Tribological Properties of SiCp/A356 Composites Against Semimetallic Materials under Dry and Wet Conditions

Due to their low density and excellent friction performance, SiCp/A356 composites are increasingly used to produce brake disks for metro and intercity trains. To evaluate how wetness affects its tribological properties and surface morphologies, the friction and wear behavior of SiCp/A356 composites against a semimetallic brake pad material was investigated using a ring-on-disk configuration under dry and wet conditions. The coefficients of friction and wear rates were measured, and the surface morphologies of the third body layer were observed during tests. The test results showed that the coefficient of friction was consistently maintained between 0.35 and 0.4 for varied loads and velocities under dry surface conditions, whereas the values fluctuated dramatically under wet conditions. The third body layer was created during the rubbing process. Analysis of the third body layer revealed that it consisted of a mixture of SiCp/A356 composites, semimetallic materials and their oxides. The surface morphologies of the third body layer tested under dry conditions were continually distributed with shallow microplows and black adhesion pits. However, those under wet conditions were discontinuous and contained uncovered regions, cracks or peeling for varied loads and velocities. In contrast to dry conditions, an evolutionary mechanism model was proposed to describe the effect of humid conditions on tribological behavior, considering the effect of water on the third body under humid conditions. The tribological properties of SiCp/A356 composite brake disks under humid conditions, such as rain and snow, should be noted.