Influence of process parameters on the formation and quality of joining zones during induction brazing

Contact materials for electrical switch gears are widely used for connecting and disconnecting electric circuits. These contacts are two component systems, where the contact tips are brazed to the carriers prior to installation. The contacts used in the present work is a 3 layered sandwich structure consisting of a silver-tin oxide (Ag-SnO2) layer, a silver (Ag) inter-layer and a thin layer of the braze. The carrier itself is copper (Cu) - plated steel. The brazing process is accomplished by a high frequency inductive heating process. By varying the brazing parameters, namely, temperature and time, their influence on joint formation is investigated. The brazing joint of the contact tips were characterized by microscopy (light and electron microscopy) and physical analytical techniques (energy dispersive X-ray analysis. The mechanical characteristics were determined with Vickers microhardness. Investigations indicated that, comparatively, the variations in temperature had a greater influence on joint zone formation and their mechanical properties. It was further demonstrated that the extended hold times lead to a higher degree of joint zone filling due to a large reduction in pore volume fraction.