Investigation of Gas-Tightness of Bimetallic Busbar Joints by Utilizing Percolation Theory

In power engineering, joining aluminum and copper conductors is a frequent issue. Due to the proven influence of the diffusion of oxygen on the long-term behavior, this material combination is predominantly not long-term stable. To achieve longevity, the oxidation in the contact interface must be limited. Thus obtaining gas-tightness to prevent the diffusion of oxygen molecules in the contact interface may be one solution to achieve a long-term stable bimetallic joint. One approach to describe this mechanism is the percolation theory. This stochastic procedure describes which filling of a regular structure of basic geometric elements in the apparent contact area may result in gas-tight areas in the contact interface. Regarding research of bimetallic connections under various conditions, no mechanical joining parameters of aluminum-copper busbar connections to achieve gas-tightness were found so far. In this paper, it is evaluated, whether joining parameters that could ensure gas-tightness can be derived using the 3D-percolation theory. Therefore, the long-term behavior of bimetallic busbar joints depending on the mean mechanical stress in the contact interface is investigated. Furthermore, the effect of contact aid compounds on the joint resistance ensuring gas-tightness is analyzed. It is discussed, whether the percolation theory is suited to describe the gas-tightness of the contact interface of aluminum-copper-connections.