Friction stir welding (FSW) is a solid-state joining process in which a rotating tool is used to mix and join the two pieces of material together. This produces an extremely complex thermomechanical environment wherein materials experience plastic deformation at elevated temperatures, creating a weld zone consisting of a wrought microstructure instead of the solidification microstructure produced by fusion welding methods. FSW results in joints with superior mechanical properties compared to materials joined using fusion welding techniques.

FSW -successfully utilised to join aluminium alloys- has been used to produce very high-quality joints in titanium alloys with no voids or defects; however, issues such as the tool life and the cost of the tools have limited its widespread use. In addressing such issues lower rotational speed (and sufficiently lower heat input) is desirable as it will be less demanding towards the tooling. Then, such process conditions should be monitored and optimised.
Furthermore, monitoring temperature is important in utilising FSW for titanium alloys. This is to ensure high temperature, achieved due to frictional and viscous heating, does not produce an undesirable microstructure, and consequently harm its mechanical properties.
Using computational fluid dynamics (CFD), this work is presenting a model to predict the temperature profile around the tool. There are several challenges in setting up such a model, including correct representation of viscosity for the studied material (Ti6Al4V) and accurate heat transfer calculations. While discussing these challenges, this work will be presenting some of the initial results of the model supported with microstructural examinations