中文摘要：

为提髙汽车车身用双相钢（DP钢）激光焊接构件在动态载荷下应用的可靠性,研究焊接速度对1.4mm厚DP780钢脉冲激光焊接接头组织和不同应变速率下拉伸性能的影响规律.结果表明,不同激光焊接速度下DP780钢接头均存在熔合区硬化和外侧热影响区软化现象,随焊接速度增加,接头的软化程度降低.接头的强度随应变速率增加而增加,抗拉强度和断裂延伸率随焊接速度增加呈先增加后减少的趋势.当焊接速度为400mm/min时,接头表面成形性好、熔深和熔宽适中、无焊接缺陷、外侧热影响区软化程度最低（软化率为9%）,熔合区硬度适中,接头整体强度和塑性指标达到最佳值.

英文摘要：

In order to improve the service reliability of the welded component for auto-body under the dynamic load,the effects of laser welding speed on the microstructure and tensile properties at various strain rates of the pulsed laser welded joints of 1.4 mm thick DP780 steel were studied. The results showed that the DP780 welded joints exhibit the hardening in the fusion zone and the softening in the outer heat-affected zone under various welding speeds. The softening degree of the welded joints decreases with increasing welding speed. The strength of the welded joints increases with increasing strain rate, and the ultimate tensile strength and fracture elongation increase first and then decrease with increasing welding speed. The welded joints with good surface morphology,moderate weld width and penetration,no weld defect are fabricated when the welding speed is 400 mm/min. And the softening degree of the outer heat-affected zone is the lowest with the softening fraction of 9% and the hardness in the fusion zone is moderate. The overall strength and ductility of the DP780 welded joint reach an optimum value under the welding speed of 400 mm/min.