Aluminum replaces copper for automotive power

In all kinds of vehicles, electric power and electronics are becoming more important, with copper as the conductive material of choice. However, copper is heavy and expensive, so car makers are interested to use cheaper and lighter aluminum instead, especially for fully electric vehicles. Recently, scientists from the Technische Universitaet Muenchen (TUM), in collaboration with BMW engineers, found out what tricks make it possible to replace copper with aluminum.

Before aluminum can replace copper in power supply 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.

The possibility of using 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.