Microstructure and Properties of Spot Welded Joints of Hot-Stamped Ultra-High Strength Steel Used for Automotive Body Structures

Metals

Xiaoyu Ran¹  Lianjin Li¹  Liwen Feng¹  Huijun Li²  Zhixia Qiao³ 

[1] School of Mechanical Engineering, Tianjin University of Commerce, Tianjin 300134, China;School of Mechanical, Materials, Mechatronics and Biomedical Engineering, University of Wollongong, Northfields Avenue, Wollongong, NSW 2500, Australia;Tianjin Key Laboratory of Refrigeration Technology, Tianjin University of Commerce, Tianjin 300134, China;

关键词: spot welding;    hot-stamped hardened steel;    microstructure;    martensite;    bainite;   

DOI  :  10.3390/met9030285

来源: DOAJ

【 摘 要 】

Hot-stamped ultra-high strength steels have been widely used in automobile structural parts. Considering the high splash tendency in resistance spot welding due to their extremely high hardness, in this work, microstructural characteristics and mechanical performance of the resistance spot welded ultra-high strength steels are investigated. The results indicate that the interface between the nugget and heat-affected zone (HAZ) is the weakest zone where fractures initiate. In tensile shearing tests, a qualified spot welding joint failed with a button-shaped fracture. Welding defects would significantly decrease the load-carrying capacity and lead to interfacial fracture, except for a button-shaped fracture. In spot welding, it was found that a specific mid-frequency alternating current (AC) input mode, in which a 6 ms cooling cycle was inserted between every two neighboring current pulses, can avoid the splash in the spot welding of hot-stamped hardened steels.

【 授权许可】

Unknown