Modeling and analysis of effect of tool geometry on temperature distribution and material flow in friction stir welding of AA6061-T6

A fully-coupled 3-D model of FSW was developed for 4-mm-plates of AA6061-T6 aluminum alloy based on the Finite Volume Method in ANSYS Fluent 14.5 software. Two types of the model, one with the tool and another without tool, were developed for different tool geometry, and analysis was done for temperature distribution in the workpiece and tool using system coupling for the first model and workpiece only in later one. A parametric study was carried out at different tool rotational speeds regarding temperature distribution and material flow analysis for all tool geometries at a single rotational speed. The behavior of materials was changed when passing through the different tools, and it was affected by thermal history, viscosity, and strain rate for particular tool geometry. Temperature-dependent material properties and a user-defined function viscosity code have been incorporated in the model, considering the workpiece as a non-Newtonian viscous fluid. A better material mixing was observed in the case of threaded pin geometry using a steady-state laminar flow model. All tapered tool geometries were unable to mix material properly just below and around the pin tip due to very low-velocity magnitude in this region, which may lead to a kind of defect. The asymmetric temperature distribution was observed in the workpiece. At higher rotational speed, peak temperature was observed higher in the workpiece, and the heat flow was more in the tool. Validation of the model was done by performing experiments.