Tailoring droplet transfer and molten pool flow during hybrid laser arc welding of nickel base alloy

• Welding seams with nickel base alloy filler metal was fabricated by novel hybrid laser arc welding. • Three-dimensional reconstruction and trace line extraction were utilized to characterize the weld formation of high viscosity nickel base alloy. • The stability of droplet transfer and molten pool flow was improved under arc leading mode and reasonable arc energy ratio. • The sufficient growing, necking and detaching of droplets under stable molten pool flow realized the best short-circuit transfer. Hybrid laser arc welding 9 %Ni steel with nickel base alloy C-276 was fabricated with different leading modes and energy ratios. Weld seam characteristics, formation stability and droplet transfer were investigated by three-dimensional reconstruction, electric signals and high-speed images with the increased arc energy ratio in laser leading mode and arc leading mode. The results showed that arc leading mode was better. The weld seam was smooth and sound, without hot cracks and spatters under reasonable arc energy ratio (#5 parameter). Three-dimensional reconstruction results indicated that the welding toe trace line was straighter in arc leading mode and the standard deviations of weld toes and peak trace line were 0.157, 0.160 and 0.116, respectively. The droplet bottom blasted to form forward spatters, resulting in depressions in the weld toe in laser leading mode. Short-circuit transfer was obtained in arc leading mode. The short-circuit behavior was accompanied with explosion because of the low electromagnetic contraction force at low arc energy ratio. A smooth short-circuit transfer occurred as the arc energy increased. With the further increase of arc energy ratio, the spatters were obvious due to large hindering forces. This indicated that hybrid laser arc welding of nickel base alloy was feasible.