The aim of the study was to analyse mechanical properties and microstructure of joints obtained using friction stir welding (FSW) technology. The focus of the study was on overlap linear FSW joints made of 1.4541 DIN 17441 steel sheets with thickness of 1.2 mm. Tools used during friction stir welding of steel joints were made of W-Re alloy. The joints were subjected to visual inspection and their load bearing capacity was evaluated by means of the tensile strength test with analysis of joint breaking mechanism. Furthermore, the joints were also tested during metallographic examinations. The analysis performed in the study revealed that all the samples of the FSW joints were broken outside the joint area in the base material of the upper sheet metal, which confirms its high tensile strength. Mean load capacity of the joints was 15.8 kN. Macroscopic and microscopic examinations of the joints did not reveal significant defects on the joint surface and in the cross-sections.
Welding strength is very important in safe use of polypropylene sheets. The determination of welding parameters and design of the welding tool has an impact on the weld strength. The welding parameters can be determined experimentally. In this study, Charpy impact test is used to determine suitable welding parameters in welding of polypropylene sheets with FSW method. At the same time, the weld zone microstructure is examined and Shore hardness measurements are made. The impact tests were performed on samples cut from the welded sheets. The impact tests values and hardness values were presented graphically. According to the test results, some welded parts behaved similar to the matrix material. In some welding parameters, Charpy impact test values were obtained close to values of the main materials. The suitable welding parameters were determined for polypropylene sheets welding.
Aluminum 6082-T6 panels were joined by friction stir welding utilizing a bobbin tool. A thermal simulation of the process was developed based upon machine torque and the temperature dependent yield stress utilizing a slip factor and an assumed coefficient of friction. The torque-based approach was compared to another simulation established on the shear layer methodology (SLM), which does not require the slip factor or coefficient of friction as model inputs. The SLM simulation, however, only models heat generation from the leading edges of the tool. Ultimately, the two approaches yielded matching temperature predictions as both methodologies predicted the same overall total heat generation from the tool. A modified shear layer approach is proposed that adopts the flexibility and convenience of the shear layer method, yet models heat generation from all tool/workpiece interfaces.
This work presents a numerical simulation of aviation structure joined by friction stir welding, FSW, process. The numerical simulation of aviation structure joined by FSW was created. The simulation uses thermomechanical coupled formulation. Th model required creation of finite elements representing sheets, stiffeners and welds, definition of material models and boundary conditions. The thermal model took into account heat conduction and convection assigned to appropriate elements of the structure. Time functions were applied to the description of a heat source movement. The numerical model included the stage of welding and the stage of releasing clamps. The output of the simulation are residual stresses and deformations occurring in the panel. Parameters of the global model (the panel model) were selected based on the local model (the single joint model), the experimental verification of the local model using the single joint and the geometry of the panel joints.
In the present study, butt joints of aluminum (Al) 8011-H18 and pure copper (Cu) were produced by friction stir welding (FSW) and the effect of plunge depth on surface morphology, microstructure and mechanical properties were investigated. The welds were produced by varying the plunge depth in a range from 0.1 mm to 0.25 mm. The defect-free joints were obtained when the Cu plate was fixed at the advancing side. It was found that less plunging depth gives better tensile properties compare to higher plunging depth because at higher plunging depth local thinning occurs at the welded region. Good tensile properties were achieved at plunge depth of 0.2 mm and the tensile strength was found to be higher than the strength of the Al (weaker of the two base metals). Microstructure study revealed that the metal close to copper side in the Nugget Zone (NZ) possessed lamellar alternating structure. However, mixed structure of Cu and Al existed in the aluminum side of NZ. Higher microhardness values were witnessed at the joint interfaces resulting from plastic deformation and the presence of intermetallics.
Sound joint of hollow-extruded 6005A-T6 aluminum alloy was achieved by friction stir welding and its high cycle fatigue performance was mainly investigated. As a result, the joint fatigue limit reaches 128.1 MPa which is 55% of the joint tensile strength. The fatigue fracture mainly occurs at the boundary between the stir zone and thermo-mechanically affected zone due to the large difference in the grain size. This difference is caused by the layered microstructure of the base material. The shell pattern with parallel arcs is the typical morphology in the fracture surface and the distance between arcs is increased with the increase of stress level. The specimen with the fracture located in the stir zone possesses a relatively low fatigue life.