Tribology and particle emission from Al–SiCp MMC brake discs with secondary aluminum

Abstract This study evaluated the friction, wear, and airborne brake wear particle (BWP) emissions of aluminum-based metal matrix composite brake discs fabricated from recycled aluminum alloy reinforced with silicon carbide particles (Al–SiCp MMC). The study further conducted a comparative analysis of the friction, wear, and BWP emissions of Al–SiCp MMCs against those of a commercial gray cast iron (GCI) brake disc, which served as a reference. The results show that the steady-state coefficient of friction for all Al–SiCp MMC brake discs remained consistently between 0.4 and 0.45, within the typical range for brake materials. A clear transfer layer was observed on the surfaces of Al–SiCp MMC discs after testing, resulting in apparently milder wear due to material transfer and reduced BWP emissions. Al–SiCp MMC brake discs resulted in higher wear rates for the mating pins than the GCI discs, with wear rates increasing as the fraction of secondary aluminum in the matrix increased. Within the measurement range of this study, both GCI and Al–SiCp MMC brake discs exhibited monomodal number-weighted particle size distributions in the steady state, with the mode size of approximately 0.5 µm. Future research should employ advanced particle samplers capable of detecting nanosized particles and explore more severe testing conditions, including higher contact pressures, speeds, and temperatures.