Revolutionizing Aluminium Recycling: Automotive scrap sorting by LIBS technology

Aluminium is key to circularity in automotive manufacturing, as it can be fully recycled without losing its material properties, and recycling requires only about 5% the energy needed to produce primary aluminium. However, aluminium alloys from vehicles must be properly segregated before recycling, to prevent high-quality wrought alloy scrap from ending up in secondary casting alloys. 

HOW STAMPING SCRAP GETS COMBINED

Aluminium automotive closures, such as doors, hoods, and decklids, each consist of two parts, an inner one and an outer one. The inner facing sides are mostly made of 5xxx alloys, which are better adapted to complex forming. The external sides are made of 6xxx alloys, which have an excellent surface aspect.

Even though the naked eye cannot see the difference between the two alloy families, they are physically distinct. The composition of 5xxx alloys is mainly aluminium and magnesium (up to 5 wt. % Mg), while 6xxx combines aluminium with silicon (Si) and a much lower percentage of Mg.

When automotive manufacturers stamp parts from aluminium sheets or coils, they trim off or cut out around 30 to 40% of the metal. Unfortunately, they often lack the resources to sort stamping scrap into alloy families. And once mixed, stamping scrap cannot be recycled back into either alloy family. It has too much Si for 5xxx, negatively impacting formability, and too much Mg for 6xxx, affecting its strength. Instead, the mixed scrap is usually downcycled into secondary casting alloys. 

PUTTING LIBS TO WORK

Researchers are studying ways to separate 5xxx and 6xxx alloys that have been mixed together. One of the most promising solutions is laser-induced breakdown spectroscopy (LIBS). It uses laser pulses to ablate a small volume of the material’s surface, which forms a plasma containing excited atoms and ions. When the plasma cools, it emits light with distinct spectral peaks, or rays, characteristic of the different elements present in the material.  

Researchers have been studying LIBS technology for years, but in-line LIBS was never considered appropriate for industry, due to limited throughput. Thanks to recent developments, industrial machines fitted with several LIBS guns in a row are now available on the market, and can sort up to five metric tons of scrap per hour. 

The scrap pieces travel on a high-speed conveyor belt, where a laser locates them and measures the 2D shape of their upper surface. One of the LIBS guns then moves towards each piece and analyzes it in milliseconds. Depending on the results of the analysis, the piece either drops straight down or is pushed out horizontally by air pressure nozzles.

A GLOBAL FIRST

OSR Metallrecycling - a German recycling specialist and one of Constellium’s suppliers, has invested in an industrial LIBS line, and is working with us and a German premium OEM on a collaborative project. Together, we have developed, industrialized, and commercialized the world’s first sorting operation where mixed 5xxx and 6xxx stamping scrap is sorted, remelted, and processed back into full-value ABS products. We have obtained a purity above 95% for both alloy families, allowing us to directly incorporate the sorted scrap into our melting furnaces and cast ingots dedicated to the manufacture of automotive sheet. 

Since the project’s launch in March 2023, more than 3,000 metric tons of LIBS-sorted scrap have been used at Constellium’s automotive plant in Neuf-Brisach, France (more than 6,000 metric tons to date as of Q4 2024). We are continuing this industrial sorting in 2024, and are actively looking to expand with other customers and sorting lines.

Technology such as LIBS will be essential to recycling end-of-life vehicles containing aluminium closures, removing barriers to the circularity of wrought aluminium sheet and extrusions. After elimination of steel, plastics, Cu wires, and other metals, LIBS is the final step in recovering end-of-life 5xxx and 6xxx alloys separately.