ARI awarded REMADE grant to recycle aerospace scrap

11/13/2019

Mike Koon, Grainger Engineering

Airplane Graveyard
Airplane Graveyard

Ever wonder what happens to aircrafts at the end of their useful life? They are sent to aircraft graveyards. The Arizona desert is home to several aircraft graveyards. Planes that are no longer in operation are parked there.  The Applied Research Institute at the University of Illinois at Urbana-Champaign is hoping to give these planes a new lease on life by recycling the aluminum alloys (principally the high-end AA7075) that are used to build these planes. 

The 12-month project is supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) through the REMADE Institute (Advanced Manufacturing Office Award Number DE-EE0007897). REMADE is a national coalition of leading universities and companies forging new clean energy initiatives and enabling early stage applied research of key industrial platform technologies that could dramatically reduce the embodied energy and carbon emissions associated with industrial-scale materials production and processing.

This project lays out an approach to develop a new process for recycling (AA7075) aluminum scrap into a high strength castable aluminum alloy. The project will focus on developing approaches to overcome the technical challenges (such as hot tearing and macrosegregation), which limit industry’s ability to process and ultimately reuse up to 35,000 metric tons of aluminum scrap annually. 

According to Mohamed Aboukhatwa, ARI Senior Research Scientist, up to this point AA7075, a premium aluminum alloy used in the aerospace industry, has been recycled into lower-value alloys, but this is the first effort by researchers to fully recycle AA7075 efficiently so that it can continue to be used as a high-end material. 

“Right now it can be downcycled into products with less stringent performance requirements, but if you want to get something that is equivalent to the original AA7075 properties, you’ll need to go through multiple thermomechanical processing cycles, so you’re not saving energy anymore,” Aboukhatwa said. “Our idea is to actually increase recycling and decrease downcycling of this alloy.” 

Compared to steel, the production of aluminum is extremely energy intensive, starting from mining and continuing with separation and refining processes. In fact, the amount of energy to produce aluminum is 20 times greater than the energy required to recycle it. AA7075 is a high strength, yet lightweight alloy, which makes it ideal for the aerospace industry. The alloy can’t be produced directly. Instead, it is subjected to complex thermomechanical processing routes, which adds significantly to the production costs.

“Recovering the AA7075 aluminum scrap and trying to cast it directly is technically challenging,” Aboukhatwa explained. “Specifically, when it’s cooling after being cast, it has a very high tendency to experience hot cracking because of its extended solidification range. We are attempting to take this alloy from the scrap and cast it directly. To reach this objective, the project is relying on coupling computational thermodynamics modeling with a multi-scale experimental investigation.”

Once completed, the ARI REMADE project will not only provide an avenue to fully recycle AA7075, it will also save energy on the production of the metal as compared to producing the material from scratch. The expected energy benefits are estimated at 6.5 petajoules (PJs) per year with an emissions reduction of about 370,000 metric tons of carbon dioxide per year. 

ARI is teaming with Eck Industries, a premium aluminum casting house that specializes in casting engine products as the industry partner on this project.

“Eck will perform thermal analysis and mechanical property testing to validate the modeling, and then we’ll down select the candidate alloy compositions for pilot-scale casting and keep doing so until we arrive at an optimum composition. At the end of the year, Eck will showcase our approach by casting cylinder heads directly from scrap AA7075. If we can successfully cast such intricate geometry without cracks, we can cast a multitude of industrial components.