In this study, 4 mm thick Al 5083 H321 plates were joined with Friction Stir Welding (FSW) method using different process parameters. In order to reveal the effects of different process parameters (Tool Shoulder Diameter, RPM, Direction of Rotation, Feed Rate), a total of 36 tests were carried out from 4 test parameters in a full factorial test setup. Tensile tests were performed with the test specimens cut from the welded plates, and their strength and mechanical properties were examined. In addition, the welding quality was subjected to an X-ray test, and quality control was passed. The ductility of the weld joints was demonstrated by the three-point bending test performed separately from the butt and root parts. Welded joints maintain their ductility without welding defects on bending tests by bending up to a 150° bending angle. On the other hand, it has been determined that the Al5083-H321 plate was pre-hardened by cold deformation; the heat generated during FSW causes recrystallization during welding, which resulted in a joint efficiency of 56%. The microstructural investigation and hardness tests proved the recrystallized regions.