Abstract：Automotive safety and crash energy absorption have increased the demand for higher strength,energy-absorbing materials and their joining technology. Laser tailor-welded of DP980 dual phase steel and 22MnB5 hot-forming steel is used to investigate the effect of welding heat input on the microstructure and mechanical properties. By keeping the laser output power constant(1.3 kW) and varying the welding speed to control the welding heat input,the relationship between the welding heat input and the microstructure and mechanical properties of the tailor-welded joints was investigated. The microstructure and properties of the different sub-regions of the joint were examined using optical microscopy(OM),scanning electron microscopy(SEM),micro-hardness tester and tensile test machine. The results show that when the welding speed varies between 16 and 26 mm/s,a complete and defect-free fusion zone is obtained; as the welding speed increases,not only does the weld surface depression gradually improve,and the width of the weld heat affected zone(HAZ) also decreases. Hardness tests indicated the presence of softened zones in the joint,mainly in the tempered zone and incomplete phase transformation region of the heat affected zone on the DP980 side,while the fine grain zone, coarse grain zone,heat affected zone of 22MnB5 and weld metal zone of DP980 together formed the hardened area of the joint. Furthermore,the tensile strength of the welded joints remained between 576 and 597 MPa,with the corresponding fractures occurring in the base metal zone of 22MnB5 and accompanied by significant necking. The post-break elongation of the joints ranged from 11.9% to 15.5% between the post-break elongation of the DP980(11%) and the 22MnB5(22%). The study also showed that the greater the heat input during welding,the coarser the microstructure of the same area of the joint.
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