Research on T-configuration aluminum constructions effectively decreases fuel consumption, increases strength, and develops aerial structures. In this research, the effects of friction stir welding (FSW) tool offset (TO) on Al–Mg–Si alloy mixing and bonding in T-configurations is studied. The process is simulated by the computational fluid dynamic (CFD) technique to better understand the material mixing flow and the bonding between the skin and flange during FSW. According to the results, the best material flow can be only achieved at an appropriate TO. The appropriate TO generates enough material to fill the joint line and results in formation of the highest participation of the flange in the stir zone (SZ) area. The results show that, in the T-configuration, FSW joints provide raw materials from the retreating side (RS) of the flange that play a primary role in producing a sound mixing flow. The selected parameters were related to the geometric limitations of the raw sheets considered in this study. The failure point of all tensile samples was located on the flange. Surface tunneling is the primary defect in these joints, which is produced at high TOs. Among the analyzed cases, the most robust joint was made at +0.2 mm TO on the advancing side (AS), resulting in more than 60% strength of the base aluminum alloy being retained.

One of the main challenging issues in friction stir welding (FSW) of stiffened structures is maximizing skin and flange mixing. Among the various parameters in FSW that can affect the quality of mixing between skin and flange is tool plunge depth (TPD). In this research, the effects of TPD during FSW of an Al-Mg-Si alloy T-joint are investigated. The computational fluid dynamics (CFD) method can help understand TPD effects on FSW of the T-joint structure. For this reason, the CFD method is employed in the simulation of heat generation, heat distribution, material flow, and defect formation during welding processes at various TPD. CFD is a powerful method that can simulate phenomena during the mixing of flange and skin that are hard to assess experimentally. For the evaluation of FSW joints, macrostructure visualization is carried out. Simulation results showed that at higher TPD, more frictional heat is generated and causes the formation of a bigger stir zone. The temperature distribution is antisymmetric to the welding line, and the concentration of heat on the advancing side (AS) is more than the retreating side (RS). Simulation results from viscosity changes and material velocity study on the stir zone indicated that the possibility of the formation of a tunnel defect on the skin–flange interface at the RS is very high. Material flow and defect formation are very sensitive to TPD. Low TPD creates internal defects with incomplete mixing of skin and flange, and high TPD forms surface flash. Higher TPD increases frictional heat and axial force that diminish the mixing of skin and flange in this joint. The optimum TPD was selected due to the best materials flow and final mechanical properties of joints.

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In the present investigation, friction spot extrusion welding was investigated for dissimilar AA2024-T3 and AA5754-O materials, under the effect of three different shoulder plunge depths of 0.25, 0.35 and 0.45 mm, keeping other parameters constant. The welded specimens were evaluated by visual inspection, optical microscopy, scanning electron microscopy, electron backscattered diffractions, and tensile testing. The results revealed that the effective metallurgical bonding and mechanical locking were obtained in case of weld produced by plunge depth of 0.45 mm. The metallurgical bonding is obtained between extruded material and surfaces of predrilled cavity, whereas mechanical locking is obtained through filling an extruded material in the predrilled cavity. The plunge depth variations influence the grain structures of processed zones. Increased plunge depth of 0.45 mm results in effective materials mixing with zigzag pattern of oxide layer mixed in the stir zone. In case of weld produced by plunge depth of 0.25 mm, the oxide layer was found as separating layer between workpieces. The weld produced by maximum plunge depth of 0.45 mm was resulted to higher fracture load of 5198 N. Trans-granular ductile fracture was observed for weld produced by plunge depth of 0.45 mm.