Tailoring the microstructure and mechanical behavior of AFSD 6061 aluminum alloy through heat treatment

Additive friction stir deposition (AFSD), a solid-state additive manufacturing process, exhibits significant potential for the fabrication of aluminum alloys. However, the unique thermomechanical history of AFSD makes the heat treatment (HT) response of certain aluminum alloys unclear. In this study, 6061 aluminum alloy samples produced via AFSD were subjected to solution treatment at 535 °C for durations ranging from 10 to 50 min in 30 min increments, followed by artificial aging treatment at 165 °C for 6 h. The influence of solution time on microstructure evolution and mechanical properties was systematically investigated. With increasing solution time, the grain size increased from 68.57 μm to 185.41 μm. Compared to the as-deposited sample, anomalous grain growth (AGG) of varying degrees was observed. The proportion of high-angle grain boundaries (HAGBs) within the microstructure gradually increases with extended solution treatment time, while the density of geometrically necessary dislocations (GNDs) is significantly reduced. The uniform dispersion of fine β″ phases and β′ phases within the grains significantly enhances the mechanical properties. At a solution treatment time of 50 min, the material exhibits a tensile strength of approximately 315.13 MPa along the building direction (BD), a yield strength of 273.03 MPa, and an elongation of 20.8%. Additionally, the microhardness after HT increases to 123.9 HV_0.1 relative to the as-deposited sample. This study demonstrates that shortening the solution treatment time mitigates the severity of abnormal grain growth (AGG) while simultaneously promoting the precipitation of strengthening phases, thereby optimizing the overall mechanical properties of the alloy.