TY - JOUR

T1 - Making sustainable aluminum by recycling scrap

T2 - The science of “dirty” alloys

AU - Raabe, Dierk

AU - Ponge, Dirk

AU - Uggowitzer, Peter J.

AU - Roscher, Moritz

AU - Paolantonio, Mario

AU - Liu, Chuanlai

AU - Antrekowitsch, Helmut

AU - Kozeschnik, Ernst

AU - Seidmann, David

AU - Gault, Baptiste

AU - De Geuser, Frédéric

AU - Deschamps, Alexis

AU - Hutchinson, Christopher

AU - Liu, Chunhui

AU - Li, Zhiming

AU - Prangnell, Philip

AU - Robson, Joseph

AU - Shanthraj, Pratheek

AU - Vakili, Samad

AU - Sinclair, Chad

AU - Bourgeois, Laure

AU - Pogatscher, Stefan

N1 - Publisher Copyright: © 2022 The Authors

PY - 2022/4/7

Y1 - 2022/4/7

N2 - There are several facets of aluminum when it comes to sustainability. While it helps to save fuel due to its low density, producing it from ores is very energy-intensive. Recycling it shifts the balance towards higher sustainability, because the energy needed to melt aluminum from scrap is only about 5% of that consumed in ore reduction. The amount of aluminum available for recycling is estimated to double by 2050. This offers an opportunity to bring the metallurgical sector closer to a circular economy. A challenge is that large amounts of scrap are post-consumer scrap, containing high levels of elemental contamination. This has to be taken into account in more sustainable alloy design strategies. A “green aluminum” trend has already triggered a new trading platform for low-carbon aluminum at the London Metal Exchange (2020). The trend may lead to limits on the use of less-sustainable materials in future products. The shift from primary synthesis (ore reduction) to secondary synthesis (scrap melting) requires to gain better understanding of how multiple scrap-related contaminant elements act on aluminum alloys and how future alloys can be designed upfront to become scrap-compatible and composition-tolerant. The paper therefore discusses the influence of scrap-related impurities on the thermodynamics and kinetics of precipitation reactions and their mechanical and electrochemical effects; impurity effects on precipitation-free zones around grain boundaries; their effects on casting microstructures; and the possibilities presented by adjusting processing parameters and the associated mechanical, functional and chemical properties. The objective is to foster the design and production of aluminum alloys with the highest possible scrap fractions, using even low-quality scrap and scrap types which match only a few target alloys when recycled.

AB - There are several facets of aluminum when it comes to sustainability. While it helps to save fuel due to its low density, producing it from ores is very energy-intensive. Recycling it shifts the balance towards higher sustainability, because the energy needed to melt aluminum from scrap is only about 5% of that consumed in ore reduction. The amount of aluminum available for recycling is estimated to double by 2050. This offers an opportunity to bring the metallurgical sector closer to a circular economy. A challenge is that large amounts of scrap are post-consumer scrap, containing high levels of elemental contamination. This has to be taken into account in more sustainable alloy design strategies. A “green aluminum” trend has already triggered a new trading platform for low-carbon aluminum at the London Metal Exchange (2020). The trend may lead to limits on the use of less-sustainable materials in future products. The shift from primary synthesis (ore reduction) to secondary synthesis (scrap melting) requires to gain better understanding of how multiple scrap-related contaminant elements act on aluminum alloys and how future alloys can be designed upfront to become scrap-compatible and composition-tolerant. The paper therefore discusses the influence of scrap-related impurities on the thermodynamics and kinetics of precipitation reactions and their mechanical and electrochemical effects; impurity effects on precipitation-free zones around grain boundaries; their effects on casting microstructures; and the possibilities presented by adjusting processing parameters and the associated mechanical, functional and chemical properties. The objective is to foster the design and production of aluminum alloys with the highest possible scrap fractions, using even low-quality scrap and scrap types which match only a few target alloys when recycled.

KW - Alloy design

KW - Aluminum

KW - Corrosion

KW - Precipitation

KW - Processing

KW - Properties

KW - Recycling

KW - Sustainability

KW - Thermodynamics

UR - http://www.scopus.com/inward/record.url?scp=85130182706&partnerID=8YFLogxK

U2 - 10.1016/j.pmatsci.2022.100947

DO - 10.1016/j.pmatsci.2022.100947

M3 - Review article

AN - SCOPUS:85130182706

VL - 128.2022

JO - Progress in materials science

JF - Progress in materials science

SN - 0079-6425

IS - July

M1 - 100947

ER -