The automotive industry is facing enormous challenges. Electric mobility is gaining more and more ground and changes vehicle concepts to hybrid electric and battery electric vehicles. Energy recovery systems in electric cars can save most of the braking energy in the battery, and thus reduce the energy of friction in the conventional braking system. In addition, piloted driving promises predictive driving and autonomous braking, even in emergency situations. Both developments provide the opportunity to reconsider material concepts for brake rotors. Under certain conditions an application potential might rise even for light materials having a lower melting temperature than cast iron. aluminium-based Metal Matrix Composites (AMC) offer the opportunity to support lightweight design and to reduce wear and particle emission due to their different friction behaviour. Four aluminium-based brake rotor concepts were tested on a brake dynamometer by using a synthetic load spectrum (SLS) and a standard road cycles (SRC). The tests were carried out section-wise by using the so-called interrupted monitoring method in order to investigate the influence of ordinary braking situations with different loads and rotor temperatures on friction and wear and on the development of the wear-reducing tribolayer. Scientific explorations were primarily done by using a Large Chamber Scanning Electron Microscope at the University Erlangen-Nürnberg. The chemical composition of the tribolayer was analysed by using Energy Dispersive Spectroscopy EDS. The results show that the necessary tribolayer only forms on reinforced aluminium alloys. The maximum operating temperature can be verified at not less than 450 °C and the amount of wear of the favoured Al-AMC is less compared to cast iron rotors.

Gulden Florian, Höppel Heinz Werner, Göken Mathias, Materials Science & Engineering, Institute I, Friedrich-Alexander-Universität Erlangen- Nürnberg (FAU), Germany; Stich Anton, Gramstat Sebastian, AUDI AG, Germany.