FS welds have a sound joint for the lack of voids, cracks and distortions. When compared to the base material, friction stir welding (FSW) joints exhibit a finer crystal grain in the weld nugget, and advancing side has a clearer boundary with the weld nugget than that of the retreating side. The fatigue life of FS welds is 6-14 times longer than that of MIG-pulse welds under the stress ratio R = 0.1 and the calculated fatigue characteristic values of each weld increase from 42.32 MPa for MIG to 68.47 MPa for FSW at 2 x 10(6) cycles. In the high-cycle regime, the fatigue strength of the FSW joint is almost equivalent to that of the base material. The fatigue fracture of FSW revealed regions of crack initiation, stable crack growth and overload. (c) 2005 Elsevier B.V. All rights reserved.