Researchers in China and Germany have used recycled scrap to develop a total of 14 new iron-based alloys, which are significantly stronger and over eight percent cheaper than conventional alternatives.
The project was carried out by the Chinese Shanghai Jiao Tong University, the City University of Hong Kong, the East China University of Science and Technology, the Central South University, and the Max Planck Institute for Sustainable Materials, in Germany.
For the research the team created a machine-learning method to turn metal scrap impurities into stronger alloys rather than removing them. This generated 14 new iron-based allows with up to 15.2 percent greater tensile strength, or 73.2 percent better elongation at fracture.
“The conventional approach to dealing with impurities in metal scrap is to dilute them by adding virgin material,” Liuliu Han, PhD, partner group leader of the Max Planck Institute for Sustainable Materials and one of the corresponding authors of the study, said. The new approach reduced production costs by 8.1 percent.
Making impurities useful
The world produces about two billion tons of metal per year, which mostly comes from newly extracted materials. However, this production also accounts for about 40 percent all industrial greenhouse gas emissions, and 10 percent of the global energy consumption.
While recycling could significantly reduce this environmental matter, metal scrap often contains impurities and varies in chemical composition. This is exactly what complicates the production of alloys with predictable mechanical properties.
While producers typically solve this problem by adding fresh metals to dilute the impurities, the process requires additional energy and increases carbon emissions. To address this challenge, the researchers’ machine-learning framework treats the impurities as potentially useful alloying elements.
The system uses algorithms and neural networks to find the most suitable metal mixtures and processing methods. It analyzes factors like temperature, processing time, tensile strength, and elongation to predict which combinations could deliver better performance. The most promising designs are then tested, and the results are fed back into the system for future predictions.
Stronger, cheaper alloys
To test the method, the team used ductile iron, a common industrial material that is known for its strength and flexibility, and can tolerate impurities. Approximately 120 million tons of ductile iron are produced globally each year.
The scientists then evaluated 17 alloy designs that the framework proposed, and 14 proved to have the best combinations of strength and ductility in the existing recycled-iron dataset. These new alloys demonstrated up to 15.2 percent greater tensile strength without losing stretchability, or 73.2 percent greater stretchability without sacrificing strength.
According to the scientists, the alloys were produced entirely from recycled scrap without adding virgin iron. They are certain the technology could be extended to recycled steel, aluminum, and copper alloys, and find use transportation, energy infrastructure, and industrial manufacturing.
Han elaborated how the approach turns metal impurities into an advantage. “We therefore developed a new machine-learning strategy that turns these impurities from a problem into an advantage, enabling us to design alloys that not only tolerate contaminants but can even benefit from them,” he said in a statement.
The study has been published in the journal Science Advances.