| Autogenous laser welding is widely recognized as an important joining technology in diverse industries due to its advantages, such as less distortion, higher welding speed, deeper weld penetration, and ease of automation. It is mainly used to join the thin metal sheets like zinc-coated steel plates and alluminium alloys. In the case of welding of thick plates, autogenous laser welding is often disadvantageous. Limited by the laser power, a full weld penetration is hard to obtain in a single pass. The small laser focal spot restricts the gap tolerance of autogenous laser welding. The preparation of coupons is more complicated, leading to an increase in the manufacturing costs. Another disadvange of autogenous laser welding is its high cooling rate that likely causes an excessive hardening and high residual stress in the weld zone. The crack-susceptible metals are prone to produce the solidification cracks because of its rapid cooling rate in combination with its large depth/width ratio. Filler materials and an additional heat source are required to increase the weld penetration of autogenous laser welding, improve its gap bridging capability, and slow its cooling rate.;Laser welding assisted by a hot wire is one of promising solutions. The mechanical and microstructural properties of the welds could be adjusted by using an additional heat source and by selecting the proper filler wire. In order to study its welding characteristics, the dynamics of the molten pool during welding were visualized by using a high-speed charge-coupled device (CCD) camera assisted by a green laser. The effects of welding parameters, such as the position of the hot-wire tip with respect to the laser focal spot and the hot-wire voltage, were investigated to obtain sound welds with good quality. The temperature field and thermally-induced residual stress of laser welding assisted by a hot wire was investigated by using the FE method. An X-ray diffraction technique was used to measure the residual stress at the weld beads, and to verify the numerical results. The verified numerical results provided detailed information about the evolution and distribution of the residual stress during welding. The advantages of laser welding assisted by a hot wire were also investigated.;Hybrid laser-arc welding is another promising method to mitigate the disadvantages of autogenous laser welding. The synergetic effect between laser beam and electrical arc was investigated by using a spectral diagnostic technique assisted by a high-speed CCD camera. The spectrometer was used to study the plasma characteristics of the hybrid laser-arc welding. The CCD camera was applied to make the welding process visible and to monitor the interaction between laser beam and arc. The effects of two welding parameters on the synergistic effect, the welding current and the offset distance, were studied. Optimal values of the offset distance and welding current were found to obtain the maximum weld penetration. The effect of the arc on the mechanical and microstructural properties of the in the hybrid laser-arc welds was also studied. By using a 10 kW disk laser, hybrid laser-arc welding was used to weld the 17-4 PH stainless steel plates in a thickness up to 19 mm. The welding procedure was optimized to achieve the full weld penetration in a single pass. The effects of the welding parameters on the formation of porosity were investigated. The microstructural evolution and cracking susceptibility of 17-4 PH SS welds were studied to remove the solidification cracks along the weld centerline. |
