Study: Solid phase manufacturing transforms recovered aluminum into high-performance alloys without melting

A new research study from researchers at the Department of Energy’s Pacific Northwest National Laboratory (PNNL), Richland, Washington, published in Nature Communications reveals that metal scrap can be transformed and upgraded directly into high-performance, high-value aluminum alloys without conventional melting processes.

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The study demonstrates that aluminum manufacturing scrap can be transformed into metal alloys through a new method called solid phase alloying that perform on par with identical materials produced from primary aluminum, indicating this approach can provide a low-cost, environmentally sustainable pathway to bringing more high-quality recycled metal products to the marketplace, PNNL says in a new release.

Diagram by Nathan Johnson | Pacific Northwest National Laboratory

The Laboratory Directed Research and Development program at PNNL supported the study as part of the Solid Phase Processing Science Initiative. PNNL researchers Tianhao Wang, Zehao Li, Tingkun Liu, Xiang Wang, Arun Devaraj, Cindy Powell and Jorge F. dos Santos also contributed to the research. 

“The novelty of our work here is that by adding a precise amount of metal elements into the mix with aluminum chips as a precursor, you can actually transform it from a low-cost waste to a high-cost product,” saus Xiao Li, a PNNL materials scientist and lead author of the research study. “We do this in just a single step, where everything is alloyed in five minutes or less.”

The solid phase alloying process converts aluminum scrap blended with copper, zinc and magnesium into a precisely designed high-strength aluminum alloy product in a matter of minutes compared with to the days required to produce the same product via conventional melting, casting and extrusion. The research team used a PNNL-patented technique called Shear Assisted Processing and Extrusion, or ShAPE, to achieve the results. However, the researchers note that the findings should be reproducible with other solid phase manufacturing processes.

Through the ShAPE process, a high-speed rotating die creates friction and heat that disperses the chunky starting ingredients into a uniform alloy with the same characteristics as a newly manufactured aluminum wrought product. The solid phase approach eliminates the need for energy-intensive bulk melting, which combined with the low-cost feedstocks originating from scrap, has the potential to sharply reduce the cost of manufacturing these materials, PNNL says.

The team used mechanical testing and advanced imagery to examine the internal structure of the materials produced through solid phase alloying, showing the ShAPE alloy imparts a unique nanostructure at the atomic level. During ShAPE, atomic-scale features called Guinier-Preston zones form within the alloy, which are known to improve strength in metal alloys. Compared with conventional recycled aluminum, these alloys are 200 percent stronger and have increased ultimate tensile strength, according to PNNL, which could translate into longer-lasting and better-performing consumer products. 

“Our ability to upcycle scrap is exciting, but the thing that excites me the most about this research is that solid phase alloying is not just limited to aluminum alloys and junk feedstocks,” says Powell, chief science and technology officer for energy and environment at PNNL and a coauthor of this study. “Solid phase alloying is theoretically applicable to any metal combination that you can imagine, and the fact that manufacturing occurs wholly in the solid state means you can begin to consider totally new alloys that we’ve not been able to make before.” 

The solid phase alloying process could be used to create custom metal wire alloys for various 3D printing technologies, Li says. For example, wire arc additive manufacturing, or WAAM, is used to 3D print or repair metal parts. In this process, a roll of wire feeds into a robotic welding torch, which melts it to build 3D parts.

“It’s difficult to obtain feed wires with customized compositions for wire-based additive manufacturing,” Li says. “Solid phase alloying is a fantastic way to produce tailored alloys with exact compositions such as 2 percent copper or 5 percent copper.”