Study On The Aluminum Matrix Composites Used For Automobile Brake Disc

It is the development direction of automobile industry to promote the automobile lightweight The brake disc is an important part of automotive braking systems, the performance of braking is directly related to driving safety of the vehicle.Using lightweight aluminum alloy replace the cast iron and forging steel,which are widely used in automobile brake disc, can effectively realize the auto lightweight.In this paper,based on the application of brake disc maded of aluminum matrix composites on automobile vehicles, the high-silicon aluminum alloy(Al-30%Si) and SiC reinforced aluminum matrix composites(SiCp/Al-7%Si) are selected for the study.In order to improve the friction and wear properties,the different metamorphic process were optimized for Al-30%Si alloy to refine the primary silicon organization. By using the combination of implosion method and internal cooling mechanical stirring to produce SiC reinforced aluminum matrix composites, combined with XRD, SEM and EDS detection means to study the effects of implosion method on the microstructure of SiC reinforced aluminum matrix composite and investigated wettability of SiC. On these basis, taking a Santana car as reference, the brake-simulating tester model MM1000Ⅱ were used to research the impact of different munufacture techniques, different braking speed and brake pressure on the friction and wear properties of aluminum matrix composite brake discs.Compare with the gray cast iron(HT250) automotive brake disc, the wear mechanism of aluminum matrix composites was discussed to provide experimental basis for the application of the material in the automobile brake discs.The manufacture results show that:in the internal cooling metamorphic processes, the mass fraction of stirring head had the most influence on the average grain size and the shape factor of the primary silicon.By using the optimal metamorphic process, the average grain size of the primary silicon can be refined from 256μm to 43μm and the shape factor can be rounded from 0.1 to 0.6. In the study of composite modificati processes show that mass fraction and heat preservation time of A15TiCCe2P observably affected the refinement of primary silicon of Al-30%Si, Through the optimal metamorphic process, the average grain size of the primary silicon can be refined from 256μm to 25μm, the shape factor can be rounded from 0.1 to 0.7 and can get a good primary silicon tissue. By implosion method to produce SiCP/Al-7%Si composite materials,the wettability between SiC and aluminum melt have been improved significantly,and it can get uniform distribution when the speed of stirring is 800 r/min and the size of SiC particle is 80μm.The friction and wear results show that wear resistance of Al-30%Si brake disc after internal cooling modification method and complex modification method increases with the decreasing of the average size of primary silicon, but the friction coefficient decreases, Compare with the gray cast iron, the friction coefficient of Al-30%Si under the optimal metamorphic process is slightly lower, but the wear rate is significantly lower. The wear rate of SiCp/Al-7%Si composite materials decreases with the increasing of SiC content, but corresponding coefficient of friction increases. Compare with the gray cast iron,SiC reinforced aluminum matrix composites has higher friction coefficient and narrower fluctuation range of friction coefficient, but the wear rate is nearly. It’s showed that SiCp/Al-7%Si composite materials have more appropriate applications in auto brake disc. Friction and wear mechanism of the aluminum matrix composites is closely related to the manufacture process, the unmetamorphosed Al-30%Si alloy present delamination wear.The metamorphosed Al-30%Si alloy and SiCp/Al-7%Si composite present that the fine enhancing phase (SiC, Si) distributing in Al matrix stand out and become a supporting body. Grinding parts in the surface layer form a thin transfer layer, playing a role in reducing aluminum body wear and the wear behavior present abrasive wear and adhesive wear.