| As a kind of important nanomaterials, one-dimensional carbon nanomaterials (including carbon nanotubes and carbon nanofibers) have excellent electrical and mechanical properties. In the one-dimensional carbon nanomaterials research, there are still many problems to be solvedo-morphology and micro-structureAlong with the rapid development of industries such as motor vehicles, civil aviations, and household appliances, etc. Al alloys have became one of the most important casting structural materials, due to their light weight, high strength and excellent working properties. Casting Al alloys have been widely applied in making cylinders, wheel hub, piston, gear-box, arrester and operation systems, etc. Generally, during Al-Si alloys casting, its mechanical properties and fabricating characteristics including toughness and cutability become worse due to the formation of large acicular and plate eutectic Si phase, which will extremely separate the a-Al matrix and induce a local stress concentration. Therefore, in order to manufacturing the high quality Al alloys, it is of important significances to make more economical, high effective and environmental friendly modifiers and grain size refiners, and molten Al alloy purifying materials.In the present work, after several years researches, a series of achievements have been taken in the areas involving preparation of high effective, fast-modification and high Sr content Al-Sr20 master alloy, high cleanliness Al-Ti-B refiner, Al-Ti and Al-Zr master alloys, and Al alloy molten physical purifying materials and equipments. In addition, the modification mechanism of high Sr content Al-Sr20 master alloy and refine mechanism of the novel Al-Ti-B refiners were deeply researched and characterized by using optical microscope, scanning electron microscope (SEM), X-ray diffraction and measurements of the mechanical properties. It is expect to supply the theoretical results for further developing new products and applications.This dissertation is divided into eight Chapters.The first Chapter is the introduction. It describes the research background, importance of this work and main contents of the present work. The present research situations and further developing trends of the topics were reviewed including modification and refining mechanism, Al-Sr master alloys, ternary Al-Ti-B alloys and binary refiner alloys. The second Chapter introduces systematically on the preparation and application of high effective, fast-modification and high Sr content Al-20Sr alloy, which was firstly developed by present research work. The content contains technique characters, key manufacturing processes, and comparisons between the present Al-Sr20 master alloy and the regular Al-Sr10 master alloys. in this work, we propose a novel "direct reaction-hot extrusion" manufacturing technique for producing high Sr content Al-20Sr master alloy. It mainly contains four processes:1) Alloying using a medium-frequency induction furnace with complementary mechanical and electromagnetic stirring; 2) Degassing and deslagging by using a rotary degassing method; 3) Casting coarse alloy bars; 4) Producing Al-20Sr master alloy wire by using a hot-extrusion process of cross-section area large deformation. It provides many advantages, such as high recovery, good reproducibility, no delitescence of modification, no corrosion on equipments, environmental friendly, and also good workability with smooth surface, no bubbles, no peeling and no cracking. This Al-20Sr master alloy has been industrially applied in Al-Si alloys casting in automobiles and motorcycle wheels, etc.It has been known that the modification property of a Al-Sr maste alloy depends mainly upon the morphology and size of the A14Sr intermetallic phase. In the third Chapter, the microstructures, grain size, hardness, elastic modulus and fracture surfaces of the A14Sr phase in the Al-Sr20 and Al-Sr10 were comparatively characterized by using optical microscope, XRD, SEM, EDS, microhardness and nano indenter, etc. Experimental results revealed that the intermetallic A14Sr phase in the Al-Sr20 alloy is homogeneously distributed in the Al matrix with small size and roundish shapes in a range 5-30μm, while in the Al-Sr10 alloy, the A14Sr phase shows shapes of rectangular stripe and plates with the length in a range of 20-150μm and width in 10-30μm. This is why the Al-Sr20 master alloys exhibit advantages including high recovery, good reproducibility, no delitescence of modification, and also good workability with smooth surface, no bubbles, no peeling and no cracking, when using the present advanced "direct reaction-hot extrusion" manufacturing technique.In Chapter four is the research and application of the high cleanliness Al-Ti-B grain size refiners on fabrications of AlTi5B1 and AlTi5B0.2, and their characters. Comparing to the traditional technique, the present refiners were prepared by using a villiaumite method with electromagnetic actions, and simultaneously, also use the Al2O3 as a cover absorbent. Consequently, the influence of inclusions such as Fe, Si, Mg and Ca, etc. upon the refiner cleanliness was greatly reduced, and therefore, increased the refining effect and also decreased the contamination for the refined Al alloys. For the further research, the microstructures, phases, TiA13 grain size and hardness, and fracture surfaces, etc. were characterized by using optical microscope, XRD, SEM, EDS, microhardness and nano indenter in the fifth Chapter. The refining mechanism of the AL-Ti-B was theoretically calculated and discussed.Chapter six introduces novel processes for preparing high cleanliness binary Al-Ti and Al-Zr refiners. In the present technique, the Ti scraps or Zr scraps combined with pure Al to manufacture the Al-Ti and Al-Zr binary refiners at the low temperatures. The advantages includes reuse of the Ti and Zr scraps and low temperature alloying, which can greatly avoid the burning, oxidation, and absorption of the alloys during fabrication, and improve the quality and reduce the cost. It also exhibits a significance for environmental protectionsIn Chapter seven, a new kind of purifying materials for Al alloy melton-mico-pores ceramics materials and the multi-grade purifying filtrators. In this work, due to the problems and disadvantages the regular used purifying tubes, a new tube was prepared according principle of spumy ceramics. And then, the filtrators were made of the combinations of the ceramics tubes and plates with multi-grades. It has been demonstrated that the present filtrators exhibit advantages including high efficient and more economic process for filtrating Al alloy meltonsChapter eight is a full summary of the dissertation. And finally, a brief introduction of published papers and patents, and participated project during graduate study are given. |
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