Investigation on Metallographic Analysis of Electron Beam Ti6Al4V Alloy Welds

Abstract

Electron beam weld quality is evaluated by careful selection of weld parameters and by control of the temporal distribution of electron beam on surface of work piece. Moreover, the integral effect of the electron beam current and weld velocity on weld joint is significant during electron beam welding (EBW) process. In the present work, bead-on-plate EBW of Ti6Al4V alloy plates of 5 mm thickness is carried out to examine the influences of various process parameters with respect to microstructure evolution and weld bead shapes and dimensions. Also, a relationship among input thermal energy, macro- and microstructural characteristics of electron beam Ti6Al4V alloy weldments is established. The experiments were carried out with beam current ranging from 15 to 30 mA and welding velocity from 1200 to 1400 mm min−1. Moreover, a constant focus current and accelerating voltage of 2030 mA and 60 kV are considered. Furthermore, welding modes such as melt-in and keyhole modes are examined with respect to the linear energy and welding process efficiency along with microstructure evolution. In addition, the magnitude of temperature in the heat-affected zone of electron beam welded Ti6Al4V alloy samples is determined using Rosenthal’s analytical model at distinct weld regimes. Furthermore, Marangoni and Fourier numbers are employed to investigate weld pool characteristics at distinct weld regimes. Based upon the results, it is observed that electron beam power has a significant influence on weldment profile and penetration level while the welding speed has a noteworthy impact on the solidified structure of fusion zone. Also, three weld regimes were identified under the specified welding conditions. Keyhole mode welding is achieved for linear energy above 77 J mm−1, and melt-in mode welding is attained when linear energy is below 45 J mm−1. Moreover, transition mode welding is identified when the linear energy is in between 56.57 and 75 J mm−1. Furthermore, the efficiency of welding process was assessed by relating electron beam power with fusion zone area. It was recognised that a higher linear energy promoted a higher process efficiency comparative to a lower linear energy. A lower linear energy promoted a rich domain of acicular \(\alpha^{1}\) solidified structure in the fusion zone when compared with higher linear energy. Moreover, the integrity of bead-on-plate welds of Ti6Al4V alloy is of sound quality and without any internal weld defects.