Electromagnetic Self-Piercing Riveting of 1.5 GPa Hot Stamping Boron Steel and Aluminum Alloy

In recent years, the automotive industry has focused on developing dissimilar material joining technologies to achieve both lightweight structures and high strength. Particularly, 1.5 GPa grade hot-stamped steel (22MnB5) and aluminum alloys have gained attention due to their excellent mechanical properties, necessitating the selection of suitable processes for their application in automotive component manufacturing. A representative fastening process is Self-Piercing Riveting (SPR), which applies high fastening force to a rivet, enabling it to pierce the upper material and plastically deform the lower material. This process provides high-quality joints, improved fatigue behavior, and is recognized as an environmentally friendly process. Lately, for ultra-high strength materials, Electromagnetic Self-Piercing Riveting (E-SPR) has been studied. E-SPR operates on principles similar to SPR but uses electromagnetic forces to drive the punch at significantly higher velocity, allowing for faster and more efficient joining. This process can concentrate fastening forces, resulting in improved joint quality for high-strength materials. This study aimed to achieve high-quality E-SPR joints between 1.5 GPa grade hot-stamped steel and aluminum alloys without any assistant process. In order to carry this out, the effects of rivet and die geometries on joint quality were analyzed, and suitable configurations were selected. For the selected rivet and die, the study examined the effect of charging energy on joint quality in terms of cross-sectional dimensions and tensile shear load. Based on these results, HD3-type rivet, FM-type (flat) die, and 8.5 kJ charge energy were selected as the optimal process values for 1.5 GPa grade hot-stamped steel and 5052-H32 aluminum alloy.