Influence of tack operation on metallographic and angular distortion in electron beam welding of Ti-6l-4V alloy

Abstract

Electron beam welding process is one such advanced fusion welding technique that fabricates structural parts with high dimensional precision and induces minimum thermal stresses and distortion. However, with incorporation of tack procedure prior to full pass electron beam welding process the effect of distortion and stresses in welded parts is lowered significantly. In the present work, an attempt has been made to investigate the effect of incorporation and elimination of tack operation prior to full pass electron beam welding process in 5 mm thick butt-jointed Ti6Al4V alloy plates. The influence of electron beam current is analyzed for tack and full pass electron beam welding procedures with an aim to produce full penetrated defect free weld joint. The characteristics difference in terms of macro and microstructural properties, microhardness distribution and welding induced angular deformation is evaluated for electron beam welded specimens. It is found that the weld width, undercut defect, and angular deformation was reduced by 7.6%, 4.2%, and 22%, respectively due to incorporation of tack procedure prior to full pass welding operation. The refined martensitic phases were observed in the fusion zone of tack welded specimens due to solidification process which enhanced the hardness of the joints. Moreover, finite element results revealed that induced thermal stresses are highly localized and longitudinal stress is more prominent across the weld joint. The angular deflection and plastic strain magnitude is estimated to be lower in specimens that are joined initially with tack operation. Moreover, the numerically computed angular deflection magnitude validates well with the experimentally measured deflection values.