Evaluation of the effect of filler metal interlayer on the weld joint quality in fiber laser welding of alloy steel (A516)

Laser welding of A516 steel was performed using the filler metal to serve as the interlayer. The effects of laser welding parameters on the melt pool microstructure, weld bead shape, dimensions of the melt pool, and temperature field around the melt pool were investigated. The results indicated that the nozzle distance had the most significant influence on the temperature around the molten pool. As the maximum energy of the laser beam was irradiated on the center of the filler, the highest value of the temperature near the fusion zone was about 360°C. The welding speed, determining the overlap factor, had a considerable effect on the weld bead shape. The laser power, therefore, could determine laser beam line energy to melt the filler volume effectively. Enhancing the laser power up to 450 W increased the temperature to about 300 °C; also, the melting rate of the filler used was almost completed and the weld bead appearance was clearly improved; therefore, the width of the melt pool was increased by about 10%. Increasing the nozzle distance from 3 to 7 mm also reduced the width of the molten pool by about 75% and 40% with and without the filler, respectively. By using the filler metal, the geometry of the welding bead changed from a concave one to a convex one. The major fusion zone microstructure of the fusion zone was an acicular ferrite characterized by needle-shaped ferrite crystallites.