Microstructure characteristics and mechanical properties of stationary shoulder friction stir welded 2219-T6 aluminium alloy at high rotation speeds

Stationary shoulder friction stir welding has been used to weld 4-mm-thick 2219-T6 aluminium alloy at high rotation speeds. Strain plastic damage was applied to demonstrate the formation mechanism of welding defects at high rotation speeds above 2000 rpm. A three-way converging zone in the joint, in which materials of different microstructure characteristics converged from three directions during high tool rotation speed welding, was found. At the relatively high tool rotation speed, the significant differences in the microstructures would result in weld defects in this zone. It could be attributed to material toughness damage at high strain rate. With increasing tool rotation speed, the tensile strength of the joint constantly decreased. When the tool rotation speed varied from 2000 to 2600 rpm, the tensile strength decreased from 305 MPa (68.2% of the BM) to 238 MPa (53.2% of the BM).