Understanding the process-structure-property relationship of lightweight aerospace alloys processed using additive friction stir deposition.

May 2023
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Recently additive manufacturing has become an alternative method to fabricate components with forged-like properties and reduced lead times when compared to traditional manufacturing methods. However, some fusion-based additive manufacturing methods create deleterious effects, such as hot cracking and alloy vaporization, on the mechanical performance of lightweight aerospace alloys. A novel solid-state additive manufacturing process, known as Additive Friction Stir Deposition (AFSD), offers the ability to combat these deleterious effects by fabricating fully dense components with forged-like properties in lightweight alloys. This research investigates the process-structure-property (PSP) relationship of magnesium alloy WE43 and aluminum alloy 7020, through in-depth characterization of the resulting microstructure and mechanical properties post AFSD processing. The first work on the PSP relations of AFSD processed magnesium alloy WE43 is focused on the microstructural evolution of the as-deposited WE43 in comparison to forged feedstock. Additionally, mechanical performance was evaluated between the forged feedstock and the as-deposited WE43 to elucidate the role of microstructure on the mechanical properties with particular interest in the quasi-static and fatigue performance of each method of manufacturing. The subsequent research on AFSD of AA7020 investigates the microstructural evolution and mechanical performance of the as-deposited AA7020 in comparison to wrought AA7020 feedstock. Additionally, the strain-rate effects and cyclic behavior were assessed between the feedstock material and the as-deposited AA7020 to determine the effects of the microstructural evolution during the AFSD process on the monotonic and fatigue properties. Particular interest was focused on quantifying the as-deposited layer dependence and failure mechanisms from the resulting monotonic and cyclic loading experiments compared to the wrought material. The final work establishes a fundamental relationship between acceptable process parameters and build direction mechanical properties on AFSD processed AA7020. Additionally, the effect of process parameters on the microstructural evolution of the AFSD AA7020 was investigated. An emphasis on failure mechanisms of select parameters to elucidate the role of processing conditions on the mechanical performance was assessed to achieve depositions with isotropic behavior.