汽车侧撞区前围横梁及A柱斜支撑通常为热冲压成形零件，前围板则采用成形性极好的深冲软钢薄板冲压而成，此区域形成了典型的差强差厚三层板电阻点焊接头.前期研究中表明强强、强弱界面承载差异极大造成焊点整体承载能力严重下降，本文则侧重研究不同搭接顺序对焊点整体力学性能的影响.以B1500HS-1.4mm、B1500HS-1.6mm两种热成形钢和DC06-0.8mm软钢3种差强差厚材料为研究对象，对比强强弱和强弱强两种不同搭接顺序的电阻点焊接头不同界面下的接头力学性能，并对两种电阻点焊接头熔核形成过程、熔核区显微组织、界面熔核尺寸以及显微硬度进行了对比研究与分析.结果表明：不同搭接顺序下的点焊接头具有不同的接头抗剪峰值载荷和断裂能量，点焊接头熔核过程显微组织形成过程揭示了强弱强搭接顺序下的点焊接头承载能力提高机理.最后，给出A柱侧撞区域强弱强搭接的合理设计，从而提高车身整体耐撞性能.
Front wall beams and the support of A-Pillar are usually hot-stamped parts in side impact of vehicle, and front panel is made of mild steel with excellent formability by stamping, hence the area has formed a typical three-sheet resistance spot welded joints of unequal thickness and strength. In order to improve the overall load bearing capacity of spot welding joints, the paper investigates the influence of different lapping orders on overall mechanical properties of welded joints. Based on three kinds of material with unequal thickness and strength， B1500HS-1.4mm, B1500HS-1.6mm and DC06-0.8mm, the mechanical properties of different interfaces of two welded joints (strong-strong-soft and strong-soft-strong) under different lapping orders were compared. The nugget forming process, microstructure of nugget, fusion zone size and microhardness were also studied and analyzed. By investigating microstructure formation of nugget process of welded joints under different lapping orders, this paper reveals that the joint of strong-soft-strong can increase the bearing capacity. Finally, the article gives a reasonable design of strong-soft-strong lap joint in side impact of A-pillar and improves overall crashworthiness of vehicle.
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