【作者】 张颂阳；

【导师】 耿茂鹏；

【作者基本信息】 南昌大学 ， 材料加工工程， 2007， 博士

【摘要】 镁合金具有小的密度、高的比强度、比刚度，好的导热性，良好的阻尼减震能力等优良性能，能承受较大的冲击振动负荷和便于回收等特点，广泛应用在交通工具、电子工业产品、航空航天等领域，符合对材料的轻量化和绿色化的要求，其表现出强劲的发展势头。半固态技术综合了液态铸造成形、固态压力加工的优点，被认为是二十一世纪最具有发展前途的近净成形方法之一，得到了越来越广泛的关注。双辊铸轧工艺是将快速凝固和变形结合在一起的技术，近十年来该技术在国际上引起了极大重视，全面解决其产业化的关键技术是目前冶金及材料领域的一项前沿课题。该技术不仅可以显著提高生产效率、节约能源和降低生产成本，在改善铸轧板带坯质量方面亦具有很大潜力。当前世界范围的镁合金消费量呈不断增长的趋势，我国是镁资源大国，但是镁合金的加工生产水平落后，成本过高，严重制约了其应用市场的拓展，极大地限制了镁合金的发展。因此，开发适合于镁合金的低成本短流程技术，是扩大镁合金应用所必须解决的关键技术。将水平双辊连续铸轧技术与半固态加工技术相结合，得到半固态板带连续铸轧成形技术，将是一种全方位高效、节能、短流程、近终形的加工方法。把这种技术应用于镁合金的加工成形，可以说是具有国际领先水平的技术，具有一定的创新性。其重要的现实意义在于可以扩大半固态加工技术的应用范围，扩大铸轧技术的应用范围，可以发展我国镁合金加工应用技术，为镁合金薄板材和箔材提供基础材料，使生产镁合金薄板材和箔材成为可能，满足我国市场对运输工具，便携式电子产品高可靠、轻量化要求，有利于我国镁资源，特别是西部镁资源的开发利用。本文研究了AZ91D镁合金的半固态铸轧成形过程。在自制半固态铸轧试验设备上，首先通过半固态搅拌装置制浆，得到具有近球形的的非枝晶半固态组织；再利用半固态浆料具有良好的流动性，进行铸轧试验，得到半固态铸轧板带；取样观察板带显微组织，并测试了相关性能。另外本文还利用有限元软件，在计算机上仿真模拟半固态铸轧试验过程，与实际试验进行了对比；在数值模拟和实际试验的基础上，利用正交设计和人工神经网络对半固态铸轧过程的工艺参数进行了优化。本文的研究得到了以下成果：1．在自制半固态铸轧试验设备上，顺利进行了半固态镁合金水平双辊铸轧试验，得到半固态铸轧板带，其微观组织是具有近球形的非树枝状先结晶相均匀分布在基体上。2．实验发现铸轧对半固态组织具有圆整化作用，铸轧前的先结晶固相颗粒棱角分明，保留枝晶痕迹，而在铸轧以后先结晶相颗粒比较圆整。在固相率上，铸轧后固相率比铸轧前明显提高。这种趋势在不同的铸轧温度都有所表现，只不过不同的铸轧温度固相率也不同，温度越低固相率越大。3．采用浆料流动时的对流换热系数折算成紊流导热系数的方法来考虑铸轧系统中半固态浆料运动中的热传导和对流传热，采用热焓法处理液相的结晶潜热，建立了半固态AZ91D镁合金铸轧过程的温度场数学模型。数值模拟结果表明，在铸轧入口处，板带心部温度较高，表面附近厚向温度梯度较大，而在铸轧出口处温度分布从板带中心向边缘比较均匀的降低，温度梯度较小。数值模拟还分析了铸轧温度，铸轧速度，铸轧辊辊缝的大小，铸轧辊的冷却能力，铸轧辊直径的大小等工艺参数对铸轧过程温度场的影响。4．在正交试验和人工神经网络优化的基础上我们得到了半固态铸轧工艺过程的最佳工艺。其中半固态制浆工艺参数为搅拌速度1000r／min，静置时间5 min，搅拌时间5 min，浇注温度560℃；铸轧过程工艺参数是铸轧温度723K，铸轧速度0.5m／s，铸轧辊辊缝2mm，铸轧辊的冷却能力小水流冷却，铸轧辊直径210mm。并且得到了实际试验的验证。5．基于试验过程和试验结果，认为半固态制浆工艺和铸轧成形工艺是两个即独立又密切联系的过程，具有比较大的耦合自由度。6．半固态铸轧板带的再加工实验表明：AZ91D半固态镁合金铸轧板带具有较大的变形能力(压下量)。所得到的AZ91D镁合金半固态铸轧板带的塑性比较好，180度反复弯曲板带，仍不断裂，显示出良好的可塑性。最大冷变形量达28％，最大热变形量达47％。更多还原

【Abstract】 Magnesium alloy, which fulfills the requirements of lightweight and friendly to environment for materials, has very vast development foreground as a new engineering materials because of its low density, high strength-to-weight ratio, high modulus, good heat conductivity, superior damping characteristic, good machinability, and so on. Semi-solid metal processing technology, synthesized the merits of liquid-casting technology and solid-press forming technology, is catching many researchers’attention in various fields and is regarded as one of the near-net shape forming technologies with wide application in 21 century。Twin roll casting process is a kind of technology which combines fast solidification and continuous deformation progresses together. In recent ten years, there has been growing interest in the research of twin-roll rapid casting of thin-strip near end product shape in the world, which is thought to be one of the most potential technologies in the metallurgy and material field. The process has many advantages over the conventional casting technique. The primary advantages are of enhancing production efficiency, saving energy and reducing production cost, at the same time, it is potential to improve quality of casting strip.Today the consuming of Magnesium in the world wide are becoming more and more, China is a rich resource country of Magnesium。But our production levels is backward and its manufacturing cost are very high, which reduced the market ratio and limited the development of Magnesium。So it is crucial to expoit the new low cost and short stage technology applied to produce Magnesium and enlarge its using。The technology of Semi-solid strip by Rolling-Casting is a whole new technology which is high efficience、energy conservation、short stage and near end product shape, which is the combination of the semi-solid technology and the roll casting technology。Magnesium Alloy manufactured by this technology is a technological innovation which can widen the application of the semi-solid and cast-roll technology, can develop the manufacture of Magnesium to provide next procedure with the strip, fulfills the requirements of lightweight and friendly to environment for materials, develop our resouces especially in western zone。This paper researched the process of the semi-solid AZ91D by casting-rolling。Firstly the semi-solid slurry was gotten by the semi-solid manufacturing equipment which is the nondendritic grain; secondly, the slurry was casted and rolled on the casting-rolling equipment and got the semi-solid casting-rolling strip; then the microstructure and the properties was tested。Furthermore, the simulation experiment was carried out in computer by the finite element method. On the numerical and experimental base, the technical parameter was optimized by the orthogonal design and neural network.The result is1. The experiment of AZ91D semi-solid castin-rolling was carried out on the equipment made by ourselves, AZ91D semi-solid castin-rolling strip was gotten, whose microstructure is the the first crystallization non-dendrite particle distribute in the matrix.2. it was found that there is an obvious effect on the semi-solid microstructure by casting and rolling in the experiment. Before and after casting and rolling the microstructure is different, before is somewhat dendritic, after is near ball which is the globurization by casting and rolling。The solid ratio is different with the casting-rolling temperature, low temperature high solid ratio。3. The numerical model was studied by deal with heat conduction and convection in the flow of the slurry using the conversion of the convection coefficient, deal with the latent heat because of the crystallization using enthalpy. The simulation showed that the temperature gradient higer nearer the entrance of casting-rolling, the temperature gradient lower nearer the exit of casting-rolling. It was also studied the effect of the temperature of casting-rolling, the speed of casting-rolling, the gap of roller, the temperature of roller and the diameter of roller on the temperature field of casting-rolling.4. On the numerical and experimental base, the technical parameter was optimized by the orthogonal design and neural network. The optimum slurry manufacture parameters is stirring speed: 1000r/min, static time: 5 min, stirring time: 5 min, casting temperature 560℃。The optimum casting-rolling parameters is casting-rolling temperature 723K, casting-rolling speed: 0.5m/s, roll gap: 2mm, roll coiling: small water cool, roll diameter: 210mm。5. on the base of the experiment the process of slurry manufacturing and casting-rolling is two dependent and independent process, which can freely combined together。6. The further hot-cold working showed: AZ91D semi-solid castin-rolling strip has a big plasticity。The cold total deformation is 28%, the hot total deformation47%。更多还原