A transformative hybrid solid-state additive manufacturing process, Additive Friction Stir Deposition (AFS-Deposition), will recycle metal waste/scrap at a forward operating base (FOB) to either fabricate or repair components. In this project, two specific metal waste streams from the deployed Military Occupational Specialty (MOS) units are identified: (1) scrap metal from machine chips generated by maintenance-MOS activities and (2) expeditionary airfield (EAF) aluminum landing mats from EAF-MOS activities. These two waste streams generate chips and metal strips, respectively, that will be processed by AFS-Deposition. Wherein the novel solid-state AFS-Deposition process, metals are deposited additively layer-by-layer through a hollow rotating tool. The project's low-power approach incorporates the advantages of additive manufacturing and grain refining into a single process, allowing fabrication of small and large parts, can use a variety of metals in different forms, does not require secondary processing or atmospheric controls, has superior build rates yielding enhanced mechanical properties, can be operated by a machine shop technician, and is ISO container transportable. The process has been demonstrated with both powder and solid feedstock material. Very importantly for FOB use, the AFS-Deposition process does not require metal powders, which can be difficult, energy intensive, or impractical to produce in theater. Aluminum alloys fabricated by the AFS-Deposition process, to-date, have produced full densities and refined grain structures.

The technical approach will implement a transformative solid-state deposition approach - AFS-Deposition, to reuse metal machine chips and solid metal waste at a FOB to test the hypothesis that fully dense samples with isotropic wrought mechanical properties can be produced from two waste streams; metal chips and stacked metal strips. This collaborative effort requires a multidisciplinary team with a combined skill set of processing science, microstructural characterization and mechanical testing. The three-year research program is divided into three main complimentary technical tasks. Task 1 will demonstrate feasibility of the process for this purpose by making fully dense deposits using recycled aluminum materials, including machine chip scraps and landing mats. Risks and constraints of the process will be investigated in this task.  Additionally, University of Alabama (UA) will be modeling the AFS-Deposition process in Task 1 to specifically elucidate the role of oxide layer dispersion during the AFS-Deposition process. Furthermore, the AFS-Deposition process modeling subtask supports the fabrication and subsequent characterization tasks to establish a complete iterative feedback loop. Task 2 characterizes the recycled material from the nano- to the macroscale. Finally, in Task 3, mechanical characterization and physics-based modeling build off the previous tasks where the monotonic and fatigue properties are quantified to understand dominant intrinsic and extrinsic structural features. The modeling in Task 3 aids in elucidating the role of oxide dispersion and microstructural evolution on performance of the AFS-Deposition recycled materials.

(1) Recycling and Sustainability: Providing a flexible and robust metal recycling option that may be applied to both non-ferrous and ferrous material systems provides the joint services a superior technological capability to manufacture components in the field and repair damaged structures/vehicles/armor with a new superior similar or dissimilar structural material, thus reducing time and energy for new components or repairs. This specifically benefits the warfighter by averting risk associated with transporting new components and reducing wait-time for critical components to ensure mission success. Additionally, the ability for a low-power metal recycling-to-component open-atmosphere fabrication process minimizes personnel and environmental hazards associated with dangerous chemicals involved in some phase change metal recycling programs.

(2) Basic science: The knowledge obtained through the research for processing recycled aluminum alloys via AFS-Deposition will provide new insight on microstructural, texture, and phase evolution under non-conventional, environmentally friendly processing conditions.