Experimental and Simulation Analysis of the Mechanical Deterioration Mechanisms in SiCp/A356 Composites Under Thermal Cycling Load

SiCp/A356 brake discs experience cyclic thermal loading during service, leading to a certain degree of mechanical deterioration in the brake disc material (SiCp/A356 composites), thereby reducing the thermal fatigue resistance of the brake disc, ultimately threatening the braking safety of urban rail trains. To investigate the mechanical deterioration patterns and mechanisms of the SiCp/A356 composites, thermal cycling experiments were conducted, along with simulation methods and microstructural analysis. The results indicate that the upper temperature limit of thermal cycling determines the microstructural damage modes and degree in SiCp/A356 composites, and the damage degree is positively correlated with mechanical deterioration. A temperature of 200 °C is identified as suitable for long-term service of SiCp/A356 composites. Thermal cycling induces thermal mismatch stress and residual stress within the material, serving as the primary driving forces for microstructural damage. Thermal cycling reduces the dislocation density in the near-interface (Al-SiC interface) matrix, improving the material's ductility. However, dislocation accumulation in the matrix far from the interface results in stress concentration, promoting matrix damage and crack formation, thereby compromising mechanical properties. The sole strengthening phase, Mg₂Si, is susceptible to aggregation and coarsening, leading to reduced mechanical properties after peak aging. The principal cause of interface crack is the stress concentration caused by dislocation accumulation, ultimately leading to interface failure. This research provides important guidance for the operation and maintenance of SiCp/A356 brake disc.