Parametric optimisation and microstructural analysis on high power Yb-fibre laser welding of Ti–6Al–4V

• Underfill and root concavity defects were not observed under all welding conditions.
• Either reinforcement or excessive penetration was observed to a certain degree under all welding conditions.
• The level of porosity was less than the critical size limit under all welding conditions.
• No weld cracking phenomenon was observed but some embrittlement due to contamination was identified.

In this work thin sheets of Ti–6Al–4V were full penetration welded using a 5 kW fibre laser in order to evaluate the effectiveness of high power fibre laser as a welding processing tool for welding Ti–6Al–4V with the requirements of the aircraft industry and to determine the effect of welding parameters including laser power, welding speed and beam focal position on the weld microstructure, bead profile and weld quality. It involved establishing an understanding of the influence of welding parameters on microstructural change, welding defects, and the characteristics of heat affected zone (HAZ) and weld metal (WM) of fibre laser welded joints. The optimum range of welding parameters which produced welds without cracking and porosity were identified. The influence of the welding parameters on the weld joint heterogeneity was characterised by conducting detailed microstructural analysis.