'Dirty' Aluminium Alloys: Scrap-related production & sensitivity to tramp elements

Recycling rates: Definitions, industry branches, and regional aspects

Since the introduction of the Hall–Héroult and Bayer processes in the late 19th century, between one and one-and-a-half billion metric tons of aluminum have been produced globally. Approximately three quarters of this volume remain in active use today. Roughly one third each is found in buildings and infrastructure, electrical equipment, and the transportation sector. Aluminum used in packaging, by contrast, re-enters the recycling system within weeks.

Around 30% of global aluminum production now originates from recycled scrap, though this share varies regionally—approximately 30% in the United States and around 50% in the European Union. On a global average, the total recycling rate is roughly 40%. The yield from scrap-based aluminum production is very high, about 98%, since losses during recycling rarely exceed 2%. The main sources of recycled aluminum from old scrap are transportation (about 33%), packaging (26%), cables and electrical equipment (13%), and building applications (16%).

The aluminum scrap market has expanded in parallel with overall aluminum demand. Global aluminum scrap availability grew from 18 million tons in 2009 to 33 million tons in 2019, corresponding to an average annual growth rate of about 6%. In the same period, aluminum production from old scrap rose from roughly one million tons in 1980 to 20 million tons in 2019. However, assessing recycling performance remains challenging, as different institutions use differing metrics. The most common are the recycling input rate, the total recycling rate, and the end-of-life recycling rate.

The recycling input rate represents the share of aluminum produced from both new and old scrap relative to total aluminum output (including primary and secondary sources) entering manufacturing. The overall recycling efficiency rate expresses how much of the available scrap—new and old—is successfully transformed into recycled aluminum. The end-of-life recycling efficiency rate refers specifically to old scrap, quantifying how much post-consumer aluminum is converted into new material. Related measures include the end-of-life collection rate, which shows how much old scrap is recovered relative to what is theoretically available, and the end-of-life processing rate, which compares the aluminum produced from old scrap with the amount collected.

Operators of remelting plants commonly measure their recycling performance by the ratio of total scrap input (new and old) to total aluminum output. Depending on region, company type, and product specialization, this figure typically falls between 60% and 95%. It is crucial, however, to distinguish between end-of-life recycling performance and the total recycled amount. From a metallurgical perspective, direct alloy-to-alloy recycling—where an item is remelted into the same alloy type—provides the best compositional consistency. Economically, though, this is not always feasible, particularly for products with long service lives such as vehicles and buildings.

Global aluminum demand currently exceeds scrap availability by around two thirds, with regional variations. Consequently, aluminum should ideally be reused promptly once it returns as scrap, even when the exact same alloy type is not immediately required. For short-lived products like beverage cans and packaging, direct recycling into equivalent products is more common and efficient. Recycling rates for such items range widely, from about 30% to nearly 100%, depending on local collection systems and market conditions.

Recycling performance differs significantly between industry sectors. For transportation and building materials—where products have long lifetimes—recycling fractions typically range from 80% to 95%. The transportation sector has long been a major source of aluminum scrap, while scrap from buildings only started contributing significantly in the 2000s as structures built decades earlier reached the end of their lifespans.

In transportation, scrap mainly consists of body panels, frames, bumpers, and structural parts made from 2xxx (Al–Cu), 5xxx (Al–Mg), 6xxx (Al–Mg–Si), and 7xxx (Al–Zn–Mg/Cu) alloy classes. Cast aluminum alloys such as A356, 360, and A380 from engines and other components form another large fraction. Some alloy classes are incompatible for direct remelting due to differences in silicon, zinc, and copper content, requiring careful segregation to maintain alloy quality.

In the building sector, aluminum content is typically below 1% by weight, but recovery rates approach 95% because many components—such as cladding, window frames, and shading systems—are easily dismantled and economically valuable compared to other demolition residues. The composition and aluminum intensity of buildings vary widely. Industrial and commercial structures contain far more aluminum than residential ones, and usage is significantly higher in warmer climates. As architecture trends toward lightweight and corrosion-resistant materials, aluminum demand in construction continues to grow.

Traditionally, building applications have relied on the corrosion-resistant 5xxx and 6xxx alloy classes, prized for their strength, moderate cost, and weldability. More recently, 3xxx (Al–Mn) alloys and 5xxx alloys with higher magnesium content are gaining use. While limited alloy mixing is possible, it is far more efficient and sustainable to collect and process these alloy families separately to ensure high-quality recycled feedstock for both construction and transportation markets.