Friction Self-piercing Riveting of Various Dissimilar Materials

Higher specific strength materials such as magnesium (Mg) alloys, high strength aluminum (Al) alloys, carbon fiber reinforced polymer (CFRP), and advanced/ultra-high strength steels (AHSS/UHSS) have been considered for lightweight multi-material autobody structures to aim for decarbonization. The thermal, chemical, and physical properties of individual materials impede the integration of such lightweight materials into autobody structures. In addition, these materials are generally low ductile at room temperature, making conventional mechanical joints and fastenings susceptible to cracking. To resolve technical challenge, friction heat during joining process was utilized to locally improve ductility so that cracking issue can be mitigated. In this presentation, we report our latest progress for joining of numerous dissimilar material combinations including CFRP-Mg (or Al), 7xxx Al-7xxx Al, and 7xxx-UHSS by friction self-piercing riveting (F-SPR) as a single class joining technology. Process and performance prediction models were developed to guide joining process optimization. Good mechanical joint performances from lap shear and cross-tension testing were achieved with crack-free joints. To mitigate galvanic corrosion at the rivet/multi-material interface, different surface coatings and modifications were applied to the rivet material. Solution immersion testing showed that surface coatings and modifications of the rivet material reduced galvanic corrosion of the AZ31B.