| A new advanced thermal management material with excellent thermal properties, which composed Aluminum with high volume fraction of Silicdn, was obtained in this thesis. Pressureless infiltration (PLI), developed in recent years, is an available method to produce Metal Matrix Composites (MMCs), and it is characterized by simplified process and low costs. In the thesis, 61-81vol.% Sip-Al composites were prepared by Al-Alloys melt infiltration into Si particles porous preforms without external pressure. Si particles porous preforms preparation, spontaneous melt infiltration process, solidification of Al-Si alloys melt in the interspaces among Si particles, microstructures and thermal properties of the composite, were systematically investigated in the work. The main results are as follows:1. A kind of vacuum pressureless infiltration equipment (VPI) was designed and made by selves. The system of VPI equipment mainly includes vacuum chamber, heating unit, worktable with its drive unit, vacuum pumping unit, gas-charge unit and control unit, etc. This equipment would meet the need of Al or Cu matrix composites prepared by pressureless infiltration or vacuum infiltration in a high vacuum or special atmosphere.2. Si particles porous preforms were prepared by cold isostatic pressing process (CIP). Its average porosity is about 31.3%.3. High volume fraction Sip-Al composites were fabricated by Al-alloy melt infiltration into Si particles porous preforms without external pressure successfully. Its thermal conductivity is 94.8-128.7W/(m K), its thermal expansion coefficient is 5.1-7.8X 10-6/K(50℃-100℃) and its density is less than 2.5g/cm3 respectively.4. The process of Al-alloys melt infiltration into Sip porous preforms was investigated. It is necessary that the existence of Mg in Al-alloys and N2 atmosphere. Mg element in Al- alloys can promote infiltration process, but the oxide film on the surface of Si particles may make against infiltration process. An approximate parabola curve of infiltration depth versus infiltration time was proved. It was observed that infiltrating front of Aluminum alloys melt liquid was characterized by aplane state.5. Solidification of Al-alloys liquid in the interspaces among Si particles was investigated primarily. Because of the effect of Sip porous skeleton, the primary Si and the eutectic Si were separated on the surface of Sip porous skeleton under slow cooling conditions, and there were no typical eutectic microstructures in the Al- alloys phase of the composites.6. The observed results of composites microstructures showed that Si particles caused passivation, they were fused and involved one another into a continuous three-dimension meshwork. The interface of Si/Al phases was clean and no reactants existed. The main mechanisms of continuous netlike Si phase were dissolution-deposition and appendiculate deposition of Si. Furthermore, form-mechanism of few fine pores in the microstructure was investigated.7. Thermal properties of Sip/Al composites were measured and investigated. Microstructure of the continuous netlike Si phase is good for improving thermal properties and restricting thermal expansion of Sip/Al composites. Few fine pores remained in composites were helpful for reducing thermal expansion coefficient of the composites. As increasing of environmental temperature, the thermal conductivity of the composites descended, while CTE of the composites rose at first (within 50℃-150 ℃) and declined later (about > 150℃).
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