Investigation of Al ₂ O ₃ -Ni Coated Cast Iron Brake Rotors Under Modified Brake Dynamometer Test Standards

Due to the reduced or less-frequent usages of the friction brakes and the lower brake rotor temperature on electrical vehicles (EV), corrosion would much likely occur on brake rotors. Using hard braking to clean the corroded rotor surfaces often leads to extra rotor surface wear. Improvement in corrosion and wear resistance is an important technological topic to brake rotors for EVs. Many original equipment manufacturers (OEM) and their suppliers are exploring surface treatments including laser cladding and thermal spray processes on cast iron rotors to combat the corrosion issues. However, mentioned surface coating processes increase the cost of brake rotors and there is a need to search for cost-effective coating processes. In this research, a new Al₂O₃-Ni composite coating was proposed for preparation of a commercial cast iron brake rotor using plasma electrolytic aluminating (PEA) followed by electroless nickel plating (ENP) processes. The added nickel was to fit in the intrinsic pores of PEA coating and reached to the coating top surface. The brake rotor with the corrosion-resistant PEA-ENP coating was tested with modified SAE Brake Dynamometer Standards J2522. In the modified brake dynamometer test, the number of stops in all the Fade sections were decreased from 15 to 6 to maintain the test temperature below 500 °C. The paper presents the dynamometer test results including coefficient of friction (COF), surface morphology and wear performance. The average tested COF was around 0.31-0.34 while the coating on the cast iron brake rotor remained integrated after the modified dynamometer test. The test results indicate that the new PEA-ENP coating is a potential process to improve brake rotor wear and corrosion resistance for EVs. Dynamometer tests with unmodified standards will be conducted in the future to further confirm the validity of the PEA-ENP coating applications in actual brake systems.