Aluminum alloys offer rare earths balance

The U.S. Department of Energy has published a portfolio of research and development projects on the commercialization of aluminum-cerium alloy that offers a possible solution to the overabundance of the most abundant rare earth element.

The clean energy transition depends on critical materials like rare earth elements that power wind turbine generators, electric vehicles, and other clean energy technologies, materials, and processes.

Typically, REEs are found together in mineral deposits, which are then painstakingly separated from one another to use only those REEs needed for whichever function it serves.

Mined as some mix of the 14 stable rare earths, only certain ones are in demand, creating a balance problem – producing enough of certain rare earths that are more "popular" creates an overabundance of the less desirable.

Take neodymium and praseodymium, for example, two rare earths considered to be highest in demand as they are a primary ingredient in permanent magnets used in the aforementioned EVs, wind turbines, etc.

These are typically in what could be considered medium abundance in a rare earths deposit but are the primary material being mined for.

Add that to more scarce rare earths necessary for green technologies – such as dysprosium and terbium, which are among the rarest of rare earths – then every little bit counts as more and more magnets will be needed for ever more engines.

This has created a rare earth balance problem.

Cerium is the most abundant of the rare earth elements, yet it has practically no demand. This means that efforts to produce enough neodymium, praseodymium, dysprosium, and terbium is creating an oversupply of this light rare earth.

The issue with oversupply lies in it offering no value to a mine and ultimately piling up.

However, a new aluminum-cerium alloy created by DOE's Advanced Materials and Manufacturing Technology Office offers a potential new market for cerium, adding an enticing revenue stream for current and future REE mines.

Shore up cerium

DOE's Advanced Materials and Manufacturing Technologies Office (AMMTO), along with the Critical Minerals Institute (CMI), have been working together to address the rare earths imbalance.

Pairing cerium with aluminum to create aluminum-cerium alloys with tailored properties has essentially unlocked an array of applications for the underappreciated rare earth.

In 2020, recognizing the achievements of the alloy, the Aluminum Association awarded the official designation of this new class of Al-Ce alloys. This designation allows for the launch of global industrial applications and creates more opportunities for industry to produce the alloys using the designations and to enable CMI commercialization.

In the ensuing years, CMI added several projects to its portfolio of Al-Ce alloys to boost scale-up, licensing, and commercialization efforts. These projects, supported by AMMTO, bring together the advanced expertise of researchers from CMI, DOE's National Labs, and universities.

The various development projects in CMI and scale-up of processing have received significant support from Eck Industries, an aluminum foundry in Wisconsin, that signed an exclusive license with CMI to commercialize Al-Ce alloys.

Finding uses for cerium not only supports domestic rare earth mining operations by providing innovative materials to U.S. manufacturers, but it also provides a separate potential value stream from the most likely rare earth in an REE mine.

Al-Ce alloy benefits

The alloy developed by CMI has proven to be adaptable, lightweight, resistant to corrosion, and stable in temperatures up to 500 degrees Celsius (932 degrees Fahrenheit).

Furthermore, there are reductions in energy and emissions associated with the production of Al-Ce alloy because it doesn't require heat treatment – an energy-intensive process to soften metals and improve formability.

So far, the alloy has been used across a diverse range of applications, including cylinder heads, turbochargers, and turbine blades for hydroelectric turbines, pistons, and rotors.

The impacts of Al-Ce alloy are fairly significant – not only creating a new market for cerium which addresses the rare earth balance problem, where economic value is spread over a broader set of REEs beyond just magnet REEs but also increasing market demand that drives production of critical rare earth elements needed for those magnets. Also, due to the alloy's unique microstructure and resulting properties, Al-Ce alloy can be used to reduce energy use across multiple large-scale transportation applications.

Commercialization efforts

Several projects being conducted throughout the country are furthering the potential uses of Al-Ce alloy.

• A project led by Orlando Rios from the University of Tennessee, Knoxville, is exploring the specific issues that would enable the deployment of a stronger aluminum-cerium alloy at high temperatures, high ductility, and lower cost that could be used in high-performance applications such as pistons, turbochargers, and cylinder heads.

• A project led by Hunter Henderson from Lawrence Livermore National Laboratory is looking to develop high-volume and high-value applications for overproduced cerium. The project features high-value-added aluminum-cerium-based alloys, opening the market to early adopters and diversifying future cerium demand. In their research, the project demonstrated metal 3D printing of aluminum rare-earth element alloy forms an internal degradation-resistant nanostructure. It also established the enhanced thermal performance of Al-REE alloys – proving eligibility for high-temperature applications previously unavailable to other aluminum alloys.

• Two projects led by Ryan Ott at Ames National Laboratory are exploring the improvement of energy efficiency and economics of aluminum recycling through overly produced rare earth mining byproducts, specifically cerium; and the enhancement of overly produced elements such as cerium while decreasing the usage of critical REEs such as neodymium. In the first project, research has demonstrated that adding small amounts of cerium to aluminum has increased alloy tolerances to impurities such as copper and iron and improved overall corrosion resistance. These additions also allow for lower-quality aluminum to be used in the production of high-value alloys, reducing the need for both energy and cost-intensive high-purity aluminum additions. In their bolder study, the project is aimed at developing and finding new pathways for materials and manufacturers, a broader sweeping benefit to the enigma that rare earths exhibit.

With some of the most well-established national labs and universities working on pushing this overlooked and underappreciated rare earth to the limelight. Once commercialization has been established, rare earth miners can potentially begin to offload the stockpiles they might have accumulated or, for those not in operation yet, add to their resource estimates to make the already enticing mines even more so.