Study on the influence of Al-Si welding wire on porosity sensitivity in laser welding and process optimization

Al-Si welding wire is commonly used in the aluminum alloy welding due to the excellent heat crack-resistance and corrosion-resistance, but the presence of large-sized pores hinders its widespread application in the field of laser welding. This study focuses on the cause of pores formation in the laser welding using Al-Si wires with different Si contents and investigates the dynamic behavior of laser keyhole by a high-speed camera-based molten pool monitoring system. The results showed that with the increase of wire Si content from 5% to 12% (wt. %), the keyhole stability decreased and the weld porosity increased. According to the thermodynamic calculations, the increased Si content enhanced the Reynolds number of molten pool, resulting in increased turbulence tendency. It caused the molten pool being more susceptible to external disturbances, which decreased the stability of keyhole. Furthermore, the reduced dynamic viscosity of molten pool increased both the depth-to-width ratio of keyhole and its opening and closing frequency. These combined effects ultimately contributed to the increased susceptibility to pores formation. Based on the above results, a circular oscillating laser was introduced to guide the regular flow of molten pool. The beam oscillation improved the resistance to fluctuations of molten pool and reduced the depth-to-width ratio of keyhole. Besides, the high-frequency rotating keyhole could capture and re-melt the formed pores. An optimal laser oscillating welding was determined using response surface methodology to control the porosity within the acceptable range.