Preparation Technology,Friction And Wear Properties And Mechanisms Of Aluminum Matrix Composite Brake Rotor And Coupled Pad Used For High-speed Train

Brake rotor is one of the key parts involved to security of service of vehicle. There exist two problems for brake rotors made of cast iron: overweight which affects dynamical properties of the train and excessively high temperature on friction surface during braking which deteriorates the mechanical properties of brake rotors. Aluminum alloy matrix composite has a series of advantages such as low density, high specific strength and specific modulus, high wear resistance, low coefficient of expansion, high coefficient of heat conductivity and high cooling rate. So aluminum matrix composite is proper for brake rotors which can greatly reduce the weight of the brake system of train that improves dynamical properties of the train, and significantly lower the surface temperature of the brake rotor that increases safety coefficiency of service of vehicle. Research on application of aluminum matrix composite for brake rotor materials is still in experimental stage abroad, and fewer reports are available in these fields at home. In this dissertation, Al-Si/SiCp composites brake rotor with diameter of 1200mm was firstly fabricated by a novel spray deposition technology, and simultaneously coupled brake pad was prepared by a novel dry-powder processing route, termed as two-step pressing process. A wedge pressing technology was developed to densify the as-produce Al-Si/SiCp composite brake rotor. The friction and wear properties and mechanisms of both Al-Si/SiCp composites brake rotor and brake pad were investigated. The conclusions are drawn as following:1. Regularity of fabrication in aluminum matrix composite ring-shaped performs with large dimensions and effects of parameters were investigated, based on the novel crucible movable spray deposition technology and equipment. The optimal parameters are that the diameter of the delivery tube is 3.8mm, spray gas pressure is 0.8MPa, spray height is 200mm, and transferring pressure of SiC is 0.5MPa. Based on these parameters, the performs with the outer diameter 1200mm, the inner diameter 600mm and thickness 100mm were prepared. Composition and microstructure homogeneity combined with fine primary silicon grain and uniform distribution of SiC reinforced particles of 15% were achieved. The experimental results show that the fraction of primary silicon grains increase with increasing of silicon content and the diameter of these grains is less than 5μm, which demonstrates a higher cooling rate; Besides, the hardness and ultimate tensile strength of composite increase with increasing of silicon content.2. Based on the conception that large deformation can be obtained through accumulation of little deformation, a novel processing, wedge pressing, was specially...