Metal scrap upcycled into high-value alloys with solid phase manufacturing

The research is published this week in the journal nature communicationsshowing that scrap aluminum from industrial waste streams can produce high-performance metal alloys. The performance of upcycled aluminum is comparable to the same material produced from virgin aluminum, suggesting this approach can provide a low-cost route to bringing more high-quality recycled metal products to market. By converting waste into high-performance aluminum products, this new method, called solid-phase alloying, not only enhances material properties but also contributes to environmental sustainability.

“The novelty of our work is that by adding precise amounts of metallic elements to a mixture with aluminum chips as a precursor, it can actually be converted from a low-cost waste into a high-cost product,” Xiao Li said , PNNL materials scientist and lead author of the study. “We can do this in one step and everything is alloyed in five minutes or less.”

An innovative solid-phase alloying process converts aluminum scrap mixed with copper, zinc and magnesium into a precisely engineered, high-strength aluminum alloy product in minutes, whereas it would take days to produce the same product using traditional melting, casting and extrusion. The research team used PNNL’s patented technology “Shear Assisted Processing and Extrusion” (ShAPE) to achieve their results. However, the researchers note that these findings should be reproducible with other solid-phase manufacturing processes.

In the ShAPE process, high-speed rotating dies create friction and heat that disperse the bulk starting ingredients into a uniform alloy with the same properties as a newly manufactured aluminum forged product. The solid-phase approach eliminates the need for energy-intensive bulk melting and, combined with low-cost feedstock from scrap, has the potential to significantly reduce the cost of manufacturing these materials. For consumers, this means recycled aluminum products will have a longer life and better performance at a lower cost, whether they are part of vehicles, building materials or household appliances.

Core strong metal alloy

The science team used mechanical testing and advanced imaging to examine the internal structure of upcycled materials produced from solid-phase alloys. Their results showed that the ShAPE upcycled alloy has a unique nanostructure at the atomic level. During the ShAPE process, atomic-scale features called Guinier-Preston zones are formed within the alloy. These features are known to increase the strength of metal alloys. Compared with traditional recycled aluminum, the strength of the upgraded recycled alloy is increased by 200%, and the ultimate tensile strength is also improved. These properties translate into more durable, better-performing products for consumers.

“Our ability to upcycle scrap is exciting, but what excites me most about this research is that solid-phase alloys are not limited to aluminum alloys and waste feedstocks,” said Cindy Powell, chief science and technology officer at DOE . “In theory, solid-phase alloys are suitable for any combination of metals you can imagine, and the fact that fabrication occurs entirely in the solid state means you can start thinking about entirely new alloys that we couldn’t make before.”

Li said the solid-phase alloying process can be used to create customized wire alloys for various 3D printing technologies. For example, wire arc additive manufacturing (WAAM) is used to 3D print or repair metal parts. In the process, a roll of welding wire is fed into a robotic welding gun, which melts it to build the 3D part.

“It’s difficult to get feeders with custom compositions for wire-based additive manufacturing,” Li said. “Solid phase alloying is an excellent way to produce custom alloys with precise compositions such as 2% copper or 5% copper.”

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