The new Euro 7 standard, set to be in place by 2026, will be the first legislation to
attempt to cap the emissions produced by a friction brake system. This has prompted
brake manufacturers to seek alternative solutions to reduce the emissions generated by
conventional grey cast iron (GCI) friction brake systems. With electric vehicles becoming
the future of modern vehicles, their regenerative braking system will cause friction brakes
not to be used as frequently as in an internal combustion engine vehicle. This may lead
to a build-up of corrosion on the brake rotor that may not only affect the performance
and service life of the brakes but also increase particle wear emissions when braking.
This study compares the friction, wear and emission characteristics of two aluminium-
based rotors with those of a conventional GCI rotor. Aluminium metal matrix composites
(Al-MMC) and plasma electrolytic oxidation (PEO)- treated aluminium (Al-PEO) rotors
were the two selected aluminium-based alloys alternative to GCI. As these lightweight
materials could be a solution to reduce the risk of corrosion failure, possibly lower brake
emissions, and improve the overall efficiency of the vehicle by reducing its unsprung mass.
Generally, all 3 rotors produced satisfactory and stable coefficient of friction (CoF), both
before and after corrosion. However, wear and emissions from the GCI rotor increased
significantly after the corrosion cycle. The Al-MMC rotor also suffered some deleterious
effects of corrosion, mainly due to SiC particles being dislodged from the surface.
Although there was some evidence of surface damage away from the rubbing surface,
the Al-PEO rotor produced the lowest particulate emissions of all 3 rotors, both before
and after corrosion. These results suggest that, with further optimisation of the PEO processing conditions and a more compatible pad material, the Al-PEO rotor is a viable
and more environmentally-friendly alternative to the current GCI system.
