Laser welding with filler wire was applied to Q345D in a narrow gap under ultrasonic assistance, and the dynamic characteristics of plasma were studied by high-speed imaging and spectral acquisition. The results showed that the plasma area decreased gradually with increasing distance between the ultrasonic loading position and welding seam. The electron density and temperature of the plasma with ultrasonic assistance were higher than those without ultrasound. The electron density was approximately 1016~1017 cm-3, and the plasma temperature was approximately 4000~6000 K. Ultrasonic assisted laser wire filling welding can bring about cavitation effect and significantly reduce the porosity problem.
Keywords: narrow-gap laser welding with filler wire; plasma electron density; plasma morphology; plasma temperature; ultrasonic assisted.