Microstructure and Mechanical Properties of Laser Tailor-Welded Joint of Dissimilar Thickness DP1180/DP590 Dual-Phase Steels

Laser tailor-welding was conducted on 1.2 mm thick DP1180 dual-phase steel plate and 1.5 mm thick DP590 dual-phase steel plate, and then microstructure and mechanical properties of the joint were studied. The results show that no spatter was observed on weld surface of the joint, indicating a good forming quality. The weld zone was composed of coarse columnar crystals and had a two-phase structure of lath martensite and ferrite. The heat affected zone consisted of critical zone, fine grain zone and coarse grain zone, whose structures were all composed of martensite and ferrite. The heat affected zone at the DP1180 steel side was wider than that at the DP590 steel side. The highest microhardness was found in the weld zone of the joint, with an average value of 369 HV. Fracture occurred in the base metal of DP590 steel during tensile. The tensile strength of the joint was the same as that of the DP590 steel; the elongation of the joint was 14.7%, about half that of the DP590 steel.