Synergistic influence of rotational and travel speeds on microstructure and property in AlMg alloy via Additive Friction Stir Deposition

Abstract

Additive Friction Stir Deposition (AFSD), as a novel solid-state additive manufacturing (AM) process, demonstrates substantial potential for fabricating high-integrity components using lightweight aluminum alloys. In the present study, the synergistic effects of tool rotational speed and travel speed on the microstructural evolution and mechanical performance of AA5083 alloy manufactured via AFSD were systematically investigated. Real-time monitoring of axial force and spindle torque was employed to enable in situ evaluation of thermo-mechanical conditions, which were quantitatively correlated with heat input, strain accumulation, and the resultant tensile properties. This research approach revealed the underlying mechanisms through which coupled process parameters regulate dislocation activity, grain refinement, and strengthening behavior in AFSD-fabricated aluminum alloys. An increase in rotational speed resulted in elevated heat input, thereby facilitating dynamic recovery and grain coarsening. In contrast, a higher travel speed reduced thermal input while increasing plastic strain, which contributed to the formation of more refined microstructures. Under high heat input conditions (i.e., tool rotational speed of 800 rpm and travel speed of 200 mm/min), the deposited AA5083 alloy exhibited an average grain size of 8.47 μm, with an ultimate tensile strength (UTS) of 296.7 MPa and a yield strength (YS) of 137.2 MPa. Notably, dislocation accumulation was identified as the dominant strengthening mechanism under this condition. Under lower heat input and higher strain conditions (i.e., tool rotational speed of 600 rpm and travel speed of 280 mm/min), finer grains were achieved (with an average size of 6.75 μm), accompanied by a comparable UTS (295.0 MPa) and a slight improvement in YS (139.1 MPa). This improvement in YS is attributed to the synergistic contribution of dislocation strengthening and grain boundary strengthening. These results confirm that lower heat input combined with higher strain rates enhances microstructural refinement without compromising mechanical strength, thereby providing a viable strategy for optimizing the AFSD process of AlMg alloys. The findings of this study advance the understanding of process–structure–property relationships in AFSD-fabricated alloys and provide support for the development of tailored process parameter sets for high-performance structural applications.