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采用不同的点焊工艺参数对研发的1 700MPa级Si-Mn系热成形淬火钢板与低碳钢板DC04进行异种材料之间点焊,并对焊接接头的拉伸性能、显微硬度分布及微观组织特征等进行了分析。结果表明,焊接电流对点焊接头熔核直径和抗剪强度具有显著的影响,而焊接时间的影响相对较小。超高强度钢板侧的热影响区存在两个明显的软化区和硬化区,即在靠近母材处存在一个硬度明显低于母材的软化区,其组织为回火马氏体;在靠近熔核处存在一个硬度明显高于母材的硬化区,其组织为细小的马氏体。点焊接头熔核部位为柱状粗大马氏体组织,其硬度明显低于超高强度钢板母材且远高于低碳钢板母材。低碳钢板热影响区低的硬度和明显粗化的铁素体组织,使得点焊接头单向拉伸时均从低碳钢板的热影响区一侧破断。
Different spot welding parameters were used to spot-weld the developed 700 MPa Si-Mn thermoformed and low-carbon steel DC04. The tensile properties, microhardness distribution and microstructure of welded joints Features, etc. were analyzed. The results show that the welding current has a significant influence on the nugget diameter and shear strength of the spot welding joint, but the welding time has a relatively small influence. There are two distinct softening and hardening zones in the HAZ on the side of ultra-high strength steel, that is, there is a softening zone with a hardness lower than that of the parent material close to the base metal. The structure is tempered martensite. At the nuclei there is a hardened zone with significantly higher hardness than the parent metal, which is organized into fine martensite. Weld nugget site for the columnar martensite coarse, the hardness was significantly lower than the ultra-high-strength steel base metal and much higher than the low-carbon steel base metal. The low heat-affected zone of the low-carbon steel has a low hardness and a marked coarsening of the ferrite structure, so that the spot welded joint is broken from the heat-affected zone side of the low-carbon steel in the unidirectional stretching.