Abstract
This paper examines the impact of oxide coatings on the surfaces of feedstock material used for Additive Friction Stir-Deposition (AFS-D). The AFS-D is a solid-state additive manufacturing process that uses severe plastic deformation and frictional heating to build bulk depositions from either metallic rod or powder feedstock. Since aluminum alloys naturally form an oxide layer, it is important to determine the influence of the feedstock surface oxide layer on the resultant as-deposited microstructure and mechanical properties. In this study, three AA6061 square-rod feedstock materials were used, each with a different thickness of aluminum oxide coating: non-anodized, 10-micron thick, and 68-micron thick. Macroscale depositions were produced with these feedstock rods using the AFS-D process. Optical and electron microscopy showed that the two oxide coatings applied through anodization were efficiently dispersed during the AFS-D process, with oxide particles distributed throughout the microstructure. These oxide particles had median sizes of 1.8 and 3 μm2, respectively. The yield and tensile strengths of these materials were not measurably impacted by the thickness of the starting oxide coating. While all three feedstock material variations failed by ductile rupture, the elongation-to-failure did decrease from 68% to 55% in the longitudinal direction and from 60% to 43% in the build direction for the thickest initial oxide coating, 68 microns.
Highlights
Solid-state additive manufacturing (AM) provides a valuable approach for printing near-net shape metallic materials layer-upon-layer [1]
Larger alumina particles were observed in the AA6061-2.8%alumina deposition, which was produced from the feedstock with thicker anodized layers (68 μm) (Figure 4c)
From the results and discussion, below are the conclusions addressed from this research: Oxide layers on the surface of the Additive Friction Stir-Deposition (AFS-D) feedstock bars do not measurably impact the strength of the deposited material but may degrade the ductility: increasing the amount of alumina from 0% to 2.8% in the deposit decreased the elongation in the longitudinal direction from 68% to 55%, and in the build direction from 60% to 43%
Summary
Solid-state additive manufacturing (AM) provides a valuable approach for printing near-net shape metallic materials layer-upon-layer [1]. The major concerns from fusion-based AM summarized by Frazier [2], such as hot cracking, elemental segregation, shrinkage, and gas porosity, could be alleviated by non-beam-based solid-state AM demonstrated by Yu et al [3]. Another advantage of solid-state AM is the isotropic mechanical properties from the refined, equiaxed grains in the final depositions [3]. Additive Friction Stir-Deposition (AFS-D) is a more recent solid-state AM technique, and it applies severe plastic deformation and frictional heating from a rotating tool to build metallic materials through layer-by-layer deposition. Van der Stelt et al [4] and
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