Fatigue behaviour of dissimilar Al alloy/galvanised steel friction stir spot welds fabricated by scroll grooved tool without probe

Al alloy sheet was friction stir spot welded (FSSW) to galvanised steel sheet by a scroll grooved tool without probe. Tensile and fatigue tests had been conducted using tensile shear specimens, and the results were discussed in comparison with Al/steel dissimilar FSSW joint, in which steel sheet was not galvanised. Energy dispersive X-ray analyses revealed that Zn coating was melted or softened and circumferentially resolidified around the nugget. Intermetallic compound between Al and Fe was formed along the interface resulting in the joining of Al to steel. Tensile shear strength of Al/galvanised steel weld was lower than that of Al/steel one without galvanising. However, Al/galvanised steel welds exhibited higher fatigue strengths. Finite element method analyses around the nugget revealed that circumferentially resolidified Zn brought about the stress relaxation at the edge of the nugget, resulting in the better fatigue performance of Al/galvanised steel welds.