Influence of weld parameters on weld regimes and vaporization rate in electron beam welding of Ti6Al4V alloy

Abstract

Electron beam welding (EBW) is the most preferable and efficient joining technique to weld titanium alloys, since it provides a vacuum atmosphere and eliminates the use of shielding gas during the welding process. The present work is focused on understanding the electron beam weld parameters which controls the weld limits, microstructural and mechanical properties and vaporization rate of metal elements in the Ti6Al4V alloy. The influence of power density on characteristics of electron beam welded Ti6Al4V alloy at constant linear energy conditions is examined. The welding experiments were performed to evaluate the weld geometry, weld regimes, microstructural properties and microhardness characteristics using fundamental parameters such as power density and interaction energy per unit volume (IE). Moreover, the vaporization heat transfer model of the EBW process is developed by employing Fourier’s law of heat conduction to estimate the vaporization rate of Ti6Al4V alloying elements. The rate of vaporization of major alloying elements of Ti6Al4V is analysed with respect to power density. Based upon the results obtained, it is witnessed that the weld bead geometry, weld limits and grain size are controlled by power density for constant linear energy conditions. Also, the solidified microstructure in the weld zone at different power density significantly effects the final strength of the weld joint. The conduction and keyhole weld limits are identified for power density values below 0.31 W cm−2 and above 2.12 W cm−2, respectively. The transition mode welding in the Ti6Al4V alloy is identified by a nominal increase in aspect ratio for a wide range of power density and IE values. The results also established that the size of β grain in the fusion zone reduces with increase in power density at constant linear energy condition. Also, the average α1 martensitic grain size in the weld zone is determined to be higher in keyhole welds (128 µm) relative to conduction welds (48 µm) on account of higher solidification rate. In effect, the solidified martensitic phases influence the microhardness distribution proportionately across the weld sample of Ti6Al4V alloy. Vaporization of metal elements of the Ti6Al4V alloy is induced in few milliseconds and evaporation rate of ‘Al’ element is least followed by ‘Ti’ and ‘V’ elements. It is also observed that by reducing the power density from 2.54 to 2.12 W cm−2, keyhole mode welding can be acquired and vaporization rate of ‘Al’ is reduced by 20.5%.