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The friction and wear characteristics of automotive friction materials are strongly dependent on the composition and microstructure of the rotor surface. In this study we investigated the compositional and microstructural changes occurring in the surface layers of cast iron brake rotors during dynamometer tests with a typical organic friction material. Rotors were studied in the as-manufactured, lightly ground and sanded, and as-burnished conditions, as well as after 30 stops from 60 mph at a deceleration rate of 15 ft/s2. Optical and scanning electron microscopes were used to examine the surfaces. Minimum disturbance of the microstructure was found in the sanded surface, but the as-manufactured and burnished surfaces exhibited considerable disturbance. After the 30 stops the pearlite was transformed locally into martensite. Composition analysis of the burnished rotor surface showed high magnesium content.

A drag dynamometer was used to investigate the influence of rotor properties on the wear of automotive brake linings. The effects on lining wear of temperature, surface roughness, thermal conductivity, microstructure and composition were studied quantitatively, and the mechanisms governing lining wear were elucidated. Lining wear at high temperatures increases exponentially with increasing temperature, and decreases exponentially with increasing thermal conductivity of the rotor. The wear increases parabolically with increasing surface roughness of the rotor. Also, coupling of a lining with a rotor having compatible composition and microstructure is very important for controlling the lining wear.