A significant amount of vehicle weight resides in the conventional cast iron brake discs. This "un-sprung mass" further compounds the effects of rotational inertia and impacts fuel consumption and subsequent CO2emissions. In addition, non-exhaust air pollution from brake dust (disc and pad wear comprising nano-particles, PM2.5 and PM10) is of high concern due to public health issues, and the possibility of premature deaths and reduction in life-expectancy. Thus, there is a strong impetus to develop alternative approaches that reduce both CO2 and PM emissions in future vehicles.
Light materials such as aluminium alloys present attractive options as potential solutions to help reduce vehicle weight, and consequently improve fuel economy, reduce emissions and the overall sustainability of vehicles. The main challenge for using aluminium alloys is their relatively low maximum operating temperatures (MoT) as well as poor surface properties which lead to excessive corrosion and wear. Keronite plasma electrolytic oxidation(PEO) is an environmentally safe coating process which offers aluminium alloys multifunctional characteristics such as high hardness, strong adhesion, low stiffness and a continuous barrier which is capable of offering protection against corrosion, wear and extreme heat likely to be experienced by brake discs.
Brake discs for the rear axle of a high performance sportscar have been manufactured in AA6082-T6 aluminium alloy, with and without vents. These were subsequently coated with a Keronite PEO ceramic layer. Full-scale dynamometer tests have been conducted against a standard Low Metbrake pad using a modified AK Master test at increasing levels of initial braking temperature (IBT) until a physical limit is reached. Microstructural characterisation of coating and brake pad wear and tri bolayer have been studied extensively using SEM and EDX. In addition, post-dyno test discs have been exposed to salt fog testing, and their corrosion behaviour and relative interactions with the tri bolayer have been investigated. The overall relative performance and the degradation mechanisms have been discussed and the potential to use PEO coated light alloy discs have been proposed.
Prof. Suman Shrestha, Vice President - Applications Engineering, Keronite International Ltd; Dr. Robin Francis, Keronite International Ltd; Dr. Andrew Smith, Alcon Components Limited