More secondary aluminium for die casting: Trimet expands recycling loops

Aluminium can be recycled repeatedly. For high-value applications, however, it is not enough simply to melt down as much scrap as possible. What matters is which alloys and residual elements are present in the input material and what property profile the metal is intended to provide. Segregated collection by alloy type, metallurgical analysis and alloy-specific processing are essential if recycled aluminium is to replace primary metal.

Recycling becomes a matter of supply security

The issue is also gaining importance from an industrial policy perspective. Under the European Critical Raw Materials Act, aluminium is classified as a strategic raw material. Expanding domestic recycling capacity is therefore intended not only to reduce the use of primary aluminium, but also to lessen dependence on imports and stabilise the supply of raw materials.

A further advantage is the substantially more favourable energy balance. According to the German Umweltbundesamt, producing secondary aluminium from scrap requires only around five per cent of the energy needed to produce primary aluminium. The actual benefit in a specific case depends, among other factors, on the quality of the scrap and the effort required for sorting, processing and remelting.

More capacity in Gelsenkirchen and Essen

To this end, Trimet has installed new melting equipment at its recycling plant in Gelsenkirchen, increasing production capacity to as much as 70,000 tonnes of recycled aluminium per year. From August 2026, the furnaces are to be operated with a hydrogen-rich fuel gas which, according to the company, causes lower CO₂ emissions than natural gas. Solar panels on the roofs of the buildings provide additional electricity.

The Essen site has also been expanded. Additional storage areas increase capacity by around 16,000 tonnes and make it possible to separate aluminium scrap more systematically by alloy. This is intended to prevent different material grades from being mixed and to keep more scrap suitable for high-value applications.

Recycled-content alloy for large castings and structural components

Of particular relevance to high pressure die casting is the announced recycled-content version of trimal-38. According to Trimet, the AlSi8ZnMn die-casting alloy was developed for large structural components and is suitable for battery housings and other crash-relevant applications. It achieves its mechanical properties in the as-cast condition and requires no subsequent heat treatment. The company particularly highlights its high ductility and formability, as well as its good casting and demoulding characteristics.

For the recycled-content version, Trimet plans to adjust the alloy composition so that the proportion of secondary aluminium can be increased substantially without impairing the mechanical properties. Earlier studies by the company have shown that trimal-38 can accommodate a higher proportion of recycled material containing iron and copper. trimal-04 is already available: a recycled-content alloy for ductile die-cast components which, according to the company, has become established as an alternative to the primary alloy trimal-05.

Closed loops require clean material streams

Alongside alloy development, Trimet is expanding return systems with customers. Production scrap is to be collected separately by alloy and reused in suitable alloys. The higher the requirements for purity, strength, ductility or conductivity, the more important this separation becomes. The company cites aluminium wire as an example, since even small quantities of impurities can affect further processing.

For die casters, this means that scrap must be separated, labelled and returned in consistent quality during production. At the same time, alloy producers need to know which residual elements can be tolerated or compensated for through the alloy formulation.

New sorting site in Hamm

Another component is a new site in Hamm, which is scheduled to begin operations at the end of 2026. Trimet plans to sort and process aluminium scrap there and prepare it for further use. Laser-based analysis methods are intended to determine the metallurgical fingerprint of the scrap and enable it to be assigned more precisely to suitable alloys.

With these investments, Trimet is bringing several stages of the recycling chain closer together: collection, analysis, sorting, processing, melting and alloy development. For the die-casting industry, the key question is whether these processes can produce materials with consistent, reproducible properties for demanding components. Particularly in the case of large castings and structural components, recycling is therefore becoming a materials-engineering challenge – and a factor in supply security.