Microstructure Evaluation of Vaporizing Foil Actuator Welds of 1 GPa Strength Steel

Demands for weight reduction in automobiles have been constantly increasing due to its environmental impact, leading to increased interests in light metals such as aluminum and magnesium. However, for most structural applications that require large energy absorption, implementation of high strength steel is still a pervasive solution.When the high strength steel having a high martensite fraction (DP 980) is joined by resistance spot welding, a softening zone is generated in the welds, leading to the reduction of the strength of the welds. In addition, high strength steels generally contain a large amount of carbon and alloying elements. As a result, the carbon equivalent exhibiting hardenability increases, having the welded part become weak, and making it difficult to secure the performance required by the part or the vehicle body.Vaporizing foil actuator welding (VFAW) which is one of the solid-state welding techniques utilizes a high-pressure pulse generated by the vaporization of an aluminum foil to cause high speed collision of flyer and target sheets to create solid-state bonds with negligible melting at the weld interface. So, VFAW produces joints with little to no HAZ.In this study, to examine the vaporizing foil actuator welding properties of 1 GPa grade high strength steel, microstructure analysis and hardness test were performed. The test results were compared with the resistance spot welding properties of the same material. Key words: 1 GPa grade steel, Vaporizing foil actuator welding, Mechanical properties, Microstructure