Fabrication Of SiC Particulate Reinforced Aluminium Matrix Composites By Pressureless Infiltration

Metal matrix composites are one of composites reinforced by ceramic phases,being made of ceramic and metal or alloy. MMCs have been receiving significantattention in recent years, particularly in the area of processing techniques. In manyinstances the properties of a reinforced metal have been shown to provide aperformance advantage over a monolithic metal, but the high cost of producing thecomposites has prohibited widespread commercial use. Of the many potential metalmatrix system, aluminium alloy matrix composites have been the object of muchresearch, primarily due to the light weight, low cost, and ease of fabrication ofaluminium. SiC reinforced Aluminium matrix composites have many excellentand unique properties, such as high specific strength and stiffness, low heat expandmodulus and good wear resistance, and therefore, increasing attention has beenpaid to it in automotive, communication apparatus and aerospace applications. Forfabrication of SiC particulate reinforced aluminium matrix composites withexcellent properties and low cost, various means have been investigate and inventby many people. However, fabrication of composites through these routes is stilllimited to relatively simple shapes due to the expensive tooling required forprocesses. Pressurelesss infiltration technique is the best way of those to solve theproblem of properties and cost of SiC particulate reinforced aluminium matrixcomposites.The pressureless infiltration technique means that the spontaneous orpressureless infiltration of ceramic preforms by liquid metals, with capillarypressure in the metal, and it offers the potential to be an alternative, simple,low-cost processing route for the manufacture of near-net shape silicon carbidereinforced aluminum matrix composites. But it also has many disadvantages, suchas the poor wetting between ceramic and metal, under the atmosphere protect of N2or Ar, the long time and low rate of infiltration, the difficult control of volumefractions of ceramic particulates, and so on. Therefore, many works should be paidmore attention to investigate, including the infiltration mechanism of meltpressureless infiltration, the atmosphere control of infiltration process, controllingthe harmful product of interface reaction, reducing volume fractions and themechanical properties and applications of composites by pressureless infiltration.The major research efforts of the present study are as follows:(1) Fabrication of SiC particulate reinforced aluminium matrixComposites by Pressureless InfiltrationThe SiC particulates reinforced aluminium MMCs in the present study weresuccessfully fabricated by pressureless infiltration technique based on theexperiment research. The penetration process is that the pressureless orspontaneous infiltration of Al-Si alloy into the loose bed in air, contains thereinforcement SiC particle with non-preoxidizing treatment and K2TiF6 or K2ZrF6.(2) Kinetics of melt pressureless infiltration into the loose bed andmechanism of K2TiF6 function of penetration processThrough dynamics analysis of melt penetrating into loose bed, it can beconcluded that the infiltration channel is consist of two different types of capillary,circular cylindrical and toroid capillary. The penetration process can be describedthat melt first penetrate the wide pore, circular cylindrical, and then it continuecross the narrow pore, tetrahedral and octahedral, and finally surrounding the SiCparticulate. Based on the analysis, we establish the kinetics model of meltpenetrating into the circular cylindrical capillary. With the experiment of DTA andEDS, the mechanisms of K2TiF6 or K2ZrF6 improving the infiltration capability ofAl melt is found that the reaction between K2TiF6 or K2ZrF6 and Al, the heat ofreaction and temperature enhancing are reasons that destroyed the oxidation filmand improved the wetting of SiC and Al.(3) Influencing factors of pressureless infiltration processInfluencing factors of pressureless infiltration process were detailedlyinvestigated by experimental research. The experimental parameters of fabricationtechniques which are appropriate to fabricate SiC particulates reinforcedaluminium matrix composites by pressureless infiltration technique in air areoptimized and suggested respectively. The best parameters are that temperature is800℃, quality rate of K2TiF6 and SiC is 1:1, the size of SiC particulate is about150μm, the time of infiltration is 30 min, the alloy is Al-13wt%Si.(4) Microstructure and abrasive wear behavior of SiCp/Al composites bypressureless infiltration techniqueThe microstructure and interfacial behavior were revealed by the studies of themicrostructures of the SiC particulates reinforced aluminium MMCs. The productsof reaction between K2TiF6 and Al alloy melt surround SiC particulates. Because ofaddition of Si element, the interface between SiC and Al not form the harmfulproduct Al4C3. The wear resistance of the composite was increased with theaddition of the volume fraction of the SiC particulates.In a word, the research of the present study lies not only in the moreembedded comprehension of pressureless infiltration technique as well as thecorrelation theories, but also provides the referable ideas for pressurelessinfiltration in air coming truth, and will provide the more important experimentdata and theoretical basis.