Microstructure evolution and mechanical characterization of friction stir welded titanium alloy Ti–6Al–4V using lanthanated tungsten tool

Abstract: Friction stir welding (FSW) exhibits significant advantages to join titanium and its alloys compared to other welding methods. FSW of 3 mm thick titanium alloy Ti–6Al–4V sheets was carried out using a lanthanated tungsten alloy tool. The traverse speed was varied from 40 mm/min to 200 mm/min in steps of 80 mm/min by keeping other parameters constant. The microstructure evolution was observed using conventional and advanced characterization techniques. The micrographs revealed a fully developed lamellar structure at 40 mm/min and a recrystallized structure in rest of the joints. An increase in β phase was observed at HAZ while TMAZ showed a distorted structure. The average grain size was observed to reduce with an increase in traverse speed. No tool wear debris was observed in the stir zone while a worm hole defect was noticed at 200 mm/min. Ti–6Al–4V hardened..