Design Of Graded Composite Brake Disc And Research Of Processing, Microstructure And Properties During Fabrication And Forming

The particle-reinforced metal matrix composites (PMMCs) has specific strength and stiffness and superior wear resistance, so many researchers and engineeres have focused on the fabrication and forming process of composites, but the widespread use of composite was limited for the consideration of technology and cast in the past. The mechanical properties of PMMCs are influenced by the fabrication process parameters, the properties of metal matrix and reinforced particles and interface structure between reinforced particles and metal matrix. But the connection between the properties and structure has not understood completely, and available data is so scarce that the application of composites is limited on a large scale. In this paper, the finite elements analysis (FEA) was applied to develop new product of PMMCs based on the constitutes in composites, the fabrication and centrifugal casting forming of particle-reinforced composites was researched deeply, and the effects of process parameters on the microstructure, composition and properties of composites is also researched systemically, and the characteristic of processing, microstructure and mechanical properties is illustrated widely. The main results are as following:The temperature field and thermal stress field of brake disc with functional graded material (FGM) composites are researched under emergency braking by the finite element analysis (FEA) comparably, Attempts have been made to develop a novel brake disc, which can optimize brake's working conditions. The results show that the temperature and thermal stress of FGM brake disc are the lowest among the three types of brake disc, and the distribution of temperature and thermal stress is also more uniform than the others. Furthermore, the FGM composite brake disc can decrease mass and increase life cycle. The primary design of FGM brake disc was carried out and refered to a new idea for the preparing of FGM brake disc.The fabrication of SiC particle reinforced Zl104 composites is researched deeply, in which the volume fraction of SiC particles is 20 percent, and the average diameter is 15.8μm, and the mass of composites arrive to 32Kg in one cycle. The fabrication parameters and the mechanism of dispersing and wetting of SiC particles in aluminum alloy melt were discussed. The results showed that the dispersing of SiC particles in melt involves three stages, which are the incubation stage, the incorporation stage and the uniform stage based on the wettability of SiC particles. It is helpful for the further understood of the fabrication processing.The microstructure, interface microstructure and mechanical properties of SiCp 20Vol.%/Zl104 composite samples were analyzed in detail. It is observed that there is no deleterious reaction in the interface between matrix alloy and SiC particle, and a little conglomeration of SiC particles and porosity are the main reasons for the decreasing of mechanical properties comparing to the matrix alloy.The centrifugal casting processing of PMMCs cylinder (internal diameter is 70mm, outer diameter is 130mm and the height is 110mm) researched in detail. The results show that the distribution of SiC particles and constitution of composite material located in different location changed in the process of centrifugal casting, and the properties and microstructure were also influenced. And an experimental mode about solute transfer and alloy solidification under centrifugal force has been received.The heat treatment processing of Zl104 alloy and the SiCp/Zl104 composites located in the reinforced zone and particle free zone of cylinder has been also researched based on the aging dynamics, and the microstructure and mechanical properties has been also discussed during heat treatment, results show that the adding of SiC particles has great effect on the heat treatment dynamics, the evolution of chemical composites and microstructure enhance the solute diffusion rate, so the the aging dynamic was shorted.The mechanical properties and microstructure of Zl104 alloy and SiCp/Zl104 composites located in the reinforced zone of cylinder have been discussed before and after heat treatment. It is observed that the fracture of composites includes brittle fracture of SiC particles and tough fracture of matrix alloy, and the fracture of SiCp/Zl104 composites in whole is characterized as brittleness, the micro-void and dislocation density located in the interface lead to the fracture of matrix alloy ahead the fracture of SiC particles for the as casting samples, so the mechanical properties of samples decreases greatly comparing with the matrix alloy. After heat treatment processing, the microstructure of the matrix alloy in composites can be modified, and the local stress concentration and micro-void in alloy also can be reduced too, therefore, the fracture mode of samples is characterized as brittle facture of SiC particles, and the Brinell hardness and tensile strength of composites increase greatly compared with as casting sampes.The wear behaviour and microstructural characterization of the wear surface of Zl104 alloy SiCp/Zl104 composites located in the reinforced zone of cylinder before and after heat treatment against GCr15 steel under unlubricated conditions using block-on-ring wear sliding wear tester.Results showed that the wear is charactered as grain abrasion, adhering abrasion and fatigue abrasion, and all of the wear mechanisms occurred at the same time. The wear behavior of as casting composites samples was mainly governed by the adhering abrasion and fatigue abrasion, in which the majority of SiC particles or precipitation of hard particles were fragmented and no longer acted as major load-bearing components. After solution treatment, the plastic of matrix alloy increase greatly, and the loading can transfer from SiC particles to the matrix, the wear behaviour of samples is charactered as grain abrasion. After aging treatment, the wear behaviour of samples is charactered as fatigue abrasion.Composites discal part, in which the SiC particles have graded change along the diameter of the ring, has been accompleted. It is analyzed that the process parameters during centrifugal casting can be controlled by the adjustment of the solidification times and the solidification modes of SiCp/Al-Si composites, plated specimen with ideal distribution of SiC particles along the diameter of the plated part can be fabricated successfully, and the hardness along the diameter of the plated part is also change fuctionally.The research on the constitution design, material fabrication and forming processing showed that it is feasible to preparing FGM's production. The grasp of the fabrication of SiC 20%wt/Zl104 composites and the forming processing of FGM cylinder as well as plated part and the understanding of microstructure and mechanical properties will be an instruction for the development of FGM brake disc.