Evaluation of the wear resistance of aluminium-based hybrid composite brake discs under relevant city rail environments

Lightweight hybrid composite brake discs consisting of a A357/SiC aluminium matrix composite (AMMC) top layer and an AA6082 Al alloy bottom base are fabricated by friction-stir processing. These hybrid AMMC brake discs demonstrate excellent wear and friction performance in full-scale dynamometer braking tests under relevant environments for operating a city rail vehicle. Characterisation and analysis conducted on the tested brake discs correlate these performances to a series of improvements in microstructures and properties. They include the presence of thermally stable and hard SiC particles enhancing wear resistance, especially at elevated temperatures, the refinement of microstructures by the uniform distribution of these SiC particles as well as secondary particles resulting in minimised crack initiation, and the generation of gradient hardness and tensile properties leading to increased resistance to external impacts and reduced internal thermal stress. The excellent performance of the lightweight hybrid composite brake discs confirms its high technology readiness level to replace heavy iron and steel brake discs in city rail vehicles.