| The thick plate welding is often used in shipbuilding, aerospace and automotive industries and so on. The technology of the ultra narrow gap laser-arc hybrid multi-pass welding has unparalleled advantages. In the hybrid welding process of thick plate, the difficulty lies in the control of stability. Therefore, the technology process of ultra narrow gap laser-arc hybrid multi-pass welding was deeply studied, and the microstructure and mechanical properties of the weld joints were also analyzed.Firstly, the influence of groove gap on the weld formation need to be analyzed, leading to conclusion that the more narrow groove gap can obtain better weld formation in the reasonable process parameters which the width is 1mm and the groove angle is 4 degrees. Thus in 16 mm thick plate, the first pass welding reasonable parameters is obtained that current and welding speed are the main factors affecting the weld forming, the DLA and defocus are less significant. However, the laser power is 2.5Kw, the microstructure can improve the mechanical properties of welding joints. Finally the welding of 30 mm thick plate was completed successfully.After the welding, microstructure of each region was observed. The weld microstructure is mainly composed by ferrite and pearlite, but the arc area is the columnar dendrite, and the laser area is the relatively small columnar crystal, the central area is the fine equiaxed dendrite. The microstructure of HAZ consists of coarse grain zone, fine grain zone and incomplete recrystallization zone. The organization of the remelted zone is ferrite, but the grains can be refined, which reduce the hardness of the welding joints effectively. The highest hardness in weld joint center is coarse grain region, and the both sides of the remelted zone are the softening regions, but according to the tensile properties test, this region will not be the weakness of the joint. So, the experiment on multi-pass laser-arc hybrid welding is feasible. |
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