Impact of Different Surface Finishes on the Serviceability of Bolted Connections After High Temperature Aging

Due to its good electrical contact properties, silver is frequently used as plating for conductors in bolted connections. During operation, adhesion between silver contact surfaces can occur. This is a result of solid-state diffusion facilitated by high surface pressure and elevated temperatures. Such cold-welding causes contact members to stick together even after the removal of the bolt. Separating the joint by force may result in damage to the plating in the contact area, which can lead to an increased contact resistance. For applications such as electrical vehicles, maintaining serviceability of electrical connections even after several years in the field is an important requirement. In this paper, the separability and the electrical resistance of bolted connections with varying surface finishes, such as silver, hard silver, silver alloys, and nickel, are investigated. The connections were stored at temperatures up to 180°C for 2000 h. During the 2000 h, several mating cycles were performed on the connections. The goal of this investigation is to evaluate the various combinations of surface finishes with regards to their ability to avoid cold welding. The goal is to mitigate the need to replace parts by ensuring a low contact resistance over the lifetime of the connection, including several mating cycles.