| Metal matrix composites is a new material which is produced by joining another material or reinforcement into one metal. Intermetallics reinforced Aluminium matrix composites have many excellent and unique properties, such as high specific strength and stiffness, low heat expand modulus and good wear resistance, and therefore, increasing attention has been paid to it in automotive, communication apparatus and aerospace applications. In order to get metal matrix composites with better properties , various means have been investigate and invent by many people, pressueless infiltration is a good technique.The pressureless infiltration technique means that metal liquid infiltrate into preform spontaneously by capillary, metal matrix composites are produced finally. At the same time there are reactions between elements. This technique offers the potential to be an alternative, simple, low-cost processing route for the manufacture of near-net shape silicon carbide reinforced aluminum matrix composites. But it also has many disadvantages, such as the poor wetting between ceramic and metal, under the atmosphere protect of N2 or Ar, the long time and low rate of infiltration, the difficult control of volume fractions of ceramic particulates, and so on. Therefor, many works should be done to research infiltration mechanism, reduce limited conditions, improve atmosphere, get better Microstructure finally.The major research purpose is to simplify the pressureless infiltration process. Making pressureless infiltration happen under air condition, and the process happen rapidly, get fine intermetallic reinforced Al matrix composites at last. The major research efforts of the present study are as follows:(1)AlFeSi,AlSiV reinforced aluminium matrix Composites by pressureless reactive infiltrationAlFeSi,AlSiV reinforced aluminium MMCs in the present study were produced successfully by pressureless infiltration technique based on the experiment research. The process is that the pressureless or spontaneous infiltration of Al-Si alloy into the loose bed in air contains K2TiF6.(2)Analyze microstructure of composites produced by pressureless reactive infiltrationThere are two kinds of reinforcements in the composites produced by pressureless reactive infiltration. One reinforcement like diamond is AlFeSi of AlSiV; another reinforcement like needle isβ-Al5FeSi;(3) Hardness and abrasive wear behavior of composites produced by pressureless infiltrationThe hardness of composites increased greatly compared with Al-13Si especially on the surface. The material shows great wear resistance because there are many reinforcements in the surface of composites.(4) Decrease limited condition of pressureless reactive infiltrationThrough dynamics analysis of melt penetrating into loose bed, it can be concluded that most pressureless infiltration experiments must include Mg under N2 because of non-wetting between liquid and solid. There are two wetting system in this experiment: Al-Si and VFe. So it is no need to include Mg and N2 in the experiment, and the limited condition is decreased.(5) Results of infiltration under different conditionsIt is concluded that AlSi infiltrates into VFe successfully when the system is heated to 650℃or preserved for 5mins under 800℃. The best microstructure is found when the system is preserved for 30mins under 800℃. (6)Mechanism of K2TiF6 function in the processThe system must include K2TiF6 if there is no N2. It is analyzed that liquid metal penetrate Al2O3 on the surface of Al liquid, so Al and K2TiF6 reactive . Heat the reaction released and KF,AlF3 reaction created dissolves Al2O3 rapidly. So AlSi and VFe contact the infiltration takes place. |
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