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Self-piercing riveting (SPR) is a mature method to join dissimilar materials in vehicle body assembling. Friction self-piercing riveting (F-SPR) is a newly developed technology for joining low-ductility materials by combining SPR and friction stir spot welding processes. In this paper, the SPR and F-SPR were employed to join AA6061-T6 aluminum alloy and AZ31B magnesium alloy. The two processes were studied in parallel to investigate the effects of stack orientation on riveting force, macro-geometrical features, hardness distributions, and mechanical performance of the joints. The results indicate that both processes exhibit a better overall joint quality by riveting from AZ31B to AA6061-T6. Major cracking in the Mg sheet is produced when riveting from AA6061-T6 to AZ31B in the case of SPR, and the cracking is inhibited with the thermal softening effect by friction heat in the case of F-SPR. The F-SPR process requires approximately one-third of the riveting forces of the SPR process but exhibits a maximum of 45.4% and 59.1% higher tensile–shear strength for the stack orientation with AZ31B on top of AA6061-T6 and the opposite direction, respectively, than those of the SPR joints. The stack orientation of riveting from AZ31B to AA6061-T6 renders better cross-section quality and higher tensile–shear strength and is recommended for both processes.

Friction self-piercing riveting (F-SPR) process has been proposed to achieve crack-free joining of low-ductility materials by combining SPR process with the concept of friction stir processing. The inhibition of cracking in an F-SPR joint is related to the in-process temperature as well as plastic deformation of materials, which are controlled by the process parameters, i.e., spindle speed and feed rate. However, the relationship between F-SPR process parameters and the temperature characteristics within the joint has not been established. In the current study, a coupled thermal-mechanical model based on solid mechanics was setup to study the F-SPR process of aluminum alloy and magnesium alloy. Temperature and strain rate-dependent material models and preset crack surface method were integrated in the model and geometry comparisons were conducted for model validation. Based on this model, the evolutions of temperature and plastic deformation in the rivet and the sheets of an F-SPR joint were obtained to reveal the formation mechanism of the joint. The temperature distribution and evolution of the sheet materials were correlated with F-SPR process parameters, and a critical spinning speed of 2000 rpm at a feed rate of 1.35 mm/s was determined capable of inhibiting cracking in the magnesium sheet.