Electrical contact resistance is important to the performance of electrical switches and other current-carrying interfaces. This study investigates the behavior of electrical contact resistance for an aluminum sphere-on-flat contact as s function of current through the interface. It is observed that the contact resistance may either increase or decrease with increasing current, depending on the current level as well as the current history. At low current levels the voltage drop across the interface increases initially with increasing current until it saturates, after which the voltage level remains constant. If the current is increased beyond the value corresponding to saturation, a subsequent decrease in current yields a corresponding decrease in voltage, so that the associated current cycle shows substantial hysteresis. However, subsequent cycles of current are reversible so long as the voltage remains below the saturation point. Such behavior suggests that irreversible morphological changes occur at the interface when the current exceeds the level associated with the attainment of voltage saturation.

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