Effect of forging pressure on microstructural characteristics and tensile properties of linear friction welded Ti-6Al-4V alloy joints

Abstract

Ti-6Al-4V (also called as Ti64) is often used in the aerospace applications for its high strength to weight ratio. Ti64 can be welded by almost all the fusion welding processes but it led to the development of coarse-grained microstructure in the fully deformed zone, severe deformation, and high residual stresses. To reduce these complications, solid state welding processes are now adopted in the aerospace industries because it avoids total melting of materials and provides finer grain structures in the nugget region. Among different solid-state techniques, linear friction welding (LFW) is highly suitable to join the blade to disk assembly in the next generation aero engines. In order to get a joint with higher efficiency, the process parameters such as oscillating frequency, friction pressure, friction time, forging pressure and forging time are to be optimized. Hence, in the current investigation an effort has been made to study the effect of forging pressure on microstructure and tensile properties of LFW Ti64 joints. The tensile strength of the joints was evaluated as per the ASTM standards. The microstructure of various regions of welded joints was examined using optical microscopy (OM) and scanning electron microscopy (SEM). From this study, it is understood that wider interface is observed for lower forging pressure and decrease with increase in forging pressure. The tensile strength increases with increases with forging pressure and it gradually decreases over increasing the forging pressure. The microstructure shows evidence of fine structure in the weld region i.e., FDZ. The TMAZ region of the grain is plastically deformed and reoriented in the direction of the friction motion.