Numerical Investigation on Thermal Fluid Flow-Induced Porosity During EBW of Aluminum Alloy

This study proposes a novel dynamic composite heat source combining discrete tracking and vapor heating, which can precisely capture the transient energy deposition at the keyhole wall, and further discusses the formation mechanism of weld defects by investigating keyhole evolution and melt pool flow behavior. The weld morphology and dimensions predicted by the simulation are in good agreement with the experimental data, revealing the coupled mechanism between keyhole instability and porosity formation, as well as the generation mechanism of process-type porosity mainly influenced by the keyhole dynamic characteristics and the melt pool flow field together; specifically, keyhole instability forms a vapor cavity that will generate bubbles to participate in melt pool flow if it cannot be re-fused with the keyhole, and the bubble trajectory is related to buoyancy, gravity and liquid flow in the melt pool, with larger bubbles less likely to escape due to greater liquid viscous force. In addition, this study finds that increasing weld power and weld speed helps improve keyhole stability, weaken melt pool circulation intensity and shorten bubble escape path, thereby fundamentally revealing the formation mechanism of porosity defects during electron beam welding (EBW) of aluminum alloy, providing an effective numerical tool for optimizing EBW process parameters, and proposing corresponding inhibition measures to improve weld quality.