Replacing Cerium with Mischmetal in Cast Aluminum Alloys
Cerium (Ce) is the most abundant rare earth (RE) element, and is in fact more abundant in the terrestrial crust than Cu or Pb. Al-Ce-based alloys form Al-Al11Ce3 eutectic structure with a very fine microstructure which provides good strength and ductility, as well as coarsening- and creep resistance to these alloys, well beyond Al-Si based eutectic.
RE elements are mixed in ore, and Ce and La oxide mixtures are often left over after other RE are extracted for various applications. After reduction, the resulting Ce-La alloys are called Mischmetal (MM). MM has a lower cost, energy consumption, and CO2 footprint than pure Ce because less elemental separation is needed.
Al-Ce, Al-La, Al-Nd, and Al-Pr phase diagrams are highly similar on the Al-rich side with similar eutectic phase structure and mechanical properties. Our research will investigate: (i) how MM composition influences the Al-MM alloys' eutectic compositions and mechanical properties; (ii) how additional alloying elements can strengthen the Al-MM alloys, based on various mechanisms such as solid solution strengthening, precipitation strengthening, and load transfer.
We aim to develop castable, high-performance Al-MM alloys with high strength that can replace heavier titanium-based aerospace parts operated at elevated temperatures (>300°C), while having lower cost, energy consumption, and CO2 footprint during production than Al-Ce alloys.
- Liu, Yang, Richard A. Michi, and David C. Dunand. "Cast near-Eutectic Al-12.5?Wt.% CE Alloy with High Coarsening and Creep Resistance." Materials Science and Engineering: A 767 (2019): 138440. https://doi.org/10.1016/j.msea.2019.138440.
- Sims, Zachary C., David Weiss, Orlando Rios, Hunter B. Henderson, Michael S. Kesler, Scott K. McCall, Michael J. Thompson, Aurelien Perron, and Emily E. Moore. "The Efficacy of Replacing Metallic Cerium in Aluminum-Cerium Alloys with LREE Mischmetal." The Minerals, Metals & Materials Series, 2020, 216-21. https://doi.org/10.1007/978-3-030-36408-3_30.
- U.S. Department of Energy (Office of Energy Efficiency & Renewable Energy)