Influence of Ultrasound on Pore and Crack Formation in Laser Beam Welding of Nickel-Base Alloy Round Bars

Abstract

Welding by laser beam is a method for creating deep and narrow welds with low influence on the surrounding material. Nevertheless, the microstructure and mechanical properties change, and highly alloyed materials are prone to segregation. A new promising approach for minimizing segregation and its effects like hot cracks is introducing ultrasonic excitation into the specimen. The following investigations are about the effects of different ultrasonic amplitudes (2/4/6 µm) and different positions of the weld pool in the resonant vibration distribution (antinode, centered, and node position) for bead on plate welds on 2.4856 nickel alloy round bars (30 mm diameter) with a laser beam power of 6 kW. The weld is evaluated by visual inspection and metallographic cross sections. The experiments reveal specific mechanisms of interaction between melt and different positions regarding to the vibration shape, which influence weld shape, microstructure, segregation, cracks and pores. Welding with ultrasonic excitation in antinode position improves the welding results.

Investigations on the Specifics of Laser Power Modulation in Laser Beam Welding of Round Bars

“…The distance to each other and to the specimen is 50 mm aiming above the specimen to reduce the keyhole's gas plume and at the specimen bottom for cooling and melt drop prevention since the gas jet fans out. The general parameters have been determined by previous investigations [22][23][24] at 8 kW average welding power and 0.95 m/min welding speed.…”

Suppression of Bottom Porosity in Fiber Laser Butt Welding of Stainless Steel

“…Lei et al [16] suggested that the porosity at the weld seam is greatly improved by the cavitation and acoustic streaming of the ultrasonic vibration on the weld pool in ultrasound-assisted laser welding of AZ31B magnesium alloy. Grajczak et al [21] found that porosity can be eliminated when the weld pool is located in the antinode position during ultrasound-assisted laser welding of nickel-based-alloy round bars. He and Shen [17] analyzed the effects of different welding positions on porosity in laser welding of aluminum alloys and observed the minimal porosities in vertical down welding, with high stability of the keyhole.…”