A comparison between LBW and hybrid laser-GMAW processes based on microstructure and weld geometry for hardenable steels

Welding processes are present in most industry sectors. Conventional arc welding processes, such as the gas metal arc welding (GMAW) process, have limitations when applied to join thick materials. In this scenario, the laser beam welding (LBW) process has proved to be an alternative to achieve high penetration depths, eliminating the need for joint beveling, although not without limitations. Proneness to surface and internal discontinuities are some of them. Recently, hybrid laser-arc welding (HLAW) process has come up as a promising joining process, combining the advantages of the GMAW and LBW processes on a single melting pool, counteracting defects, and enhancing process efficiency. Despite the high complexity of the hybrid process, its advantages derive not only from geometrical and mechanical issues but also from metallurgical features or characteristics. Twelve LBW and HLAW welding tests were performed using 5, 6, 7, 8, 9, and 10 kW of laser power. The HLAW results show higher robustness against weld defects, as well as greater penetration depths and bead widths then pure LBW. The microstructures in all regions of the welds were analyzed, showing their correlation between the welding parameters and processes performed. Due to a distinct thermal cycle resulting from the two simultaneous heat sources, the weld bead produced by the HLAW process presented reduction of 100 HV in the microhardness on the upper region and consequently reduction of its brittleness. The results obtained clearly indicate the metallurgical and operational advantages of the HLAW process compared with the individual LBW process.