Abstract
In order to adapt to the development trend of a lightweight automobile and meet the safety requirements of key automotive parts, it is necessary to study the relationship between microstructure and mechanical properties of the dissimilar and different thickness materials welded joint. In this work, a dissimilar welded joint of high strength vehicle steel ASSAPH440 with 2.0 mm thickness/galvanized cold rolled sheet DC52D+ZF45 with 2.6 mm thickness formed by CO2 laser welding was studied. The microstructure of the welded joint was analyzed by metallographic structure and mechanical properties were discussed in terms of their tensile strength and microhardness. The results indicated that a high-quality welded joint with an average tensile strength of 643 MPa and an elongation of 22.7% was obtained at a welding speed of 30 mm s−1 and the laser power of 2200 w in CO2 laser welding, the tensile strength of laser welded joint was more than that of the both based metals. The center of the welding seam was composed of slender lath martensite with a few small white pieces of ferrite. The microstructure of the Heat Affected Zone (HAZ) on the DC52D+ZF45 side was smaller than that of the HAZ on the ASSAPH440 side, and its mechanical properties were superior. The highest microhardness was obtained at the center of the cross section of the welding seam, and the microhardness of the welding seam on the DC52D+ZF45 side was higher than that of the welding seam on the ASSAPH440 side. The tensile fracture appeared at the base metal of DC52D+ZF45 steel as a result of the strength of ASSAPH440 was more than that of DC52D+ZF45. The performance of the laser welded joint met the technical requirements of automobile manufacturing engineering.
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