电磁振荡强度对半连铸7075铝合金微观组织的影响

在 70 75铝合金半连铸过程中 ,通过同时施加一个稳恒磁场和一个交变磁场 ,使金属熔体产生受迫振荡的方法。实验研究了电磁振荡强度对晶粒细化的影响规律。结果表明 :电磁振荡法获得的铝合金晶粒尺寸较CREM法的小 ,且随着电磁振荡强度的增加 ,铸锭微观组织变得更加细小和均匀。对在电磁振荡作用下 ,合金凝固组织的细化机理进行了探讨。     

电磁振荡下半连铸Al合金凝固组织的细化机制

在半连铸7075铝合金过程中, 通过同时施加稳恒磁场和交变磁场的方法, 使凝固熔体产生受迫振荡, 研究了电磁振荡的强度和频率对晶粒细化的影响规律. 对电磁振荡作用下, 合金凝固组织的细化机理进行了探讨. 结果表明 电磁振荡法获得的晶粒尺寸要较CREM法所获得的小, 且随着电磁振荡强度增加及频率降低, 铸锭整体组织变得更加细小和均匀.     

多元合金激光增材制造凝固组织演变模拟

针对多元合金激光熔覆过程,基于有限元方法和元胞自动机技术建立了多元合金激光熔覆熔池三维传热传质及凝固组织形貌演变模型,通过自行开发的宏微观耦合接口程序实现了三维熔池模型和多元合金凝固组织演变模型的耦合. 针对IN718激光熔覆过程中的传热传质和凝固组织演变过程进行了模拟,研究了基板初始晶粒尺寸、异质形核及多层熔覆扫描路径对熔覆层凝固组织形貌的影响机理,并对模拟结果进行了试验验证. 结果表明,模拟结果与实际物理过程吻合较好,所开发的耦合模型能够真实反映多元合金激光熔覆过程.     

5056铝合金稳恒磁控激光深熔焊接过程熔池流动与传热行为分析

针对外加稳恒磁场条件下6 mm厚度5056铝合金激光深熔焊接过程,建立了热场—流场—电磁场耦合熔池瞬态动力学数值模型,求解了特定时刻温度场、速度场与电磁场分布,建立了熔池沿不同方向的Peclet数模型,分析了不同磁场感应强度对熔池流动与传热行为的影响.结果表明,稳恒磁场条件下熔池中产生显著的哈特曼效应,表现为液态金属M...     

磁场在材料制备中的应用

总结近几年来国内外有关磁场在材料制备中的应用现状。分别讨论和分析了稳恒磁场、旋转磁场、交变磁场、脉冲磁场和强磁场在金属凝固过程中对金属凝固组织的影响。由于稳恒磁场、旋转磁场、交变磁场、脉冲磁场和强磁场在金属凝固过程中改善凝固组织的机理各不相同,在电磁学、流体力学和金属凝固原理的理论基础上,对磁场影响金属凝固组织的主要机理分别进行了讨论。另外,根据磁场发展技术的局限性对磁场在凝固过程中的应用和进一步研究进行了展望。     

电磁场对真空差压铸造ZL205A合金补缩特性研究

采用交变磁场辅助真空差压铸造技术制备了ZL205A合金试样,通过表征合金试样致密度,分析凝固压力、交变磁场及交变磁场-真空差压协同场对ZL205A合金凝固补缩行为的影响。结果表明,相同交变磁场作用下,试样的致密度随凝固压力增大而增大;而在相同的凝固压力下,试样的致密度随交变磁感应强度增加而先增大后减小;交变磁场-真空差压协同场对金属液的搅拌、振荡和挤渗作用,改变了铸件的凝固补缩行为,细化晶粒,提高铸件的致密度。当励磁电流强度为10A,凝固压力为350kPa时,交变磁场与真空差压的协同作用效果最好。     

交变磁场对ZL205A合金块状偏析的影响

采用自制的交变电磁场凝固装置,研究了交变磁场对ZL205A合金块状偏析组织和晶粒尺寸的影响,分析了交变磁场对ZL205A合金块状偏析组织的作用机理。结果表明,交变磁场不仅可以细化晶粒,也可有效减少晶粒内部的块状偏析组织。当励磁电流为5A时,平均晶粒尺寸可降至74.6μm,比未施加磁场时下降了25.37%,ZL205A合金中微量元素的块状偏析缺陷得到明显改善。     

脉冲磁场对Mg-Gd-Y-Zr合金凝固及力学性能的影响

在Mg-Gd-Y-Zr合金凝固过程中施加不同频率的脉冲磁场,研究脉冲磁场对Mg-Gd-Y-Zr合金凝固的影响.实验结果表明,脉冲磁场使Mg-Gd-Y-Zr合金晶粒细化,在频率为5 Hz条件下获得最佳的晶粒细化效果,平均晶粒尺寸从未加脉冲磁场条件下的65 pm细化到37 pm.脉冲磁场的搅拌导致熔体磁过冷及熔体温度梯度降低是晶粒细化的主要原因.脉冲磁场的施加使抗拉强度和延伸率较常规铸造合金分别提高了4.8%、78.5%.     

外加磁场对镁合金焊接接头疲劳性能的影响

在镁合金TIG焊焊接过程中引入外加纵向磁场,通过对其焊接接头的疲劳试验、断口分析和显微组织观测,研究了外加磁场对焊接接头疲劳寿命的影响规律及作用机理.结果表明,外加磁场与电弧、溶池中的导电粒子相互作用产生电磁搅拌,改变焊接熔池液态金属结晶过程中的传热和传质过程,从而改变晶粒的结晶方向,细化一次组织,球化净化杂质,减少偏析,提高接头的力学性能和疲劳性能.外加磁场状态下焊接接头的疲劳寿命高于无磁场下的疲劳寿命,达到母材的90%.     

励磁电流-凝固压力协同对真空差压铸造ZL205A合金晶粒尺寸的影响

通过测试交变磁场-凝固压力协同场下ZL205A合金晶粒尺寸,研究交变磁场-凝固压力协同场对ZL205A合金晶粒尺寸的影响机理。结果表明,在凝固压力不变的情况下,随着励磁电流强度增加,ZL205A合金试样的平均晶粒尺寸先增大后减小;随着凝固压力增大,当励磁电流强度小于10A时,交变磁场-凝固压力的协同作用将促进合金晶粒长大;而当励磁电流大于10A时,交变磁场-凝固压力的协同作用将抑制晶粒长大。     

Distributions of Electromagnetic Fields and Forced Flow and Their Relevance to the Grain Refinement in Al-Si Alloy Under the Application of Pulsed Magneto-Oscillation

Distributions of electromagnetic fields and induced forced flow inside a metal melt are crucial to understand the grain refinement of the metal driven by pulsed magneto-oscillation (PMO). In the present study, PMO-induced electromagnetic fields and forced flow in Ga-20wt%In-12wt%Sn liquid metal have been systematically investigated by performing numerical simulations and corresponding experimental measurements. The numerical simulations have been confirmed by magnetic and melt flow measurements. According to the simulated distribution of electromagnetic fields under the application of PMO, the strongest magnetic field, electric eddy current and Lorentz force with inward radial direction inside the melt are concentrated adjacent the sidewall of cylindrical melt at the cross section of middle height of coil. As a result, a global forced flow throughout the whole cylindrical column filled with Ga-20wt%In-12wt%Sn melt is initiated with a flow structure of two pair of symmetric vortex ring. The PMO-induced electromagnetic fields and forced flow in Al-7wt%Si melt have been numerically simulated. The contribution of electromagnetic fields and forced flow to the grain refinement of Al-7wt%Si alloy under the application of PMO is discussed. It indicates that the forced flow may play a key role in the grain size reduction.     

Refinement mechanism of low voltage pulsed magnetic field on solidification structure of silicon steel

The grain refinement of a silicon steel solidified with a low voltage pulsed magnetic field (LVPMF) was investigated by experiments and modeling. The experiment results show that complete fine equiaxed grains are acquired by applying the LVPMF. The effects of process parameters, such as the melt cooling rate and superheating on the solidification structure, were also studied. Complete fine equiaxed grains can be obtained under a larger range of cooling rate or superheating when the LVPMF is applied. The magnetic force and the melt flow during solidification were modeled and simulated to reveal the grain refinement mechanism. The simulation results show that the LVPMF has a double role in electromagnetic convection and electromagnetic vibration on the alloy melt. We propose the refining mechanism: The melt vibration and convection can promote nucleus multiplication, which contributes to heterogeneous nucleation enhancement and leads to a high nucleation rate and grain refinement.     

Simulation of the Influence of Pulsed Magnetic Field on the Superalloy Melt with the Solid-Liquid Interface in Directional Solidification

The effect of the pulsed magnetic field on the grain refinement of superalloy K4169 has been studied in directional solidification. In the presence of the solid-liquid interface condition, the distributions of the electromagnetic force, flow field, temperature field, and Joule heat in front of the solid-liquid interface in directional solidification with the pulsed magnetic field are simulated. The calculation results show that the largest electromagnetic force in the melt appears near the solid-liquid interface, and the electromagnetic force is distributed in a gradient. There are intensive electromagnetic vibrations in front of the solid-liquid interface. The forced melt convection is mainly concentrated in front of the solid-liquid interface, accompanied by a larger flow velocity. The simulation results indicate that the grain refinement is attributed to that the electromagnetic vibration and forced convection increase the nucleation rate and the probability of dendrite fragments survival, for making dendrite easily fragmented, homogenizing the melt temperature, and increasing the undercooling in front of the solid-liquid interface.     

Simulation of electromagnetic-flow fields in Mg melt under pulsed magnetic field

The effects of a pulsed magnetic field on the solidified microstructure of pure Mg were investigated.The results show that microstructure of pure Mg is considerably refined via columnar-to-equiaxed growth under the pulsed magnetic field and the average grain size is refined to 260μm under the optimal processing conditions.A mathematical model was built to describe the interaction of the electromagnetic-flow fields during solidification with ANSYS software.The pulsed electric circuit was first solved and the...     

基于磁场作用下的金属凝固研究现状

利用磁场辅助金属凝固,不仅可以细化晶粒、改善凝固组织的力学性能,同时由于磁场和熔融态金属是非直接接触,还可以避免缺陷的引入,进而已成为研究热点。针对磁场作用下的金属熔体形核和晶核生长特点,对金属凝固过程进行深入分析,从磁场对金属凝固的影响原理和仪器设备两个方面进行总结,综述磁场作用下金属凝固的研究进展;分别从铁磁性、顺磁性、抗磁性三种磁性金属在磁场作用下试验研究进行梳理分析。结果表明：磁场引发的洛伦兹力、热电磁力、磁转矩及磁取向等作用通过影响金属熔体的形核和晶核生长,最终改善凝固组织性能;磁场设备利用永磁铁或者电磁铁产生磁场环境;三种磁性金属在磁场环境下凝固后的性能改善体现在力学性能、导电性能、磁性能等方面。最后归纳磁场辅助金属凝固过程中所存在的问题,并展望未来的发展趋势。     

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.     

Hot Tearing Susceptibility of AXJ530 Alloy Under Low-Frequency Alternating Magnetic Field

Herein, a hot tearing measured system with external excitation coil and a differential thermal analysis system with applied magnetic field were used to study the effects of low-frequency alternating magnetic field on the solidification behavior and hot tearing susceptibility(HTS) of the AXJ530 alloy under different magnetic field parameters. The hot tearing volume of the castings was measured via paraffin infiltration method. The microstructure of the hot tearing zone of the casting was observed using optical microscopy and scanning electron microscopy, and the phase composition was analyzed using X-ray diffraction and energy depressive spectroscopy. The experimental results show that the solidification interval of AXJ530 alloy was shortened and the dendrite coherency temperature of the alloy decreased with the increase in frequency of alternating magnetic field. Under appropriate magnetic field parameters, the electromagnetic force could enhance the convection in the melt to promote the flow of the residual liquid phase, refine the microstructure, and optimize the feeding channel in the late solidification stage, which reduced the HTS of the alloy. However, when the magnetic field frequency was increased to 15 Hz, the induced current generated excessive Joule heat to the melt. At this time, the thermal action of the magnetic field coarsened the microstructure of the alloy, resulting in an increase in HTS of the alloy.     

液态金属电磁离心凝固的力场分析

运用磁流体动力学原理，对在稳恒磁场中高速旋转的液态金属凝固时的受力状态进行了理论解析，结果表明在电磁力场、离心力场和重力场共同作用下，旋转液态金属中受到大小周期变化的径向压力和切向分力，后者起电磁搅拌作用，是细化电磁离心凝固组织的根本原因．     

Microstructure refinement of AZ91D alloy solidified with pulsed magnetic field

The effects of pulsed magnetic field on the solidified microstructure of an AZ91D magnesium alloy were investigated. The experimental results show that the remarkable microstructural refinement is achieved when the pulsed magnetic field is applied in the solidification of AZ91D alloy. The average grain size of the as-cast microstructure of AZ91D alloy is refined to 104 μm. Besides the grain refinement, the morphology of the primary α-Mg is changed from dendritic to rosette, then to globular shape with changing the parameters of the pulsed magnetic field. The pulsed magnetic field causes melt convection during solidification, which makes the temperature of the whole melt homogenized, and produces an undercooling zone in front of the liquid/solid interface by the magnetic pressure, which makes the nucleation rate increased and big dendrites prohibited. In addition, primary α-Mg dendrites break into fine crystals, resulting in a refined solidification structure of the AZ91D alloy. The Joule heat effect induced in the melt also strengthens the grain refinement effect and spheroidization of dendrite arms.