Today’s vehicle emissions standards are based on the tailpipe, measured in grams of CO2 per mile or kilometre. With Euro 6 and new CAFE standards on the way, more stringent limits are incoming. As a result, there are already compelling reasons for OEMs to consider bringing more aluminium into their material mix. At one third of the density of steel, its lightweighting benefits remain hard to beat, even with developments in advanced high strength steel (AHSS).
But more and more discussions are now being had about moving away from an exclusively tailpipe-based measurement system, and towards a vehicle life-cycle emissions system. Along with fuel consumed during the use-cycle, this would take into consideration a number of factors, including raw material extraction, manufacturing and the scrap from end-of-life vehicles in the process, and end-of-life recycling. Without these, proponents argue, the pursuit of reduced tailpipe emissions could result in unintended consequences – namely, increasing overall CO2 emissions.
This adds a new dimension to the steel versus aluminium debate. WorldAutoSteel, an advocacy group comprised of 22 steel producers, has long argued that from a life-cycle assessment (LCA) perspective, steel provides the best solution. Their research acknowledges that aluminium makes for lighter body structures, but suggests that overall, A/B segment vehicles using substantial amounts of aluminium in their body structure subsystems produce 1% more GHG emissions over their lifetime, compared with other vehicles in their case study which use average steel designs. The group concludes that if six million of their case study cars were converted to aluminium, CO2 emissions would increase by 2.7 million metric tons, and that this would require 2.4 billion trees to offset – an area twice the size of Tokyo.
“With respect to the amounts of CO2 generated in primary aluminium production, WorldAutoSteel’s studies use quite old data. They also use the lower end of material substitution rates” – Mario Greco, Aluminum Transportation Group
This, they suggest, is because steel production emits seven times less in the way of greenhouse gas. The energy-intensive nature of primary aluminium production is well known. Aluminium is an extremely reactive metal which is never found naturally in its pure state, but rather in bauxites, which are refined for their aluminium oxide (alumina). Breaking the bonds between aluminium and oxygen requires reductive electrolysis, in which current is run through the material once it is dissolved in molten cryolite. This requires large amounts of energy.
In short, the steel industry is convinced that it can offer OEMs a better way forward in the face of evolving legislation. For now, LCA-based standards remain unimplemented, but legislative shift remains possible. This is particularly the case with greater numbers of new energy vehicles (NEV) hitting the road. Research from the EU has already pointed to the fact that a battery electric vehicle (EV) used on a coal-powered grid can potentially produce more CO2 than a conventional vehicle would, due to CO2 costs associated with ‘fuel’ production. For NEVs to provide real benefit, energy must come from renewable sources.
The question is, what does the aluminium industry make of this? Mario Greco, Chairman of the Aluminum Transportation Group (ATG), believes that fundamentally, WorldAutoSteel has used data that is skewed in its favour, and that the group has ignored standards set between themselves and the Aluminium Association in performing LCA on vehicles. Confusion reigns as a result.
“If the steel industry is loud, we can be louder” – Michael Hahne, Novelis Europe
“With respect to the amounts of CO2 generated in primary aluminium production, their studies use quite old data,” he argues. “They also use the lower end of material substitution rates, which is problematic because when you perform a calculation for LCA, the biggest portion of lifecycle CO2 generation is during the use phase of the vehicle, when it is being driven on the roads. If, in the analysis, you use a lower substitution level for aluminium versus steel, it will not reflect the weight savings possible with aluminium. This is one area they continually skew in their favour.”
In other words, Greco dismisses the idea that steel wins the LCA debate. “This has been proven by studies done by Ford,” he says, “and in a peer reviewed study published by Oak Ridge National Laboratory in 2014. It shows significant reductions in lifecycle CO2 with the use of aluminium-intensive designs.”
The study referred to, first presented at the 2014 Society of Automotive Engineers World Congress, does indeed conclude that use of aluminium in new vehicles to boost fuel economy offers the smallest total carbon footprint among competing materials. It supports Greco’s argument that the use-phase is the most energy-intensive part of a vehicle’s life, accounting for more than 90% of automobile energy consumption and carbon emissions. Mining, production and manufacturing account for only 10%. Initial gains made by steel’s lower production phase emissions are therefore erased once a vehicle is out on the road.
“If you look at today’s situation, we can already recover 95% of the aluminium contained in end-of-life vehicles, and return it to the material cycle. Scrap generated by our customers is an important source of material” – Michael Hahne
According to researcher Sujit Das, “A full life-cycle environmental analysis confirms that, when compared to both traditional and advances steels in the areas of cumulative energy demand, potential ozone depletion and other likely factors in climate change, aluminium rises to the top as the best choice for the environment.”
Michael Hahne, VP Automotive at Novelis Europe, stresses that when it comes to LCA, the aluminium industry has an equally compelling case: “If the steel industry is loud, we can be louder,” he says. The important factor, he argues, is aluminium’s infinite recyclability, as re-melting the metal for further use is far less energy intensive than primary production, requiring around only 5% of that used for bauxite refining and electrolysis: “This clearly differentiates us from all other materials, and the more we can recycle, the bigger the benefits. If you look at today’s situation, we can already recover 95% of the aluminium contained in end-of-life vehicles, and return it to the material cycle. Scrap generated by our customers is an important source of material.”
Novelis, which also supplies the packaging industry, is the world’s largest aluminium recycler, with aspirations for a completely closed-loop system. Nearly 100% of aluminium cans in Europe, it says, are now recycled, and the job is on to increase the amount of recycled content in vehicles. Over the last two years, says Hahne, the company has returned some 50,000 tonnes of the metal back into production – the equivalent of 200,000 Jaguar XE bodies, he points out, which has ultimately prevented the release of 500,000 tonnes of CO2. Innovations like the company’s Novelis Advanz grade are designed for easy reintroduction into the manufacturing process.
“Through a combination of good recycling capabilities and the lighter weight of the aluminium during the in-use phase of the cars, we believe the LCA is favourable for aluminium” – Peter Basten, Constellium
But of course, a car is a far more sophisticated product than a beverage can, and recovering the material from end-of-life vehicles can be tricky, particularly given the increase in multi-material designs. Steel’s ferrous nature gives it an advantage in this regard, with magnets easily able to recover scrapped material from shredded cars. Aluminium is non-ferrous, but Peter Basten, President of Packaging and Automotive Rolled Products at Constellium, explains that there are mature processes in place to counter this, called eddy currents (also known as Foucault currents). Conductors are used to create a magnetic field through induction, sorting different materials across different distances.
“This can segregate different types of material,” he says. “Magnetic parts like steel, for example, are taken out of the mix. And so through a combination of good recycling capabilities and the lighter weight of the aluminium during the in-use phase of the cars, we believe the LCA is favourable for aluminium.”
The company, he concludes, continues to invest heavily in recycling. Key will be having facilities worldwide, given that many vehicles will travel to different regions of the world once they reach the end of their life in the West. The aluminium industry does not deny the fact that its primary production process is less environmentally friendly, but with efforts ongoing, it hopes to reduce its dependence on the process.