OBRABOTKAMETALLOV technology Vol. 24 No. 4 2022 Fig. 6. Fracture surface characteristic images of FSW joints of Ti-4Al-3Mo-1V alloy Fig. 7. Tensile strength bar graphs of Ti-4Al-3Mo-1V alloy, obtained by modes 1-3 of secondary phases [12, 14]. Also with growth of the length of the welded joint a decrease in the value of the ultimate tensile strength along its length is registered. This may be related to the conditions for the removal of heat, which accumulates due to the low thermal conductivity of titanium alloys, or to the wear of the welding tool. The maintenance of high temperature in the welding zone provides the growth of number and size of particles of secondary phases that contribute to the softening of material. At the same time, the influence of the tool wear factor, in this case, is not significant, because the tool was previously covered with a layer of titanium alloy during the preliminary pass. In addition, visual inspection of the tool used for welding showed that there were no wear features on the tool surface, only a layer of titanium alloy adhesively bonded to the tool surface (Fig. 8). Thus, the tool made of heat-resistant alloy ZhS6U after welding joints from Ti-4Al-3Mo-1V alloy with a total length of more than 0.5 m, shows a sufficiently high resistance to associated temperature and mechanical loads and can be effectively used for FSW of titanium alloys.
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