Preliminary Study On Performance Test And Preparation Of High Carbon-Graphite/Aluminum Composite Material For Piston

The performance of piston material has been put forward higher requirements, with the development of the internal combustion engine to light weight, high power, low fuel consumption, low emission, long life. Therefore, a new development trend is to develop new piston materials to adapt to the different working conditions and the working environment. graphite/aluminum composite material is an excellent material for piston, and is characterized by self lubrication, low friction coefficient, good thermal conductivity, thermal expansion coefficient, etc.This paper has tested and analyzed a piston with high carbon graphite/aluminum composite material on the components of organization, physical properties, friction and wear properties. The test results show that, microstructure of the high carbon-graphite/aluminum composite material is compact, graphite content is up to 53.3%; thermal expansion coefficient is 7.2×10-6/℃; thermal conductivity is 135w(m*k)-1; the friction coefficient is 0.2; compressive strength at room temperature is up to 240Mpa, and the bending strength is 138MPa. Compared with the traditional aluminum alloy piston material ZL105, density of high carbon-graphite/aluminum composite material is reduced by 20%; the thermal expansion coefficient is reduced by 66%; coefficient of thermal conductivity decreases 10%. the other advantage are the anti friction and wear resistance and dimensional stability.At the present time, the processing technique of graphite/aluminum composite material is liquid phase method including casting and vacuum pressure dipping infiltration method. And it is difficult to produce a graphite/aluminum composite material with high graphite content and the compacted microstructure because of the poor wetting property and the large difference of density. In the process of producing graphite/aluminum composites material by powder metallurgy, the content of component materials can be arbitrary regulation, as is a very large superiority for preparation with high volume fraction of particle reinforced composite materials. Therefore, the powder metallurgy technology is used to the processing of graphite/aluminum composite material. It is a analysis of the microstructure, thermal conductivity, friction and wear properties of graphite/aluminum composites of graphite/aluminum composite material with the optimum preparation technology, as is compared with the traditional aluminum alloy piston material ZL105.In the following process:pressure 500MPa, sintering temperature of 570℃ for 1.5h, an analysis of powder metallurgy technology used to processing graphite/aluminum composite material is carried out. The study shows that graphite/aluminum composite density reached 95% and the radial thermal conductivity average value is 140w (m*K)-1. And phase analysis shows that the graphite/aluminum composites in preparation process does not appear interface reaction product and graphite exists as the free state of elemental. The experimental results of friction and wear test shows that, the friction coefficient of graphite/aluminum composite material is small and the average friction coefficient is 0.15. And the higher the graphite content, the smaller the friction coefficient of the stable friction stage. Compared with ZL105, friction process of graphite/aluminum composite material is more stable. Thermal conductivity measurements shows that:thermal conductivity of graphite/aluminum composite material producing by powder metallurgy is more different between the height direction and the radial. The radial thermal conductivity average value is 140w(m*k)-1, while the axial average value is 50w (m*k)-1. The experimental results of compressive strength shows that:compressive strength of composite material decreases with the increasing graphite content, and compressive strength of the composite is 203MPa when the graphite content is 15wt%. The experimental results of friction and wear test shows that:the higher the graphite content and load, the smaller the friction coefficient. The friction coefficient is 0.25 when the graphite content is 15wt%.Compared with foreign piston of high carbon-graphite/aluminum composites and aluminum silicate material ZL105, the graphite/aluminum composite material producing by powder metallurgy has poor mechanical properties. For example, compressive strength with 15wt% graphite content is about 84% of the foreign piston of high carbon graphite/aluminum composites. The coefficient of thermal conductivity are anisotropic, and friction coefficient is consistent.