Microstructure and Mechanical Properties of Resistance-Spot-Welded AISI-1008 Steel Lap Joints Using Multiwalled Carbon Nanotubes as an Interlayer

The present study deals with the microstructural analysis and mechanical properties of resistance-spot-welded AISI-1008 steel joints utilizing multi-walled carbon nanotubes (MWCNTs) as an interlayer. A thin layer of approximately 50 µm thickness of MWCNTs coating is used as an interlayer between the mating surfaces of the lap joints. The microstructural investigation of the weld nugget was accomplished by light microscopy, scanning electron microscopy, and transmission electron microscopy. An enhancement of ~45% in weld strength at one of the welding parameters is obtained in lap-shear tensile tests due to the MWCNT interlayer. The shear dimple fracture is the prime mode of failure as has been confirmed by fractography. At lower and higher welding energies, interfacial and button pull-out modes of failure were observed to occur, respectively. Microhardness studies along the nugget cross section revealed a marginal increase in hardness owing to the presence of MWCNTs and also the interplay of various strengthening mechanisms.