Process and performance characteristics of an improved friction-stir riveting process

Abstract

Friction-stir riveting is a new mechanical fastening technique developed in recent years. It combines the spinning and extruding actions of friction-stir spot welding, and the interlocking created by embedding a rivet in the sheets in self-piercing riveting, producing a joint which strength stems from a compact stirred or mixed zone, an embedded solid rivet, and solid bonding. In this study a set of improved rivet design and tooling, based on the understanding of friction-stir riveting process and the joint formation gained in previous investigations, was used to join aluminum alloy sheets. The evolution of microstructure during riveting was investigated using the new rivet and tooling, and the joint structural characteristics were analyzed. A detailed study was also conducted on the effect of rivet depth of feed, the joint structures created, and the performance of these joints, compared with those using the previous rivet design and tooling. Afterwards, a statistical analysis was conducted to optimize the riveting process. Using the new rivet and tooling, and optimized riveting parameters, joints with peak load consistently exceeding 8 kN were obtained in joining 2-mm AA5052 sheets. The strength of the new friction-stir riveted joints is much higher than those obtained through other mechanical joining techniques, and even higher than resistance spot welding in joining aluminum sheets.