凝固过程中的脉冲磁场和脉冲磁力研究

用数值模拟方法研究了凝固样品中的脉冲磁感应强度和电磁力的分布特性。模拟结果表明，脉冲磁场凝固条件下，脉冲磁感就强度和电磁力分布具有轴向、径向分布的不对称性和不均匀性。这种分布特性有助于了解脉冲磁场对金属凝固组织的细化作用。     

定向凝固过程中的流动效应

在类合金(NH₄Cl-H₂O溶液)定向凝固晶体生长实验装置上,利用ϕ30μm煤粉作示踪粒子,再现糊状区内微通道流以及通道出口处的流体流动,并测算了各处流体的瞬时速率.分析认为:凝固初期,糊状区内固相体积分数较大,内部流体流动受阻;随着固相体积分数减少,糊状区孔隙率增大,流体充分发展;当平均固相体积分数降至0.42,接近最小值0.38时,当量雷诺数达到临界值(247),糊状区内形成微通道;随着通道宽度逐渐扩大,液相区内热流体进入微通道.微通道内稀冷液体向上流,浓热液体向下流,促使通道内溶液再结晶.     

静磁场作用下镁合金AZ61凝固过程研究

AZ61是典型的变形镁合金，是具有优越性能的金属材料，但仍有很多方面还有待研究。对镁合金AZ61在静磁场作用下的凝固过程进行了研究，并且与无磁场作用下AZ61的凝固过程进行了比较。结果表明，在施加静态磁场条件下镁合金的液相线温度和固相线温度均有较大幅度的改变，液固区间有增大现象；同时，静磁场显著净化了镁合金组织，夹杂物数量显著减少，并且夹杂物的形状从正常的“爪”形转变为“球”形，减少了夹杂物对镁合金性能的不良影响。     

DSM11合金定向凝固工艺的研究

研究了定向凝固速度对DSM11合金组织结构和性能的影响.结果表明,在获得柱状晶生长的条件下,随凝固速度提高,枝晶间距细化,合金中的γ'相、碳化物和共晶组织细而均匀;当凝固速度为11mm/min时,出现严重的枝晶分叉和不连续现象.凝固速度变化对合金高温持久性能影响显著.凝固速度为7 mm/min时,合金持久性能最高,对应枝晶间距和共晶含量的低谷,伴随着细小枝晶和均匀的显微组织.     

磁场对金属材料凝固的影响

控制并得到合适的凝固组织一直是材料工作者研究的方向。近年来人们对金属在磁场中的凝固做了一系列研究,取得了一定成果。主要介绍了磁场对金属凝固过程的影响,包括磁场驱动流体流动、控制宏观偏析、改善凝固组织等,并对未来的研究工作进行了展望。     

高纯铝定向凝固提纯技术应用研究

高纯铝是目前最主要的电子新材料,通过定向凝固工艺获得的高纯铝具有纯度高、成本低的优势,该法目前被产业界广泛采用。简单介绍了定向凝固技术的原理,重点分析了国内外高纯铝定向凝固技术的新工艺、新方法,最后对高纯铝定向凝固技术存在的问题及发展趋势进行了分析总结。     

定向凝固过程中固液界面稳定性的研究现状

界面稳定性是金属定向凝固过程中一个很重要的问题,关于它的研究也层出不穷。综述了这一领域的主要进展,着重讨论了基于MS理论研究的各种界面稳定性理论,并指出电磁场对界面稳定性的影响,同时分析了需进一步研究的主要方向。     

连续定向凝固过程铜铬合金的组织与缺陷

研究了铜铬合金的连续走向凝固的工艺条件及相互之间的匹配关系,以及铜铬合金的显微组织及其表面缺陷形成的原因.结果表明:结晶器高度10~25mm,冷却距离25 mm,合金温度1210~1280℃,牵引速度0.2~1.0mm/s,冷却水量720L/h时,可制得Cu-0.6% Cr合金材料.     

金属连续定向凝固技术

针对日趋活跃的金属定向凝固技术,阐述定向凝固技术的基本原理,以及其特点.简要说明了金属定向凝固技术的应用.介绍了目前金属定向凝固技术在国内外的发展状况,存在的问题及未来的前景.     

Nb30Ti35Co35合金定向凝固组织演化和显微硬度研究

三元以及多元合金凝固过程中,多组元间相互耦合和溶质再分配造成其凝固路径及其组织异常复杂,到目前为止尚未建立起完整统一的三元共晶凝固理论模型,凝固组织和机械性能的本质关系亟待研究。基于此,针对Nb₃₀Ti₃₅Co₃₅共晶合金(实测Nb₃₁Ti₃₄Co₃₅)开展了不同抽拉速率(v=3,5,15,30,70μm·s^-1)下的定向凝固实验研究,测量其显微硬度(H),旨在探索不同抽拉速率下合金的微观组织演化规律,并构建组织和性能之间的关系。结果表明：除极少量初生α-Nb外,常规铸态合金几乎完全由共晶(α-Nb+TiCo)组织构成,相类似地,定向凝固合金组织中也含有相同的组织类型(少量的Ti₂Co除外),即初生α-Nb和共晶(α-Nb+TiCo)组织;随着抽拉速率的逐渐增加,初生相α-Nb依次经历了“圆球状→团簇状→枝晶状”的转变,稳态生长区内共晶组织逐渐粗化,共晶排列不规则且相间距明显变大,淬火界面失稳并依次经历胞状界面到...     

Progress in Research on Solidification in a Strong Static Magnetic Field

Strong magnetic fields available from superconducting magnets are opening a way to new phenomena that could lead to new methods in materials processing including solidification. The principal research involving solidification in strong static magnetic fields is emphasizing four aspects: control of crystal orientation, convection damping, thermoelectric magnetohydrodynamics (TEMHD) and change in thermodynamics. Under high magnetic intensity, aligned structural textures are induced in both magnetic and non‐magnetic materials. Since in strong magnetic field the melt flow is suppressed by convection damping, the microstructure being formed during solidification is affected heavily; this phenomenon applies to eutectic, monotectic and peritectic alloys as well as to dendritic morphologies typical of directional solidification. If strength and orientation of a magnetic field are controlled appropriately, this strong damping effect will generate more homogeneous crystals as a result of achieving diffusion‐controlled solute transport conditions. TEMHD more easily occurs in strong magnetic fields, resulting in equiaxed crystals even under directional solidification. It is evidenced experimentally and theoretically that the thermodynamics of phase transformation and nucleation are changed by strong magnetic fields.     

Structure Evolution and Solidification Behavior of Austenitic Stainless Steel in Pulsed Magnetic Field

 To understand the solidification behavior of austenitic stainless steel in pulsed magnetic field, the solidification process is investigated by means of the self made high voltage pulse power source and the solidification tester. The results show that the solidification structure of austenitic stainless steel can be remarkably refined in pulsed magnetic field, yet the grains become coarse again when the magnetic intensity is exceedingly large, indicating that an optimal intensity range existed for structure refinement. The solidification temperature can be enhanced with an increase in the magnetic intensity. The solidification time is shortened obviously, but the shortening degree is reduced with the increase of the magnetic intensity.     

电磁场在材料凝固过程中的应用

介绍了各种电磁场处理在材料凝固过程中的应用和存在的问题，对从事冶金和铸造领域研究的人员具有一定参考价值。     

Microstructure Formation in AlSi7Mg Alloys Directionally Solidified in a Rotating Magnetic Field

To produce high stressed automotive components like engine frames and cylinder heads in foundry industry often AlSi7Mg alloys are used. During mould filling and casting melt flow affects the development of the microstructure, which defines the mechanical properties. In this paper the microstructure formation in AlSi7Mg0.3 and AlSi7Mg0.6 alloys during directional solidification is investigated. To induce a forced melt flow a rotating magnetic field is applied. For that purpose a Bridgman‐type gradient furnace is equipped with a rotary ring magnet. For detailed investigation of the shape of the solid‐liquid interface and the primary dendrite spacing a decanting device is used. As a result, the forced melt flow substantially changes the dendritic solidification microstructure. The rotating magnetic field generates a radial secondary flow in and ahead of the mushy zone, which causes an enrichment of eutectics in the centre of the samples. At lower solidification velocities this locally leads to the transition to mixed columnar‐equiaxed or even to equiaxed growth. In that case the solid‐liquid interfaces of the decanted samples show a significant depression in the centre part. In the out‐of‐centre region columnar growth still exists and the primary dendrite spacing decreases with increasing melt flow.     

A Preliminary Study of Electromagnetic Confinement and Directional Solidification of Platy Specimens of Stainless Steels

A method for producing metal and alloy ingots from their melts by electromagnetic moulds instead of physical moulds is proposed. This technique is based on eddy current flowing in the alloy material and electromagnetic pressure on the surface of the specimen from an induction coil around the specimen. A theoretical model for the distribution of the electromagnetic field in the material is established and the electromagnetic pressure exerted on the melt surface as well as the temperature field in the sample are set up. For a growing platy ingot with polyhedral cross section a three‐dimensional numerical analysis of the electromagnetic pressure and temperature field is carried out. As a result of the extensive experimental study and theoretical analysis, platy samples of rectangular cross sections are successfully obtained by the electromagnetic container‐less confinement process.     

电子束诱导定向凝固过程中晶体形貌对杂质分布的影响

产业条件下,利用电子束诱导定向凝固技术提纯多晶硅实现晶硅尾料的循环再利用,在硅锭中包括类单晶和柱状晶两种晶体形貌。与多晶区域相比,类单晶区域电阻率和少子寿命等电学性能分布比较均匀,铁杂质的含量分布也较均匀,其质量百分数平均值为0.000031%。电子束诱导定向凝固过程中类单晶的出现,不仅可以保证铸锭提纯区金属杂质成分均匀,而且可以进一步促进杂质向铸锭顶部富集,铸锭顶部的铁杂质含量高达0.101%。因此,利用电子束诱导类单晶生长成为可能,促进金属杂质的去除,为循环硅料的再生提供途径。