Influence of Brake Pad Porosity and Hydrophilicity on Stiction by Corrosion of Friction Material against Gray Cast Iron Rotor

An adhesion phenomenon between brake pad and rotor frequently appears as a result of prolonged static exposure to corrosive environments. In these highly oxidative conditions, electrochemical reactions occur on the gray cast iron brake rotor surface to produce iron oxide(s), which can then penetrate the brake pad surface porosity, causing adhesion of the brake pad(s) to the rotor. In some instances the shear load necessary to detach the brake pad from the rotor is sufficiently high and becomes a real issue in the field. The corrosive mechanisms and magnitude of material interactions involved in this issue are very complex. These complexities are in part due to the heterogeneity of the rotor and friction material compositions, but also brake geometry, loading conditions, and environmental variations are large contributing factors. As most of these factors are of upmost necessity, it was the goal of this study to focus our understanding on other factors of influence which are: friction material porosity and hydrophilicity. The study used several “stiction” (corrosive adhesion) tests designed to evaluate the detachment loads due to corrosive environments, using simplified non-commercial metal free formulations. Furthermore, the stiction test samples were analyzed post-test by optical microscopy and scanning electron microscope (SEM).