OBRABOTKAMETALLOV Vol. 24 No. 4 2022 technology Ta b l e 2 Chemical composition of ZhS6U alloy, wt. % Fe Nb Ti Cr Co W Ni Al Mo Si Rest ≤ 1 0.8–1.2 2–2.9 8–9.5 9–10.5 9.5–11 54.3–62.7 5.1–6 1.2–2.4 ≤ 0.4 ≤ 0.6 To prevent intensive oxidation of titanium alloy as a result of thermomechanical effect of the tool, welding was carried out in a shielding argon atmosphere, fed under pressure through a nozzle into a welding zone. Cooling fluid was supplied and removed into the inner cavity of the tool to increase its durability. The schematic of the friction stir welding process is shown in Figure 1. Welding of specimens was carried out according to the modes given in Table 3. The axial force on the tool was varied from mode to mode; moreover the axial forces during penetration of the tool in material FPN and tool motion in the welding direction FW were different. The tool rotation frequency ω and the welding speed V were constant while changing modes. A length of the received weld seams for each mode was 100–180 mm. In order to form a titanium alloy layer on the working surface of the welding tool, a preliminary pass was made by the tool in the material to be welded at a length of 25 mm before welding the experimental specimens. Preliminary pass parameters were: axial forces FPN/FW = 2,300/2,600 kg, frequency of the tool rotation ω = 375 rpm, welding speed V = mm/min. All samples of weld joints were cut by EDM method in the direction transverse to the welded joint so that it was located in the middle part of the specimen. Samples for metallographic studies were grinded, Fig. 1. Schematics of friction stir welding process Ta b l e 3 Modes of Ti-5Al-3Mo-1V alloy friction stir welding No. FPN, kg FW, kg ω, rpm V, mm/min 1 2,300 2,600 375 86 2 2,500 2,800 375 86 3 2,700 3,000 375 86
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