Experimental and computational analyses of material flow characteristics in friction stir welding

In this work, two-dimensional isothermal characteristics of material flow around the cylindrical tool pin during the friction stir welding (FSW) process are investigated by using both experimental and numerical approaches for the wide range of traverse speed (50–110 mm/min) and rotational speed (75–425 rpm) of the tool pin. The experimental results, obtained using particle image velocimetry (PIV) flow visualization technique, are supplemented with the computational fluid dynamics (CFD) modelling based on COMSOL Multiphysics. The rheological behaviour of experimental material with a rheometer yielded as non-Newtonian shear-thinning nature under the broader shearing (10⁻³–10³ s⁻¹) at the room temperature 25 °C. Both experimental and computational characteristics of material flow in terms of local velocity and strain rate profiles complement each other with the best level of accuracy and show an increase in both with increasing rotational speed. During FSW process, two flow zones, namely, rotational and transitional zones, are formed around the tool pin. The rotational zone is symmetric and has 1 mm width around the tool pin at 300 rpm and 50 mm/min. Finally, both PIV and CFD analyses have replicated an industrial process in an efficient manner. PIV technique has been successfully demonstrated for in-situ flow visualization of FSW process and overcoming the issues with earlier tracer-based techniques, but selecting a transparent material is a minor concern. The consistency established between the experimental and CFD results further provides that the CFD approach can efficiently and reliably be used to gain the precise mechanisms of the FSW process and to select the appropriate design and engineering parameters.