Abstract: Taking the thickest 10 mm 2219C10S aluminum alloy butt weld in the common bottom tank of a module of a new generation launch vehicle in China as the object, effects of welding parameters on the quality and properties of self-reacting friction stir welding of 10 mm thick 2219 aluminum alloy were studied. From the surface forming results, it could be seen that selection of rotation speed of tool had an important influence on the weld quality, when the rotation speed of tool was greater than or equal to 250 r/min, different degree of metal scratch defects appear on the weld surface, when rotation speed of tool was 200 r/min, the weld with good surface formation could be obtained in a large range of welding speed. According to analysis of weld microstructure, there was a phenomenon of “nugget bulge” in the nugget zone with the condition of n≥250 r/min. However, nugget zone presented a typical “dumbbell shape” with the condition of n=200 r/min, which was consistent with the forming law of weld surface. Under different conditions, micro-hardness of welded joints presented a distribution with typical “W” type, but with the increase of welding speed, average micro-hardness of welded joints increased gradually. The mechanical properties of the weld showed that tensile strength of welded joints was above 310 MPa, and elongation was stable in the range of 7.0%～7.5%, and fracture of welded joints was typical ductile fracture.Highlights: The friction stir welding process of 2219 aluminum alloy double shoulders with a thickness of 10 mm was studied. The process parameters which had great influence on quality of welded joints and performance were determined. The range of welding parameters for obtaining good performance of welded joints was obtained, which lay a foundation for the subsequent engineering application of this technology.