共查询到19条相似文献,搜索用时 281 毫秒
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基于枝晶生长的基本传输过程和元胞自动机(Cellular Automaton,简称CA)-有限元(Finite Element,简称FE)模型基本原理,建立了适应双辊连续铸轧纯铝薄带工艺特点的凝固过程形核和晶体生长的数学模型.模型耦合了宏观温度场和微观组织模拟计算,考虑了溶质扩散、曲率过冷和各向异性等重要因素的影响,定义了界面单元捕获规则,能够模拟凝固过程中枝晶生长的形态.应用本模型对双辊连续铸轧纯铝薄带凝固过程中等轴晶生长、等轴晶多晶粒生长及柱状晶生长、柱状晶向等轴晶演化进行模拟并与实验结果进行对比,模拟结果与实验结果吻合较好,验证了模型的正确性. 相似文献
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以等价比热客法处理结晶潜热和以假设的流线边界划分网格节点,建立了连续铸轧铝合金薄带凝固过程的宏观速度场、传热、溶质传输和凝固组织形成的微观数学模型以及连续铸轧铝合金薄带凝固过程的宏观-微观耦合数学模型.同时,以固相分数为媒介,采用宏微观不同的网格尺寸和时间步长,实现了宏观模型与微观模型的耦合. 相似文献
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采用耦合溶质场、温度场和流场的相场模型,对Ni-Cu合金凝固过程中多枝晶生长进行模拟,研究了多枝晶生长形貌及温度场和溶质场分布.结果表明:熔体流动显著改变凝固前沿的传热和传质,从而影响枝晶生长.受过冷熔体冲刷,枝晶逆流侧前沿溶质浓度和温度低,枝晶臂尖端生长迅速;枝晶顺流侧前沿溶质浓度和温度高,枝晶臂尖端生长缓慢.在熔体... 相似文献
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利用元胞自动机和有限差分(CA-FD)法,采用宏-微观两种尺度,将宏观温度场与微观枝晶生长过程耦合在一起,再现了Fe-0.06%C二元合金焊接熔池的凝固过程.同时,探讨了边界散热速率对焊接熔池中枝晶生长形貌及晶粒尺寸的影响;分析了形核基底数与枝晶生长间的关系;并用实验对模拟结果进行了验证.结果表明,在熔池凝固过程中,温度梯度沿散热边界向绝热边界方向不断减小,等温线弧度不断增大;熔池散热边界附近的液相中溶质浓度远远高于绝热边附近和模拟区域中心的液相溶质浓度;模拟区域内的温度梯度随着边界散热速率的增大而升高.此外,随着形核基底的增加,柱状晶数量基本不变;而等轴晶数量不断增多,分布范围逐渐扩大,但尺寸有所减小.模拟结果反映了焊接熔池的凝固过程,并与实验结果吻合,为实际焊接工艺的选取提供了一定的参考. 相似文献
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建立了三维格子玻尔兹曼方法(LBM)-元胞自动机(CA)耦合数值模型,并用该模型模拟研究了Al-4.7%Cu(质量分数)固溶体合金的凝固过程。该耦合模型采用元胞自动机方法模拟枝晶的生长,同时采用基于分子动力学理论的格子玻尔兹曼方法模拟合金凝固过程中的温度场、流场以及溶质场。模拟结果再现了合金凝固过程中的三维枝晶形貌变化以及溶质富集过程,并将三维流场因素考虑进去,定量研究了自然对流、过冷度对单枝晶形貌和成分分布的影响。研究表明,在纯扩散条件下,枝晶呈现对称的生长现象,模拟自由枝晶稳态生长的尖端速度、尖端半径和过冷度的关系与Lipton-Glicksman-Kurz(LGK)理论模型吻合得较好。在自然对流条件下,枝晶的生长形貌呈现不对称性,即枝晶生长在迎流方向上得到了促进,在顺流方向上受到了抑制。熔体过冷度对枝晶生长的影响较大,过冷度的增加导致枝晶生长加快,二次枝晶增多且呈现出粗化现象,枝晶尖端固液界面处的溶质浓度偏高,加重了溶质偏析。 相似文献
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采用Tong和Beckermann等提出的耦合流场相场模型对纯镍凝固中多晶粒枝晶的生长过程进行模拟,研究了多晶粒枝晶的生长形貌和温度分布.结果表明,熔体流动显著改变凝固前沿的传热,从而影响枝晶生长.受熔体流动和多晶粒之间相互影响的共同作用,枝晶在4个最优生长方向上的形貌呈现不对称;熔体流动还改变了枝晶的水平最优生长方向,使得水平主枝向上游倾斜;此外,二次枝晶出现径向熔化和轴向熔化等粗化方式. 相似文献
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提出局部区域放大法以弥补金属凝固过程微观模拟已有算法的不足 .局部区域放大法是选取金属中局部特殊区域进行晶粒形核和长大微观模拟 ,而属于宏观范畴的温度场和溶质场的模拟计算则仍然应用于整个金属 ,之后对模拟结果进行放大显示 ,类似放大镜原理 .该方法显著减少微观模拟计算量 . 相似文献
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A.Z. Lorbiecka R.Vertnik H.Gjerkeš G. Manojlovič B.Senčič J. Cesar B.Šarler 《计算机、材料和连续体(英文)》2008,8(3):195-208
A numerical model is developed for the simulation of solidification grain structure formation (equiaxed to columnar and columnar to equiaxed transitions) during the continuous casting process of steel billets. The cellular automata microstructure model is combined with the macroscopic heat transfer model. The cellular automata method is based on the Nastac's definition of neighborhood, Gaussian nucleation rule, and KGT growth model. The heat transfer model is solved by the meshless technique by using local collocation with radial basis functions. The microscopic model parameters have been adjusted with respect to the experimental data for steel 51CrMoV4. Simulations have been carried out for nominal casting conditions, reduced casting temperature, and reduced casting speed. Proper response of the multiscale model with respect to the observed grain structures has been proved. 相似文献
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为了模拟不同冷却状态下的连铸坯的凝固组织,利用反算确定了SCM435钢325 mm×280 mm连铸坯的换热系数,采用有限元法模拟了连铸传热过程,获得了连铸坯的温度场及冷却速率,在此基础上与元胞自动机耦合模拟了连铸坯的凝固组织.研究发现,表面细晶区很大,且在连铸结晶器中完成形核并长大形成,而柱状晶开始形核于结晶器末端.降低形核数,晶粒密度、最大晶粒面积、平均半径存在不同程度的改变,其中晶粒的最大截面积增加了2.7倍,而微调成分对晶粒密度与平均半径影响较小,但同样凝固条件下晶粒不均匀程度有所加剧. 相似文献
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目的 研究真空条件下Ti–43Al合金在连铸过程中的传热特性及其微观组织特点。方法 通过ProCAST铸造仿真软件,基于非稳态连铸计算模型建立了连铸过程的温度场模型,获得了连铸板材在凝固过程中的温度场及其固相率的分布规律,并采用CAFE计算模块对连铸板材的微观组织结果进行了预测。结果 连铸坯表面与结晶器接触的位置温度下降速度较快,熔池的深度在整个连铸过程中处在较为合理的水平上;连铸板材两侧表面的细晶区非常狭窄,并形成了由板材表面向板材心部生长的柱状晶区,在靠近铸件心部的位置发生了CET转变。结论 越靠近铸坯心部,温度梯度和过冷度越小,越有利于发生CET转变,使铸坯由外生长转变为内生长。数值模拟预测所得的结果与验证实验结果吻合得较好。 相似文献
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1Cr18Ni9Ti不锈钢双辊薄带凝固组织区的形成机理 总被引:3,自引:0,他引:3
在双辊薄带连铸实验和薄带凝固组织特征分析的基础上,结合对薄带凝固组织区的模拟预测结果,研究了1Cr18Ni9Ti不锈钢双辊薄带凝固组织区(特别是等轴晶区)的形成机理.结果表明:1Cr18Ni9Ti不锈钢双辊薄带凝固组织中的等轴晶区不但在凝固类型为半固态时形成,在轧制或理想型时也能形成.其形成机理为,熔池中悬浮游离晶体的沉积、聚集以及在枝晶生长前沿的长大和薄带离开二铸辊最小间隙(铸辊出口)后,薄带/空气界面换热系数骤然降低抑制了柱状枝晶的生长,并促使薄带中部未凝固熔体中游离晶体的择优长大. 相似文献
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Q. Li Y. K. Zhang L. G. Liu P. Zhang Y. Zhang Y. Fang Q. X. Yang 《Journal of Materials Science》2012,47(9):3953-3960
This study focuses on the numerical simulation of the temperature fields of the 304 stainless steel during twin-roll strip
casting process. The cracks and fratographs of the 304 stainless steel strip with the practical casting parameters were observed
by Scanning Electron Microscopy. The exit temperature of the 304 stainless steel during twin-roll strip casting process was
measured. Meanwhile, it was simulated by means of finite element model. The observed results show that the strip from outside
to inside are composed of refined crystal zone, columnar crystal one, and equated axis crystal one. The cracks occur on the
strip surface, extended to interior along the columnar crystal boundary, and then, ended at the juncture between the columnar
crystal zone and equated axis crystal one. The simulated result was compared to the measured temperature, which showed a good
agreement, thus indicating that this model is valid and accurate. Then, by employing this model, the effects of the casting
parameters, such as casting speed and casting temperature, on the freezing point position of the 304 stainless steel during
twin-roll strip casting process were simulated too. The simulated results show that, the freezing point position is decreased
with the increasing casting speed and casting temperature. For producing high-quality strip of 304 stainless steel during
twin-roll strip casting, the limits of casting speed and casting temperature are 1.1 m·s−1 and 1,570 °C, respectively. 相似文献
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Grain refinement of horizontal continuous casting of the CuNi10Fe1Mn alloy hollow billets by rotating magnetic field (RMF) 总被引:1,自引:0,他引:1
Rotating magnetic field (RMF) is used in horizontal continuous casting of CuNi10Fe1Mn alloy hollow billets. The result shows that the formerly inhomogeneous columnar grain macrostructure turns into homogeneous equiaxed grain with the application of RMF. The microstructure without RMF transforms from coarse and disordered dendrites to dense dendrites which have obvious orientation, while the microstructure with RMF from center to edge displays the evolution from spherical grains to disordered dendrites without orientation. The mechanical properties are improved remarkably. 相似文献
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Aleksandra Patari? Marija Mihailovi? Zvonko Guli?ija 《Journal of Materials Science》2012,47(2):793-796
This study presents an attempt to obtain the better quality of an aluminum super-high strength alloy by application of electromagnetic
field during the casting process. The conventional continuous casting process of aluminum alloys causes many defects, such
as surface imperfections, grain boundary segregation, non-uniform grain size, and porosity. The better ingot surface along
with the homogeneous fine-grained microstructure, and hence the better mechanical properties of the ingot, can be achieved
by applying the electromagnetic casting process. The microstructure characterization, accompanied by quantitative metallographic
assessment, reveals that it is possible to avoid or decrease many defects of as cast ingots during electromagnetic casting
process. In this article, the microstructure of the samples of as cast 7075 aluminum alloy, obtained with and without electromagnetic
field influence, was analyzed by optical microscope and the variation of key alloying elements content, i.e., Zn and Mg, through
the ingot cross section was examined by chemical analysis. Besides, the microstructural parameters such as dendrite arm spacing,
interdendritic space width, as well as eutecticum and intermetallic phases volume fraction, were measured using linear method.
The electromagnetic field influence on the microstructure of the as cast 7075 Al alloy was evaluated based on measured quantitative
metallographic data. 相似文献
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M. Stolbchenko O. Grydin A. Samsonenko V. Khvist M. Schaper 《Forschung im Ingenieurwesen》2014,78(3-4):121-130
The production of thin aluminium-steel clad strips by means of twin-roll casting is one of the prospective trends in the development of sheet production. The main advantages of twin-roll casting are low specific energy and resource consumption. Besides this, the resulting compound has a high bonding strength owing to the presence of a continuous thin layer of intermetallic phases having an approximate thickness of 3 µm at the interface of the two metals. At the same time, the quality of the clad strip depends on the microstructure and properties of the aluminium layer formed directly from a melt. A deformation immediately following the solidification of the metal between the two rotated, internally water-cooled rolls has a substantial influence on this aluminium layer. Due to the complexity of observing the processes occurring in the melt pool, a numerical simulation became one of the main methods for their investigation. Simulation is widely used to describe the process of twin-roll casting of monomaterial strips, but so far it has not been used for to comprehensively analyse the process of twin-roll casting of clad strips. In the present paper, a two-dimentional finite-element simulation of the system “clad strip—water-cooled rolls” using the ANSYS software is proposed. A joint analysis is carried out of the heat transfer, viscous flow of aluminium melt, its solidification and deformation resulting in the temperature distribution in the cast metal as well as in the tool. The dependences of the deformation strain and outlet temperature of the clad strip on the main technological process parameters; obtained by numerical simulation, are shown. 相似文献
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目的 研究电磁搅拌对CoCrMo合金熔模铸件晶粒尺寸的影响,解决熔模铸造CoCrMo合金铸件晶粒粗大的问题。方法 将CoCrMo合金熔化后,在其凝固过程中分别施加不同工艺参数的电磁搅拌,并对其凝固后的组织进行表征分析。同时,采用有限元法对电磁搅拌在金属熔体中的电磁场和流场进行数值模拟。结果 在不同的电磁搅拌参数下,CoCrMo合金铸件凝固组织出现了不同程度的细晶效果,浇道处的细晶效果优于铸件试棒处的。铸件试棒处的晶粒尺寸最小能控制在1 mm以下,等轴晶率最高能提升至31%。数值模拟结果表明,在电磁搅拌过程中,铸件试棒的磁场、电流和洛伦兹力都呈周期性变化,铸件试棒内部的流速随搅拌时间的延长而增大,最后趋于稳定。结论 电磁搅拌对CoCrMo合金的凝固组织产生了明显的细化效果,促进了柱状晶向等轴晶转变。电磁搅拌的时间越长,铸件凝固组织的细化效果越好,铸件厚大部位的细晶效果越显著。结合实验结果和数值模拟结果发现,在电磁搅拌过程中,熔体流动引发枝晶断裂是晶粒细化的主要原因,而电磁场促进异质形核为次要原因。 相似文献