The Influence of Different Oscillation Paths on the Microstructure and Properties of Laser-Welded Joints of Al-Si-Coated 22MnB5 Steel

The Al-Si coating coated on press-hardened steel brought problems such as element segregation, weld softening, and poor mechanical properties to laser-welded joints. The influence of different oscillation paths on the microstructure and properties of laser-welded joints of Al-Si-coated 22MnB5 steel were studied. The findings indicated that the concave degree of the upper surface of the weld with circular path was significantly smaller than that of the linear path, the "8" path, and the "infinity" path. The microstructure of the welds under the four paths calculated by Pandat software was martensite and ferrite, which was consistent with the experimental results. Compared with the linear path, "infinity" path, and "8" path, the oscillating laser beam with circular path caused the fluid in the molten pool to form a stable eddy current effect along the oscillating direction, which promoted the diffusion of Al. The content of alpha-ferrite in the weld with circular path was reduced to 7.8%, and the tensile strength of the welded joint exceeded 1500 MPa. During the tensile process, the cracks in the weld originated at the interface of large-size alpha-ferrite and martensite near the weld surface. Except for the circular path, the main crack in the weld under the other three paths formed branching cracks toward the enrichment of ferrite. The fracture of the weld under the four paths was composed of cleavage surface and small dimples, but the ductile zone of the fracture with circular path was significantly bigger than that of the other three.