热镀锌双相钢HC420/780DPD+Z电阻点焊工艺与性能研究

Study on Spot Welding Process and Joint Properties of Hot Dip Galvanized Dual Phase Steel HC420/780DPD+Z

为获得1.5 mm厚的汽车用热镀锌双相钢HC420/780DPD+Z的电阻点焊工艺窗口,采用中频逆变式电阻点焊机对其进行点焊试验,通过电极压力等参数调整,获得由不同焊接时间、焊接电流等组成的焊接工艺窗口。并通过显微硬度测试、剪切拉伸、十字拉伸试验以及金相检测等方法,对点焊接头性能进行综合评价。研究结果表明,在焊接时间为410~430 ms时,焊接电流工艺窗口为3.4~3.6 kA,可获得无缩孔、裂纹的焊接接头;接头的平均抗剪力为14.88 kN,平均十字拉伸力为7.1 kN;熔核区的显微硬度为402~455 HV,热影响区硬度为237 HV,未见脆化现象;电极寿命大于500个焊点,均满足GWS-5A标准要求。在此工艺下,接头的力学性能优异,显微组织主要为马氏体,硬度分布规律表明熔核区硬度最高。此外,焊接接头的失效模式主要为界面断裂和纽扣型熔核断裂,其中纽扣型熔核断裂具有更高的承载能力和能量吸收能力。

To acquire the resistance spot welding process window for automotive hot-dip galvanized dual-phase steel,spot welding experiments were performed on 1.5 mm thick HC420/780DPD+Z using a medium-frequency inverter resistance spot welding machine.By adjusting parameters such as electrode pressure,a welding process window consisting of various welding times and currents was established.The performance of the spot-welded joints was comprehensively assessed through microhardness testing,shear and cross-tensile tests,and metallographic examination.The research indicates that un‐der the optimal welding process window with a welding time of 410~430 ms and a welding current of 3.4~3.6 kA,defect-free welded joints without shrinkage pores or cracks can be achieved.The average shear strength of the joints is 14.88 kN,and the average cross-tensile strength is 7.1 kN.The microhardness in the nugget zone ranges from 402~455 HV,while the hardness in the heat-affected zone is 237 HV,with no signs of embrittlement observed.The electrode life exceeds 500 weld points,meeting the requirements of the GWS-5A standard.With this process,the mechanical properties of the joints are su‐perior,and the microstructure is primarily composed of martensite,with the hardness distribution indicating the highest hard‐ness in the nugget zone.Additionally,the failure modes of the welded joints are predominantly interfacial fractures and button-type nugget fractures,the latter of which has greater load-bearing capacity and energy absorption capability.