Thermal behaviour and material flow in FSW of high-strength aluminium alloys: Role of tool design and process conditions

In this study, a 3D thermo-mechanical finite element model was developed in Abaqus/Explicit to simulate the friction stir welding (FSW) of AA7075-T6 aluminium alloy, incorporating a Johnson-Cook constitutive law to represent the material’s viscoplastic behaviour. The model was validated against experimental temperature measurements and microstructural observations. Two tool geometries, a flat-shouldered tool and a scrolled-shoulder threaded tool, were compared under rotational speeds ranging from 1100 to 1700 rpm and welding speeds between 70 and 120 mm/min. The simulations revealed that rotational speed is the dominant parameter influencing heat generation, with the peak temperature rising by approximately 250 °C as the rotational speed increased from 1100 to 1700 rpm. Conversely, increasing the welding speed from 70 to 120 mm/min reduced the peak temperature by about 100-130 °C, due to shorter tool-workpiece interaction times and reduced frictional heat input. At 1320 rpm and 70 mm/min, the maximum temperature reached 253 °C numerically and 187 °C experimentally, showing good qualitative agreement between model and experiment. The use of a scrolled-shoulder tool produced higher and more uniformly distributed temperatures, improving material flow and reducing surface defects compared with the flat-shouldered design. Overall, the validated model accurately captured the thermal behaviour of FSW, demonstrating that optimised tool geometry and process parameters can significantly enhance joint quality, refine the stir zone microstructure, and minimise thermal gradients in high-strength aluminium alloys.