Steel vs Aluminium

Follow the evidence when weighing steel stamping and aluminium mega-casting

High-pressure die-casting (HPDC) and the use of aluminium in vehicle designs has become one of the automotive industry’s shorthand terms for progress and innovation in vehicle manufacturing. Fewer parts, fewer welds and simplified assembly processes all sound compelling.

However, while mega-casting might enable these simplified processes, it’s also critical for vehicle manufacturers to understand the environmental impact of those decisions.

As policymakers have become increasingly engaged in the development of regulatory policies that reduce greenhouse gas (GHG) emissions and energy use, manufacturers should also consider the impacts of their material decisions from a life cycle perspective. Simpler processes do not necessarily lead to lower impacts.

A new paper published in the SAE International Journal of Sustainable Transportation, Energy, Environment and Policy suggests that stamped steel remains the preferred, evidence-based choice for creating sustainable vehicle structures. The paper is intended to give OEMs the data and methodologies they need to make the best decision as far as life cycle impacts are concerned – particularly considering factors such as carbon emissions, energy demand, local grid mixes, and sourcing and scrap.

Beyond the production line

The study examined the environmental impacts of replacing stamped steel components with aluminium HPDC mega-castings. Through literature reviews , life cycle assessment modelling and extensive interviews, the authors assessed cradle-to-gate carbon emissions and energy demand associated with each design.

Their conclusion is straightforward: material decisions should be guided by evidence, not excitement. OEMs should assess the full life cycle implications when weighing up the decision between stamped steel and aluminium, ideally with a life cycle-based study conforming with ISO 14040/14044 standards.

Steel’s sustainability advantage

One of the study’s key findings is that stamped steel often enables the most sustainable route to next-generation mobility when decisions are judged across the full life cycle, and not just assumptions based on parts count or factory floor processes.

Using a 150 kg vehicle component as an example, the research found that a megacasted design showed approximately 2x to 4.7x higher global warming potential (GWP) than a functionally equivalent design in stamped steel.

Cradle-to-gate emissions for a stamped steel part in the USA were calculated at around 4.87 CO₂eq/kg. This rises to around 9.7 kg CO₂eq/kg for an aluminium mega-casting.

In China, based on the country’s more carbon-intensive primary aluminium production, this rose from 5.0 kg to 23.5 kg CO₂eq/kg.

The findings highlight the importance of considering raw material sourcing, local energy grids and production impacts when evaluating which material to use.

The energy equation also favours steel

The study also clearly suggests a significant difference in total energy demand between steel stamping and mega-casting, exploring the impact of average grid energy mixes in the USA and China.

For the same 150 kg component, stamped steel production required around 60.9 MJ/kg of energy in the USA and 61.4 MJ/kg in China. An equivalent aluminium mega-casting was 2.5x to 3.6x higher, requiring 153 MJ/kg in the USA and 220 MJ/kg in China.

The full business case
The study also highlights several additional considerations to help build a full business case around this important material decision.

These include higher installation costs, maintenance requirements and significantly shorter tool life for HPDC tooling. The authors note that mega-casting dies may require replacement after 100,000-150,000 uses, compared with six million or more uses for conventional steel stamping dies. Multiple sources cited by the authors also suggest that steel stamping is most likely to remain the most financially viable option in brownfield manufacturing environments.

Why OEMs and policymakers need to follow the evidence

In an automotive industry that is more competitive than ever, OEMs are understandably exploring ways to evolve or even reinvent their vehicle manufacturing processes. These decisions need to be made in such a way as to not create unintended consequences by increasing GHG emissions and energy use over the life cycle of these vehicles.

The study’s message is clear: OEMs and policymakers should evaluate material and manufacturing choices using full life cycle evidence.

When these factors are assessed as a whole, the research suggests that stamped steel continues to offer a compelling and sustainable option for next-generation vehicle structures and manufacturing processes.

Conducting your own life cycle comparison between stamped steel and aluminium mega-casting? Read the full SAE article here.