Material flow behaviour in the Friction Stir Spot Welding of aluminum alloys

Friction stir spot welding (FSSW) is a technological process that it allows to obtain junctions characterized by good mechanical properties and to perform them in a simple and fast way. The detailed knowledge of material flow around rotating tool, and of the microstructural evolution occurring during this process, constitute the fundamental input to realize analysis and simulation models in order to determine a optimal tool design and high structural efficiency welds. In the present research, an integrated mechanical-metallurgical-morphological analysis has been performer, to evaluate the influence of the different technological parameters on the characteristics of the joint. The experimental plan has been realized varying the tool sinking, the tool rotation rate and the performance time during the sinking. The process has been performed on AA6082 T6 whit thickness equal to 1.0 mm and on AA105 O aluminum sheets of 0.5 mm. The latter material (AA1050) has been utilized as weld marker of the material flow. Realized joints have been subjected to macrographic analysis that allowed to determine flow material variations. Beginning from the macrographies of the transversal section of every joint, a morphological analysis has been effected on the variation of the surface of interface among the two materials. For each image the threshold image has been so obtained. The presence of two different types of surfaces in the different zones of the joint has been emphasized. Furthermore micrographic analysis, tensile tests and micro-hardness Vickers tests allowed to determine microstructural variations and strength characteristics of the joints in order to chose the best set of operative parameters. The same experimental plan has been performer on two AA6082 T6 aluminum sheets with thickness equal to 3.0 mm. On the realized joints, tensile tests have been performed to correlate the variations of flow to the resistance of the joint.