Role of copper and zinc additives in the stiction phenomenon of automotive braking systems

• Published in: Materials and corrosion Vol. 75; no. 8; pp. 1005 - 1017
• Main Authors: Motta, Michele, Iodice, Valentina, Xicola, Agusti Sin, Truccolo, Alberto, Fedrizzi, Lorenzo, Andreatta, Francesco
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.08.2024
• Subjects: Brake disks; Braking; Braking systems; Composition effects; Contact force; Copper; Corrosion effects; Corrosion tests; Electrochemical cells; Electrochemical impedance spectroscopy; Electrode polarization; Friction; friction material; galvanic corrosion; gray cast iron; Motor vehicles; Porous materials; Stiction; Vermiculite; Water absorption; Zinc
• ISSN: 0947-5117; 1521-4176
• DOI: 10.1002/maco.202414322

The braking system of a motor vehicle is a multi‐material system, subjected to various aggressive conditions. Corrosion of the brake disc during stationary periods can determine the onset of a high adhesion force (stiction) capable of compromising the reliability of the braking system during vehicle motion. The purpose of this work is to study the effect of the introduction of Cu and Zn in the friction material composition. This effect was investigated through electrochemical measurements (electrochemical impedance spectroscopy, potentiodynamic polarization, and stiction tests), conducted using an electrochemical cell simulating the parking brake, complemented by the examination of the brake disc and pad surfaces and water absorption tests. The results suggest that porous components, like vermiculite, in the composite friction material led to high contact force. Moreover, 10 wt% of Cu in the friction material does not significantly affect its stiction behavior in our testing configuration. In contrast, 10 wt% Zn in the friction material significantly reduces the stiction propensity by acting with a complex synergistic mechanism combining physical and chemical shielding effects. The stiction effect of an organic asbestos‐free friction material is compared with two materials containing 10 wt% Cu and 10 wt% Zn in place of barium sulfate. The stationary brake is simulated using an electrochemical cell. The presence of Cu leads to no significant differences in the stiction behavior. Moreover, the plugging mechanism of zinc, with multiple shielding actions, is highlighted as the main protection mechanism from the stiction phenomenon.