Optimizing friction stir welding parameters for ductility enhancement in AA2029 aluminum alloy and SS316L stainless steel structures: a numerical simulation study

The main aim of this study is to select a suitable tool pin profile to maximize the tensile behavior (Ultimate Tensile Strength and Tensile Elongation) of Friction stir welded aluminum alloys of AA 2024 and AA 6061. The age-hardnable aluminum alloys of 2xxx, 6xxx and 7xxx series are extensively used in automobile and aircraft industries because of its high strength to weight ratio, formability and ductility. These alloys are vulnerable to cracking (2xxx and 7xxx) and highly melt (6xxx) in conventional fusion welding techniques. Friction stir welding is an emerging solid state welding technique which is best suitable for joining these aluminum alloys. The influential process and tool parameters that are affecting the FS welded joints are such as tool rotational speed, welding speed, axial load and tool pin profile. Dissimilar friction stir welded joints of AA 2024 and AA 6061 aluminum alloys are fabricated using a friction stir welding process to examine the influence of the tool pin profiles on tensile properties on various crucial process parameters. A Box-Behnken design with four input parameters, three levels and 30 runs is used to conduct the experiments and Response Surface Method (RSM) is used to develop the mathematical model. The experimental results were predicted at the 95% confidence level. The macro defects in the welds and the modes of tensile fracture are discussed in detail to reveal the root cause of failure in the fabricated samples. The rotating tool equipped with a square pin generated the highest ultimate tensile strength (143 MPa) with a 12% elongation. A microstructure variation on dissimilar alloys which result 44% reduction in tensile strength on AA2024 and 51% reduction in tensile strength on AA6061 aluminum alloys was observed on the stir zones.

This paper explicates the joining of AA 6061/TiO2 composites by the friction stir welding (FSW) process. FSW experiments were conducted as per the three factors, three-level, central composite ivy– face-centered design method. Mathematical relationships between the FSW process parameters, namely tool geometry, welding speed, and tool rotational speed, and the output responses such as hardness, yield strength, and ultimate tensile strength were established using response surface methodology. Adequacies of established models were assessed through the analysis of variance method. Further, the paper elucidates the application of the teaching–learning-based optimization (TLBO) algorithm to identify the optimal values of input variables and to obtain an FSW joint with superior mechanical properties. The optimized experimental condition obtained from the TLBO yields an FSW joint with a UTS of 174 MPa, yield strength of 120 MPa, and hardness of 126HV. The study revealed that the result of the TLBO algorithm matched the findings of the FSW experiments.

Fusion welding of A319 aluminium cast alloys will lead to many problems such as porosity, micro-fissuring and hot cracking. However, Friction Stir Welding (FSW) can be used to weld these cast alloys without the above-mentioned defects. The FSW process parameters such as tool rotational speed, welding speed and axial force play a major role in deciding the weld quality. The experiments were conducted based on three factors, three-level and Central-Composite-Face-centred (CCF) design with full replications technique. Models were developed to predict tensile strength of FSW A319 alloy using Response Surface Methodology (RSM) and Artificial Neural Network (ANN). The results obtained through RSM were compared with ANN. It is found that the error rate predicted by the artificial network is smaller than predicted by the RSM. [Received 2 February 2008; Revised 15 July 2008; Accepted 10 August 2008]

Effects of pin thread on the in-process material flow behavior during friction stir welding: A computational fluid dynamics study

Friction stir welding (FSW) is a solid state welding process in which a non-consumable rotating tool with a specially designed pin and shoulder is inserted into the abutting edges of sheets or plates to be joined and subsequently traversed along the joint line. In FSW, a pin tool with different shapes spins against the edges of two metal pieces of same or different thickness positioned next to each other. As the pin travels along, it creates friction that generates heat, mixes, and joins the alloys without melting them. To optimize the process, several researchers created pins of different shape, and geometry, and used them in FSW but varied the depth, rotational speed, and tilt angle of the pins. Statistical analysis has been used to identify the most optimum combination of tool and weld parameters that could support high-speed production. Many studies support that the faster FSW is carried out, the stronger (better weld quality) the resulting welds will be. The objective of this paper is to predict the effects of some of the process parameters on the performance of the aluminum alloy components joined using ANSYS simulation tool. Although not reported in this paper, the mechanical and metallurgical properties of the welded members have been measured in the laboratory. The goal is to gain an understanding of how FSW can be used to successfully join aluminum alloys and to study the effect of the various process parameters on the process. The material used is AA6061 as it is one of the popular choices for automotive applications. Experiments have been conducted to validate some of the simulation results from ANSYS software.

For the Friction stir welding (FSW) between aluminum and steel is important to fabricate vehicles with light weight and high strength for safety at low cost. For the fabrication of sound weld, it is necessary to control the material flow during FSW. In this study, the material flow during FSW was elucidated by numerical simulation by computational fluid dynamics (CFD) analysis and simulation experiment by transparent Poly-vinyle chloride (PVC) as simulant of aluminum and tracer material. Based on this material flow analysis, several shapes of welding tool were examined for control of material flow during FSW. Scroll shoulder is effective for enhancement of stirring zone by increasing material velocity around the probe. Flute and fine screw probe promote the material flow in depth and horizontal direction. The welding tool with scroll shoulder and flute and fine screw probe achieved sound weld with highest tensile strength of 120.4 MPa.

An in-situ neutron diffraction technique was used to investigate the lattice strain distributions and micromechanical behavior in a friction stir welded (FSW) sheet of AA7475-T761. The neutron diffraction experiments were performed on the spectrometer for material research, STRESS-SPEC, at FRM II (Garching, Germany). The lattice strain profiles around the weld center were measured as a function of the applied strain during the tensile loading and unloading. The anisotropic elastic and plastic properties of the FSW aluminum alloy were simulated by elasto-plastic self-consistent (EPSC) model to predict the anisotropic deformation behaviors involving the grain-to-grain interactions. Material parameters used for describing the constitutive laws of each test position were determined from the measured lattice strain distributions for different diffraction hkl planes as well as the macroscopic stress-strain curve of the FSW aluminum alloy. A good agreement between experimental results and numerical simulations was obtained. The present investigations provided a reliable prediction of the anisotropic micromechanical behavior of the FSW aluminum alloy during tensile deformation.

In this research, dissimilar butt joining of an Al–Mg alloy (AA5083) to austenitic stainless steel (A316L) by using friction-stir welding (FSW) process was examined. FSW parameters and joint design were optimized, owning to achieve the best joint strength. The processed FSWs at the optimized traverse speeds of 16, 20, and 25 mm/min with the sound surface appearance were considered for further cross-sectional investigations, microstructural characterizations, and mechanical testings. In situ reactions at the interface of Al–Mg alloy and stainless steel during FSW processes were studied by using field emission-scanning electron microscopy (FE-SEM) and line-scan energy-dispersive X-ray spectroscopy (EDS) analysis. As expected from the monitored thermal histories during FSW joining, the features indicating the formation of tunneling like defects were observed at low heat inputs (low w/v ratios). Moreover, some discontinuous thin intermetallic layers (with the thickness of ∼0.5 μm) were formed at the joint interface at the expressed processing conditions. Mechanical performances of the prepared dissimilar joints were assessed during transverse tensile loading and Vickers indentation micro-hardness testing. The joint strength ratio to the ultimate tensile strength (UTS) of the weakest base metal (BM) was improved up to ∼93 %, as all of the dissimilar FSWs failed from the Al–Mg base alloy, with a Vickers hardness enhancement of ∼460 % at the interface.

Despite the remarkable capabilities of friction stir welding (FSW) in joining dissimilar materials, the numerical simulation of FSW is predominantly limited to the joining of similar materials. The material mixing and defects’ prediction in FSW of dissimilar materials through numerical simulation have not been thoroughly studied. The role of progressive tool wear is another aspect of practical importance that has not received due consideration in numerical simulation. As such, we contribute to the body of knowledge with a numerical study of FSW of dissimilar materials in the context of defect prediction and tool wear. We numerically simulated material mixing and defects (surface and subsurface tunnel, exit hole, and flash formation) using a coupled Eulerian–Lagrangian approach. The model predictions are validated with the experimental results on FSW of the candidate pair AA6061 and AZ31B. The influence of tool wear on tool dimensions is experimentally investigated for several sets of tool rotations and traverse speeds and incorporated in the numerical simulation to predict the weld defects. The developed model successfully predicted subsurface tunnel defects, surface tunnels, excessive flash formations, and exit holes with a maximum deviation of 1.2 mm. The simulation revealed the substantial impact of the plate position, on either the advancing or retreating side, on the defect formation; for instance, when AZ31B was placed on the AS, the surface tunnel reached about 50% of the workpiece thickness. The numerical model successfully captured defect formation due to the wear-induced changes in tool dimensions, e.g., the pin length decreased up to 30% after welding at higher tool rotations and traverse speeds, leading to surface tunnel defects.

The requirement of weight reduction, high thermal conductivity and strength at low temperatures and high corrosion resistance has identified the use of Al alloys together with steel in various fields. The use of Al alloys together with steel warrants efficient joining of Al alloys with steels. Friction stir welding (FSW) is a potential candidate for the joining of difficult-to-weld similar and dissimilar materials due to its inherent advantages as a solid state joining process. In order to speed up the research activities that lead to industrial level implementation of FSW of dissimilar Al alloys and steels, modelling and simulation can play a vital role. In this work, a central composite-response surface method (RSM) model is developed to predict the ultimate tensile strength (UTS) of friction stir-welded dissimilar Al alloy AA5052 H32 and HSLA steel IRS M-42-97. The adequacy of the model is verified by the analysis of variance (ANOVA) and computed values of the actual and adjusted R2 values. The model is validated by the results of experimental trials at parameter combination other than that experimented as per the DOE matrix and found in agreement with an average error of −0.34 %. From the analysis of the developed model, it is observed that the UTS of the joint is very sensitive to the primary FSW parameters, and, as such, the range of primary FSW parameters that could produce significant joint strength is very narrow. Also, it is observed that the tool rotational speed, welding speed and axial force have a significant interaction effect on the UTS of the joint. The analysis of the model and discussion on the effect of FSW parameters on the tensile strength of the joint are supported by the results of scanning electron microscopy and EDS analysis at the joint interface of selected joints.

2024-T3 aeronautical aluminum alloy is a high-strength hard aluminum alloy, belonging to the Al-Cu-Mg series. It is mainly used for manufacturing various high-load mechanical parts such as aircraft skeletons. 2024-T3 aluminum alloy is difficult to be welded with traditional fusion welding, especially welded with another material such as titanium alloy or copper alloy. The welding quality of 2024-T3 aluminum alloy can be improved effectively by friction stir welding, which is favored in the aerospace and shipbuilding fields. Accurately grasping the welding transient evolution mechanism is the key to improving welding quality. It plays an important role in promoting the application of friction stir welding in industry. In this paper, the material physical parameters that change with the temperature were calculated by using the CALPHAD method, and the numerical model for friction stir welding was established. The transient changes in the temperature and stress field of the workpiece and the load of the stirring head were obtained. The temperature, stress, and strain of the advancing side and retreating side were compared and analyzed. The temperature of the workpiece surface and the stress around the keyhole were revealed. Zeiss Sigma 500 field emission scanning electron microscope was used to perform micro-characterization experiments, and the accuracy of the model was verified by comparing the simulation with the experiment. This research is of considerable significance for accurately revealing the mechanism of friction stir welding.

This paper presents the numerical simulation of the Friction stir welding (FSW) process obtained by using the DEFORM 3D software package. Numerical simulations are based on experimental research, welding of aluminum alloy AA6082-T6 by FSW method, which has the thickness of 7.8 mm. The aim of this paper is to determine the reliability of numerical simulations in the FSW process, which is followed by large deformations, where influential geometric and kinematic parameters are varied. Numerical research was done on the basis of the adopted five-phase orthogonal experimental plan with a variety of factors on two levels and repetition at the central point of the plan for four times. The parameters varied in the experiment are: Welding speed v mm/min, a rotation speed of tool ω rpm, angle of pin slopes α o, a diameter of the pin d mm, diameter of the shoulder D mm. During the performing of the FSW process, forces were measured in three normal directions: Axial force Fz, longitudinal force Fx and side force Fy, as well as the temperature in the adopted measuring positions of the workpiece. The experimental results obtained in this way were compared with the numerical experiment in the same adopted measuring positions, i.e., in the paper an analysis and comparison of the obtained experimental and numerical data of the measured forces and the generated temperature field were made.

Flow-coupled thermo-mechanical analysis of frictional behaviors at the tool-workpiece interface during friction stir welding

The present work addresses optimization of these friction stir welding process variables to maximize joint strength efficiency of welded polycarbonate sheets by using particle swarm optimization algorithm over response surface method based regression model. Initially, parametric influence on weld quality characteristics namely weld bead profile, bead geometry with associated microstructure along with micro‐hardness deviation through the weld centerline and stress‐strain behavior of the weld have been studied in detail as per full factorial design of experiments by using three different tool pin profiles such as cylindrical, square and triangular. The center point experiment i. e. tool rotational speed of 1800 min−1 and welding speed of 20 mm/min, and square tool pin profile were found to be the optimum combination with a maximum joint strength efficiency of 60.06 %. The regression model of weld ultimate tensile strength was developed by using response surface methodology which was found to be significant. Therefore, this model was further used for parametric optimization by using both response surface methodology and intelligent particle swarm optimization approaches. A slight improvement in joint strength efficiency with better optimization capability was found by using particle swarm optimization technique as compared to response surface methodology.

Friction stir welding (FSW) now definitively reached a large interest in the scientific community and what is more in the industrial environment, due to the advantages of such solid state welding process with respect to the classic ones. The latter aspects are relevant also with reference to joints characterized by a complex geometry. What is more, advanced FEM tools permit to develop effective engineering of the processes; quantitative results can be acquired from numerical simulations once basic information, as the process mechanics and the material flow, are certain. Material flow plays a fundamental role in FSW since it determines the effectiveness of the joints or, in turn, the insurgence of defects. In the paper, the material flow in the FSW of aluminum alloys T-joints is investigated at the varying of the most relevant technological and geometrical parameters with numerical simulations and experiments. In particular, to investigate the metal flow, a wide campaign of experimental tests and observations was developed utilizing a thin foil of brass as marker, placed at the interface of the two blanks to be welded. Some relevant conclusions on the process mechanics and on the actual material flow determining the material bonding are outlined, permitting an insight of the FSW of T-joints.