Effects of different shielding gases and power waveforms on penetration characteristics and porosity formation in laser welding of inconel 690 alloy

Abstract

A high power Nd-YAG laser was used to perform bead-on-plate (BOP) welding on high viscosity Inconel 690 alloy plates of 3 mm in thickness with three different shielding gases (Ar, He, and N2). Adopting a rectangular laser power waveform, four different peak-base power differentials (ΔP) were applied with a constant average power of 1.5kW. A comprehensive investigation was performed into the influences of the shielding gas, the flow rate, and the value of ΔP on the characteristics of the resulting welds, including the weld morphology, the penetration depth, the plume volume, and the porosity formation. The results showed that the weld penetration depth, the depth-to-width ratio, the weld surface roughness and the degree of weld spattering all increased with increasing ΔP. The choice of shielding gas had a significant effect on the porosity ratio (Pr) of the weld. The weld formed under Ar shielding had the highest Pr, while that formed under N2 shielding had the lowest. Under He shielding, the gas flow rate had a significant effect on the porosity ratio. However, under the higher density gases of Ar and N2, the porosity appeared to be insensitive to the flow rate. Finally, an increased ΔP yielded a significant reduction in Pr for the welds with higher porosity. © 2007 The Japan Institute of Metals.