Analytical bonding criteria for joint integrity prediction in friction stir welding of aluminum alloys

• The solid bonding phenomenon occurring in FSW has been studied through experiments and numerical simulations.
• An analytical bonding criterion has been applied to FSW for the first time.
• The pressure–time (Pivnik and Plata) criterion may give wrong predictions when high welding speed is used.
• The pressure–time–flow criterion is better suited for the local prediction of bonding phenomena in FSW.

In this study, two bonding criteria, previously used for porthole die extrusion, are applied to FSW starting from the local value of the main field variables calculated through a specifically developed 3D numerical model of the process. Their applicability and effectiveness have been assessed through an experimental and numerical campaign carried out with the main process parameters varying in a wide range. The pressure–time–flow criterion was demonstrated to be better suited for FSW processes when large welding speed is used.