article · Materials
Friction stir spot welding provides a solid-state joining method relevant to structural components. This investigation evaluated four-millimetre-thick lap joints of aluminium alloy AA5052-H32 fabricated at tool rotation speeds of 500, 1000, and 1500 revolutions per minute with a constant dwell time of two seconds. Across all parameters, the process induced dynamic recrystallisation, substantially refining the stir zone grain size from forty micrometres in the base material down to between four and eleven micrometres. Consequently, the stir zone exhibited greater hardness than the original base alloy. Decreasing the rotation speed reduced the heat input, which yielded finer grain structures, increased hardness, and superior mechanical resistance. The joint processed at 500 revolutions per minute achieved the finest grains at four micrometres and the highest maximum tensile-shear load of 4330 newtons, whereas operating at 1500 revolutions per minute reduced this load capacity to 2569 newtons.
Selecting optimal processing parameters is vital for creating robust structural welds in aluminium components. By demonstrating that lower rotation rates enhance joint strength through grain refinement, this work offers clear technical guidance for manufacturing lighter, stronger welded assemblies without compromising the fundamental material hardness of the base metal.
This research is directly applicable to automotive, aerospace, and shipbuilding manufacturers using aluminium alloy AA5052-H32 sheet components. By defining tool rotation rates that maximise joint shear strength, the findings support process optimisation in manufacturing plants. As an applied laboratory study detailing operational welding parameters and mechanical outcomes, it offers empirical data that engineers can adapt for production-line testing and tooling development.
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Friction stir spot welding (FSSW) of similar AA5052-H32 joints has numerous benefits in shipbuilding, aerospace, and automotive structural applications. In addition, studying the role of tool rotation speed on the microstructure features, achieved textures, and joint performance of the friction stir spot-welded (FSSWed) joint still needs more systematic research. Different FSSWed AA5052-H32 lap joints of 4 mm thickness were produced at different heat inputs using three tool rotation speeds of 1500, 1000, and 500 rpm at a constant dwell time of 2 s. The applied thermal heat inputs for achieving the FSSW processes were calculated. The produced joints were characterized by their appearance, macrostructures, microstructures, and mechanical properties (hardness contour maps and maximum tensile-shear load) at room temperature. The grain structure and texture developed for all the FSSWed joints were deeply investigated using an advanced electron backscattering diffraction (EBSD) technique and compared with the base material (BM). The main results showed that the average hardness value of the stir zone (SZ) in the welded joints is higher than that in the AA5052-H32 BM for all applied rotation speeds, and it decreases as the rotation speed increases from 500 to 1000 rpm. This SZ enhancement in hardness compared to the BM cold-rolled grain structure is caused by the high grain refining due to the dynamic recrystallization associated with the FSSW. The average grain size values of the stir zones are 11, 9, and 4 µm for the FSSWed joints processed at 1500, 1000, and 500 rpm, respectively, while the BM average grain size is 40 µm. The simple shear texture with B/-B components mainly dominates the texture. Compared to the welded joints, the joint processed at 500 rpm and a 2 s duration time attains the highest tensile-shear load value of 4330 N. This value decreases with increasing rotation speed to reach 2569 N at a rotation speed of 1500. After tensile testing of the FSSWed joints, the fracture surface was also examined and discussed.
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DOI: 10.3390/ma16093423
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