Aluminium in Vehicle Construction

Aluminium, the metal your can of bubbly drink is made of, has been used for cars for seven decades and the material is no stranger to automotive engineers. Even in the 1930s, Audi engineers produced a lightweight racing car using aluminium extensively while in the post-WW II period, shortage of steel inspired Land Rover to use aluminium for the body panels of its 4WD vehicles.

In later decades, various other automakers also adopted the metal but mainly for low-volume models like the Lotus Elise; GM’s EV1 electric car; the Honda NSX and also the Insight hybrid car. Land Rover was the only company to make use of it on all its models, produced in large numbers, but not for the structural members

Generally, the main aim of using aluminium has been to save weight. This has been particularly crucial for cars with electric motors where the power output is low and body weight has to be kept way down to ensure adequate performance.

Use of aluminium has been growing rapidly as its benefits have been appreciated more and more. Quite apart from the excellent resistance to rusting (ask the farmers in Cameron Highlands who have decades-old Land Rovers!) and high recyclability, aluminium is a highly desirable material to use because the weight-savings can be achieved easily without resorting to other expensive technology.

“Engineers know that aggressive weight reduction is the best way to improve fuel economy, emissions and performance. For these reasons, as well as improved corrosion resistance and recyclability, automakers are increasingly turning to lightweight, high-strength aluminium,” says Dr. Richard Klimisch, Vice-president of The Aluminium Association in the USA.

And although it may be hard to believe, aluminium is actually 40% stronger than steel, even though it is lighter. On a per-kilogram basis, aluminium is twice as strong as steel. So use of aluminum in light trucks reduces the weight differential between cars and trucks, thereby reducing the risk of serious injuries passengers in the cars when two such vehicles collide. The strength of aluminium, in relation to passive safety, has been confirmed with the crash tests that the Audi A8 was subjected to in the USA, where it passed with top marks and was regarded as one of the safest cars on the market.

So why has it taken so long for aluminium to become the third most-used material in cars, this year surpassing plastics? Because the metal is much more expensive and manufacturing processes are different from the conventional ones used for making cars from steel. Audi began to focus on using it in a bigger way from the early 1990s and adapted techniques from the aerospace industry. In terms of development and production technology, the Audi Space Frame (ASF) that was developed for the R&D program had no precursors in the field of automobile manufacturing when it was introduced in the A8 in 1994.

Audi pursued the revolutionary concept, now used for the A2, for the following benefits:

1. Aluminium reduces vehicle weight; compared to steel for the same given size, aluminium is between 30% ~ 40% lighter. Thus if engine output remains the same, performance is improved and fuel consumption reduced. Moreover, lighter cars have superior handling.

2. The ASF guarantees effective occupant protection. In crash tests conducted on production A8 sedans, the ASF has proved particularly rigid and dimensionally stable. A large amount of energy is absorbed when the crumple zones deform.

3. The aluminium structure results in a body which is light in weight yet exceptionally rigid, both torsionally and flexurally. This has the highly positive effects of reducing vibration and ensuring high-precision steering.

4. Using aluminium for automobile construction helps to reduce environmental pollution. This is evident if the amount of energy consumed in the entire materials cycle and aluminium’s excellent recycling properties are taken into account.

The use of recycled aluminium is ecologically sound. If a material can be recycled sensibly and economically after years of use, no unnecessary waste is produced. Aluminium can be recycled to an almost unlimited extent. Assuming the same composition, recycled (secondary) aluminium has the same qualities as the primary material. In the recycling process, the individual components of the ASF can be turned back into what they were before: extruded sections become extruded sections again, and so do cast nodular joints and panels.

At the moment, around 90% of the aluminium used in vehicles can be recycled. This has a positive effect on energy consumption, since only a fraction of the energy needed to obtain primary aluminium is required to produce secondary aluminium.

In comparable driving conditions, if the amount of energy required for producing an aluminium body is compared with that required for producing a steel body with the same function, the following pattern emerges: even if new aluminium only is used, the additional energy consumed is compensated for after around 60,000 kms, thanks to the fact that the aluminium body weighs 40% less. If around 75% secondary aluminium is used, the amount of energy consumed during body production drops below the amount used to produce a steel body. And less energy is consumed as soon as the vehicle takes to the road.

One drawback, though not a very serious one, is that the aluminium construction requires specialised techniques for repair work if it is damaged. This is due to the fact that the aluminium body uses alternative connecting techniques such as adhesives and rivets instead of welding. Audi also conducted studies into the frequency of damage to a vehicle’s structure during an accident and found it to be around 5%. If damage does occur to the ASF, specialized tools and equipment are needed for the repair procedure. Therefore Audi distributors which sell the A8 are required to have structural repair facilities centres which has specialized MIG welding machines and a Celette repair bench utilized in combination with Audi chassis alignment jigs.