偏晶体系合金熔体-液相分离凝固的结构演变历程及机制

Properties of liquid alloys and their variation are important and complicated scientific problems. Solidification of alloys begins with melts, and also melts influence the structure and properties of solidified materials directly. Monotectic alloys have great application value and unique liquid phase separating solidification characteristic, however, the effects and mechanism of their melts on the feature of solidification have not been clear. Around the liquid-liquid separating solidification characteristic of the monotectic alloys and the problem of their structural organization separation, this project aims at investigating the evolution rules of the intrinsic structure of the alloy system, studying the effects of melt change on the solidified character and exploring the theory and techniques effectively controlling liquid phase separation. By using some proper methods such as liquid X-ray diffraction, synchrotron radiation, electrical resistivity and other physical property testing analysis, solidified technique and theory calculation, we will study the evolution rules of the melt features, determine the influence of pre-crystallization, cooling speed and some other factors on the solidification behaviour, research the relation between the liquid and solid state, then find the key technique and mechanism of melt under thermal rate treatment to control liquid separation and set up models characterizing the structure evolution process from the melt to monotectic solidification. The launch of this project is conducive to deeply probing into the properties of the alloy melts, improving the theory of liquid alloy structure and solidification , promoting the development of alloy melting techniques and the preparation techniques for high-performance composites.

液态合金的性质及其变化是重要而复杂的科学问题。合金的凝固源于熔体，熔体直接影响凝固材料组织结构和性能。偏晶合金具有重要的应用价值和独特的液相分离凝固特性，但是熔体对凝固特性的影响及其机理尚不清楚。本项目将围绕偏晶合金的液-液相分离凝固特性及由此产生的组织偏析难题，深入探究热诱导下该体系合金液态本征结构演变对凝固特性的影响、探索有效控制液相分离的理论和技术。将运用液态X射线衍射、同步辐射、液态电阻率等物性测试分析、凝固结晶技术和理论计算等方法，掌握偏晶熔体本征结构的演变规律，明确预结晶的熔体状态和冷速等因素对偏晶合金凝固行为的影响，探索合金液-固态关联性，借此研究控制液相分离的熔体热速处理关键技术及作用机理，构建偏晶合金熔体向偏晶凝固历程中结构演变的模型。本项目的开展将深入认知液态合金的性质，完善合金熔体结构及凝固理论，推进合金熔炼技术和高性能复合材料制备技术的发展。

合金的凝固传递着合金液-固态结构的信息，因此合金熔体的结构、性质和状态对合金材料的凝固行为、合金微观组织和性能具有重要的影响。偏晶合金具独特的液相分离凝固特性，利用液液相分离可以设计和制备第二相弥散分布于基体的复合材料或具有核壳结构的复合材料，具有重要的应用价值，但偏晶合金熔体对凝固行为的影响及其机理尚不清晰。本项目用电阻率、DSC及计算模拟等方法验证了Al基偏晶合金熔体微观结构不均匀性，分析了三元Al基偏晶合金的液液相分离机制，并深入地分析和探究了不同热状态下熔体结构转变与偏晶合金凝固组织相关性，着重研究了冷却速率、三元合金成分及浇铸温度等参数对三元难混溶合金凝固行为的影响，探讨了不同体系难混溶合金的难混溶区间，并分析了不同难混溶合金核壳结构组织的形成机制，并对不同热历史条件下三元偏晶合金熔体结构演变与凝固组织的相关性进行了研究讨论。项目利用过热或热速处理等通过引入大的温度梯度，使得Marangoni迁移有效地抵消第二相液滴的Stokes沉积，同时提高弥散相液滴形核率，制备出弥散相分布均匀的Al-Bi-Sn偏晶合金。同时地面重力条件下通过小的冷却速率范围内的精确调控，实现了Al基偏晶合金核壳型结构调控。本项目的开展将深入认知液态合金的性质，完善合金熔体结构及凝固理论，推进偏晶合金制备技术和高性能复合材料制备技术的发展。