Product Code: JLA_6_4_223

Authors:
G. J. Shannon
J. Watson
W. F. Deans
Department of Engineering, Laser Laboratory, Kings College, University of Aberdeen, Aberdeen, U.K.

An investigation was undertaken using a 1.2 kW carbon dioxide laser for underwater butt welding of BS 4360 43A and 50D steel, in order to assess the quality of the welds and to achieve an understanding of the laser/water/material interaction. Using a high‐speed camera, the temporal behavior of the melt pool and “plasma” dynamics surrounded by an aqueous environment were monitored. Experiments were undertaken to characterize the attenuation of the laser beam in the water as a function of various focal length optics and depth of water. The effect of energy input conditions on the weld bead appearance and mechanical properties were also examined. The interaction of the laser beam with water produced a wave‐guiding mechanism in which the focused beam instantaneously vaporizes the water and directs the beam on to the workpiece. The underwater weld beads exhibited sound microstructures over a range of weld energy inputs, mainly due to the formation of a “dry region” during welding. Metallurgical analysis of the welds showed a slight increase in hardness, though other post‐weld mechanical strengths were similar to in‐air results.