Effect of laser welding process on the microstructure, mechanical properties and residual stresses in Ti-5Al-2.5Sn alloy

•Pulsed LBW was performed on thin Ti-5Al-2.5Sn alloy sheet.•Weld pool width and oxygen contents were dependent on peak power and pulse energy.•Increase in Vickers hardness of FZ due toα′ martensitic microstructure.•Maximum residual stresses were 100MPa and of compressive nature.•Tensile properties were not influenced by the presence of residual stresses. Pulsed Nd-YAG laser was employed in bead on plate configuration for welding of 1.6mm thick Ti-5Al-2.5Sn alloy sheet. The effect of laser processing parameters on the weld pool shape, pulse overlap, oxide formation, and microstructure were studied using scanning electron and optical microscope. It was found out that laser peak power had a significant influence on the FZ oxygen contents and grain size whereas, both peak power and heat input per unit length were important in defining the weld pool shape. Processing parameters for full penetration welds with acceptable joint properties and low oxygen contents were selected for further study in terms of residual stresses and mechanical properties. Formation of acicular α and α′ martensite in fusion and heat affected zone, led to an increase in microhardness by about 55 HV0.2 as compared to base metal. Induced residual stresses were found to be significantly less than the yield strength resulting in plate deformation less than 1mm. Transverse residual stresses present at different depths below the surface tend to counter effect each other resulting in tensile strength of welded specimen becoming nearly equal to that of the base metal.