article · Scientific Reports
This research assesses the effect of using eccentric shoulder tools in friction stir welding of AA6082-T6 aluminium alloy. Standard friction stir welding typically relies on a tilted tool, but tests comparing an eccentric shoulder tool against a conventional aligned shoulder tool at both 0-degree and 3-degree tilt angles showed distinct advantages for the eccentric design without tilting. Operating at 600 rpm and a travel speed of 250 mm/min, the eccentric shoulder tool at a 0-degree tilt angle produced the finest grain size in the weld nugget zone, reducing it from 5.24 micrometres in the base material to 1.63 micrometres. This configuration also achieved the highest tensile strength of 216.5 MPa, representing an 89.7 percent joint efficiency, alongside 7.71 percent elongation and the greatest hardness recovery in the weld nugget zone.
Friction stir welding often requires the welding tool to be tilted, which can complicate machine setups and limit certain industrial operations. Demonstrating that an eccentric shoulder tool produces stronger, finer-grained joints at a zero-degree tilt angle simplifies the welding process. This allows operators to achieve high joint efficiency without adjusting tool angles.
This technique could benefit manufacturing and engineering sectors that join AA6082-T6 aluminium components, particularly where machinery cannot easily accommodate tool tilting. Because the study presents applied laboratory testing under specific parameters, the approach appears to be at an applied research stage, requiring further testing across broader operational conditions before industrial adoption.
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The present research investigates the impact of eccentric shoulder tools on the microstructure and mechanical properties of friction stir welded (FSWed) aluminum alloy AA6082-T6. Two tools, one with an eccentric shoulder and one with an aligned shoulder, were employed under identical welding parameters: a rotational speed of 600 rpm, travel speed of 250 mm/min, and tilt angles of 0° and 3°. The four FSWed joints produced were characterized using optical microscopy, tensile testing, and hardness testing. The weld nugget zone (WNZ) microstructure showed significant grain size reduction from 5.24 μm for the base material to 1.63 μm, using the eccentric shoulder tool at 0° tilting angle and 2.78 μm at 3° tilting angle. The aligned shoulder tool resulted in an average grain size of 2.79 μm at 0° tilting angle and 2.23 μm of 3° tilting angle. Thus, the eccentric shoulder tool with a tilt angle of 0° exhibited the smallest average grain size. The mechanical properties obtained are consistent with the microstructure, where the joint produced using the eccentric shoulder at a 0° tilting angle showed the highest tensile strength of 216.5 MPa (89.7% joint efficiency) and 7.71% elongation. In contrast, the aligned shoulder tool resulted in coarser grains and a lower mechanical performance. In addition, this joint exhibited the highest hardness recovery in WNZ. The current study implies that the eccentric shoulder tool can eliminate the need for a tilting angle during FSW, which is required in some applications.
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DOI: 10.1038/s41598-025-91065-1
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