脉冲磁致振荡下纯铝凝固磁场与流场分布的数值模拟

脉冲磁致振荡可以细化金属晶粒,为了研究其作用机理,采用ANSYS有限元模拟软件对脉冲磁致振荡下纯铝凝固磁场与流场分布进行了数值模拟.模拟结果显示,由于电磁趋肤效应,线圈中脉冲电流只在熔体表面感应产生电磁力,且随时间出现指向内部的压力与指向外部的拉力交替变化,沿径向有指向熔体顶部与底部交替变化.交变电磁力可以振荡熔体表面率先析出的晶核而使之游离,增大熔体形核率.同时感应电磁力迫使熔体产生流动,会利于晶核的均匀分布与温度场、浓度场的均匀化.     

定向凝固过程的数值模拟进展

针对定向凝固模拟的研究现状,概述了其中几种用于凝固的模拟方法,如三维枝晶胞膜跟踪法、电磁成形法、相场法等,并着重介绍了相场法。最后,在分析现有相场模型不足的基础上,指出了该领域研究中亟需解决的问题,并对今后的发展方向作了分析。     

定向凝固中行波磁场和高频交流磁场的复合磁场模拟计算

利用ANSYS平台的开发环境,在ANSYS自有的APDL参数化功能和电磁场理论知识的基础上,结合定向凝固过程中的复合电磁场特点,提出了求解频率相差多个数量级的复合电磁场的方法,以及后处理中求复合电磁场平均值的方法,实现了复合电磁场的模拟计算。后处理结果分析表明,复合电磁场的磁通密度为单一行波磁场的磁通密度与单一高频交变磁场的磁通密度的矢量和,复合磁场产生的洛伦兹力要远大于各种频率的单频率场的线性叠加。     

强脉冲磁场对Al-Cu共晶合金定向凝固组织的影响

用自行研制的脉冲磁场发生装置，研究了在强脉冲磁场作用下Al-Cu共晶合金的定向凝固组织，分析了脉冲磁场强度对合金定向凝固组织的影响。结果表明：脉冲磁场对Al-Cu合金凝固组织有着显著的细化作用：脉冲磁场强度对细化效果起着关键性的作用；同时指出了实验中的新现象和新问题。     

定向凝固简化空心叶片热应力数值模拟

定向凝固叶片在凝固过程中产生的热应力会导致叶片最终存在残余应力、变形甚至裂纹而使得叶片报废,故研究叶片凝固过程的热应力变化具有重要意义.通过数值模拟的方法可以对叶片的凝固过程热应力进行模拟,得出应力变化情况,对叶片可能产生的缺陷进行预测.文中采用商用软件ProCAST对定向凝固简化空心叶片的热应力场进行数值模拟,分析空心叶片凝固过程中的热应力变化情况,并通过切割法测量了铸件的残余应力,模拟结果与实验结果吻合较好.     

熔体凝固速度场的ANSYS数值模拟

用ANSYS有限元软件对脉冲磁场作用下，LY12铝合金凝固过程中的速度场作了数值模拟，模拟结果和实验现象相吻合，通过数值模拟发展，用数值模拟方法不仅可以初步了解凝固过程中熔体的运动状态，而且还可以了解凝固组织细化和产生缺陷的原因，是一个值得注意的研究方向，因此有较大的实用价值。     

研究合金定向凝固组织的脉冲磁场设备的研制

介绍了脉冲电磁场发生设备的工作原理 ,设计等。并介绍了其如何与合金的定向凝固设备结合 ,以实现对合金的定向凝固组织在脉冲电磁场作用下的研究。     

激光熔凝的数值模拟及其在激光定向凝固中的应用

建立了一套激光熔凝的数学模型和计算方法 ,给出了两种条件下熔池深度与扫描速度的关系曲线。计算结果与实验值吻合良好 ,验证了模型的有效性。根据计算分析了激光工艺参数与激光定向凝固组织的关系。据此通过工艺参数的匹配 ,在熔池顶部得到了与扫描方向完全一致的凝固组织     

高温合金定向凝固数值模拟研究进展

高温合金定向凝固过程中存在着传热、流动、传质的宏观传输,凝固收缩、补缩,溶质再分配、迁移,晶粒生长和熔化等行为共同作用下的多相共存、多物理场耦合作用、跨尺度的复杂过程,导致复杂形状叶片铸件中频繁出现杂晶、雀斑、小角度晶界、条纹晶等缺陷。由于过程的不透明以及合金的高成本,发展数值模拟技术对深入认识高温合金定向凝固过程的机理、建立精准有效的控制方法具有重要意义。综述了近年来在镍基高温合金定向凝固数值模拟领域相关的研究进展,并对其应用进行了展望。     

超强磁场定向凝固试验装置的研制

将强磁场与LMC定向凝固技术相结合,研制出了一套新型强磁场下定向凝固装置.该装置兼有快速液淬固定液固界面的功能,其主要性能指标为温度梯度GL=260℃/cm,最高温度1600℃,抽拉速度R=0.5～104μm/s,定向凝固在充H2或惰性气体保护气氛下进行.定向材料最大尺寸为φ10×150(mm).通过调整试样、加热温度及凝固速率,可满足各种不同要求的定向凝固试验.     

金属近快速定向凝固过程的数值模拟

从非稳态传热角度并按照柱坐标系中二维传热方式对Bridgman装置中Al柱状试样近快速定向凝固过程进行了数值模拟,分析了试样在近快速定向凝固过程中液固界面前沿的温度梯度和生长速度随试样抽拉速度的变化规律.计算结果表明:在30～3 000 μm/s的抽拉速度范围,随着抽拉速度的提高,液固界面前沿的温度梯度在(145士l0)K/cm范围变化,生长速度与抽拉速度的差别不超过5%.研究结果为实验研究近快速定向凝固组织形态转变提供了可靠的控制参数依据.     

Al3003铝合金激光脉冲焊温度场数值模拟

采用有限元法对超级电容器壳体焊接结构在激光脉冲焊接时的温度场演变规律进行模拟计算.在实际构件上截取各条焊缝试样进行宏观观察,确定焊缝的几何参数.在热扩散仪上对材料的热导率和比热容进行测试,获得有限元计算所需的准确的材料热物理参数.在材料试验机上对材料进行高温拉伸试验,通过多个温度点的应力应变曲线判断材料的熔点温度.结果表明,脉冲激光焊接能量集中,不会造成整个构件的整体温升,在整个焊接过程中电芯及橡胶元器件均不会发生损坏.     

Numerical simulation on directional solidification of Al-Ni-Co alloy based on FEM

The ratio,of the temperature gradient at the solidifiationfront to the solidification rate of solid-liquid interface,plays a large part in columnar grain growth.The transient temperature fields of directional solidification of Al-Ni-Co alloy were studied by employing a finite element method.The temperature gradient at the solidification front and the solidification rate were analyzed for molten steels pouring at different temperatures.The results show that with different initial pouring temperatures,the individual ratio of the temperature gradient at solidification front to the solidification rate soars up in the initial stage of solidification,then varies within 2,000-6,000℃.s.cm-2,and finally goes down rapidly and even tend to be closed to each other when the solidification thickness reaches 5-6 cm.The simulation result is consistent with the practical production which can provide an available reference for process optimization of directional solidified Al-Ni-Co alloy.     

Grain refinement of Sn-Pb alloy under a novel combined pulsed magnetic field during solidification

The combined pulsed magnetic field (C-PMF) obtained by simultaneously imposing pulsed and static magnetic field during solidification has been proposed to refine the solidification structure. Compared to the imposition of a single pulsed magnetic field, a more refined structure can be observed under C-PMF. The key factors to affect grain refinement under C-PMF consisted of the vibration frequency characterized by the static magnetic field, pulsed discharge voltage, and the vibration frequency characterized by the pulsed discharge frequency. The microstructure revealed that the grain size decreased with the increasing static magnetic field. The pulsed discharge voltage had an optimum value for obtaining fine grains. Furthermore, when the pulsed discharge frequency was equal to the intrinsic frequency of the liquid metal in a filled cylindrical vessel, resonance vibration occurred in the liquid surface, and grain refinement was promoted.     

Quantitative phase field simulation of deep cells in directional solidification of an alloy

The formation of deep cells after the onset of Mullins–Sekerka instability during the thin-film directional solidification of a succinonitrile/acetone alloy has been simulated quantitatively by phase field modeling. The solute trapping introduced by the diffusive interface is corrected by a simple interface model, so that at the interface the equilibrium segregation is restored and the Gibbs–Thompson relation is satisfied. With the increasing pulling speed, the transitions from planar to λ_c/2 shallow cells, smaller wavelength finite-depth cells, and deep cells are clearly illustrated. The formation of deep cells with change of overall morphologies is performed, and its wavelength transition is consistent with the reported experiments. Furthermore, during the development of a cellular pattern starting from a planar interface, the crossover wavelength under different solidification speeds, where the deformation is comparable to the wavelength, agrees reasonably well with the Warren–Langer theory.     

Ti-45Al合金焊接熔池凝固过程数值模拟

采用元胞自动机法和有限差分法建立了宏微观耦合下的焊接熔池微观组织凝固模型,对Ti-45Al合金焊后凝固过程中的枝晶生长形貌和溶质场浓度分布进行模拟,并通过试验对模拟结果进行验证. 讨论分析了焊接热输入、内部形核数和表面传热系数对枝晶生长及形貌的影响. 结果表明,熔池内的组织主要由柱状晶和等轴晶两种形态组成. 热输入的增加和传热系数的减少均有助于柱状晶的生长,而内部形核数越大则越有利于等轴晶的生长. 所建立模型的计算结果与试验结果在关于枝晶生长的定向研究中有较好吻合.     

行波磁场对定向凝固Pb-Sn合金枝晶生长的影响

在1g的重力加速度条件下,研究熔体对流对向上生长的定向凝固Pb-33%Sn合金枝晶生长行为的影响。熔体对流由行波磁场进行调制。当行波磁场方向由向上转变为向下时,一次枝晶间距逐渐增大,一次枝晶间距的分布更加紧凑,且峰值趋于降低。分析表明：行波磁场对熔体对流的调制作用与改变重力加速度的效果类似,当抽拉速率为50μm/s,行波磁场强度为1mT时,在向上和向下的行波磁场作用下有效重力加速度分别为3.07g和0.22g。     

Numerical simulation of boundary heat flow effects on directional solidification microstructure of a binary alloy

The boundary heat flow has important significance for the microstructures of directional solidified binary alloy.Interface evolution of the directional solidified microstructure with different boundary heat flow was discussed.In this study, only one interface was allowed to have heat flow, and Neumann boundary conditions were imposed at the other three interfaces.From the calculated results, it was found that different boundary heat flows will result in different microstructures.When the boundary heat flow equals to 20 W·cm-2, the growth of longitudinal side branches is accelerated and the growth of transverse side branches is restrained, and meanwhile, there is dendritic remelting in the calculation domain.When the boundary heat flow equals to 40 W·cm-2, the growths of the transverse and longitudinal side branches compete with each other, and when the boundary heat flow equals to 100-200 W·cm-2, the growth of transverse side branches dominates absolutely.The temperature field of dendritic growth was analyzed and the relation between boundary heat flow and temperature field was also investigated.