Contact conditions on nugget development during resistance spot welding of Zn coated steel sheets using rounded tip electrodes

► Nugget formation in resistance spot welding process strongly depends on interfacial conditions. ► The global heat produced in the assembly is mainly governed by the evolution of the contact surfaces. ► Zinc coating on the steel sheet influences the interfacial conditions, particularly the contact resistances. ► Ejection of molten zinc at periphery of the contact zones does not radically change the nugget formation and development. ► The nugget growth and maximum size are predicted using finite element simulation.