Hybrid laser arc welding process evaluation on DH36 and EH36 steel

The effects of laser power, arc power, and laser-arc separation on the macrostructure, microstructure, and welding arc were characterized in hybrid laser arc welds on DH36 and EH36 steels. Experiments were done to study a range of arc and laser powers at a constant laser-arc separation and a range of laser powers and laser-arc separation at a constant arc power. High-speed video captured images of the welding in process, and arc voltage and current were also measured. Two distinct weld macrostructure morphologies were observed. The first had a uniform fusion zone, and the second had a two- part fusion zone with an upper laser and arc combined region and a lower laser-only penetration region at the root. This two-part fusion zone was only observed for partial joint penetration welds, and process parameter maps were made to define the windows for both morphologies. Complete penetration welds always exhibited a uniform fusion zone. Decreasing the laser-arc separation increased the total penetration of the uniform fusion zone welds and reduced the size of the laser-only penetration region in the two-part fusion zone welds. The formation of acicular ferrite was promoted by increasing the arc power and increasing the laser-arc separation. Laser power did not have a major effect on the weld metal microstructure. Small laser-arc separations and low laser powers added a low-frequency large globular/short circuiting metal transfer mode to the predominately spray arc. Welding with larger laser-arc separations and higher lasers powers did not exhibit this low-frequency transfer but did have a mid frequency small globular free-flight transfer that was not observed in the gas metal arc welding (GMAW) only arc.