Effects of pulsed and continuous Nd–YAG laser beam waves on welding of Inconel alloy

Abstract

In the present work a 2·5 kW high power Nd–YAG laser is used in the bead on plate (BOP) and butt welding of Inconel 690 plates of thickness 3 mm. Welding is performed using a rectangular laser pulse, for which the peak to base power ratio Wr is reduced from an initial value of 10 to a value of 1, maintaining an identical mean power of 1·7 kW. Therefore, the welding mode changes from a pulsed wave to a continuous wave. The BOP results indicate that the depth of the weld penetration increases at a lower travel speed and/or a higher value of Wr. In the butt welding process, as Wr is increased from 1 to 10, the cellular microstructure of the weld remains relatively unchanged, but the macroporosity formation ratio decreases from 7·1% to 0·6%. At low values of Wr, macroporosity is identified primarily in the root region. However, as Wr increases, the associated periodic high power increases the agitation of the molten pool and probably causes bubbles to float upwards. Consequently, at higher values of Wr, the regions of macroporosity are distributed randomly throughout the weld. Although microcracks are not apparent within any of the welds, each weld exhibits slight microporosity. This microporosity decreases as Wr increases. The present results confirm that a pulsed laser beam with an appropriate peak power can be used to achieve a compromise between the mechanical properties and surface roughness of the weld for Inconel 690 in Nd–YAG laser welding.