Abstract:A two-dimensional mathematical model based on volume-of-fluid method is proposed to investigate the heat transfer, fluid flow and keyhole dynamics during electron beam welding (EBW) on 20 mm-thick 2219 aluminum alloy plate. In the model, an adaptive heat source model tracking keyhole depth is employed to simulate the heating process of electron beam. Heat and mass transport of different vortexes induced by surface tension, thermo-capillary force, recoil pressure, hydrostatic pressure and thermal buoyancy is coupled with keyhole evolution. A series of physical phenomena involving keyhole drilling, collapse, reopening, quasi-stability, backfilling and the coupled thermal field are analyzed systematically. The results indicate that the decreased heat flux of beam in depth can decelerate the keyholing velocity of recoil pressure and promote the quasi-steady state. Before and close to this state, the keyhole collapses and complicates the fluid transport of vortexes. Finally, all simulation results are validated against experiments.

Key words: heat transfer; fluid flow; keyhole dynamics; electron beam welding; mass transport; vortex; recoil pressure; backfilling