Comparative study of FSW and TIG welding of AA3003 aluminium flange joints under varying tool geometries and rotational speeds

Flange joints are widely used in pipelines, heat exchangers, and pressure-retaining aluminium structures, yet their behaviour under friction stir welding (FSW) remains insufficiently explored in the literature. This study addresses this gap by evaluating the combined effects of tool geometry and rotational speed on the microstructural and mechanical performance of FSW AA3003 flange joints, with Tungsten Inert Gas (TIG) welding used as a benchmark. The conical-pin tool produced superior weld quality, generating refined stir-zone grains (7.26 µm), higher hardness (46 HV₀.₂), and the highest tensile strength (185 MPa) owing to enhanced material flow and dynamic recrystallisation. The cylindrical pin yielded slightly lower properties (44 HV₀.₂, 165 MPa), while TIG welds exhibited coarse dendritic structures and reduced strength. Hydrostatic testing further demonstrated the sealing advantage of FSW, with conical-pin welds remaining leak-tight up to 32 bar, compared with failure at 23–25 bar in TIG joints. These results establish optimised FSW, particularly with conical-pin geometry, as a high-integrity, energy-efficient, and sustainable joining method for aluminium flange assemblies.