Cars, electrification and aluminium sheets!

Driving for a sustainable future means a reduced carbon footprint. Electrification resolves the carbon footprint of the use phase using green electricity. This does little to the carbon footprint bound by the materials and components manufactured and used in cars. Much of this comes from the technology used, the associated carbon footprint, and resource efficieny for simple products such as car body parts made from aluminium sheets. This is the focus of the ClimAl project at JU and Materials and Manufacturing.

The carbon footprint of a car and elctrification

A Volvo XC40 with an internal combustion engine has a life-span carbon equivalent of 58 tons, whereas 26 tons are generated from the materials used in the car's fabrication. Electrification and the use of green electricity, which is, in principle, already a reality in Sweden, reduced the use phase of a car to nearly zero emissions. The car battery corresponds to roughly 50000km of driving a petrol car, measured in carbon equivalents. This is seen below in the Life Cycle Analysis of the Volvo XC40 and Polestar car models as comparable cars. The added carbon equivalents from the battery are naturally unwanted but allow a total reduction of 31 tons of carbon dioxide carbon equivalents. The extra price for the reduction gives clear positive results in a green electricity environment. Under a global electricity mix, the gain is small, and it is important to reduce the car's weight and quickly increase the amount of green electricity. These matters are well understood, and the required actions are, without question, challenging but reasonably straightforward. Use water, sunshine and wind to generate electricity. If any of these are not possible, nuclear power will have a positive climate impact, even though it is associated with other issues that make it hard to judge the long-term costs and consequences. The time frame required would put us in a future age of humanity, as we would see the people during the Stone Age. This makes that decision more complex than grabbing the obvious resilient, low-hanging fruits of wind, water and sun.

Beyond electrification then what?

The Life-Cycle analysis by Röyne and Bolin shows another rather unpleasant problem for materials scientists and the manufacturing industry. The carbon footprint of the material and manufacturing process is very little affected by using green electricity. The reason for this is that steel coke is used in the process, and for aluminium, the electrolysis process reducing aluminium oxide to aluminium is made with consumable carbon-based electrodes generating large amounts of carbon dioxide. These are more complex challenges that will take time to solve and change, as many of the reduction processes require rather unpleasant agents if carbon-based reduction processing is not used.

One contribution is to increase the electrification of the melting and casting facilities, which would affect the grey portion of the bars. Other means of heating and melting based on hydrogen with low-temperature oxygen burners would increase energy efficiency and reduce carbon footprint with a lower investment cost than electrification, which would require new furnaces. There are, however, ways to change the energy used for hating that may apply to both short and long-term perspectives. However, safe cars require materials with high ductility, strength, and crashworthiness. This is a challenge for recycled materials and drives the use of primary or virgin materials. This is the biggest challenge for materials scientists and the manufacturing industry: choosing, producing, and designing secondary materials for usage. It is also about increasing the use of aluminium to reduce the weight of cars so that there will be an improved effect for regions of the world with less green electricity.

The ClimAl project.

The ClimAl project, or Climate-smart high-performance Aluminium sheet, is about using recycled materials for aluminium sheets.

The first question is, "Why work on aluminium sheets with a high recycled content?"
The answer is that aluminium sheets have obvious applications in a car, but some cannot be replaced by extrusions or giga/mega/hyper casting. Casting processes have considerable potential for using recycled materials, and extruded materials have come much further in the journey towards higher recycled content in materials, such as Circal by Hydro. This has not yet happened. This has the foundation that after rolling, the material needs to be conditioned and treated to be formable, which is a critical element of using aluminium sheets.

Recycled materials in the current recycling system will be contaminated by copper and iron. Recycled material is also likely to have a higher amount of aluminium oxide impurities from remelting and handling a second time. Regarding castability, copper may be affected, and iron may have some influence. This is commonly managed with alloying additions such as manganese, for instance. However, after casting, the material is required to be rollable. Rollability is more difficult with large particles, and the heat treatment to soften the material in the homogenisation step after casting is greatly affected by the amount and number of particles (caused by the iron contamination and the necessary manganese additions). In the ClimAl project, the rollability will be investigated to see how the particles affect rollability and how the rolling process can improve the components' manufacturing steps in the sheet metal forming process following the rolling.

Sheet metal forming is heavily influenced by the state of the material, meaning that anisotropy in the form of texture will affect the possibility of optimal performance. Grain size is heavily affected by the presence of the particles through the PSN mechanism (Particle-stimulated nucleation) and restricted by the so-called Zener pinning effect (growing grain bounds have difficulties growing past a particle. These effects strongly imply that the amount of intermetallict , theri size and nature will significantly impact the formability. In addition, the oxides will act as microcracks, significantly hampering ductility and making high recycle contents a significant challenge.

The fact that sheet metals have a given large mass in a car makes increasing the amount of recycled materials essential to reduce the carbon footprint of cars. This is particularly important for electric cars, whose extruded and sheet metal content is higher today than that of other cars.

This is why the ClimAl project started with a clear vision of working towards a zero-emission state.