三层板电阻点焊接头界面力学性能

目的为掌握汽车侧撞区域三层板电阻点焊接头不同界面的承载能力,研究三层板接头力学性能。方法以B1500HS-1.4 mm/B1500HS-1.6 mm/DC06-0.8 mm三层板电阻点焊接头为研究对象,通过剪切拉伸试验结果,对比分析不同界面的力学性能,并对焊点熔核区显微组织、界面熔核尺寸、显微硬度以及失效模式进行研究与分析。结果在三层焊中,当上下两侧板材强度相差很大时,不同界面的三层板点焊接头具有不同的峰值载荷和断裂能量,强强界面的剪切承载能力是强弱界面的6倍;熔核区不同板材处的马氏体含量以及界面熔核尺寸均影响点焊接头的力学性能;热成形钢一侧影响区因原始全马氏体组织出现了软化;拉剪试验条件下,B1500HS-1.4 mm/B1500HS-1.6 mm界面点焊接头失效模式为纽扣失效,B1500HS-1.6mm/DC06-0.8 mm界面点焊接头失效模式为先纽扣失效,后母材撕裂。结论在汽车耐撞设计中应通过承载分配,将碰撞结构力传导至强强界面,并通过隔离设计尽量避免强弱界面受到结构力影响,以提高碰撞性能。

Mechanical Properties of Three-layer Resistance Spot Welding Joint Interface

The paper aims to understand the bearing capacity of different interfaces of three-layer resistance spot welding joints by studying the mechanical properties of B1500HS-1.4 mm/B1500HS-1.6 mm/DC06-0.8 mm three-layer joint in side impact of vehicle. Based on results of shear tensile test, the mechanical properties of different interfaces were analyzed and the microstructures, fusion zone size, microhardness and failure mode of nugget area were researched and analyzed. Different interfaces of the three-layer spot welding joint had different peak load and fracture energy when the strength of the upper and lower sides was very different. Shear bearing of the joint in-terface composed of two high strength steels (B1500HS-1.4 mm/B1500HS-1.6 mm) was 6 times as big as that of the joint interface composed of both strong and soft steels. The martensite content at different plates in the nugget area and the weld nugget size along sheet/sheet interface affected the mechanical properties of the spot weld joint. Softening appeared in the heat-affected zone of hot-stamping steels due to their full content of marten site. The failure mode of B1500HS-1.4 mm/B1500HS-1.6 mm interface spot welding was button failure; and the failure mode of B1500HS-1.6 mm/DC06-0.8 mm interface was button and pullout failure. To increase the crash capability, it is suggested to transmit the crash force to the interface of high strength steels by load allocation and avoid transmission of crash to the softer interface by isolation design.