Si元素对镀锌高强钢点焊接头液态金属脆化破坏的影响机制研究

液态金属脆化（LME）是镀锌QP钢、TWIP钢等高强汽车钢电阻点焊中易于产生的一种典型缺陷，极大阻碍了此类高强钢在汽车行业中的推广和应用。申请人与宝钢的合作团队在前期研究中发现镀锌高强钢中Si含量与电阻点焊接头中LME裂纹的产生有直接的关联，但Si元素的作用机理及其与LME裂纹产生的内在关联机制尚未厘清。本项目拟基于QP高强钢中Si元素含量的针对性调控，并结合接头力学性能测试、微区凝固过程分析、组织演变表征和接头的应力场及温度场分布仿真模拟等研究手段，系统研究镀锌高强钢点焊接头LME裂纹产生的规律及内在作用机制。基于LME裂纹附近的元素与物相属性尤其是Si元素的分布特征，诠释Si元素与镀锌高强钢点焊过程LME裂纹形成的内在关联机制，由此建立点焊接头成分调控与力学性能的关联模型，并为镀锌高强钢点焊接头力学性能的改进提供理论依据与研究基础。

The development and application of galvanized high strength steels containing QP and TWIP steels is hindered by the formation of liquid metal embrittlement (LME), which is a typical defect in the spot welded joint for galvanized high strength steels. It is found that there exists a direct correlation between Si content and the formation of LME, while the internal effect of element Si and the its intrinsic mechanism relieving the LME cracks are still unclear. Based on the adjustment of Si content in QP steel, the characteristics including the mechanical properties, micro-zone solidification process, microstructure evolution and stress/temperature fields will be investigated to obtain the distribution law of the LME cracks in this project. Based on the element distribution characteristics, especially for the element Si, and phase characterization in the region near the LME cracks, the formation mechanism of LME cracks during spot welding is anticipated to be revealed. Combined with the mechanical property test, the intrinsic interaction mechanism between the composition modulation and property improvement is anticipated to be clarified. This project is helpful to reveal the formation mechanism of LME, and it will offer theoretical basis and direct experimental evidence for the microstructure modulation and mechanical property improvement of the spot welded galvanized high strength steels.