Influence of Oxygen on the Aging of Electrical Joints with One Bare and One Coated Aluminum Contact Member

The use of aluminum in electrical power engineering has increased over the last years. A major challenge of this material is the creation of stable electrical joints to other metals. The contact resistance of a joint that involves a bare aluminum contact member and a coated contact member, e.g., silver-or tinplated, increases drastically after the installation. Up to now, the reasons forth is behavior have not been profoundly researched. The deterioration of the con tact resistance is not limited to elevated temperatures under load, but already takes place to some ex tent at room temperature. Therefore, aging mechanisms such as force reduction, formation of inter metallic compounds, electro migration and rubbing wear can b e ruled out. In this paper oxygen as a possible source for the failure is examined. Different ways of the oxygen into the contact plain are considered: Firstly, oxygen that is attached to the coated contact member before the joining can react with the aluminum. Secondly, oxygen from the ambient air can diffuse into the contact plain after the joining. In order to deter mine the varying causes for the increase in contact resistance, experiments in ambient air and an inert gas atmosphere (N2) were performed.