Characterization of sliding Al-Cu Electrical contacts

Two sets of Al-Cu electrical contact systems have been investigated. Current-carrying Al (Cu) wire brushes were in contact with a rotating Cu (Al) slip ring in a high-vacuum (2 X 10^-6torr) system which was backfilled to 1 atm of humidified CO2. Measurements were made of 1) the electrical contact resistances of Cu brush-Al slip ring and Al brushCu slip ring systems, 2) the surface topographies of the contact faces of the brush, the slip ring wear track, and the wear particles by scanning electron microscopy (SEM), and 3) the transfer of material across the interface and to the wear particles by electron probe microanalysis (EPM). Currents up to 30-A de were used. After an initial "wear-in" the contact resistance dropped to the order of milliohms. The contact resistance of the Al brush-Cu slip ring was consistently higher than for the Cu brush-Al slip ring system. After several thousand revolutions the contact resistance began rising erratically as the slip ring surface roughened and the wear particles became larger. In both systems Al was transferred across the interface and to the wear particles. However, only in the Al brush-Cu slip ring case did Cu transfer across the interface.