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Ti6Al4V titanium alloy is friction stir welded using a W-Re rotational tool. The effects of welding speed on the microstructure, tensile strength and fracture properties of weld are investigated. At the rotational velocity of 250 r/min, the peak temperature is lower than β transus temperature, and the weld nugget is made up of fine α phase and transformed β phase. The grain size of shoulder affected zone is bigger than that of weld nugget because of low thermal conductivity of Ti6Al4V titanium alloy. By increasing the welding speed, the grain size of weld nugget, the tensile strength and the ductility of weld all are decreased.

Based on the RNG k- model, the finite volume model of friction stir welding of Ti6Al4V alloy is established by ANSYS FLUENT software. The effect of rotational tool geometry on titanium alloy flow behaviour is exhibited. The results of numerical simulation show that the flow direction of material near the rotational tool is the same as that of the rotational direction of the rotational tools.. The flow velocity of material near the rotational tool is much bigger than that of other regions in a weldment while the peak value appears near the shoulder edge. Changing either the rotational tool shoulder diameter or the pin tip diameter, the flow direction of material during the welding process will always remain unchanged. With an increase of the shoulder and pin tip diameter, the material flow velocity increases. However, from the point of view of elimination of root defects, increasing the diameter of the pin tip is better than increasing the diameter of the shoulder.

Based on the RNG k- model, the finite volume model of friction stir welding of Ti6Al4V alloy is established by ANSYS FLUENT software. The effect of rotational tool geometry on titanium alloy flow behaviour is exhibited. The results of numerical simulation show that the flow direction of material near the rotational tool is the same as that of the rotational direction of the rotational tools.. The flow velocity of material near the rotational tool is much bigger than that of other regions in a weldment while the peak value appears near the shoulder edge. Changing either the rotational tool shoulder diameter or the pin tip diameter, the flow direction of material during the welding process will always remain unchanged. With an increase of the shoulder and pin tip diameter, the material flow velocity increases. However, from the point of view of elimination of root defects, increasing the diameter of the pin tip is better than increasing the diameter of the shoulder.