AA2219-T87 alloy was self-reacting friction stir welded at different traverse speeds. Joints produced at low traverse speed exhibit tunnel defects. The tunnel defects can be avoided by higher traverse speed, but excessive increase in traverse speed leads to the joint line remnants presenting in a linear geometry which comprises strength of the joint by providing an easier path for crack propagation. In the weld nugget zone, grains in the lower layer are coarser than those in the upper layer due to smaller extent of heat dissipation through the bottom shoulder. Extensive softening occurs in the weld zone owing to dissolution of the θ′ precipitates. Tensile strength of the defect-free joint reaches 74% of that of the base metal.