Additive friction stir deposition (AFSD) is an innovative solid-state manufacturing process capable of producing parts with fine, equiaxed grains. However, due to the complexity of extensive plastic deformation and the viscoplastic behavior of metallic materials at elevated temperatures, the analysis of material flow and stress evolution during AFSD remains at a rudimentary stage. As a developing technology, gaining a deeper understanding of the underlying physical behaviors behind the processing is appreciable. This study comprises three objectives: investigating microstructure and stress-induced acoustic wave propagation behaviors, implementing non-contact in-situ monitoring in AFSD of aluminum alloy 6061 using a far-collimation acoustic metamaterial lens, and ex-situ analysis of parameter-dependent mechanics influences in AFSD of aluminum alloys 6061. To achieve this, a novel ultrasound in-situ monitoring method, along with ex-situ residual stress measurements, is facilitated by MD and FEA simulations and been experimentally verified. Real-time asymmetric property distribution and abnormal parameter-dependence acoustic wave phase change during the AFSD of aluminum alloy 6061 were identified through the in-situ monitoring and further investigated in detail through ex-situ inspection. A key parameter, effective viscosity, was introduced to the parameter windows selections, which can affect the thermo-fluidic mechanics during the process, thereby altering the physical aspects, mechanical properties, and microstructures.