A. A. M. Da Silva, A. Zabaleta, P. Alvarez, E. Aldanondo, J. Solis, A. Echeverria, Centro de Investigacion en Tecnologias de Union LORTEK, Ordizia, Spain
Friction stir spot welding (FSSW) is a solid-state spot-like joining process suitable for overlap welding lightweight materials and advanced high strength steels for structural applications. FSSW has a potential to replace conventional joining methods such as resistance spot welding and clinching in certain automotive applications as well as to reduce manufacturing steps. The FSSW process is a variant of the linear friction stir welding process in which a rotating tool is plunged into the upper sheet (without any lateral movement) until the shoulder contacts the upper sheet generating frictional heat resulting in softening of the workpiece. FSSW leaves behind a keyhole after the weld has been performed. FSSW has been done in an Al-Mg alloy using different welding parameters (e.g. plunge rate, rotational speed and plunge depth) aiming to produce high quality connections with excellent microstructural and mechanical performance. Dwell time has been held constant in 2 seconds. FSSW welds have been accomplished using three different tools – conical parallel threaded pin and scrolled shoulder (tool 1); threaded pin and scrolled shoulder (tool 2) as well as one-flute threaded pin and scrolled shoulder (tool 3). Optical microscope has been used to analyse the macrostructural and microstructural features of the FSSW connections; while mechanical performance has been investigated in terms of tensile shear. Best mechanical performance has been obtained using tool 2; while tool 1 has presented worst mechanical behaviour. Shear strength of FSSW connections has been compared to the shear strength of single 5 mm diameter rivets using the same configuration (3 mm and 5 mm thick sheets). Results have indicated a better shear strength behaviour of FSSW connections with values up to five times higher than that of single rivets.
Summary: Friction stir spot welding (FSSW) is a solid-state joining method that produces spot-like connections without bulk melting. FSSW has been perfomed in an Al-Mg alloy using different welding parameters aiming to produce high quality connections with excellent microstructural and mechanical behaviour.
