This paper focuses on the use of the Self-Reacting FSW (SR-FSW) technology to join aluminum alloys. SR-FSW offers an innovative solution to the challenges associated with conventional Friction Stir Welding. The weld data presented in this work were obtained from welds produced using a servo hydraulically controlled Adjustable Self-Reacting Weld Head. The weld head uses two shoulders that interface with the top and bottom surface of the parts being joined. These top and bottom shoulders are independently actuated and biased to follow the profile of a work piece and supply a balanced load to the opposed surfaces of the work piece during the welding operation. The weld process and weld head configuration are discussed. In addition, the advantages that the self-reacting technology has as compared to conventional FSW are presented. Results of mechanical properties tests are presented for SR-FSW welds in Al 2219 and Al 2195, for thickness values from 8mm to 25.4mm.