OBRABOTKAMETALLOV technology Vol. 24 No. 4 2022 polished and etched. Metallographic research was carried out on a metallographic microscope Altami MET1C, confocal microscope Olympus LEXT OLS4000, as well as on a scanning electron microscope Microtrac SEM with energy dispersive X-ray microanalyzer “IXRF systems”. Static tensile tests were carried out on a universal testing machine UTS 110M-100 with a strain rate of 1 mm/min. When cutting out samples for testing, the welded joints were conveniently divided by length into 4 sections: 0–25 mm, 25–50 mm, 50–75 mm and 75–100 mm. Samples for tests were cut from each of the above-mentioned sections of the joints. Results and discussion Figure 2 shows cross-sectional images of the macrostructure of welded joints obtained by metallographic techniques. As a result of etching, three material zones are clearly identified in the structure of the welded joint: bulk material zone (BM), heat-affected zone (HAZ) and stirred zone (SZ). The heat-affected zone consists of not crystallized and partially deformed grains. Microstructure analysis of the stirred zone of welded joints showed that the material of this zone consists of fragmented and recrystallized grains of titanium alloy. In addition, it should be noted that, with other constant parameters of the welding mode, an increase in the axial force on the tool leads to a decrease in the grain size of the stirred zone (Fig. 3). This is a positive effect that contributes to the hardening of the stirred zone of the welded joint according to the Hall-Petch mechanism. Fig. 2. Macrostructure of FSW joints of Ti-4Al-3Mo-1V alloy, obtained by modes 1–3, in the transverse direction Fig. 3. Stirred zone (SZ) of FSW joints of Ti-4Al-3Mo-1V alloy, obtained by modes 1–3
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