Friction Stir Welding of Ti6Al4V complex geometries for aeronautical applications: a feasibility study

While Friction Stir Welding (FSW) of aluminium alloys can be considered a mature technology, even for complex joint morphologies, as T joints welded “in transparency”, welding of hard material still presents several open issues. In fact, welding of titanium alloys is a challenging process due to the chemical, mechanical and thermal characteristics of such materials which are subjected to atmosphere contamination resulting in joint hydrogen, oxygen and nitrogen embrittlement; additionally, due to the high melting temperature, large distortion and residual stress are found in joints obtained by traditional fusion welding processes as gas metal arc welding, electron beam welding and laser welding. In this way a solid-state process, as FSW, represents a valid choice in order to overcome problems related to the material melting. It should be noticed that FSW of titanium alloys is definitely more complex than the same process referred to aluminium alloys. In the proposed paper, a feasibility study on the production of Ti6Al4V T-joints in one welding pass, i.e. the so-called transparency welding, is presented. The main process parameters, i.e. tool rotation and feed rate have been fixed, and the main metallurgical and mechanical properties of the joint have been analysed. Macro and micro observations of the joints have been performed relating the final microstructure to the input process parameters utilized.