Friction Stir Welding Of Dissimilar Materials Research Articles

The effect of friction stir welding on the microstructure and mechanical properties of the dissimilar SS304 and Al7075-T6 alloy joints

This study focuses on the friction stir welding (FSW) of dissimilar materials, Al7075 alloy and SS304 stainless steel, in a butt configuration. The objective is to examine the impact of different operating conditions, including tool rotational speed, transverse speed, and tool offset, on the FSW process of the dissimilar sheets. Mechanical properties, specifically the ultimate tensile strength, were found to be influenced by rotational speed. Higher rotational speed resulted in decreased tensile strength due to increased heat generation in the weld zone, leading to the formation of a thicker intermetallic layer. Higher tool rotational speed and greater transverse feed rate improved weld joint performance. Microstructural changes and deformation properties were investigated using optical microscopy (OM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The FSW process caused significant grain refinement, creating a fine and equiaxed recrystallized grain structure. Intermetallic compounds like Al13Fe14, Al3Fe2, and Al3Mg2 were identified in the interface zone. In summary, this study provides valuable insights into the FSW of dissimilar materials. It sheds light on mechanical properties, microstructural changes, and intermetallic compound formation in the welded joint, contributing to the understanding of FSW for dissimilar materials.

Prediction of Axial Force on Dissimilar Aluminum Alloys Friction Stir Welding Using Design of Experiment

Friction stir welding (FSW) has become very popular for joining similar or dissimilar aluminum alloys. The heat used for this welding process is caused by friction between the welding tool and the workpiece which the axial force, the main parameter for heat generation, plays a very important role. Insufficient heat during welding will result in defective workpieces. This research is aimed to predict the axial force from the relevant factors of the FSW of dissimilar materials (aluminum alloys AA2024-T3 and AA6061-T6). The 23 full factorial design with center point was used for this experiment that consisted of 3 main factors: 1) rotation speed (rpm), 2) welding speed (mm/min), and 3) pin geometry each factor has 2 levels and 2 replications with the total of 20 experiments. The axial force data of each experiment were collected using a stationary dynamometer which obtained the data acquisition every 0.1 seconds (frequency of 10 Hz). The results from the design of experiment were analyzed by statistical method at the significance level of α = 0.05 which found that the significance and the optimum value of the main factors were rotation speed of 1500 rpm, welding speed of 35 mm/min, pin geometry of tri flat threaded, and the 2-way interaction between rotation speed and pin geometry. Furthermore, the prediction of the average axial force value on dissimilar aluminum alloys obtained from the specified parameters equals 478.91 N.

Material Defects in Friction Stir Welding through Thermo–Mechanical Simulation: Dissimilar Materials with Tool Wear Consideration

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.

Computational analysis of inter-material mixing and weld-flaw formation during dissimilar-filler-metal friction stir welding (FSW)

Purpose – Friction stir welding (FSW) butt-joining involving the use of a dissimilar filler metal insert between the retreating and advancing portions of the workpiece is investigated computationally using a combined Eulerian-Lagrangian (CEL) finite element analysis (FEA). The emphasis of the computational analysis was placed on the understanding of the inter-material mixing and weld-flaw formation during a dissimilar-material FSW process. The paper aims to discuss these issues. Design/methodology/approach – The FEA employed is of a two-way thermo-mechanical character (i.e. frictional-sliding/plastic-work dissipation was taken to act as a heat source in the energy conservation equation), while temperature is allowed to affect mechanical aspects of the model through temperature-dependent material properties. Within the analysis, the workpiece and the filler-metal insert are treated as different materials within the Eulerian subdomain, while the tool was treated as a conventional Lagrangian subdomain. The use of the CEL formulation within the workpiece insert helped avoid numerical difficulties associated with excessive Lagrangian element distortion. Findings – The results obtained revealed that, in order to obtain flaw-free FSW joints with properly mixed filler and base materials, process parameters including the location of the tool relative to the centerline of the weld must be selected judiciously. Originality/value – To the authors’ knowledge, the present work is the first reported attempt to simulate FSW of dissimilar materials.

Material flow in Friction Stir Welding

Friction stir welding (FSW) is a solid-state joining technique initially developed for aluminium alloys. The heat generated by a rotating tool softens the material in the vicinity of the tool. The material undergoes intense plastic deformation following quite complex paths around the tool, depending on the tool geometry, process parameters and material to be welded. The comprehension of the material flow is essential to prevent voids and other internal defects which may form during welding. Several techniques have been used for tracking material flow during FSW such as metallography, the use of a marker material as a tracer or the flow visualization by FSW of dissimilar materials or even the X-ray and computer tomography. Some of these techniques are useless in the analysis of welds in homogenous materials or welds between materials of the same group. The aim of this investigation is tracking the material flow in FSW between 1mm thick sheets in aluminium alloys AA 5182-H111 and AA 6016-T4, currently used in automotive industry.