Oak Ridge National Laboratory researchers have identified a mechanism in a 3D-printed alloy—termed “load shuffling”—that could enable the design of better-performing lightweight materials for vehicles. A paper on their work is published in the journal Acta Materialia.

One way to improve energy efficiency in vehicles is to make them lighter with aluminum-based materials. Researchers monitored a version of ORNL’s ACMZ—aluminum, copper, manganese and zirconium—alloy for deformation that occurs when the material is under persistent mechanical stress at high temperatures.

A team of ORNL researchers used neutron diffraction experiments to study the 3D-printed ACMZ alloy and observed a phenomenon called “load shuffling” that could inform the design of stronger, better-performing lightweight materials for vehicles. Credit: ORNL, Michi et al.

Using neutron diffraction, researchers studied the material’s atomic structure and observed that the overall stress was absorbed by one part of the alloy but transferred to another part during deformation. This back-and-forth shuffling prevents strengthening in some areas.

The dominant reinforcement phase in the alloy, θ-Al₂Cu, despite its high volume fraction of ∼10%, does not provide load transfer strengthening during creep deformation. Instead, the lattice strain evolution suggests a new mechanism we term “load shuffling” wherein the initial load is transferred away from precipitate-free zones along the grain boundaries where most of the θ-Al₂Cu particles are located to precipitate-strengthened grain interiors.

Notwithstanding the lack of load transfer strengthening, the as-fabricated AM Al-Cu-Mn-Zr alloy still possesses improved creep resistance at 300 °C relative to a cast alloy with similar composition. The proposed load shuffling mechanism explains the lack of observed L1₂-Al₃Zr strengthening at 300 °C and helps identify several strategies for improvement of elevated-temperature mechanical response of AM Al alloys.

—Michi et al.

Neutrons offer opportunities to study metallurgical phenomena in multiphase structural materials. We’ve gained unprecedented insight into elevated-temperature material behavior that will allow us to design improved aluminum alloys for extreme conditions.

—ORNL’s Amit Shyam

Resources

• Richard A. Michi, Sumit Bahl, Christopher M. Fancher, Kevin Sisco, Lawrence F. Allard, Ke An, Dunji Yu, Ryan R. Dehoff, Alex Plotkowski, Amit Shyam (2023) “Load shuffling during creep deformation of an additively manufactured AlCuMnZr alloy,” Acta Materialia, Volume 244 doi: 10.1016/j.actamat.2022.118557