Stationary shoulder FSW for joining high strength aluminum alloys

The new process of ‘stationary shoulder’ friction stir welding (SSFSW) has been directly compared toconventional (friction stir welding) using welds produced in a high strength AA7050-T7651 aluminiumaerospace alloy. The process window for each approach was first compared using torque–rotation ratedecay curves. Under optimum process conditions, SSFSW had a ∼30% lower heat input than FSW and thestationary shoulder resulted in narrower welds with a reduced heat affected zone (HAZ) width. The SSFSWwelds also had more uniform through thickness properties and performed better than conventional FSWsin cross-weld tensile tests. In addition it is demonstrated that the SSFSW process resulted in a far superiorsurface finish, although the stationary shoulder led to surface ‘speed cracking’ under certain weldingconditions. The reasons for these benefits are discussed aided by thermal and hardness modelling.