A study on Al/steel hybrid rivet welded - friction stir spot welding joints

This study investigates a novel friction stir rivet welding (FSRW) technique. That integrates the mechanical advantages of riveting with the metallurgical benefits of friction stir spot welding (FSSW) to join dissimilar Al/steel lap joints (aluminum bottom sheet; steel top sheet). Three types of joints - FSSW without rivet (W–R), with aluminum rivet (Al–R), and with steel rivet (St-R) - were systematically fabricated and evaluated. Detailed microstructural and mechanical analysis reveals that St-R joint exhibited the highest tensile strength, the average tensile load reaching 8197.4 N, which represents a 172.75% increase over W–R joints. In contrast, Al–R joints showed significantly reduced strength, attributed to interfacial microcracks and poor metallurgical bounding. The formation of a micro-interlocking structure at the steel/aluminum interface in St-R joints contributed to improved load-bearing capacity and joint integrity. The work highlights the potential of FSRW for robust Al/steel joining by optimizing rivet material selection and provides insights into the interfacial bounding mechanisms and fracturing behavior of hybrid joints.