Experimental study of the conducting spots in aluminium contact interfaces

The electrical properties of a stationary electric contact are closely related to phenomena occurring in the very small contact spots of the interface. Contact spots in aluminium-aluminium interfaces that have passed heavy direct currents have been studied. The size, shape, and appearance of the spot fractures were found to be correlated to the surface roughness and to the recorded voltage and resistance characteristics. Rough contact surfaces caused irregularly shaped contact spots to develop, while high and unstable resistances were always associated with large contact spots. The latter observation indicates that the electrical conductivity of the contact spots has been reduced by the electrical stresses: the spots have aged. Aging of a contact point leads to the formation of new current paths through the interface, in the vicinity of the original ones. The aging rate increases rapidly with increasing voltage drop across the interface