Additive friction stir deposition (AFSD), a deformation-based, near-net-shaping additive technology, is used to consolidate Al chips from automotive castings to produce fully-dense components, while addressing the energy, environmental, and efficiency challenges associated with recycling these chips via melting. Cold pressing of the chips results in feed-rods with a relative density of 68%. AFSD of these porous feed-rods leads to porosity-free material in the as-printed state. Compared to the base material of bulk cast Al, the as-printed material increases the tensile elongation from less than 1% to 17.8%, while exhibiting significant strain hardening. This upcycling effect is shown to originate from microstructure evolution during deposition, including the second-phase particles and the grain structure. The received Al chips have a hypereutectic composition and thus contain a high proportion of primary Si particles. The minor presence of Fe causes additional intermetallic particles as well. After deposition, these Si and Fe-based particles are refined, spherodized, and uniformly distributed in the Al matrix. Meanwhile, the cast Al microstructure is converted to an equiaxed grain structure with the grain size reduced from ∼ 25 μm to ∼ 2 μm. Finally, the energy consumption of AFSD-enabled upcycling is compared to melt-based recycling; potential pathways are evaluated for energy consumption reduction.

Here, we present the first demonstration of additive friction stir deposition of Ti-6Al-4V with closed-loop temperature control, wherein the print head rotation rate is adjusted in real-time to maintain a constant tool temperature during deposition. The as-printed Ti-6Al-4V is fully dense, achieving forging standard tensile properties along both the in-plane and out-of-plane directions. The measured yield strength, ultimate tensile strength, and elongation are 903 MPa, 1000 MPa, and 17% along the in-plane direction, and 948 MPa, 1024 MPa, and 16% along the out-of-plane direction. With closed-loop temperature control, the microstructure is found to be comparable along the thickness direction, contrasting the previous work performed under parameter-controlled conditions. For all the deposition conditions explored in this work, the deposited Ti-6Al-4V exhibits a lamellar microstructure with alpha laths forming inside prior beta grains, indicating higher peak temperatures than the beta transus. The increase of a pseudo heat index leads to an increase in the prior beta grain size and a decrease of the out-of-plane yield strength. Deposition of Ti-6Al-4V is seen to modify the microstructure of the substrate near the interface: the original equiaxed microstructure is replaced by lamellar and bimodal microstructures. We finally discuss the possibility of forming equiaxed microstructures in the as-deposited Ti-6Al-4V and provide evidence for different types of microstructures forming in the same deposition layer, which may be caused by the thermal gradient during reheating.

For zirconia-based technical ceramics, the unique advantages of micro-architecture geometries combined with the potent mechanical and functional properties have been challenging to implement owing to additive manufacturing restrictions. In this work, we present a stereolithography-based additive manufacturing approach involving slurry development for yttrium-stabilized tetragonal zirconia polycrystals (Y-TZP), followed by printing using a custom-built large-area projection micro-stereolithography system. After post-processing, i.e., polymer burnout and sintering, 98% relative density is reached in the printed Y-TZP parts. Thanks to the good manufacturing quality, the bulk-scale Y-TZP micro-honeycombs are able to display typical stretch-dominated behavior in out-of-plane compression, showing elastic loading (Stage I) and protracted brittle failure of individual walls over a significant strain (Stage II). For a Y-TZP micro-honeycomb consisting of 5 x 4 hexagonal cells with a wall thickness of 300 mu m and a cell diameter of 1.40 mm, the energy dissipation density is measured to be 9.45 J/g, substantially higher than other ceramic honeycombs and packings reported earlier. This energy dissipation capability is mostly attributed to the progressive wall collapse seen in Stage II deformation, in which the perimeter walls are preferentially fragmented relative to the interior walls. According to finite element analysis, this phenomenon is a result of the deviation from uniaxial compression and the presence of stress gradients in the perimeter walls. We also find evidence for stress-induced martensitic transformation in the YTZP micro-honeycomb after compression, which may be another contributor to the observed energy dissipation capability.

Additive friction stir deposition is an innovative solid-state additive manufacturing process that creates near-net-shape 3D components based on deformation bonding rather than melting and solidification. Here, we employ this process for selective cladding on thin Al-Mg-Si sheet metals and evaluate its feasibility for automotive manufacturing based on the cladding quality and substrate distortion. We show that under optimal conditions, additive friction stir deposition can produce high-quality cladding without surface or interface porosity even if the substrate is as thin as 1.4 mm. In addition, the high strength and good formability of the original Al-Mg-Si substrate are preserved in the post-cladding reinforced structure, which exhibits an ultimate tensile strength of 250 MPa and an elongation of 30 %. Despite the mechanical forces imposed by the tool during deposition, no local buckling or wrinkling is observed in the thin substrate. During cooling, however, in situ monitoring shows that mild, global substrate distortion gradually develops. Upon unclamping, the cladding-on-plate system reconfigures itself to minimize the potential energy, leading to an anticlastic curvature. Based on the curvature measurement and classical lamination theory, this work provides the first quantification of the residual stress caused by this newly-developed additive technology, in which the maximum tensile stress is estimated to be around 40 MPa in the rectangular reinforced structure and the interface mismatch strain is 7.37 x 10(-4). Both values are low thanks to the solid-state nature of the process.

Owing to the occurrence of hot cracking during solidification and vaporization of solute elements during melting, beam-based additive manufacturing has encountered serious problems in printing high-strength, nonweldable Al alloys. After aging, the mechanical properties of these alloys are often substantially inferior to their wrought alloy counterparts. Here, a deformation-based additive process is used for printing high-strength 7075 Al alloy (i.e., AA7075), wherein frictional heating is leveraged to enable rapid plastic deformation. The as-printed material consists of a refined, equiaxed microstructure and shows no surface or interface porosity. After proper solution treatment and aging, the yield strength, ultimate tensile strength, and elongation of the printed AA7075 are measured as 477 MPa, 541 MPa, and 8.2%, respectively. These values are a notable improvement from those published for beam-based additive manufacturing and are comparable to the typical properties of wrought alloy AA7075. With a comparison to the feed material, these values account for 95% of the yield strength, 94% of the ultimate tensile strength, and 78% of the elongation of the wrought AA7075-T6 with the exact same composition. Additional printing and testing show that wrought-like mechanical properties can be consistently achieved using this approach without adding new elements or nanoparticles.