Q&P980镀锌高强钢电阻点焊工艺及液态金属脆化裂纹分布

Resistance spot welding process and liquid metal embrittlement crack distribution of Q&P980 galvanized high-strength steel

通过设计电阻点焊工艺的正交实验,确定了Q&P980镀锌高强钢的点焊工艺参数范围,并对其焊接接头进行显微组织表征和力学性能分析。结果表明:熔核区组织以交错分布的板条马氏体为主;热影响区组织由板条马氏体、残余奥氏体和铁素体组成,马氏体板条平均宽度在不完全淬火区最大为4.86μm。显微硬度测试发现,焊接接头硬度值呈“W”形对称分布,硬度峰值出现在细晶区,达到559HV,硬度最低值出现在不完全淬火区,为338HV,呈现明显的软化现象。对焊接接头进行室温拉伸,最大拉剪载荷的峰值为27.92 kN,其断口形貌呈现典型的韧窝状,属于韧性断裂。由于Zn的熔点较钢基体低,镀锌高强钢点焊时易发生Zn层优先熔化并沿晶界向基体渗透,在焊接接头处可观察到明显的液态金属脆化裂纹。

By designing the orthogonal experiment of resistance spot welding process,the range of spot welding process parameters of Q&P980 galvanized high-strength steel was determined,meanwhile the microstructure characterization and the mechanical properties analysis of the welding joint were carried out.The results show that the microstructure of nugget zone is mainly staggered lath martensite,whereas the microstructure of HAZ is composed of lath martensite,residual austenite and ferrite.The maximum average width of martensite lath in incompletely quenched zone is 4.86μm.The microhardness test exhibits that the hardness value of the welding joint shows a“W”-shaped symmetrical distribution.The peak hardness appears in the fine-grain zone,which is 559HV,while the minimum hardness appears in the incompletely quenched zone,which is 338HV.The incompletely quenched zone shows obvious softening phenomenon.The room temperature tensile tests of the welding joints are carried out,and the peak value of maximum tension-shear load is 27.92 kN.The fracture morphology shows typical dimples,which belongs to ductile fracture.Since the melting point of zinc is lower than that of the steel matrix,the zinc layer is prior to melting and penetrates downward along the grain boundary of the matrix at the welding joints,and then the liquid metal embrittlement cracks can be observed obviously.