation result of velocity distribution. In order to appraise the friction stir pin design, three kinds of pin geometry, one is column pin, the second is taper pin, and the last one is screw threaded taper pin, were used in the model. The pin geometry seriously affected the simulation result of velocity distribution in the η0-easy-flow zone. The velocity distribution in the η0-easy-flow zone can be considered as the criterion of optimizing friction stir tool design. This study will benefit to direct the friction stir tool design.

Thermal models for bobbin tool friction stir welding

This study presents three thermal 3D models for bobbin tool Friction stir welding (FSW) implemented in Comsol and Matlab. The models use thermal pseudo-mechanical (TPM) heat sources and include tool rotation, an analytic shear layer model and ambient heat sinks like the machine and surrounding air. A new transient moving geometry approach has been implemented. It includes the full tool motion along the weld line, while the other two models use fixed geometry with and without moving heat source. The computational effort is small for all three models. The steady state model can be solved in approximately 5 min on a state of the art workstation. Experiments on the FlexiStir experimental welding unit have been carried out to validate the models’ outputs. The predictions of all models are in excellent agreement with each other and the experiment.

SelectConnect™ process for metallizing circuits on molded parts and components

The bobbin tool friction stir welding (BTFSW) technique was applied to a Mg-Zn-Zr alloy, ZK60-T5. The effects of shoulder diameter and stir pin geometry on the macrostructure, microstructure and mechanical properties of the BTFSW joints were studied. Weld quality was sensitive to the interaction of bobbin tool geometries and processing parameters. The reduction in the shoulder diameter led to less frictional contact and resistance and hence lowered the mechanical load imposed on the tool. The employment of the tapered stir pin reduced the traversing force, which displaced substantially less plasticized metal during the BTFSW than the cylindrical stir pin. The welding speed for the BTFSW was increased benefiting from these mechanical load alleviations. The visual aspects of the BTFSW joints, characterized by limited tunneling and voiding phenomena occurring were improved with the increase in welding speed. The BTFSW resulted in extensive softening in the stir zones of the joints due to dissolution of the β2´precipitates. The tensile properties of the joints were inferior to those of the base metal due to the crystallographic isotropy in the stir zone. The improvements in tensile properties of the BTFSW joint were achieved through texture tailoring by adding threads on the stir pin. The complicated plasticized metal flow introduced by the threaded stir pin provided a randomized crystallographic texture in the stir zone which contributed to the preferable tensile properties.

Specific Character of Material Flow in Near-Surface Layer during Friction Stir Processing of AZ31 Magnesium Alloy

Microstructure and texture evolution in the near-surface layer during friction stir processing (FSP) of AZ31 magnesium alloy was studied. Material flow was found to be a very complex process consisting of several stages. The material in front of the friction stir tool was first deformed by the rotating shoulder. Then, approaching the tool, it experienced a secondary deformation caused by the rotating pin, and finally, behind the tool, it again underwent a tertiary deformation induced by the shoulder. The texture evolution was shown to dictate the grain structure development.

Effects of Tool Design and Friction Stir Welding Parameters on Weld Morphology in Aluminum Alloys

Friction stir welding (FSW) is a complex thermo-mechanical process which produces wrought microstructure with microstructural gradients in grain size, grain orientation, dislocation density, and precipitate distribution. The type and degree of microstructural modification is a function of the particular alloy chosen, its initial temper, the tool design and corresponding weld process parameter window, and other variables like material thickness, size, fixturing, etc. Since the microstructural changes produced can dramatically affect resultant mechanical performance and corrosion response, a thorough understanding of the variables involved in those changes is needed. A design of experiments approach was used to study the effects of welding parameter selection on the microstructural changes wrought by FSW with two different sizes of the same FSW tool design. A combination of microhardness mapping and electrical conductivity testing was used to investigate potential differences. The importance of these factors and the means for characterizing them for developing standards and specifications are also discussed.

The influence of pin geometry on bonding and mechanical properties in friction stir weld 2014 Al alloy

Friction stir tool is the key art of friction stir welding process. The influence of the welding structure and the mechanical properties has been investigated. For this purpose, four different stir pins, two of them are column pin and taper pin and the other two are the same size but with screw thread, were used to carry out a welding process. Microscopic examination of the weld zone and the mechanical property tests results showed that the best bonding was obtained with screw pitched taper stir pin. The appearance of the weld is well and no obvious defect is found using this tool. The grain of the weld nugget is very fine and the precipitation distributes equably. This study will be benefit to direct the friction stir tool design.