Microstructural evolution ahead of the tool in aluminum friction stir welds

The microstructural evolution around the tool during friction stir-welding of aluminum is described. The rotating tool induces a gradual rotation of the crystal lattice with a concomitant development of elongated subgrains. Additional small subgrains form within this structure by continuous dynamic recrystallization, gradually increasing in misorientation, eventually developing high-angle (>15°) grain boundaries. The development of texture and similarities to friction stir welds in titanium alloys are also discussed.