Influence of the relative humidity and H2S - SO2 polluted air on the fretting wear behavior of silver-plated electrical contacts

Abstract

The use of connectors in electrical devices for automotive industry has significantly increased during the last decades. These connectors need to keep low and stable electrical contact resistance (ECR) otherwise disconnects may occur inducing critical failures. Close to the engine, these connectors are subjected to vibrations inducing fretting wear damage. The aim of this study is to investigate the influence of relative humidity and the presence of pollutant sulfurous gases (H2S, SO2) on the silver-plated electrical contact resistance (ECR) behavior. The ECR fretting endurance Nc (i.e. when ΔR> ΔRth = 4 mΩ) displays a fast increase above RHth(Air)=50%. The debris layer becomes more conductive so a larger wear volume is required to reach the ECR failure. At the same time, the debris layer becomes more cohesive and the wear rate decreases. Alternatively, synergic interaction between H2S, SO2 gases and relative humidity above RHth(Air&S) = 60% leads to the formation of lubricating Ag2S sulphide and Ag2SO4 sulphate tribofilm which, by decreasing the friction coefficient and the silver layer wear rate, sharply increases the ECR endurance. Finally, using simple explicit formulations, both ECR endurances under polluted and non-polluted air are formalized.