Structure-property-process relations of solid-state additively manufactured aerospace aluminum alloys

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University of Alabama Libraries

Additive manufacturing processes provide new avenues to additively repair or manufacture complex aerospace components. There has been limited success in additively manufacturing aluminum alloys and aluminum metal matrix composites that are susceptible to hot-cracking. Recently, the development of a transformative solid-state additive manufacturing process, Additive Friction Stir-Deposition (AFS-D), incorporated the benefits of additive manufacturing and severe plastic deformation processes that provided a new path to fabricate fully-dense aluminum alloy and aluminum metal matrix composite structures. In this work, the microstructural evolution and mechanical response of an Al-Cu-Mg metal matrix composite (MMC) containing 20 weight percent Al2O3 and an AA7050 isogrid structure was additively manufactured through the AFS-D process. Microstructural characterization of the tempered and overaged Al-MMC employed optical microscopy, Scanning Electron Microscopy, and Electron Backscatter Diffraction. Additionally, to quantify the mechanical response of the tempered and overaged Al-MMC, quasi-static tensile experiments were conducted in the longitudinal and transverse orientation. Dynamic tensile testing was performed on the tempered and overaged AFS-D Al-Cu-Mg material in the transverse orientation using a Split-Hopkinson pressure bar. The resulting microstructural and mechanical analysis was captured via the internal state variable (ISV) plasticity damage model. The model is consistent with continuum level kinematics, kinetics, and thermodynamics. The following research provides a foundation for rapidly additively manufacture large MMC structures through AFS-D. This study produced a fully dense AA7050 isogrid structure was manufactured without the need for additional alloying elements. Three sections of the component that exhibit differing thermomechanical processing history were evaluated for the resulting microstructure and mechanical response. The microstructural characterization of the as-deposited AA7050 employed TEM, SEM, and EBSD. The as-deposited AA7050 exhibited a refinement of the constituent particles and grains within the microstructure. Additionally, to quantify the mechanical response of the as-deposited AA7050, quasi-static tensile and high rate tensile experiments were conducted. The Internal-State Variable Plasticity model was successfully modified to be able to capture material anisotropy as a function of precipitate free zones and secondary phases size within the grain.

Electronic Thesis or Dissertation
Mechanical engineering