The Factors Governing Corrosion Stiction of Brake Friction Materials to a Gray Cast Iron Disc

Corrosion stiction at the contact interface between a brake friction material and a gray iron disc under the parking brake condition was investigated by evaluating the possible parameters that affect the shear force to detach the corroded interface. Using production brake friction materials, comprising non-steel and low-steel types, corrosion tests were carried out by pressing the brake pad onto the gray iron disc using a clamp at various conditions. Results showed that the shear force to detach the corroded interface tended to increase with applied pressure and corrosion time. On the other hand, porosity, acidity, and hydrophobicity of the friction material did not show a reliable correlation to the stiction force. The poor correlation of the stiction force with the friction material properties indicated that the stiction force was not determined by a single factor but governed by multiple parameters including surface contact areas and inhomogeneity of the ingredients. Microscopic observation of the detached disc surface showed adhered fragments that were removed from the friction material surface, thus shedding light on the possible estimation of the stiction force from the disc area covered by the friction materials. The scattered small areas without corrosion on the gray iron surface, which were well matched with hollow areas on the friction material surface, supported the importance of the contact area information in understanding the poor correlation between the stiction force and of the friction material properties.