Direct Generation of Internse Compression Waves in Molten Metals by Using a High Static Magnetic Field and Their Application

Compression waves propagating through molten metals are contributed to degassing accelerating reaction rate,removing exclusions from molten metals and refining solidifcation structures during metallurgical processing of materials,In the present study ,two electromagnetic methods are proposed to generate intense compression waves directly in liquid metals.One is the simultaneous imposition of a high frequency electrical current filed and a static magnetic field ;the other is that of a high frequency magnetic field and a static magnetic field ,A mathematical model based on compressible fluid dynamics and electromagnetic fileds theory has been developed to derive pressure distri-butions of the generated waves in a metal.It shows that the intensity of compression waves is proportional to that of the high frequency electromagnetic force,And the frequency is the same as that of the imposed electromagnetic force,On the basis of theoretical analyses ,pressure change in liquid gallium was examined by a pressure transducer under various conditions.The observed results approximately agreed with the predictions derived from the theoretical analyses and calculations.Moreover,the effect of the generated waves on improvement of solidification structures was also examined .It shows that the generated compression waves can refine solidification structures when they were applied to solidification process of Sn-Pb alloy ,This study indicates a new method to generate compression waves by imposing high frequency electromagnetic force locally on molten metals and this kind of compression waves can probably overcome the difficulties when waves are excited by mechanical vibration in high temperature environments.     

高频电磁力作用下金属液内电磁超声波的生成

为解决由机械振动产生的超声波无法在高温环境中成功应用的难题，提出了利用静磁场和交流电流、静磁场和交流磁场的相互作用分别在金属液内直接生成高强度电磁超声波的方法，运用超声波压力传感器对用这两种方法在金属液内生成的电磁超声波的强度进行了测量。研究表明：电磁超声波的强度与所施加的高频电磁力的强度成正比，频率与电磁力的频率相同；实验结果和理论解析结果基本一致；利用高频电磁力的局部作用在金属液全场范围内生成的电磁超声波可以在金属精炼及凝固过程中获得广泛应用。     

Recent development and prospect of electromagnetic processing of materials

Application of electromagnetic force to materials processing, so called Electromagnetic Processing of Materials (EPM) has been recognized as a cutting edge technology, especially in the fields of advanced materials processing. The backgroundto promote EPMis described. The present state of EPMis given through a brief introduction of several examples of the applications of a high frequency magnetic field, a DC magnetic field, DC magnetic and electric fields, and a traveling magneticfield. Furthermore, a high static magnetic field has been applied to generate compression waves in molten metals. As otherexamples of the application of a high static field, the crystal orientations in thin films in vapordeposition and electrodeposition processes and those in carbon fibers in a graphitization process are described. Finally the future view of EPM is revealed.     

Recent development and prospect of electromagnetic processing of materials

Application of electromagnetic force to materials processing, so called Electromagnetic Processing of Materials (EPM) has been recognized as a cutting edge technology, especially in the fields of advanced materials processing. The background to promote EPM is described. The present state of EPM is given through a brief introduction of several examples of the applications of a high frequency magnetic field, a DC magnetic field, DC magnetic and electric fields, and a traveling magnetic field. Furthermore, a high static magnetic field has been applied to generate compression waves in molten metals. As other examples of the application of a high static field, the crystal orientations in thin films in vapordeposition and electrodeposition processes and those in carbon fibers in a graphitization process are described. Finally the future view of EPM is revealed.     

脉冲磁场作用于钢液熔体的电磁场数值模拟

为了解脉冲磁场的电磁力特性,利用ANSYS软件,脉冲电源波形采用梯形波,对脉冲磁场作用下钢液的电磁场进行了模拟,得到了电磁力周期变化规律,脉冲频率和脉冲波型对脉冲电磁力的影响规律.结果表明:脉冲磁场作用下,电磁力瞬时发生变向,往复振荡熔体;在研究的脉冲放电频率范围内,脉冲放电频率的改变对电磁场、力场的分布影响不大;对于采用的梯形脉冲波形,电磁力随着脉冲上升沿和下降沿宽度的减小而显著增大,而当脉冲宽度增大时,脉冲电磁力呈现减小的趋势.     

静磁场在材料生产过程中的应用研究评述

在材料电磁过程研究中，静磁场尤其是强磁场材料科学是当今世界的研究热点。本文从静磁场作用下生成的洛仑兹力和磁化力两个角度系统地归纳总结了静磁场技术在材料生产领域的应用原理和实践。对静磁场下的洛仑兹力，主要介绍了流体流动、波动和对流控制、电磁振动及电磁超声波等方面的研究现状；对强磁场下的磁化力，主要介绍了其在相变、结晶配向、磁悬浮、磁对流等方面的研究进展。最后对强磁场材料科学的研究趋势和发展前景做了展望。     

在脉冲电流或脉冲磁场作用下LY12合金的凝固组织

在LY12铝合金凝固过程中施加脉冲电流或脉冲磁场，研究脉冲电流或脉冲磁场对这种合金凝固组织的影响。结果表明，脉冲电流和脉冲磁场均可使晶粒明显细化，等轴化，在脉冲电磁艇下金属凝固组织的晶粒细化机制为：在脉冲电磁场的作用下剧烈的强迫对流促进晶粒从型壁上游离，大大增加金属熔体的形核率，导致晶粒细化；温度相对均匀使得游得的晶粒得以保存下来，抑制了晶粒在某个方向上的优先,从而抑制了树枝晶的形成。     

3-D Numerical Simulation of the Electromagnetic Dam of Twin Roll Casting using Edge Element Method

The 3-dimension numerical simulation study on the electromagnetic dam used in the twin roll caster has been performed by using the edge element method. It was found that the materials and structures of the roll collars have great influence on the distribution of the magnetic flux density, eddy current density and the electromagnetic force in the molten pool. The conductive collars make the magnetic flux density decreased in the molten pool, but it also makes the magnetic force more uniformly, and the force in the low part of the molten pool where needs greater force have increased some what. The conductive collars make the EMD device more effective than the nonconductive collars.     

基于电涡流阻尼器的数控加工振动抑制

弱刚性零件在数控加工中极易发生变形、让刀等现象,对加工质量及效率构成严重影响。基于电涡流阻尼器利用导体在恒定磁场中运动或者利用时变电磁场在导体上产生电涡流阻尼力,提出并设计适用于弱刚性结构件数控加工振动抑制的电涡流阻尼器结构;结合理论建模,提出四种设计方案并对其减振性能进行测试和比较。模态实验表明,四种阻尼器方案均能较好的对工件振动进行抑制,频响函数幅值最低下降55%;模态参数辨识表明,电涡流阻尼器可使系统阻尼增加70.73%,而对其余动力学参数的影响较小。切削实验表明,该电涡流阻尼器可增加工件临界稳定切深171%,减少切削加工振动信号58%以及降低表面粗糙度89.7%。     

电磁搅拌金属熔体数值模拟的研究进展

随着电磁搅拌技术在连续铸造、半固态加工、冷坩埚熔炼等领域被广泛采用,电磁搅拌金属熔体的数值模拟技术也得到了迅速的发展,分别从搅拌磁场的数值模拟、搅拌磁场作用下金属熔体内宏观传输现象的数值模拟、搅拌磁场作用下凝固铸坯的微观组织模拟方面详细叙述了电磁搅拌数值模拟技术的发展现状,并预测了其未来发展趋势。详细介绍了电磁场、传热传质、微观组织等各种计算模型。     

Two Dimension Finite Element Simulations on the Electromagnetic Containment in Twin-Roll Strip Casting

Distribution of magnetic field and electromagnetic force in twin-roll casting of steels was studied by the metod of numerical simulation in this paper,Two-dimension finite element model ,which includes the regions of melt ,stainless collar ,coil and magnetic core ,has been constructed,By solving magnetic vector potential formulations of quasi-static electromagnetic field,distribution of magnetic flux density and magnetic force at different molten heigh is determined,Calculated results showed that intensity of the distribution of magnetic flux density increased linearly with the increased coil current ;and the magnetic force in the melt increased as a quadratic cure with creased coil current ,More attention was given to the distribution of eddy current and magnetic force in the melt ,the confine effect at different molten height was also discussed.     

Generation of electromagnetic waves by a rotating cylindrical electron layer

Generation of electromagnetic waves by electrons orbiting in crossed radial electrostatic and axial magnetic fields was studied. Frequencies and increments of the generated waves were calculated. The wave increments increase with the frequency for sufficiently large values of the radial electrostatic field strength. Strong radial electrostatic fields may considerably magnify the frequencies of waves generated in the systems.     

The frequency effect on electromagnetic confinement and shaping of liquid metal

Electromagnetic confinement and shaping is a kind of newly developing solidification technology. With the electromagnetic field imposed, the metal is melted to some superheating degree by Joule heating and is confined and shaped to the desired form by the electromagnetic force at the same time. The frequency effect of the electromagnetic field on the electromagnetic confinement and shaping is investigated. The relationship between the Joule heat, the electromagnetic force and the frequency is revealed from the viewpoint of the magnetohydrodynamics theory. The results show that, given the condition of the same magnetic field strength, the time-averaged volume electromagnetic force at the melt surface is approximately proportional to the field frequency, whilst at the same time the volume Joule heating rate is approximately proportional to the square of the field frequency. However, as the frequency increases, the shaping stability and the surface quality decrease due to the violent surface electromagnetic stir. The frequency effect is also correlative to the sample's size and electric conductivity. The bigger is the sample, the lower ought to be the frequency and vice versa. The bigger is the electric conductivity, the lower can be the frequency and vice versa. Thus there is an optimum frequency range for each different sample, which is tens to hundreds of kilohertz for the small-size or medium-size steel sample. The experimental research is carried out with aluminium, copper and stainless steel samples, and the results show good agreement with the theoretical predictions.     

The frequency effect on electromagnetic confinement and shaping of liquid metal

Electromagnetic confinement and shaping is a kind of newly developing solidification technology. With the electromagnetic field imposed, the metal is melted to some superheating degree by Joule heating and is confined and shaped to the desired form by the electromagnetic force at the same time. The frequency effect of the electromagnetic field on the electromagnetic confinement and shaping is investigated. The relationship between the Joule heat, the electromagnetic force and the frequency is revealed from the viewpoint of the magnetohydrodynamics theory. The results show that, given the condition of the same magnetic field strength, the time-averaged volume electromagnetic force at the melt surface is approximately proportional to the field frequency, whilst at the same time the volume Joule heating rate is approximately proportional to the square of the field frequency. However, as the frequency increases, the shaping stability and the surface quality decrease due to the violent surface electromagnetic stir. The frequency effect is also correlative to the sample's size and electric conductivity. The bigger is the sample, the lower ought to be the frequency and vice versa. The bigger is the electric conductivity, the lower can be the frequency and vice versa. Thus there is an optimum frequency range for each different sample, which is tens to hundreds of kilohertz for the small-size or medium-size steel sample. The experimental research is carried out with aluminium, copper and stainless steel samples, and the results show good agreement with the theoretical predictions.     

金属熔体电磁成形过程研究

以制备无污染的航空发动机叶片为背景 ,分析了金属熔体电磁成形定向凝固技术的原理 ,并以铝合金及 1Cr1 8Ni9Ti为研究材料 ,探讨了交流电磁场作用下金属熔体的感应加热熔化及约束成形过程 ,结果表明 :感应器结构决定其内部的磁场及电磁压力分布 ,感应器输入功率、熔体高度、上下液固界面位置、抽拉速度及冷却条件等参数综合影响金属加热熔化特性、熔体形状及其稳定性 ;通过控制合理的工艺参数 ,获得了截面为圆形及近似弯月面形、表面质量和内部定向组织良好的样件 .     

Effect of the simultaneous application of a high static magnetic field and a low alternating current on grain structure and grain boundary of pure aluminum

Effect of the simultaneous application of a high static magnetic field and a low alternating electric current on the solidification structure of pure aluminum has been investigated. Results show that the refinement of the solidification structure is enhanced by the electric current under a certain magnetic field. However, when the magnetic field intensity exceeds a certain value, the refinement is impaired under a certain electric current. The observation by electron backscattered diffraction (EBSD) shows the complex fields have led to the increase of the low angle boundaries with the refinement. Moreover, the application of the static gradient magnetic field is capable of modifying the distribution of the refined grains. The above results may be attributed to the formation of the cavities during the electromagnetic vibration process and the high magnetic field.     

Effect of combined magnetic field on the eliminating inclusions from liquid aluminum alloy

The effect of electromagnetic field on the removal of inclusions in the aluminum alloy was investigated. Primary silicon particles precipitating from the solidification of Al-Si hypereutectic alloy were regarded as inclusions. An experimental apparatus applied with both rotating magnetic field (RMF) and traveling magnetic field (TMF) was employed to study the distribution of silicon particles in Al-Si alloy under magnetic field. The results showed that combined magnetic field (CMF) consisting of RMF and TMF eliminated the silicon particles from the molten alloy. Compared with TMF or RMF, CMF increased the separating effectivity substantially. It was proposed that CMF provided a highly effective approach for metal purification.     

Control of solidified structures in aluminum–silicon alloys by high magnetic fields

In order to investigate the effects of high magnetic fields on the as-solidified structures of Al alloys, solidification experiments of hypoeutectic and hypereutectic Al–Si alloys under various high magnetic field conditions (up to 12 T) have been conducted. It was found that uniform magnetic fields and gradient magnetic fields affect the solidification process by Lorentz force and magnetization force, respectively. The primary silicon crystals of hypereutectic Al–Si alloys are distributed, relatively, homogeneously under uniform magnetic fields, whereas they congregate near the top surface or bottom of samples by the combined action of buoyancy and magnetization force under gradient magnetic fields. The results indicate that it is possible to control the behaviors of reinforced particles in the metal matrix and improve the material performances by using high magnetic fields in the solidification process of metal matrix composites. The experiments also showed that high magnetic fields decrease the interlamellar spacing of the eutectic structure, while there exists a certain optimum value of magnetic intensity corresponding to the minimum value of interlamellar spacing, and magnetic energy is capable of influencing thermodynamic equilibrium of solidifying system and makes the content of eutectic aluminum in eutectic structures increased.     

空心管坯电磁离心过程的数值模拟

用有限元法模拟了铸造合金的流动和热量传输过程中瞬态速度场和温度场的分布,研究了电磁场强度和离心机转速对电磁铸造空心管坯的影响.结果表明,电磁搅拌引起的熔体相对运动是凝固过程中晶粒细化的主要原因.最优的电磁搅拌条件:转速1200 r/min,磁场强度为0.08 T,磁场持续加载25 s.在一定的转速和磁场强度条件下电磁离心铸造的温度场和凝固时的温度梯度对凝固组织有重要的的影响.合金液的外层,温度梯度达到最大值,铸件的温度下降得快,容易形成细小的等轴晶.     

材料电磁加工的现状与未来展望

综述了材料电磁加工的研究现状和未来的发展动向。由于在熔化、精炼、铸造、轧制等连续铸造过程中应用了电磁场,连铸坯的表面质量和凝固组织得到改善。在电镀、金属腐蚀、金属凝固等过程中施加强磁场,改变了溶质的质量传输,提高了产品质量。