The Preparation Of Al-SiC Composites With Designed-Microstructure And Investigation Of Their Thermal Properties

The Al-SiC composites have excellent thermal conductivity,low coefficient of thermal expansion and higher specific stiffness which is favored toward electronic packing.The thermal conductivity and the coefficient of thermal expansion are influenced by the volume fraction of the composites.For detailed,the coefficient of thermal expansion and the thermal conductivity are in inversely proportion to the volume fraction,The aim of this paper is to obtain the composites with high thermal conductivity the lower coefficient of the thermal expansion,what is more,the volume fraction of the composites is unchanged.This requires to investigate the relationship of the internal microstructure of the composites between the thermal properties,thus the thermal properties of the composites can be improved by optimization design of the microstructure.In order to reveal the relationship between the thermal properties of the composites and the microstructure,it is necessary to build a simulation model of the thermal properties of the composites,which should predict the experimental result properly.Comparison among the results predicted by the classic model and FEM model individually,it is showed that FEM model is close to the experimental results.Furthermore,the mesh size of the FEM model must be less than 1/50 compared to the average particle size.Experimental results showed that the sphere cluster microstructure of Al-SiC composites with volume fraction of 60 ± 1% was prepared by pressure infiltration.The sphere cluster microstructure was designed according to the mechanism of thermal conductivity and thermal expansion.The composites have an excellent thermal properties when the diameter of the sphere structure A is about 300 ?m.The thermal conductivity and the coefficient of thermal expansion of this composites is 222±5W/m·K and 8.6±0.5 ppm/K respectively,the thermal conductivity of which is 20% higher than the composites with a volume fraction of 63% while the thermal expansion of which was kept the same.The sphere cluster structure can increase the heat flux of the composites and the Von Miss stress of particles,as a result the thermal conductivity and the coefficient of thermal expansion of the composites is improved.To further improve the thermal conductivity of the composites with the same volume fraction,the layer structure was prepared which has two kind of thickness.Incredibly,the thermal conductivity in the parallel direction of layer structure is higher(231±5W/m·K)and the coefficient of thermal expansion in the parallel direction is the same as the sphere cluster structure.But the thermal conductivity in vertical direction is low(209±5 W/m·K),and the coefficient of thermal expansion is very high(10.5±0.3 ppm/K).The thermal properties of this structure is anisotropic and when the heat flux is delivered through parallel direction,the heat flux in the coarse particle is higher.