Simulation on solidification of an Al-Ni alloy under electromagnetic stirring

The microstructure of Al-Ni alloy has a significant influence on its performance,while electromagnetic stirring is one of the most effective methods for control of solidification structure of Al alloy....     

外加磁场对镁合金焊接熔池形态的影响

以镁合金焊接熔池为研究对象,建立了移动热源作用下焊接熔池的三维数学模型. 利用大型通用有限元软件ANSYS将电磁场分析结果导入到热流场分析中,实现电磁场和热流场之间的耦合分析. 模拟了无外加磁场作用下以及外加磁场作用下镁合金焊接熔池的温度场分布和流体流动的速度矢量分布. 结果表明,外加磁场产生的电磁力驱动熔池中熔融的液态金属发生旋转运动,改变了液态金属原有的运动方式和传热方式,流体流动速度和流动范围增加,焊缝熔宽增大,熔深减小. 试验结果验证了模拟结果的可靠性.     

功率超声双振动头对A356铝合金半固态组织的影响

使用自制的交错式功率超声双振动头装置,处理A356铝合金流动熔体获得半固态浆料,研究了1000和1500W超声换能器前后排布流道、不同浇注温度和不同流道倾斜角度对A356熔体处理所获半固态组织的影响规律。结果表明,双振头斜流道对晶粒有细化作用,不同的倾斜角度对A356半固态组织细化程度不同。施振温度为620℃,流道倾斜角度为40°时,初生相晶粒最为细小,球化效果最好。     

铝硅合金软接触电磁铸造成型中耦合场计算研究

从电磁场的基本原理出发,利用ANSYS有限元软件建立铝硅合金半固态电磁铸造的磁流耦合场模型,通过数值模拟计算磁场对流场和温度场的影响。结果表明,电磁场频率直接决定流场及温度场的分布,高频电磁场感应加热效果明显、洛伦兹力主要表现为电磁压力,有利于电磁铸造约束成型。     

功率超声双振动头处理A356半固态熔体的研究

利用两套自制的功率超声双振动头试验装置,对A356铝合金流动熔体进行处理获得半固态浆料,对比分析了1.0kW和1.5kW超声换能器交错式排布流道及对向式排布流道装置处理A356合金的凝固组织,研究了合金熔体在运动状态中加上功率超声场影响下的凝固机理,分析了功率超声的机械效应、热效应及声流效应对半固态金属结晶的影响。结果表明,浆料经处理后的试样金相组织的细化、球化效果与振动头的摆放位置有关,交错式比对向式处理效果好;流道上的凝料因激冷和整个凝固过程都在流道上受到振动影响而更细小,流出流道的晶粒易长大,受到超声和斜流道影响而球化更好。     

超声及电磁场对铝合金熔体影响的数值模拟及试验研究

针对铝合金熔体的超声及电磁搅拌处理过程,创建了超声场、电磁场、流场和温度场的数学模型,并采用COMSOL Multiphysics软件求解模型,得到了超声场、电磁场和超声/电磁复合场对铝合金熔体内流场和温度场的分布规律,并通过试验对模拟结果进行了验证。结果表明,增加超声功率使得声压幅值和流场的流动速率均随之增加,同时会使熔体的温度梯度逐渐减小;施加电磁场后产生的电磁搅拌改变了熔体的流动方向且使熔体的流动速率显著增大,这对熔体的温度分布产生了较大影响;在超声和电磁复合场下,电磁场比超声场对熔体流场和温度场的影响更大,且占主导地位。数值模拟结果和试验结果符合较好。     

A 2-D FINITE ELEMENT MODEL SIMULATION OF THE MELTING PROCESS OF AI-Ti ALLOY IN VACUUM INDUCTION FURNACE WITH COLD CRUCIBLE （VIFCC）

The development of a numerical model for the melting process of AI-Ti alloy target material in vacuum induction furnace with cold crucible (VIFCC) was described. It is a two-dimensional computational methodology to calculate electromagnetic field, heat transfer field and fluid flow field . Based on the aid of the finite element method with the commercial software--ANSYS, a superimposition method of a layer of copper and a slit to simulate the VIFCC melting process was used. The method was effective to save large quantity of memory and computing time. Meanwhile, a temperature distribution profile during the melting process was obtained. Validity of the model was confirmed by comparison between the result from calculation and those from direct measurement by optical pyrometer and indirect investigation by ingot macrostructure. A relatively good agreement was found. Further, a nearly directional solidification structure was obtained under properly controlling the cooling rate and heating power. Therefore. such model developed in this article is feasible.     

Degassing effect of ultrasonic vibration in molten melt and semi-solid slurry of Al-Si alloys

In the process of semi-solid slurry preparation with direct ultrasonic vibration (UV) by dipping the horn into the melt, one of the questions is whether the gas content in the melt would be increased or not by the cavitation effect of ultrasonic vibration. By application of quantitative gas content measurement technique, this paper investigated the effect of the ultrasonic vibration on the gas content of both the melt and the semi-solid slurry of Al-Si alloys, and the variations of the gas contents in two kinds of aluminum alloys, i.e., A356 alloy and Al-20Si-2Cu-1Ni-0.6RE alloy (Al-20Si for short). The results show that ultrasonic vibration has an obvious degassing effect on the molten melt, especially on the semi-solid slurry of Al-Si alloy which is below the liquidus temperature by less than 20 ℃. The ultrasonic degassing efficiency of the A356 alloy decreases with the reduction of the initial gas content in the melt, and it is nearly unchanged for the Al-20Si alloy. The gas content of both alloys decreases when the ultrasonic vibration time is increased. The best vibration time for Al-20Si alloy at the liquid temperature of 710 ℃ and semi-solid temperature of 680 ℃ is 60 s and 90 s, respectively; and the degassing efficiency is 48% and 35%, respectively. The mechanism of ultrasonic degassing effect is discussed.     

Coupled Modeling of Electromagnetic Fleld,Fluid Flow,Heat Transfer and Solidification During Conventional DC Casting and Low Ftequency Electrmagnetic Casting of 7xxx Aluminum Alloys

A comprehensive mathematical model has been developed to describe the interaction of the multiple physics fields during the conventional DC casting and LFEC (low frequency electromagnetic casting) process. The model is based on a combination of the commercial finite element package ANSYS and the commercial finite volume package FLUENT, with the former for the calculation of the electromagnetic field and the latter for the calculation of the magnetic driven fluid flow, heat transfer and solidification. Moreo...     

Numerical simulation on electromagnetic field,flow field and temperature field in semisolid slurry preparation by A-EMS

A two-dimensional computational model coupling an annular electromagnetic stirring (A-EMS) with a macroscopic heat and fluid flow analysis in Al-alloys semisolid slurry preparation was developed. The dynamic evolutions of the electromagnetic field, flow field, and temperature field were presented successfully by commercial software ANSYS 10.0 with corresponding experimental verification. A horizontally rotational electromagnetic field and, thereby, a more intensive velocity field were uniformly distributed in the stirred melt even at commercial frequency, and thus, a lower temperature difference in the stirred melt and subsequent uniformly fine microstructures were obtained compared with the normal electromagnetic stirring. The simulation results were in good agreement with experimental ones.     

电磁搅拌对水冷热顶铸造A356合金质量的影响

通过常规铸造A356合金锭与电磁搅拌＋水冷热顶铸造A356合金棒的质量差异的对比,分析电磁搅拌＋水冷热顶铸造对铝合金棒组织性能的影响,结果表明采用电磁搅拌＋水冷热顶铸造方法生产出的A356铝合金棒的质量在各个方面均优于常规铸造A356合金锭的。     

电磁搅拌作用下铝合金凝固组织的数值模拟

建立了有限元(Finite Element)和元胞自动机法(Cellular Automaton)相结合的宏微观耦合的CA-FE模型,实现了电磁搅拌作用下Al-5％Cu合金凝固组织的数值模拟.该模型利用ANSYS软件计算电磁力,利用有限差分法计算宏观流场和温度场.在微观计算中,采用基于高斯分布的连续形核模型,并采用KGT生长模型计算枝晶尖端生长速率.模拟和实验结果表明,施加电磁搅拌后,铝合金的温度场均匀,冷却速率加快,利于组织细化.     

EFFECT OF GRAIN REFINING ON PRIMARY α PHASE IN SEMI-SOLID A356 ALLOY PREPARED BY LOW SUPERHEAT POURING AND SLIGHT ELECTROMAGNETIC STIRRING

The semi-solid slurry of A356 alloy, which is grain-refined by Al-Ti-B master alloy, is prepared by low superheat pouring and slight electromagnetic stirring. The effects of grain refining on the morphology and the grain size of the primary α phase in the slurry manufactured are researched. The results indicate that the slurry with particle-like and rosette-like primary α phases can be prepared by low superheat pouring and slight electromagnetic stirring from liquid A356 alloy grain-refined, in which the pouring temperature can be suitably raised. Compared with the A356 samples without grain refining, the grain size and particle morphology of primary α phase as well as the distribution of the grain with particle-like or rosette-like along radial in the ingot in A356 are markedly improved by grain refining.     

非晶态磁敏传感器的设计

本文以非晶态软磁合金作为敏感材料为对象,论述了脉冲感应型非晶态磁场传感器的研制。这种磁场传感器的工作原理建立在经典的电磁感应理论和非晶态软磁合金材料的线性磁化特性的基础之上,脉冲感应型非晶态磁场传感器具有灵敏度高、稳定性好、对使用环境要求低等特点,适用于检测各种微弱磁场,并能成为发展其他高级传感器的基础。     

方坯结晶器内钢液凝固及电磁制动的数值模拟

利用电磁流体力学（MHD）的基本理论及Bennon的连续介质模型,给出了方坯结晶器内钢液凝固及电磁制动的三维数学模型、磁场、流场和温度场的数值模拟表明,与钢液流场速度方向相反的电磁力是电磁制动的 直接原因;感生电流主要是集中在钢液入口处及其附近区域;电磁力能有效地改变方坯结晶器内的流场和温度场的分布,造成制动区域的下部呈现活塞流状态,降低了结晶器内高温钢液区域的温度梯度,提高了弯月面附近特别是上角部区域钢液的温度,减薄了上部凝固壳厚度。     

环缝结构对电磁连铸流场和温度场的影响(英文)

建立描述环缝式电磁连铸A357铝合金圆坯过程的数学模型,采用有限元法求解电磁场,采用有限体积法求解流场和温度场,并对电磁场和温度场的计算结果进行实验验证,分析环缝宽度、环缝位置和芯棒长度等结构参数对环缝式电磁连铸过程流场、温度场和凝固过程的影响。结果表明:环缝宽度越小,液穴中的温度梯度越小,温度场越均匀;随着芯棒长度的增加,由于芯棒的错位液穴内的循环流减小,温度梯度变大;当环缝位于铸坯边沿时,液穴中的温度梯度降低明显。     

Effects of harmonic electric field frequency on electromagnetic and flow fields of Ti-Al melt in a rectangular mold based on numerical simulation

A model was established based on Maxwell's equations and Navier-Stokes' equations to numerically simulate the electromagnetic field and flow field in a rectangular mold with sectional aspect ratio of 5:1.The FEM (Finite Element Method) and APDL (ANSYS Parametric Design Language) were employed for the model to execute the modeling,meshing,load applying and solving.The Ti-Al alloy melt was selected to illustrate and validate the effects of the harmonic field frequency on the distribution of the physical fields in the mold.The simulated results demonstrate that with an increasing frequency the electric current forms an ellipsoid cavity where it becomes much weaker,and that the melt flows more intensely with low frequency (less than 5 kHz) than with high frequency (more than 5 kHz).The melt is pinched from the central part in the mold to bipolar parts in which it forms two vortexes in each side.The maximum value of fluid velocity exists near the bipolar zone.     

超声波作用下半固态A356合金的制备与理论研究

采用自制的一套超声处理装置,研究了在此装置下施加超声振动对A356合金熔体组织的细化作用。结果表明,在此装置下加载超声功率,对A356合金的组织有细化作用,而且超声功率越大,组织细化效果越明显,另外,施振温度不同,效果也不一样,在选取施振温度分别为640、620、600℃时,施振温度为640℃时,效果最好。     

Effect of Grain-Refined on Primary α Phase in Semi-Solid A356 Alloy Prepared by low superheat Pouring and Slightil Electromagnetic Stirring

The semi-solid slurry of A356 alloy, which is grain-refined by Al-Ti-B master alloy, is prepared by low superheat pouring and slight electromagnetic stirring. The effects of grain refining on the morphology and the grain size of the primary α phase in the slurry manufactured are researched. The results indicate that the slurry with particle-like and rosette-like primary α phases can be prepared by low superheat pouring and slight electromagnetic stirring from liquid A356 alloy grain-refined, in which the pouring temperature can be suitably raised. Compared with the A356 samples without grain refining, the grain size and particle morphology of primary α phase as well as the distribution of the grain with particle-like or rosette-like along radial in the ingot in A356 are markedly improved by grain refining.     

Effect of pouring temperature on fractal dimension of primary phase morphology in semi-solid A356 alloy

The fractal dimensions of primary phase morphology in semi-solid A356 alloy prepared by low superheat pouring and slightly electromagnetic stirring were calculated, and the effect of pouring temperature on fractal dimension of primary phase morphology in semi-solid A356 alloy was researched. The results indicate that it is feasible to prepare semisolid A356 alloy slurry by low superheat pouring and slightly electromagnetic stirring, and there is an important effect of pouring temperature on the morphology and the grain size of the primary phase in semi-solid A356 alloy, in which the reduction of pouring temperature can obviously improve grain size and shape factor of primary phase in semi-solid A356 alloy under the condition of a certain stirring power. The primary phase morphology of semi-solid A356 alloy prepared by low superheat pouring and slightly electromagnetic stirring can be characterized by fractal dimension, and the primary phase morphology obtained by the different processing parameters has the different fractal dimensions. Solidification of semi-solid alloy is a course of change in fractal dimension.