Although friction stir welding (FSW) produces minimal distortion, residual stresses are created that impact fatigue and stress corrosion performance. X-ray diffraction residual stress and cold work mapping methods used at Lambda Research for FSW studies are described. Post weld surface enhancement processing can be used to place the FSW region in compression to improve fatigue performance. Deep compressive residual stress distributions produced by low plasticity burnishing (LPB) designed to improve fatigue and corrosion fatigue performance in aluminum alloy FSW are described. The LPB tooling and FSW processing are presented. Corrosion fatigue testing used for FSW samples is described and compared to fracture mechanics based fatigue life predictions calculated for the measured residual stress distributions. Residual stress and corrosion fatigue results for aluminum alloy 2219-T8751 are presented.