Characterisation of coated lightweight brake rotors

Numerical and experimental studies were undertaken using lightweight brake rotors to reduce vehicle weight and thereby improve fuel efficiency and vehicle emissions. Abaqus finite element and Matlab software were used to construct one dimensional (1D), two dimensional (2D) and three dimensional (3D) thermal models to investigate the general thermal performance of disc brakes to develop a valid method of reduced scale testing. Five small scale solid brake rotors were investigated experimentally: grey cast iron, wrought aluminium alloy (6082), the same 6082 alloy with an alumina surface layer applied by plasma electrolytic oxidation (PEO), cast aluminium MMC (AMC640XA) and the same MMC with a PEO alumina surface layer. The disc and pad temperatures, brake pressure, coefficient of friction and brake torque were monitored during the tests for each material. Surface morphology, microstructure and micro hardness of the coatings and substrate were evaluated before and after the tests. Numerical simulations confirmed the equivalence between the full and small scale disc thermal performance using the proposed scaling methodology and also provide a good agreement with the experimental results.
The coated 6082 alloy rotor was shown to give good thermal and friction performance up to relatively high rubbing surface temperatures of around 500oC. This rotor failed at a surface temperature of about 550oC due to brittle fracture of the wrought aluminium substrate. The proposed scaling methodology was shown to be a valid method of investigating a rotor design concept in the laboratory at low cost and reduced operating time. The PEO coating on aluminium alloy was denser and more uniform compared to the PEO coating on aluminium MMC. In addition, the PEO coating improved the hardness and thermal resistance of both the aluminium alloy and aluminium MMC. A sensitivity analysis based on the Taguchi approach was carried out on the PEO coated aluminium alloy rotor to investigate the effect of various parameters on thermal performance. Optimisation of the structure was carried out using a genetic algorithm to design coated aluminium alloy discs that are potentially technically viable on small-medium passenger cars.