X. Cao, M. Jahazi, NRC Institute for Aerospace, Montreal, QC, Canada; J. Cuddy, A. Birur, Standard Aero Ltd, Winnipeg, MB, Canada
Ti-6Al-4V is the most widely used titanium alloy and falls in the α + β category. Due to its high strength and light weight, along with good tensile and creep properties up to about 300ºC, it is widely used for turbine disks, blades, and airframe structural components. Conventionally, TIG and plasma arc welding techniques are used to weld titanium alloys. CO2 laser welding of Ti-6Al-4V alloy has also been reported. However, little has been published about the weldability of Ti-6Al-4V alloy using high power solid-state Nd:YAG laser. This work reports on the laser weldability of Ti-6Al-4V alloy with four thicknesses ranging from 0.8 to 3 mm using a 4 kW Nd:YAG laser welding system. The effects of main processing parameters including laser power, welding speed and defocusing distance on surface morphologies, welding defects, microstructure, microindentation hardness and tensile properties are investigated. The optimized process windows are determined indicating that Nd:YAG laser welding is an attractive method for Ti-6Al-4V alloy. However, the welding quality of the thinnest sheets is very sensitive to laser processing parameters and the right combination of laser power and welding speed is highly required. Very little porosity was observed in the welded joints of the thin sheets while more microporosity was observed in the thicker titanium alloy sheets. No detectable cracks are observed in all thicknesses used in the present study. The microstructure of the fusion zone revealed a needle-like martensite α’ structure formed from β phase due to the high cooling rate associated with laser beam process, leading to the increase of fusion zone hardness compared with the base metal. The microstructure of the heat-affected zone is a mixture of martenstic α’ and primary α. The effects of selected processing parameters on tensile properties are also discussed in detail.
Summary: The laser weldability of Ti-6Al-4V alloy with four thicknesses ranging from 0.8 to 3 mm was investigated using a 4 kW Nd:YAG laser welding system at various laser power, welding speed and defocusing distance. The welding quality was evaluated from surface morphologies, defects, microstructure, hardness and tensile properties.
