Corrosion of silver electrical contacts: The substrate influence

Silver and silver based alloy (90% Ag- 10% CdO) contacts welded on different substrate materials have been exposed in hostile SO2 environments in simulated laboratory conditions. The corrosion byproducts on the surface have been monitored by SEM and EDS spectroscopy. Their electrical characterization was based upon de overheat tests, current switching cycle tests and interfacial energy storage during ac current excitation. The experimental results demonstrate that the heat dissipation rates strongly depend on the substrate material selection as well as, the exposure environments. These parameters strongly affect the nominal current values. The dynamic contact resistance during make-break electrical contact operations depends upon the conductivity of the new surface layers formed as a result of chemical equilibrium established by the reaction between the environment and the primary surface material, the substrate, and the welding layers. Corrosion byproducts are formed over the contact joint and are transported to the silver surface of the electrical contact by creep. The resulting byproducts, may be either loosely attached or water-soluble. Corrosion products originate from the welding zone, the substrate material, and the underplating layer by diffusing through the pores of the plating; they aggregate on the surface and affect the heat dissipation rate and consequently the electrical performance of the component.