Thermal expansion and fatigue properties of automotive brake rotor made of AlSi–SiC composites

Al-9Si- SiC or Al-12Si-SiC composites reinforced with 10 or 20 wt% SiC particles were synthesized by stir casting method. The composites were used to produce automotive brake rotors. Microstructures of the brake rotors made of the composites revealed uniformly distributed SiC particles, primary phase (α-Al) and modified eutectic Si. Grain refining was also observed due to the addition of SiC particles. Coefficient of thermal expansion (CTE) and thermal strain responses during heating and cooling cycles between room temperature and 350 °C of the composites were investigated. Al-12Si and its composites exhibited lower CTE and near zero residual strain. Thermal fatigue studies were carried out on the brake rotors made of the composites as well as commercially available brake rotor made of cast iron, for comparison. After 80 cycles, hardness measurements, microstructure investigations and x-ray diffraction (XRD) analysis were carried out. The results showed that the strain and temperature followed the same path on cooling as on heating, indicating that both hysteresis loop and residual strain were absent. At the same time, the crystallinity of the brake rotor made of the composite was enhanced by the exposure to thermal cycling, while it was deteriorated in case of break rotor made of cast iron on the long run. (paper)