EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Self-piercing riveting (SPR) combined with adhesive bonding has been established as efficient hybrid joining technology for manufacturing lightweight car bodies. In order to exploit the advantages offered by multi-material design, this work investigates the feasibility of joining aluminum alloys with high-strength steels (HSS), however, against the favorable joining direction. Four hybrid joints were produced using different aluminum alloy sheets (AW-60xx-T4, AW-64xx-T4), HSS sheets (HC4xxX, HC4xxLA), rivet types (C5.3×8.0-H4, U5.5×5.0-H6) and an epoxy-based single-component adhesive. The force-displacement curve of the punch was monitored during the SPR process. The quality of the joints was assessed on the basis of characteristic cross-section features including overlap of the rivet head, horizontal undercut of the rivet, bottom thickness of the lower sheet and shape of the adhesive pockets. Moreover, the joint consisting of the 3.0-mm-thick AW-64xx-T4 sheet, the 1.5-mm-thick HC4xxLA sheet and the C5.3×8.0-H4 rivet was exemplarily modeled using the Simufact Forming finite element (FE) software. The axisymmetric model included the punch, the die, the blankholder, the steel rivet, the upper aluminum alloy sheet, the lower HSS sheet and the adhesive layer between the sheets. A 3D scanning system was used for capturing the actual geometries of the die and the rivet. Flow curves describing the plastic behavior of the sheets were extrapolated from the results of uniaxial tensile tests. Viscoelastic properties of the adhesive were substituted with “equivalent” elastoplastic properties, which enabled modeling the liquid adhesive as solid with strain rate-dependent flow curves. Good agreement of the joint cross-sections and of the punch force-displacement was achieved between experiments and simulations.