Additive friction stir deposition-enabled upcycling of automotive cast aluminum chips
Jake K. Yoder, Greg D. Hahn, Nanzhu Zhao, Raymond E. Brennan, Kyu Cho, Hang Z. Yu
Abstract
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.