Microstructure evolution and mechanical properties of AA6061/AA1100/AA6061 dissimilar aluminum alloy fabricated by friction stir additive manufacturing

In this study, a dissimilar aluminum alloy build of AA6061/AA1100/AA6061 was successfully fabricated using friction stir additive manufacturing (FSAM) process. Through systematic characterization, the materials flow, mixing features and microstructure evolution across specific regions along the build depth were investigated. Additionally, mechanical properties and fracture behavior of the final build were also explored. The results revealed that equiaxed grains with average grain sizes ranging from 4.9 µm to 10.5 µm were formed in central regions of each additive layers. In addition, the average grain sizes of thermal mechanical affected zones below the stir zones decreased significantly to 2.6 ~ 2.7 µm, primarily due to the subgrain refinement mechanism. Texture analysis showed a dominant presence of deformed and shear textures throughout all regions, owing to adequate shear strain suffering from tool. The major precipitates presented in stir zones consisted of Al ₈ Fe ₂ Si, β and β’. Furthermore, the FSAM build showed remarkable drops in yield strength (101.3 MPa) and ultimate tensile strength (213.0 MPa), compared to AA6061-T6 base metal. Moreover, microhardness fluctuation along the build depth were observed, owing to the variation of dislocation densities and grain orientations. These findings offer the academic foundation for further development of FSAM in producing dissimilar alloy build and promote their industrial applications.