A comparative investigation on self-piercing riveting and resistance spot welding of automotive grade dissimilar galvanized steel sheets

Self-piercing riveting (SPR) and resistance spot welding (RSW) are widely used spot joining methods in the automotive sector, with the former in developmental mode. The current work compares the joinability of dissimilar galvanized steels performed through SPR and RSW, which poses challenges during conventional RSW. Two widely used galvanized steels, CR340 and CR210, were selected for the study. SPR was optimized in terms of joint characteristics such as rivet head height, interlock distance, and remaining bottom sheet thickness. Similarly, a narrow optimal current range of 0.75 kA was optimized for RSW of steel sheets. Static and dynamic (fatigue) testing of joints was performed at optimized conditions and compared. RSW joints exhibited higher tensile-shear strength with greater scatter compared to SPR joints, whereas SPR joints showed significantly improved fatigue life. Different failure modes were observed for the two types of joints during fatigue life assessment. Failure mode for SPR joints subjected to cyclic tension-tension loading transited from rivet fracture to eyebrow cracking with decreasing applied loads, whereas RSW joints failed by eyebrow cracking at all load levels. Further, SPR joints suffered from fretting wear, whereas RSW joints showed poor dynamic performance owing to inherent geometrical notch.