Alloy selection for wear-resistant lightweight aluminium brake disc

Abstract

Brake discs for the rear axle of a high-performance sports car have been manufactured in three different lightweight materials; AA6082, AA7075 and AA2024 aluminium alloys. These were subsequently coated with a Keronite plasma electrolytic oxidation (PEO) ceramic layer. Full-scale dynamometer tests have been conducted against a standard low-met brake pad using a modified AK master test at increasing levels of braking temperature until a physical limit is reached. Microstructural characterisation of coating and brake pad wear and tribo-layer have been studied using SEM and EDX. In addition, post-dynamometer-test friction discs have been exposed to salt fog testing. Dynamometer tests give confidence that PEO-coated aluminium brake discs are a viable technical solution for vehicle lightweighting. In particular, compelling performance with respect to good coefficient-of-friction (CoF), extremely high coating adhesion, minimal disc and pad wear, low disc run-out, good heat dissipation, and good corrosion resistance has been demonstrated for Mat A (AA6082) alloy discs. Despite higher room temperature strength, the resulting performances of Mat B (AA7075) and Mat C (AA2024) are poor at higher braking temperatures, resulting in excessive coating spallation and subsequent grain boundary attack followed by severe intergranular corrosion.