This work features the investigation of the refill friction stir spot welding (RFSSW) parameters - rotational speed (RS), welding time (WT) and plunge depth (PD) - of AA2198-T8 1.6-mm thick sheets. The study was performed based on lap shear strength tests of overlapped joints welded under conditions indicated by the Taguchi method in order to determinate the optimized combination of parameters, considering the mechanical properties and process conditions. Results based on mechanical testing indicate that all the welding conditions evaluated in the current study exceed the minimum criterion for lap shear strength required for aeronautic applications. RS and PD have shown to be responsible altogether for almost 90% of the welds’ lap shear strength variation, while TS presents considerable less significant contribution to the joints’ resistance. The optimized welding condition was found for highest RS and PD levels and lowest TS.