Influence of Water Environment on Microstructure and Droplet Transfer Behavior of Magnetically Controlled Plasma-FCAW Underwater Hybrid Welding

Magnetically controlled plasma-flux cored arc welding (Plasma-FCAW), as an efficient hybrid arc welding method, is characterized by excellent deep penetration and low spatter. However, the welding process is susceptible to disturbances due to the complex underwater environment. To address this issue, a self-developed electromagnetic excitation device was used in this study to apply a transverse magnetic field to the underwater hybrid Plasma-FCAW process. This magnetic control facilitated flexible coupling between the two arcs, thereby effectively improving the stability of the hybrid welding process and the weld bead formation. On this basis, welding process experiments were carried out in water environment with different salinities and temperatures. The influence of the water condition on droplet transfer behavior, weld formation, as well as microstructure and properties was studied. The results show that increased salinity shortens the droplet transfer cycle, raises the cooling rate, and reduces the weld width. Water temperature significantly affects arc stability and droplet transfer behavior: the droplet transfer cycle shortens at low temperature, while it becomes irregular at high temperature. Both increased salinity and decreased water temperature increase the content of side-plate ferrite and acicular ferrite in the weld zone. In contrast, higher water temperature increases the pearlite content in the heat-affected zone, thereby affecting the hardness of weld.