高硼含量铝硼中间合金制备及KBF4与铝熔体反应机理研究

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	高硼含量铝硼中间合金制备及KBF4与铝熔体反应机理研究
	王青亮
学位类型	博士
导师	赵九洲
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料加工工程
关键词	铝硼中间合金制备混合技术界面反应机理 Al-b Master Alloy Production Mixing Technique Interfacial Reaction Mechanism
摘要	"固溶于铝中的微量过渡族杂质元素，如Ti、V、Mn、Cr等，对铝导电性影响很大。在生产导电铝时，常通过加入铝硼中间合金对铝熔体进行硼化处理，使铝中的过渡族杂质元素以不溶性硼化物形式沉淀析出，来提高铝的导电性。铝硼中间合金中硼含量的提高有助于增强其对铝熔体的净化效果。目前，工业生产中通常采用氟盐反应法制备铝硼中间合金，为提高硼含量，通常需添加钛剂以降低熔体黏度。采用这种熔体处理方法制备的铝硼中间合金中含有钛，将影响其对铝的净化效果。因此，研制不含钛的高硼含量铝硼中间合金，对于更好地满足导电铝生产需求具有十分重要的意义。本研究以采用氟盐反应法制备不含钛的高硼含量铝硼中间合金为核心，开展了如下工作：采用内部加盐法制备含硼量约3 wt.%的AlB2型中间合金，考察了不同加盐方法、混合方式对硼回收率及合金组织的影响。研究表明，采用内部加盐法制备铝硼中间合金时可获得较高的硼回收率。采用铝箔包裹后压入加盐法时，反应过程中有AlB12相生成，硼化物在铝基体中主要以团簇形式存在，每次压入加盐后进行快速搅拌，可有效破坏合金中较大尺寸硼化物团簇。采用铝箔包裹后压入加盐法和刚玉坩埚电磁搅拌辅助反应法制备高硼含量铝硼中间合金。结果表明，分批次加盐可有效降低熔体黏度、提高硼回收率，但随着加盐批次的增加，合金中粗大AlB12颗粒增多，AlB12团簇趋于严重。对采用铝箔包裹后压入加盐法制备的高硼含量铝硼中间合金熔体的精炼及凝固过程进行了研究。确定了最佳精炼温度为1300℃左右，最佳覆盖/精炼剂成分范围为(25~45) wt.%Na3AlF6 - (40~80) wt.%KAlF4 - (2~8) wt.%CaF2，最佳精炼时间为5~10 min。将精炼后所得合金熔体直接浇入不同模具（石墨模、铁模和砂型模）中以不同冷速进行凝固时，对合金中AlB12颗粒尺寸及空间分布情况影响不大，合金中硼含量较低时易形成粒子偏聚型凝固组织。考察了溶剂成分对KBF4与铝熔体界面反应的影响，研究了KBF4与铝熔体界面反应机理。结果表明，界面处AlF3的存在可促进界面处层状AlB12与铝熔体的脱离；采用亚共晶成分KF-AlF3溶剂时，界面处不存在AlF3，界面处形成由AlB12和AlB2两相组成的层状硼化物组织。考察了反应温度对KBF4与铝熔体界面反应的影响。结果表明，反应温度较低时，反应界面呈凸起状，样品内部无氟盐存在，界面反应过程中生成的硼化物完全以AlB12颗粒形式分布于氟盐中；随着反应温度的升高，有爬壁现象及乳化现象产生，界面处硼化物生成量增加，进入到铝熔体中的硼化物比例增加。"
其他摘要	"Trace levels of the transition elements, such as titanium, vanadium, manganese and chromium, in aluminum have a detrimental effect on electrical conductivity when in solid solution. In the production of electrical conductive grade aluminum, the transition elements are generally precipitated as insoluble borides by treating the aluminum melt with an Al-B master alloy to improve the electrical conductivity. High boron Al-B master alloys are favored for the treatment for the better purifying effect. At present, Al-B master alloys are commonly produced by reacting KBF4 with molten aluminum. In order to elevate the boron content, the existing production routes of Al-B master alloys generally involve the addition of K2TiF6 to improve the fluidity of the molten alloys. However, the Al-B master alloys produced by this method contain some Ti, which would depress the purifying effect. It is, therefore, very meaningful to fabricate the high boron Al-B master alloys containing no Ti in order to meet the needs of the production of electrical conductive grade aluminum. In order to realize this goal, following researches have been carried out: Al-3 wt.%B master alloys have been produced by mixing KBF4 into molten aluminum. The effects of the mixing conditions on the boron recovery and the microstructure have been studied. It shows that high boron recoveries can be obtained in the production of Al-B master alloys by mixing KBF4 into molten aluminum. When using the “immersion” method, there exists AlB12 phase in the produced alloys, and the boride particles distribute in the Al matrix mainly in the form of agglomerations. The vigorous stirring carried out after each immersion could effectively break up the large boride agglomerations. When using the “vortex” method, no AlB12 phase formed during the production, and the AlB2 particles are well dispersed in the matrix mainly in the form of individual particles. High boron Al-B master alloys have been produced by the “immersion” method and a novel method, in which the reactions between KBF4 and molten aluminum take place in a corundum crucible assisted by the electromagnetic mixing effect of the medium frequency furnace. The results demonstrate that the fluidity of the molten alloys can be effectively improved by adding the KBF4 salt in batches. The refining process as well as the solidification process of the high boron Al-B master alloys has been investigated. It was found the proper refining temperature is about 1300℃, the proper composition range of the covering/refining agent is (25~45) wt.%Na3AlF6 - (40~80) wt.%KAlF4 - (2~8) wt.%CaF2 and the proper refining time range is 5~10 min. Pouring the refined alloy melts into different moulds (graphite mould, iron mould and sand mould) for solidification demonstrates that the size and the distribution of the AlB12 particles in the alloys varies little with the cooling rate. A particle segregated microstructure can be formed in an Al-B master alloy of relative low boron content. The influence of the solvent composition on the interfacial reactions between KBF4 and molten aluminum has been investigated. The reaction mechanism between KBF4 and molten aluminum has been studied. It shows that the AlF3 formed at the salt/aluminum interface has an effect of promoting the separation of the boride layer from molten aluminum. No AlF3 forms at the interface and the boride layer formed at the interface is comprised of AlB2 and AlB12 while using a hypoeutectic KF-AlF3 solvent. Adding some MgF2 into the eutectic KF-AlF3 solvent has no influence on the interfacial reactions, while the addition of MgF2 into a hypoeutectic KF-AlF3 solvent has a distinct inhibiting effect on the interfacial reactions. AlF3 forms due to the reaction of molten aluminum with BF3, which forms due to the reactions of KBF4 with AlF3 and KAlF4 in the molten solvents. The interfacial phenomena during the reactions between KBF4 and molten aluminum at different temperatures of 800℃, 900℃ and 1000℃have been investigated. At the relative low reaction temperature of 800℃, the produced alloy shows a convex surface. No fluoride salts exist in the alloy and all the borides formed at the interface distribute in the salt in the form of AlB12 particles. With the increase of the reaction temperature, the alloy surface becomes concave, the salt/melt emulsification occurs as well as the phenomenon that the alloy melt climbs up along the inner wall of the crucible. Also, more boride particles form at the interface and the proportion of the boride particles entering into the molten aluminum increases. "
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64492
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	王青亮. 高硼含量铝硼中间合金制备及KBF4与铝熔体反应机理研究[D]. 北京. 中国科学院金属研究所,2012.