Effects of sidewall grain growth on pore formation in narrow gap oscillating laser welding

How to suppress the pores is one of the most important challenges in narrow gap laser welding of aluminum alloys. In order to solve this question, narrow gap oscillating laser welding (O-NGLW) of dissimilar AA6061 and AA2024 aluminum alloys was carried out. With the increase of the laser oscillation frequency (f), the pores changed from the dense and linear chain at weld center to the scattered distribution segregating at AA2024 side, and disappeared when f ≥ 400 Hz. The normalized calculated stirring Reynolds number of O-NGLW was 1369 when suppressing the pores totally, 1.39–1.75 times that of the welding without narrow gap, indicating that a stronger stirring effect induced by laser oscillation was needed to capture the bubbles. The theoretical analysis suggested that this phenomenon was closely related to the effect of columnar grains growth on bubble interception (ECGGBI). Based on the interaction between ECGGBI and the stirring effect induced by laser oscillation, the pore formation was discussed, and the reason why stronger stirring effect was needed to suppress the pores was revealed.