Aluminum to replace copper as a conductor in on-board power systems

February 7, 2011
This CAD drawing shows an innovative electrical connector based on aluminum conductors instead of copper. It's part of a project to remove obstacles to using this lighter, less expensive material in electric cars and other vehicles. Credit: Copyright TU Muenchen

Electric power and electronics are playing an ever-increasing role in all kinds of vehicles. Currently copper is the conductive material of choice. But in comparison to aluminum copper is heavy and expensive. In particular for fully electric vehicles the switch to the cheaper and lighter aluminum would be an interesting option. That is why the optimization of intricate power supply networks is now in the focus of engineering research. Scientists from the Technische Universitaet Muenchen (TUM, Germany), in collaboration with BMW engineers, have now found out what tricks make it possible to replace copper with aluminum.

At first glance it is not at all clear why is still used as in modern electric or semi-electric vehicles – when aluminum is lighter and significantly less costly. However, before aluminum can replace copper in systems, a number of technological challenges need to be surmounted. When temperatures are high – and there are many places in a car where that is the case – aluminum displays a distinct creep behavior. Conventional connectors could thus not be used, as they would become loose with time.

One possible alternative – the use of aluminum-based elements in cables and copper-based elements in connection areas – also entails problems. Because there is a high electrochemical potential between a copper contact and an aluminum cable, this kind of wiring would be very prone to corrosion. Besides, joining copper to aluminum is rather demanding with the current state of technology. In order to counteract the aforementioned difficulties, scientists of the chairs for High Voltage Technology and Power Transmission and for Metal Casting and Forming, in cooperation with the respective departments of the BMW Group, developed an innovative aluminum-based electrical connection concept in the project LEIKO.

A sheet metal cage, which is an electromagnetic compatibility requirement anyway, enhances the mechanical stability of the plug and guarantees the long-term support of the contact pressure spring. Because the necessary contact force is no longer provided by the contact elements themselves, the originally problematic creep behavior of aluminum turns into a contact stabilizing, and thus, positive property. This, in turn, also guarantees a constant contact force over a lifetime of ten years.

To this end the researchers came up with a special wedge-shaped geometry for the aluminum contacts. The aluminum creep now leads to the two contacts snuggling closer and closer together over time, thereby rendering the electrical connection better yet. Moreover, the consistent use of aluminum alloys and the ingenious application of precious metal plating made it possible to relocate the formation of corrosion-prone local elements to less critical locations in the system.

A further problem with substituting aluminum for copper is its lower electrical conductivity. In the case of high-power on-board systems in particular, the cable cross-sections, which are about 60 per cent larger, need to be taken into account in the construction of cable ducts and feed-throughs. One positive thing the scientists discovered was that because aluminum is very pliable, the standard values from copper cable processing, where bending radii are set based on the diameter, could also be used for aluminum.

In order to determine the long-term behavior of the coated aluminum contacts under even the rough conditions typical for motorized vehicles, the project partners, together with leading suppliers, have successfully initiated a further research project. Funded by the Bavarian Research Foundation (BFS), this project will deliver evidence on the aging behavior and thus the suitability of the concept by 2012.

Initial results indicate that the material substitution will lead to significant improvements in weight, cost, and ultimately emissions. "We expect the high-voltage on-board systems of most to be based on aluminum by 2020. Aluminum will find its way into low-voltage on-board systems as well, because the price of copper will rise significantly with increasing demand," says Professor Udo Lindemann from the Institute of Product Development at the TU Muenchen.

The project finds its theoretical counterpart in the Collaborative Research Center (SFB) 768, Managing Cycles in Innovation Processes, funded by the German Research Foundation (DFG). It aims to bundle competencies from computer science, engineering, economics, and the social sciences in order to look into challenges at the interfaces of innovation processes along with partners from industry. The goal of this research is to use an interdisciplinary perspective to develop industry-relevant solutions in dealing with dynamic changes in company environments, as well as in company internal process landscapes.

Another aspect of the research conducted within SFB 768 is a student project to develop an electrically driven go-cart. In order to experience the manifold challenges of innovation management first-hand, the students started with a standard base structure and went through the entire development process for all subsystems of the vehicle. The results of the LEIKO project are also integrated into the student project – the entire high-voltage on-board system is implemented in .

The results are to be incorporated in the TUM electro vehicle MUTE, which will be presented at the IAA 2011.

Explore further: Nearly Hard as Steel: Aluminum with Fullerenes

More information: Langer, S.; Lindemann, U.: Managing Cycles in Development Processes - Analysis and Classification of External Context Factors, in 17th International Conference on Engineering Design, M. N. Bergendahl, M. Grimheden, and L. Leifer, Eds. Stanford University, California, USA: Design Society, 2009, pp. 1-539 - 1-550

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not rated yet Feb 07, 2011
I hope this doesn't end up backfiring like it did when they were using Aluminum wiring in houses.
not rated yet Feb 07, 2011
Whatever happened to bismuth telluride electrical adjuncts?
not rated yet Feb 08, 2011
Another problem with this concept is the relatively low temperature at which vigorously exothermic oxidation can take place with aluminum.

A stupid idea. I can't believe they are actually considering this.

1 / 5 (1) Feb 08, 2011
Toyota Verso S sold now in Europe has aluminium cabling.
not rated yet Feb 08, 2011
All car companies care about is cost. If they can save $0.01 per car, they'll do it.
1 / 5 (1) Feb 08, 2011
Another problem with this concept is the relatively low temperature at which vigorously exothermic oxidation can take place with aluminum

That's really not a problem. Try to burn a Coke can. While powdered aluminum is explosive at certain granule sizes, bulk aluminum is quite safe to work with. Half the cars in the us have aluminum/magnesium/phosphorus alloy wheels and engine blocks. They do not burn or explode, despite being made of three chemicals that are all explosive at room temperature in powdered form. Common baking flour is nearly as explosive under just the right conditions.

There's a process growing in popularity where they can physically combine different metal powders that are not chemically compatible for an alloy and mix them then press them together into a solid block. The resulting material can have surprising properties. They then mill the block down. Some turbofans are made this way now.
1 / 5 (1) Feb 08, 2011
I should add that it gets even more interesting when you combine non-metals with the metal powders, such as ceramics or organic fibers. The resulting materials are like nothing in nature, and we're just beginning to explore the possibilities. The color-changing ink on a $20 bill is made from an aluminum hybrid material, for example.
5 / 5 (1) Feb 08, 2011
I'm pretty sure they won't be putting the same grade of aluminium in the wires that they used to in the old house wiring. Still they have a few things to make sure of. The old wire used to sing or vibrate and would fatigue and then fracture and that wasn't happening in a vibration filled auto. And they used a fairly pure grade of alum (1xxx) series as it doesn't corrode. You only get so many stress cycles out of any aluminium (wheels, airframes, wire etc) before they will crack. It's all a matter of load cycles and time not "IF". Not sure I'd want one as at best the car is going to just stop one day as a result.

The metal powder process is called sintering.
not rated yet Feb 16, 2011
Aluminum is being used in houses again (alloys 8030, 8176 and 8076 specifically) and that is because aluminum alloys are becoming increasingly reliable. Monoblocks in motors have been made out of aluminum for a while now and the dynamic resistance to load has not stopped its use. If corrosion resistance is what matters, there's alloys specifically manufactured for that that can work as an electric conductor too. Overhead transmision cables are made of aluminum and the only problem they have is sag (which has been solved with this conectors). Every material on earth will fail after a given amount of load cycles, that's not the real problem of this application, and besides, if the industrial trend is to replace copper with aluminum, why not let it get on the automotive industry? After all, Ni plated aluminum conductors are used for aeronautical purposes.

The aluminum industry has learned from its mistakes, and the're constantly developing new and innovative. Give them a chance

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