Benchmarking strength and fatigue properties of spot impact welds

Abstract

An adaptation of vaporizing foil actuator welding (VFAW), a solid-state impact welding technique for producing similar JSC590R and 6061-T6 spot-welded joints was used in this study and the mechanical and fatigue properties of the joints were characterized using lap-shear testing, microhardness measurements, optical imaging and fatigue testing and the results compared with those of resistance spot welding (RSW) joints. Results indicated that the VFAW joints had improved strength and energy absorption compared to RSW joints for both the material combinations, however the strength of JSC590R-JSC590R VFAW welds were found to be lower than RSW when corrected for nugget size. Microhardness measurements in VFAW joints showed constant hardness values across the weld length signifying the absence of a heat affected zone, whereas softening was observed in RSW joints. Optical imaging revealed the homogeneity in microstructure of VFAW joints and the inhomogeneous distribution of the microstructure in RSW joints. For JSC590R members, fatigue resistance was equivalent for VFAW and RSW, whereas improved fatigue properties were observed for 6061-T6-6061-T6 VFAW welds. Fatigue strength scaled with static strength in a predictable way and was mostly affected by the shape and type of notch formed at the end of the nugget.