Study of microstructure, mechanical properties and residual stresses in full penetration electron beam welded Ti-5Al-2.5Sn alloy sheet

Protection of the molten pool from gaseous contamination has always been of prime importance in welding of titanium alloys. A vacuum environment in electron beam welding serves this purpose and eliminates the use of shielding gas during the joining process. However, this may lead to variation in microstructure, mechanical properties, residual stress distribution and distortions compared to the widely used laser and TIG welding operations. In the present work, EBW was used to weld Ti-5Al-2.5Sn alloy sheet with welding current ranging from 14 mA to 20 mA. Owing to vacuum environment, oxygen contents in the fusion zone were very low for all the welding currents. However, welding current had a significant influence on the weld pool width, micro-hardness and grain size in the FZ. A complete martensitic transformation was not observed in the FZ at any of the welding currents used. Furthermore, maximum residual stresses upto 280 MPa (compressive) and 320 MPa (tensile) were found in the longitudinal direction near the weld centerline. The measured high residual stresses, distortions and partial martensitic transformations in FZ were attributed to a reduced cooling rate due to the absence of shielding gas in electron beam welding. (C) 2017 Elsevier Ltd. All rights reserved.