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F）remature melt solidification during mold filling and its nfluence on the as-cast structure

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Frontiers of Mechanical Engineering 2018年第1期13卷 53-65页

作者： M. WU M. AHMADEIN A. LUDWIG Chair for simulation and Modeling of Metallurgical processes University of Leoben Leoben A-8700 Austria Christian-Doppler Laboratory for Advanced Process Simulation ofSolidification and Melting Department of Metallurgy University ofLeoben Leoben A-8700 Austria Production Engineering and Mechanical Design Department Faculty ofEngineering Tanta University Tanta 31111 Egypt

Premature melt solidification is the solidifica- tion of a melt during mold filling. In this study, a numerical model is used to analyze the influence of the pouring process on the premature solidification. The numerical model considers three phases, namely, air, melt, and equiaxed crystals. The crystals are assumed to have originated from the heterogeneous nucleation in the undercooled melt resulting from the first contact of the melt with the cold mold during pouring. The transport of the crystals by the melt flow, in accordance with the so- called ＂big bang＂ theory, is considered. The crystals are assumed globular in morphology and capable of growing according to the local constitutional undercooling. These crystals can also be remelted by mixing with the super- heated melt. As the modeling results, the evolutionary trends of the number density of the crystals and the volume fraction of the solid crystals in the melt during pouring are presented. The calculated number density of the crystals and the volume fraction of the solid crystals in the melt at the end of pouring are used as the initial conditions for the subsequent solidification simulation of the evolution of the as-cast structure. A five-phase volume-average model for mixed columnar-equiaxed solidification is used for the solidification simulation. An improved agreement between the simulation and experimental results is achieved by considering the effect of premature melt solidification during mold filling. Finally, the influences of pouring parameters, namely, pouring temperature, initial mold temperature, and pouring rate, on the premature melt solidification are discussed.

关键词： premature solidification mold filling as-caststructure modeling

Influence of the Earth Magnetic Field on Electrically Induced Flows

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Journal of Iron and Steel Research(International) 2012年第S1期19卷 63-66页

作者： Abdellah Kharicha Menghuai Wu Andreas Ludwig Ebrahim Karimi Sibaki christian doppler laboratory for advanced process simulation of Solidification and melting University of Leoben8700 LeobenAustria

The present paper aims at numerical simulation of the intriguing experimental observations made by Bojarevics on the appearance of swirl in flows in an electrically induced flow.Although controlled by poloidal force,the flow rotates due to the presence of the earth magnetic field.The bulk flow rotates almost as a whole which indicates that the swirl is generated through a mechanism of 'poloidal suppression'.

关键词： fundamental MHD instability electric swirl metallurgy earth dynamo turbulence

Role of fragmentation in as-cast structure:numerical study and experimental validation

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China Foundry 2017年第5期14卷 321-326页

作者： Yong-jian Zheng Meng-huai Wu A.Kharicha A.Ludwig Chair of simulation and Modelling of Metallurgical processes Montanuniversitaet Leoben christian doppler laboratory for advanced process simulation of Solidification and melting Department of Metallurgy University of Leoben

A volume average solidification model is extended to incorporate fragmentation as the source of equiaxed crystals during mixed columnar-equiaxed solidification. This study is to use this model to analyze the role of fragmentation in the formation of as-cast structure. Test simulations are made for the solidification of a model alloy(Sn-10wt.%Pb) with two different geometries. The first one is a 2D rectangular domain(50 × 60 mm^2) as cooled from the top boundary. Solidification starts unidirectionally as columnar structure from the top. The solute(Pb) enriched interdendritic melt is heavier than the bulk melt, and sinks downwards, hence leads to solutal convection. Fragmentation phenomenon occurs near the columnar tip front. The fragments are transported out of the columnar region, and they continue to grow and sink, and finally settle down and pile up at the bottom. The growing columnar structure from the top and pile-up of equiaxed crystals from the bottom finally lead to a mixed columnar-equiaxed structure, in turn leading to a columnar-to-equiaxed transition(CET). The second geometry is a 3D plate, 100 × 60 ×10 mm^3, as cooled laterally from one side. It was cast experimentally and analyzed for the as-cast structure. The equiaxed fragments are produced in the solidification front and transported into the bulk melt, leading to a special pattern of as-cast structure: columnar structure in the cool wall side and equiaxed structure in the upper left corner near the hot wall side, extending downwards to the middle bottom region. Numerically calculated as-cast structures agree with the experiment results.

关键词：宏观结构 interdendritic 液体流动破碎 TP391.99 一

基于热溶质对流及晶粒运动的柱状晶-非球状等轴晶混合三相模型

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金属学报 2016年第9期52卷 1096-1104页

作者：李军葛鸿浩 WU Menghuai LUDWIG Andreas 李建国上海交通大学材料科学与工程学院上海200240 simulation and Modeling of Metallurgical processes University of Leoben christian-doppler Lab for advanced process simulation of Solidification and melting University of Leoben

基于Eulerian-Eulerian方法,阐述了简化枝晶状等轴晶、柱状晶以及金属液三相完全混合的凝固模型.模型考虑了等轴晶的移动及柱状晶对等轴晶的捕获,跟踪了柱状晶尖端的位置并考虑了等轴晶和柱状晶的相互竞争生长,因此该模型具备了预测柱... 详细信息

基于Eulerian-Eulerian方法,阐述了简化枝晶状等轴晶、柱状晶以及金属液三相完全混合的凝固模型.模型考虑了等轴晶的移动及柱状晶对等轴晶的捕获,跟踪了柱状晶尖端的位置并考虑了等轴晶和柱状晶的相互竞争生长,因此该模型具备了预测柱状晶向等轴晶转变(CET)的能力;为了在不过量增加计算量的前提下提高模型的精度,模型对等轴晶采取了简单的枝晶化处理,即采用简化方法描述等轴晶包络线内固相分数.分别模拟了3.25和25 t钢锭的凝固过程,成功预测了大型钢锭凝固过程所形成的底部锥形负偏析、"类-A型"偏析以及CET等现象.分析认为长细形状铸锭中出现的顶部负偏析区,是由于凝固后期所形成的局部小钢锭及等轴晶在其内部的沉积聚集而成.

关键词：数值模拟宏观偏析钢锭晶粒运动 CET