马氏体含量对合金化热镀锌双相钢电阻点焊接头组织与性能的影响

目的 研究在双相钢电阻电焊过程中马氏体含量对点焊接头组织、性能的影响规律。方法 使用电阻点焊机对DP780、DP980、DP1180 3种马氏体含量不同的锌铁合金化热镀锌双相钢进行焊接，利用欧姆表、光学显微镜、扫描电镜、拉伸机和显微硬度计等设备，对基板的电阻率、工艺窗口、接头力学性能、焊点断裂模式、金相组织进行表征。结果 在AWS D8.9M-2012焊接标准体系下，DP780、DP980、DP1180焊接电流窗口依次减小，DP780、DP980、DP1180 3种材料在最大焊接电流下的焊核直径基本一致;熔核区硬度呈增大趋势，DP780点焊接头软化不明显，DP980和DP1180的热影响区出现明显的软化现象，这主要是由母材热影响区中的马氏体回火造成的。DP780、DP980、DP1180的最大剪切力分别为23 062、27 317、28 183 N。DP780为拔核断裂模式，DP980和DP1180为部分拔核断裂模式。结论 双相钢中马氏体含量的增加会使焊接电流窗口降低，整体向焊接电流减小的方向偏移，但是会提高上限电流的焊点承载强度。

Effect of Martensite Content on Microstructure and Properties of Resistance Spot Welded Joint of Alloyed Hot-dip Galvanized Dual Phase Steel

The work aims to study the effect of martensite content on the microstructure and properties of resistance spot welded joint of alloyed hot-dip galvanized dual phase steel. The resistance spot welder was used to weld the zinc iron alloyed hot-dip galvanized dual phase steel with different martensite contents, namely, DP780, DP980 and DP1180. The substrate resistivity, process window, mechanical properties of joints, fracture mode of welding spot, and metallographic structure were characterized by ohmmeter, optical microscope, scanning electron microscope, tensile machine, microhardness tester and other equipment. The results showed that under the AWS D8.9M-2012 welding standard system, the welding current windows of DP780, DP980, and DP1180 decreased sequentially, and the weld nugget diameters of DP780, DP980, and DP1180 materials were basically the same under the maximum welding current. The hardness of nugget zone increased, the softening of DP780 spot welded joint was not obvious, and the Heat-affected zone of DP980 and DP1180 appeared obvious softening, which was mainly caused by tempering of martensite in the heat-affected zone of the substrate. The maximum shear force of DP780, DP980 and DP1180 was 23 062 N, 27 317 N, and 28 183 N, respectively. DP780 was a pull-out fracture mode, while DP980 and DP1180 were partial nuclear fracture modes. The increase of martensite content will increase the bearing strength of welded joints under upper limit current, but it will reduce the welding current window and shift to the direction of welding current reduction.