Laser-laser hybrid welding for joining of challenging materials

Modern steels containing micro-alloying constituents offer improved performance due to greater strength to weight ratio, but they are more challenging to weld and require costly post weld heat treatment. Lasers with their flexibility in terms of delivered energy can be used as a very versatile heat source where the energy can be tailored spatially and temporally according to the needs of a particular material. Normally laser welding is used in deep penetration regime to improve productivity, but in alloyed steels this leads to high cooling rates and unacceptable mechanical properties. A laser-laser hybrid welding process with two independent laser beams, combining the deep penetration capability of keyhole welding and the smooth bead profile of conduction regime, was developed in this work. The power density and the total applied energy of each laser beam could be controlled independently to tailor the transient thermal cycle during the welding process. Thick section welds were produced with better weld profile, tolerance to fit-up and control of microstructural constituent compared with standard single-beam laser welding. The process also enables efficient addition of filler wire with better meltpool stability, and lower spatter than standard laser-arc based hybrid processes. In addition, it has been demonstrated that, by changing the laser application modes, the same laser setup can be used to apply in-situ heat treatment to welded components.