J. Schneider, Mississippi State University, Mississippi State, MS; A. C. Nunes, NASA-MSFC, Marshall Space Flight Center, AL

Summary: Microstructures observed in a FSW cross-section in an aluminum alloy are related to their respective strain-strain rate-temperature histories along their respective flow trajectories. Two kinds of trajectories are present that subject the weld metal to a distinct thermomechanical process and imparting a distinct microstructure