磁场电流对FV520B钢板焊接接头性能的影响

以FV520B钢板焊接接头为研究对象,在焊接过程中外加磁场,研究了磁场电流对焊缝力学性能、显微组织的影响规律.结果表明:外加磁场可以细化金属的凝固组织,提高焊接接头的力学性能.     

磁场搅拌方式对Sn-11％Sb合金凝固组织与偏析的影响

中心偏析是钢连铸坯的常见缺陷,严重影响了产品的质量。电磁搅拌是对金属凝固过程进行控制、改善连铸坯质量的有效手段,旋转磁场电磁搅拌在钢的连铸过程中已得到广泛的应用,但螺旋磁场电磁搅拌的研究鲜见报道。以低熔点合金模拟钢的凝固过程,对采用不同电磁搅拌方式改善中心偏析缺陷的效果进行了模拟对比试验。研究了螺旋磁场电磁搅拌和旋转磁场电磁搅拌对Sn-11%Sb二元合金凝固组织的影响,并与常规条件下的凝固组织进行对比。试验结果表明,在相同电磁搅拌参数下,螺旋磁场电磁搅拌比旋转磁场电磁搅拌更能减小铸锭上下部成分之间的差异,细化晶粒,更好地促进铸锭成分均匀化效果。     

外磁场在定向凝固过程中的应用研究

以磁场对合金凝固组织的影响为基础,综述了近年来交变磁场和稳恒磁场在定向凝固过程中的应用和发展,总结了外磁场对定向凝固过程中合金微观组织的作用机制,并展望了今后的研究方向。     

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。     

采用电磁搅拌技术改善铸坯质量的探讨

一、前言电磁搅拌技术早在1922年Mcneill就论述了熔融金属的流动对凝固组织、中心偏析和夹杂物分布的影响。1934年Bruchanov利用电转磁场研究了钢水的流动对凝固组织形态的影响,以及对减少钢中气体含量、改善     

基于多重分形研究脉冲磁场周期对凝固组织的影响

为了研究脉冲磁场对凝固组织的影响,采用自发研制的脉冲磁场发生装置将脉冲磁场非接触式地施加到钛处理低碳钢的凝固过程中,利用金相显微镜和实验室设计的多重分形软件研究了不同周期的脉冲磁场对凝固组织的影响。结果表明,该钢种的凝固组织具有分形特征;随着脉冲磁场周期的延长,Δα和Δf(α)呈现为先减小后增大的规律,在脉冲磁场周期为0.5 s时,组织最为均匀。由此可以推断脉冲磁场周期对凝固组织的影响存在一个最佳值。     

强磁场下Cu-25%Ag合金的凝固行为

研究了强磁场对Cu-25%Ag(质量分数)合金凝固组织的影响,分析了不同磁场条件对合金凝固组织的作用机理.研究发现,均恒磁场和梯度磁场对合金的凝固组织有重要影响,改变了富Cu枝晶形貌和尺寸,无磁场条件下初生富Cu枝晶分布不均匀,一次枝晶比较长且粗大,枝晶主要以柱状枝晶为主;在12T磁场条件下,富Cu枝晶分布比较均匀,一次枝晶变短、粗化,枝晶主要以胞状枝晶为主;在负梯度磁场条件下,富Cu枝晶分布不均匀,在试样下部,树枝晶减少,以小平面方式生长的粗大胞晶为主.通过实验研究表明,利用均恒强磁场控制Cu-Ag合金凝固组织,细化晶粒、减小偏析是具有可行性的.     

脉冲磁场对钛处理低碳钢凝固组织的影响

采用自行研制的脉冲磁场发生装置对含Ti低碳钢的凝固过程进行控制,利用金相显微镜、扫描电镜和能谱仪研究不同放电电压条件下的脉冲磁场对钢中夹杂物的析出行为及凝固组织的影响规律,分析不同凝固冷却速度对脉冲磁场细晶化效果的影响。结果表明:随着放电电压的升高,夹杂物的尺寸先减小后增大,晶内铁素体的数量逐渐增多,凝固组织变得更细小;降低凝固冷却速度,可延长脉冲磁场对钢液凝固过程的作用时间,晶粒的细化效果更明显;当放电电压为80 V,凝固冷却速度为60℃/min时,凝固组织几乎全部由细小的相互交错的针状铁素体组成。     

液相流动在金属凝固中的作用

液态金属的流动有多种形式，它对金属冶金、凝固过程有着重要影响。文章从传输过程、凝固组织和成分偏析等三个方面对液相流动作用作了综述。通过控制液相流动的方式和行为来调节凝固过程的传输行为，达到控制或改善凝固组织和偏析程度的目的。对从事材料冶金和凝固等相关领域的研究人员有较大参考价值。     

钢凝固组织的成因、显示与控制对策

以钢凝固组织的形成、显示为研究对象，从而提出控制金属凝固组织的措施     

Analysis of Graphite Morphology of Gray Cast Iron in Pulse Magnetic Field

Theelectromagneticrefinementofmetalsolidi ficationstructureisanewlydevelopedtechnique. Themagneticfieldcanrefinethesolidificationstruc turebyactingupontheliquidmetal,suchasvibra tionandstirring.Atpresent,suchtechniquesare mainlyappliedtoalloyswithlower…     

氧化物冶金与脉冲磁场参数影响钢组织的研究

 脉冲磁场处理与氧化物冶金技术是细化组织、提升材料性能的两种常用方法,将其有机结合可进一步优化钢铁材料的性能。利用自主研制的高频感应线圈加热炉与脉冲磁场发生装置将脉冲磁场非接触式地施加在钛处理低碳钢的凝固过程中,利用金相显微镜、多重分形软件与维氏硬度仪研究了不同脉冲磁场参数对凝固组织的影响。结果表明,脉冲磁场感应强度为135~190 mT、磁场作用时间为5~10 min时,试样的金相组织最细小均匀,原始奥氏体晶粒得到明显细化,原始奥氏体晶粒面积由15.79 mm2下降到1.25 mm2,试样的硬度值由118.1HV提升到165.4HV,此参数下的脉冲磁场对凝固组织的细化程度最佳。     

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.     

Influence of Forced/Natural Convection on Segregation During the Directional Solidification of Al-Based Binary Alloys

We analyzed the columnar solidification of a binary alloy under the influence of an electromagnetic forced convection of various types and investigated the influence of a rotating magnetic field on segregation during directional solidification of Al-Si alloy as well as the influence of a travelling magnetic field on segregation during solidification of Al-Ni alloy through directional solidification experiments and numerical modeling of macrosegregation. The numerical model is capable of predicting fluid flow, heat transfer, solute concentration field, and columnar solidification and takes into account the existence of a mushy zone. Fluid flows are created by both natural convection as well as electromagnetic body forces. Both the experiments and the numerical modeling, which were achieved in axisymmetric geometry, show that the forced-flow configuration changes the segregation pattern. The change is a result of the coupling between the liquid flow and the top of the mushy zone via the pressure distribution along the solidification front. In a forced flow, the pressure difference along the front drives a mush flow that transports the solute within the mushy region. The channel forms at the junction of two meridional vortices in the liquid zone where the fluid leaves the front. The latter phenomenon is observed for both the rotating magnetic field (RMF) and traveling magnetic field (TMF) cases. The liquid enrichment in the segregated channel is strong enough that the local solute concentration may reach the eutectic composition.     

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.     

Computer Simulation of Solidification Transport Behaviours in Blade‐Like Castings under Transverse Static Magnetic Fields up to 25T

Numerical simulation of solidification transport phenomena/processes in a TiAl alloy blade‐like casting, under transverse magnetic fields of different strengths, was carried out. The simulation was based on a continuum solidification model and the computer codes developed by the authors. The simulation results show that, although the liquid flow in the bulk liquid region can be suppressed efficiently, the feeding flow in the mushy zone caused by the volume contraction, due to solidification shrinkage and thermal/solutal expansion, cannot be suppressed even under an ultra‐strong magnetic field up to 25T. This indicates that the forces driven by volume contraction are much stronger than those caused by the gravity. The natural convection can delay the directional solidification process, while the applied static magnetic field accelerates it to some extent, by weakening the natural convection. The magnetic field changes the coupled heat and species mass transfer to a diffusion type mechanism. The natural convection may be the cause for horizontal segregation. An ultra‐strong magnetic field is not necessary to achieve sufficient suppression of natural convection.