Recycled aluminium carries a fraction of the embodied carbon of primary metal, typically 5 to 10 percent, which makes it a direct lever on the carbon footprint of any vehicle or consumer product. But recycled content introduces variability that primary metal does not have: tramp elements, mixed alloy streams and traceability gaps. This guide covers how to specify and verify recycled aluminium sourced from China.
Why the carbon argument is only half the story
The decarbonisation case for recycled aluminium is strong. What determines whether you can actually use it is composition control and consistency. Secondary aluminium is made from scrap with widely varying composition, and every heat is a blend. The metallurgical problem is that elements such as iron, silicon, copper and zinc accumulate through recycling and cannot be removed economically once present.
For a component where these elements are not critical, recycled material is a straightforward win. For a high integrity structural casting or a component with tight fatigue requirements, the specification has to be written around what secondary material can actually guarantee.
Specification axes
1. Scrap source and feedstock category
The single most important question is whether the feedstock is post-consumer scrap, post-industrial scrap, or a blend. Post-industrial scrap from production offcuts and rejects is cleaner and more predictable in composition. Post-consumer scrap from end-of-life vehicles and demolition has a wider composition spread but a stronger circularity story. Suppliers frequently blend the two, and the blend ratio is not visible in the finished material.
2. Alloy designation and how it is met
Common recycled compatible alloys are ADC12 and A380 for die casting, A356 for high integrity gravity and low pressure castings, and 6061 or 6082 for extrusion. Recycled material is usually brought to specification by adding primary metal or master alloys to raise the composition to target. The recycled content percentage then reflects the mix, so ask for the mass balance calculation rather than a percentage claim alone.
3. Tramp element limits
Write explicit maximums for iron, zinc, lead, tin and cadmium. For A356, iron is the element that most affects ductility, and recycled feedstock with higher iron requires a different thermal process to achieve the same elongation.
4. Traceability documentation
Automotive and construction customers increasingly require documented chain of custody. Ask whether the supplier can produce heat number traceability from scrap intake to shipped ingot, spectrochemical analysis per heat, and where applicable a third party verified recycled content statement.
Verification steps that actually catch problems
- Per heat spectrochemical analysis (OES) against your specification limits, not a certificate of nominal alloy composition.
- Hydrogen content measurement for castings. Recycled scrap tends to carry higher hydrogen from coatings and moisture, which leads to porosity in the finished casting.
- Inclusion and oxide cleanliness check by metallography or ultrasonic inspection on a sample, especially for structural castings.
- Mechanical property testing on the actual process, not on separately cast test bars with different solidification conditions.
- Traceability audit. Ask to see the intake log and heat records for a specific shipment. A supplier with a real system can retrieve them quickly, one without will produce a generic certificate.
Common mistakes in recycled aluminium sourcing
- Accepting a recycled content percentage without a mass balance basis, or without clarifying whether the percentage is measured at the ingot stage or the finished part stage.
- Writing a specification identical to the primary metal version, then finding that no secondary producer can meet it consistently.
- Ignoring hydrogen and inclusion limits, then discovering porosity at final machining after most of the value has been added.
- Not agreeing on sampling frequency and reference sample retention period before the first order.
Recycled materials from Hunan
The green building and recycling materials cluster in Hunan includes secondary aluminium producers, recycled content verification services and downstream fabricators serving both domestic and export markets. See the LiiFoo green building and recycling materials cluster for verified supplier profiles, or contact us for a specification matched shortlist.
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