On the Aging of Electrical Joints with a Copper and an Aluminum Contact Member

Aluminum and copper are the two commonly used conductor materials in electrical power engineering. If these two materials are connected in an electrical joint without material closure, long-term stability of the connection is not reliably achieved. Previous research has attributed the witnessed rise in resistance to the formation of intermetallic compounds between aluminum and copper. However, Pfeifer has shown in her work that this cannot be the main aging mechanism for joints of the mentioned material combination. This paper explores the influence of other aging mechanisms by examining the aging of bolted joints with one aluminum and one copper busbar. Several test parameters are varied, such as the joining elements, the torque at assembling, and the surrounding atmosphere. The results lead to the conclusion that oxygen entering the contact plain during the aging process causes the formation of aluminum oxide in the a-spots. Due to its high resistivity, the joint resistance increases, leading to a failure of the connection. Selected test parameters were repeated for a model geometry consisting of a flat and a conically reduced cylinder, thus generating a point contact in contrast to the flat surface contact of the bolted joints with busbars.