Strain Rate Dependent Plasticity Model for Precipitate Hardened Aerospace Aluminum Alloy Produced with Solid-State Additive Manufacturing

In this work, a strain rate dependent plasticity-damage material model is presented for precipitation hardened aluminum alloys made using Additive Friction Stir Deposition (AFS-D). The AFS-D process is a solid-state layer-by-layer additive deposition technique that extrudes a solid consumable feedrod through a hollow rotating tool. The friction generated between the rotating tool and build plate produces enough heat to soften the exiting feedrod and promote severe plastic deformation resulting in subsequent metallurgical bonding of the deposited layer. In this study, a fully-dense AA7050 build was manufactured via AFS-D at an average deposition rate of 0.8 kg/h. The microstructural characterization of the as-deposited AA7050 revealed a refined microstructure present throughout the AFS-D build. Quasi-static and high rate tensile experiments were conducted in the through thickness and the transverse orientations for the initial and final deposition layers of the AFS-D build in order to quantify the mechanical response of the as-deposited AA7050. A gradient in the mechanical properties was experimentally observed, where the final layers deposited with the AFS-D process exhibited a higher mechanical strength compared to the initial deposition layers of the component due to coarsening of secondary phases. Finally, an internal-state variable (ISV) plasticity-damage model was modified to capture observed material anisotropy as a function of precipitate free zones (PFZ) and size of secondary phases within the grain.