Friction self-piercing riveting (F-SPR) of aluminum alloy to magnesium alloy using a flat die

Friction self-piercing riveting (F-SPR) process based on a pip die has been invented to solve the cracking problems in riveting high-strength and low-ductility light metals, such as magnesium alloys, cast aluminum, and 7 series aluminum alloys. In this paper, in order to solve quality issues caused by the misalignment between rivet and pip-die in F-SPR, a flat-die based F-SPR process was proposed and employed to join 1.27mm-thick AA6061-T6 to 3mm-thick AZ31B. The results indicate that a 1.0mm die distance is effective to avoid rivet upset and insufficient flaring. As the feed rate increases, the heat input in the whole process decreases, resulting in a larger riveting force, which in turn increases both the bottom thickness and interlock amount. Besides, solid-state bonding, including Al-Mg intermetallic compounds (IMCs), Al-Mg mechanical mixture, and Al-Fe atom interdiffusion was observed at the joint interfaces. The upper Al layer was softened, but the lower Mg layer was hardened, and both sheets exhibited a narrowed affected region with the increase of feed rate, while the rivet hardness shows no obvious change. Three fracture modes appeared accompanying the variations in lap-shear strength and energy absorption as the feed rate increased from 2mm/s to 8mm/s. Finally, the F-SPR process using a flat die was compared to those using a pip die and a flat bottom die to show the advantage of flat die on coping with the misalignment problem. (C) 2021 Chongqing University. Publishing services provided by Elsevier B.V. on behalf of KeAi Communications Co. Ltd.