The Role of Trisodium Phosphate as a Corrosion Inhibitor for Gray Cast Iron in Automotive Braking Systems: Mechanisms and Challenges

Brake pad-to-rotor adhesion (stiction), represents a significant challenge in automotive braking systems, arising from the exposure of disc-brake assemblies to aggressive environmental conditions. This issue is closely associated with the corrosion of gray cast iron brake discs, which leads to the formation of corrosion products capable of infiltrating the porous structure of the friction material during static conditions. Effective mitigation of stiction necessitates the careful design of friction materials, including the incorporation of suitable corrosion inhibitors. In this study, trisodium phosphate is investigated as an environmentally benign corrosion inhibitor. The corrosion behavior of gray cast iron is evaluated under various pH conditions that simulate the microenvironment at the disc–friction material interface, in the presence of a low concentration of phosphate ions. A combination of electrochemical techniques and surface analysis methods is employed to elucidate the inhibition mechanisms. Notably, a characteristic tubular pitting morphology is identified under mildly alkaline conditions in the presence of phosphate, and its formation mechanism is examined.