Effects of oscillation amplitude and frequency in narrow-gap laser wire-filling welding of Al alloy 5A06 on the melt pool and the mechanism of pore inhibition

This study investigates molten pool dynamics and keyhole behavior in narrow-gap oscillating laser wire welding of 5A06 aluminum alloy through numerical simulation and experimental validation. The developed Flow-3D model accurately characterizes molten pool morphology and flow characteristics. Under narrow-gap constraints, conventional laser welding generates strong rear vortices that destabilize the keyhole wall, leading to bubble nucleation. These bubbles become trapped at solidification fronts due to complex melt flow, forming porosity defects. Comparative analysis reveals circular laser oscillation effectively reconstructs molten pool flow patterns by expanding the keyhole opening diameter and reducing the metal vapor jet impact, significantly improving keyhole stability. The study demonstrates critical effects of oscillation parameters (amplitude A, frequency f) on defect control. When A<0.6 mm, insufficient stabilization results in porosity levels (≈8.2 vol%) comparable to non-oscillating conditions. At A≥1.2 mm and f ≥ 150Hz, periodic keyhole motion actively captures and removes bubbles through the keyhole channel. A porosity suppression threshold model was established based on molten pool flow analysis and bubble trajectory tracking, incorporating maximum capture distance and keyhole dynamic characteristics. This model provides theoretical guidance for process optimization in narrow-gap laser welding applications.