The Study On Preparation And Microstructure Properties Of Low Expansion Al-Si Matrix Composites

The high silicon aluminum matrix composites have some advantages such as lightweight, low inflation, high thermal conductivity, high strength, etc, so it was widelyapplied in trades included aviation, aerospace, electronic package and precisioninstruments, has become the focus of research on composites.In this paper, the Al-Si system has been taken as the research object. The highsilicon aluminum matrix composites had been prepared by the powder metallurgicalsintering process, from the high silicon aluminum alloy powder. Microstructures werecharacterized by optical metallographic microscope, scanning electron microscopy(SEM) and X-ray diffraction analysis, respectively. The density, dilatation coefficient,tensile strength and hardness of samples were separately measured as well. The rule ofeffects of treatment methods of the powder, sintering processes, sintering temperatureand time of hot pressing and pressing pressure on the micro-structures and propertiesof the materials were studied. The forming processes and mechanism were alsoanalyzed. At last, the preparation technology and technological parameters wereoptimized.Results show that the composite prepared by hot pressed sintering have a highcomprehensive performance than the cold press method. Silicon particles can besignificantly refined by the wet High-energy ball mill in the organization, and Feimpurity can be avoided, so the composite materials tensile strength is increased; Asthe silicon content increased from30%to50%, the thermal expansion coefficientreduced from14.7×10-6K-1to10.3×10-6K-1; When the sintering time increased from1.5h to1.5h, the hole and defect in the test materials reduction, the tensile strengthdecreased from85MPa to110MPa. After the sintering time further increased, theprecipitation of silica particles grew up, which make its tensile strength reduced; Asthe suppressing pressure increased to60MPa from20MPa, the physical andmechanical properties increased, when pressing pressure increased to80MPa, the silicon grain fractured, the composites performance degradation; As sinteringtemperature increased from530℃t o570℃, the physical and mechanical properties ofsamples increased. If the sintering temperature increased further, performance woulddegradation.The best preparation for the composition is hot press sintering high＋wet energyball mill pretreatment. The following process parameters are: wet milling12h,sintering temperature570℃, sintering pressure60MPa and holding time3.5h.