Corrosion phenomena in braking systems

In this work selected corrosion phenomena occurring in disc brake systems are reviewed. For the first time, a galvanic series, summarizing the electrochemical performance of several brake system components, is presented and case studies are discussed as well. The case studies focus on corrosion issues which are related with the three major components of a car disc brake system, namely the: a) Aluminum caliper; b) brake pads and associated friction materials; and c) cast iron disc. It is shown that: a) the parameters for the anodization of Aluminum calipers should be carefully tuned on the basis of the specific Al alloy, in order to obtain an anodic layer capable to withstand the galvanic coupling existing between the caliper and nobler components; b) friction materials composition must be optimized in order to avoid shear adhesion phenomena between brake pad and disc due to the growth of corrosion products at the interface between the two; and c) it is possible to mitigate the corrosion of cast iron brake discs by modulating the carbon morphology, alloy elements concentration and microstructure. The manuscript demonstrates that electrochemical techniques are of fundamental importance in order to pursue a corrosion-resistance-oriented design of future braking systems for automotive applications.