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

The microstructure of AI-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 AI alloy. To investigate the effect of electromagnetic stirring on the solidification of the ingot, the solidification of the Al-50Ni alloy in vacuum with electromagnetic stirring was described by numerical simulation in this paper; and a three dimensional mathematical model was established. The electromagnetic field was simulated by ANSYS software and the thermal-flow field was simulated by FLUENT software. The coupling between the electromagnetic field and the thermal-flow field was implemented by user-defined subroutines. It is found that the current intensity has significant influences on the fluid flow and the microstructure of the alloy. The simulation results agree well with the experimental results, and the optimum current intensity under the exprimental conditions is 80 A, while the frequency is 50 Hz.

Semisolid slurry of 7A04 aluminum alloy prepared by electromagnetic stirring and Sc, Zr additions

Slurry preparation is one of the most critical steps for semisolid casting, and its primary goal is to prepare slurry with uniformly distributed fine globules. In this work, electromagnetic stirring(EMS) and the addition of Sc and Zr elements were used to prepare semisolid slurry of 7A04 aluminum alloy in a large diameter slurry maker. The effects of different treatments on the microstructure, composition and their radial homogeneity were investigated. The results show that, compared to the slurry without any treatment, large volume slurry with finer and more uniform microstructure can be obtained when treated by EMS, Sc, or Zr additions individually. EMS is more competent in the microstructural and chemical homogenization of the slurry while Sc and Zr additions are more excellent in its microstructural refinement. The combined treatment of EMS, Sc and Zr produces premium 7A04 aluminum alloy slurry with uniformly distributed fine α-Al globules and composition. The interaction mechanism between EMS and Sc and Zr additions was also discussed.

Numerical simulation of friction stir butt-welding of 6061 aluminum alloy

A two-dimensional computational fluid dynamics model was established to simulate the friction stir butt-welding of 6061 aluminum alloy. The dynamic mesh method was applied in this model to make the tool move forward and rotate in a manner similar to a real tool, and the calculated volumetric source of energy was loaded to establish a similar thermal environment to that used in the experiment. Besides, a small piece of zinc stock was embedded into the workpiece as a trace element. Temperature fields and vector plots were determined using a finite volume method, which was indirectly verified by traditional metallography. The simulation result indicated that the temperature distribution was asymmetric but had a similar tendency on the two sides of the welding line. The maximum temperature on the advancing side was approximately 10 K higher than that on the retreating side. Furthermore, the precise process of material flow behavior in combination with streamtraces was demonstrated by contour maps of the phases. Under the shearing force and forward extrusion pressure, material located in front of the tool tended to move along the tangent direction of the rotating tool. Notably, three whirlpools formed under a special pressure environment around the tool, resulting in a uniform composition distribution.

Annulus electromagnetic stirring for preparing semisolid A357 aluminum alloy slurry

The effects of pouring temperature and annulus gap width on the microstructure of the semi-solid A357 aluminum alloy slurry prepared by annulus electromagnetic stirring(AEMS)technology were investigated.The results show that low pouring temperature and narrow annulus gap are advantageous to obtaining the small spherical primaryα(Al)phase.The lower the pouring temperature is and the smaller the annulus gap width is,the more uniform,the smaller and the more spherical the microstructure is. The microstructures obtained by the ordinary electromagnetic stirring and AEMS were compared.The results indicate that the primaryα(Al)particles are globular,small and distribute homogeneously in the slurry obtained by AEMS.But in the slurry obtained by the ordinary electromagnetic stirring,the primaryα(Al)particles are small dendrites in the edge of the slurry and they are large and rosette-like or dendritic in the inner of the slurry.

Effects of Trace Amount Modified SiC Nanoparticles and Electromagnetic Stirring (EMS) on Microstructure and Mechanical Properties of 7055 Aluminum Alloy

The effects of trace amount modified SiC nanoparticles and electromagnetic stirring(EMS)on mierostructures and mechanical properties of 7055 aluminum alloy are investigated experimentally.The result shows that the original developed coarse dendrite and columnar with obvious orientation microstructure turns into homogeneous equiaxed microstructure with the application of trace amount modified SiC nanoparticles and EMS.A minimum grain size is 96 μm and has been observed when the addition of modified SiC nanoparticles is 0.05%and the current of EMS is 100A.The ultimate tensile strength is increased by 15.8%and the elongation is improved by 50%compared to those without modified SiC nanoparticles and EMS.Moreover,the compound effects of trace amount modified SiC nanoparticles and EMS is discussed to explain the mechanisms of grain refinement and mechanical properties on 7055 aluminum alloy.

Numerical Simulation of Magnetic Field Distribution in Aluminum Melting Furnace With Electromagnetic Stirring

In metallurgical processing,effective and reliable electromagnetic stirring of the melt is one of the prerequisites for higher productivity and improved process performance.Reasonable structure and electrical parameters of the stirrer are greatly significant on improving and enhancing the stirring quality.In this paper,ANSYS software is used to research the effect of stirrer parameters on magnetic field distribution in aluminum melting furnace.The results show that magnetic flux density distributes as two humps at the direction(X)of metal length.Magnetic flux density distributes as a hump at the direction(Z)of metal width,reaches its maximum at the pool center and decays gradually toward the edge.It is also demonstrated that magnetic flux density increases by 2.65mT,as kilo-ampere-turns increase by 2.The center distance between two coils changes the distribution of magnetic flux density rather than its magnitude,while the distance from coils to the bottom of molten aluminum changes the magnitude of magnetic flux density but no change of distribution.

Evolution of residual stress field in 6N01 aluminum alloy friction stir welding joint

Based on the characteristics of friction stir welding( FSW) and Coulomb friction work theory,the residual stresses field of FSW joints of 6 N01 aluminum alloy( T5),which was used in high speed train,were calculated by using the ANSYS finite element software. During the FEM calculation,the dual heat source models namely the body heat source and surface heat source were used to explore the evolution law of the welding process to the residual stress field. The method of ultrasonic residual stress detecting was used to investigate the residual stresses field of the 6 N01 aluminum alloy FSW joints. The results show that the steady-state temperature of 6 N01 aluminum alloy during FSW is about 550 ℃,and the temperature mutates at the beginning and at end of welding. The longitudinal residual stress σ_x is the main stress,which fluctuates in the range of-25 to 242 MPa. Moreover,the stress in the range of shaft shoulder is tensile stress that the maximum tensile stress is 242 MPa,and the stress in the outside of shaft shoulder is compressive stress that the maximum compressive stress is 25 MPa. The distribution of the tensile stress in the welding nugget zone( WNZ) is obviously bimodal,and the residual stress on the advancing side is higher than that on the retreating side. With the increasing of the welding speed,the maximum temperature decreased and the maximum residual stress decreased when the pin-wheel speed kept constant. With the increasing of the pin-wheel speed,the maximum temperature of the joint increased and the maximum residual stress increased when the welding speed was constant. The experimental results were in good agreement with the finite element results.

Mechanical properties and microstructural evolution of rheocast A356 semi-solid slurry prepared by annular electromagnetic stirring

Nowadays,having an effective technique in preparing semi-solid slurries for rheocasting process seems to be an essential requirement.In this study,semi-solid slurry of A356 aluminum alloy was prepared by three-phase annular electromagnetic stirring(A-EMS)technique under different conditions.The effects of stirring current,pouring temperature and stirring time on microstructural evolution,mean particle size,shape factor and solid fraction were investigated.The rheocasting process was carried out by using a drop weight setup and to inject the prepared semi-solid slurry in optimal conditions into the step-die cavity.The filling behavior and mechanical properties of parts were studied.Microstructural evolution showed that the best semi-solid slurry which had fine spherical particles with the average size of~27μm and a shape factor of~0.8 was achieved at the stirring current of 70 A,melt pouring temperature of 670℃,and stirring time of 30 s.Under these conditions,the step-die cavity was completely filled at die preheating temperature of 470℃.The hardness increases by decreasing step thickness as well as die preheating temperature.Moreover,the tensile properties are improved at lower die preheating temperatures.The fracture surface,which consists of a complex topography,indicates a typical ductile fracture.

Microstructure of in situ Al_3Ti/6351Al composites fabricated with electromagnetic stirring and fluxes

The 6351 wrought aluminum alloy and K2TiF6-CaF2-LiCl components were selected as raw materials to fabricate in situ Al3Ti particulate reinforced aluminum alloy at 720℃via direct melt reaction method with electromagnetic stirring(EMS).CaF2 and LiCl acted as fluxes to lower the reaction temperature of the system.It is shown that the electromagnetic stirring and fluxes accelerate the emulsion process of K2TiF6.Optical microscopy,scanning electron microscopy,transmission electron microscopy and energy dispersive spectrum were utilized to analyze the microstructure and components of composites.Compared to composites fabricated without EMS and fluxes,the sizes of endogenetic Al3Ti are refined from 10-15μm to 2-4μm,which are often accompanied with silicon element.The morphology of Al3Ti or Al3TiSi0.22 exhibits triangle,quadrilateral and other clumpy patterns. Because of the Ca elements from CaF2,the sizes of Mg2Si decrease from 8-10μm to 1-2μm due to the formation of Ca2Si.

Preparation of semi-solid slurry at power frequency by annulus electromagnetic stirring method

The effect of stirring frequency on the semi-solid A357 aluminum alloy microstructure was investigated by annulus electromagnetic stirring(AEMS) method. The microstructures obtained by AEMS method and ordinary electromagnetic stirring(EMS)method were compared and analyzed. The results show that the primary α(Al) particles become more spherical and fine, and disperse uniformly in a liquid matrix with increasing stirring frequency, and higher stirring frequency is advantageous to obtain the fine spherical semi-solid microstructure by AEMS. Compared with the microstructures obtained at stirring frequency of 50 Hz in EMS, the fine spherical and uniformly distributed semi-solid microstructures can be still obtained at stirring frequency of 50 Hz in AEMS, so stirring frequency of 50 Hz is recommended in AEMS to save investment cost on frequency-conversion facilities.

Induction reheating of A356.2 aluminum alloy and thixocasting as automobile component

The development work for producing an automobile component by thixocasting using A356.2 alloy was introduced.As the first step,the alloy was electromagnetically stirred and solidified to produce a billet with non-dendritic microstructure.The microstructure depended on several process parameters such as stirring intensity,stirring frequency,cooling rate,and melt initial superheat.Through a series of computational studies and controlled experiments,a set of process parameters were identified to produce the best microstructures.Reheating of a billet with non-dendritic microstructure to a semisolid temperature was the next step for thixo-casting of the components.The reheating process was characterized for various reheating cycles using a vertical-type reheating machine.The induction heating cycle was optimized to obtain a near-uniform temperature distribution in radial as well as axial direction of the billet,and the heating was continued until the liquid fraction reached about 50%.These parameters were determined with the help of a computational fluid dynamics(CFD) model of die filling and solidification of the semisolid alloy.The heated billets were subsequently thixo-cast into automobile components using a real-time controlled die casting machine.The results show that the castings are near net shape,free from porosity,good surface finish and have superior mechanical properties compared to those produced by conventional die casting processes using the same alloy.

Effect of Temperature on Material Transfer Behavior at Different Stages of Friction Stir Welded 7075-T6 Aluminum Alloy

In this work, the morphologies of weld of 7075-T6 aluminum alloy via friction stir welding （FSW） were analyzed by optical microscopy, the temperature field was attained by numerical simulation, and the effect of temperature on material transfer behavior in the thermal-mechanical affected zone （TMAZ） at different stages was mainly investigated. The FSW process consists of three stages. It is very interesting to find that the maximum transfer displacement of material appears at the final stage of welding process, then at the stable stage and at the initial stage, which results from the difference of peak temperatures at different stages. At any stage, the material in TMAZ near the surface of weld transfers downwards, the material in the middle of weld moves upwards and the material near the bottom of weld hardly moves. In any cross section of weld, the largest transfer displacement of material appears in the middle of weld. The increase of rotational velocity and the decrease of welding speed are both beneficial to the transfer displacement of material in the middle of weld.

Horizontal continuous casting process under electromagnetic field for preparing AA3003/AA4045 clad composite hollow billets

A modified horizontal continuous casting process under the electromagnetic field was proposed for preparing AA3003/ AA4045 clad composite hollow billets. To investigate the effect of electromagnetic field on this process, a comprehensive three-dimensional model was developed. Two cases with and without electromagnetic field were compared using the simulations. When rotating electromagnetic stirring is applied, the flow pattern of fluid melt is greatly modified; the mushy zone becomes much wider, the temperature profile becomes more uniform, and the solid fraction decreases for both the external and internal alloy melt layers. These modifications are beneficial for the formation of a bimetal interface and fine and uniform grain structure of the clad composite hollow billet. Experiments conducted using the same electrical and casting parameters as the simulations verify that under the electromagnetic field the microstructure of the clad composite hollow billet becomes fine and the diffusion of the elements at the interface is promoted.

Preparation of semi-solid AlSi7Mg alloy slurry with big capability

Semi-solid AlSi7Mg alloy slurry was prepared by low superheat pouring and weak traveling-wave electromagnetic stirring.The effects of pouring temperature and stirring power on the microstructure of AlSi7Mg alloy slurry were studied.The results show that the semi-solid AlSi7Mg alloy slurry of 5 kg can be prepared.This new technology can save energy and make the pouring process convenient.When the pouring temperature is decreased at a stirring power of 0.41 kW,the shape of primary α-Al grains gradually changes from dendritic-like to spherical.When the alloy melt is poured at the temperature（630°C） with a certain superheat,the pouring process becomes easier,and the spherical microstructure of AlSi7Mg alloy slurry can be prepared by the weak traveling-wave electromagnetic stirring.When the pouring temperature is 630°C,increasing the stirring power appropriately can result in better spherical primary α-Al grains,but if the stirring power is increased to a certain value（1.72 kW）,the shape of primary α-Al grains does not obviously improve when the stirring power is continually increased.

铝合金双辊铸轧工艺进展及发展趋势

双辊铸轧工艺作为铝合金板带材先进的制备方式之一,符合当前“碳达峰、碳中和”的双碳战略要求,对推动我国高端轻质铝合金产业向绿色化、智能化方向发展起到积极的作用。文章通过系统的研究和分析,综述了铝合金双辊铸轧工艺的发展历史及现状,重点介绍了高合金化铝合金铸轧板偏析缺陷的形成机制,系统阐述了电磁外场、数值模拟在铝合金双辊铸轧工艺试验研究方面取得的进展,并对双辊铸轧工艺的发展趋势进行探讨分析,为我国高端轻质铝合金双辊铸轧工艺的发展提供借鉴和参考。

铝合金搅拌摩擦焊技术研究进展

文章综述了铝合金搅拌摩擦焊技术最新的研究进展,从焊接模拟研究、焊接参数对焊缝组织及性能的影响和铝合金搅拌摩擦焊性能研究三个角度,梳理了近年来国内外最新的研究成果;最后指出异种铝合金的搅拌摩擦焊是下一步研究的重点和方向。

Effects of A-EMS processing parameters on semisolid slurry production

A computational model coupling an electromagnetic model with a macroscopic heat and fluid flow model in semisolid A1 alloy slurry preparation by A-EMS was developed. The effects of A-EMS processing parameters such as stirring current, stirring frequency and stirring gap width on macroscopic transport phenomena during solidification were analyzed. Both the computational and experimental results showed that more intensively uniform stirring fields and uniformly fine microstructures were obtained by optimizing processing variables.

差厚铝合金2024∕7075搅拌摩擦焊的温度场数值模拟

利用Abaqus有限元软件,建立差厚7075和2024铝合金的有限元模型和改进热源模型,进行模拟搅拌摩擦焊的焊接过程,分析了不同厚度比的温度分布,以及对焊核区和热力影响区的宽度变化的影响,并验证了所建模型应用的可行性。结果表明,铝合金焊件中的温度峰值随着厚度比的变化而改变,且温度在铝合金板上呈不对称的倒“V”形分布,板材上的温度峰值随着板材厚度变大而减小。焊接过程中温度越高焊件上的热力影响区就越宽。较大的厚度比会使得焊件的热力影响区宽度和焊核区宽度偏大。模拟得到的温度值和试验数据比较,两者的误差在8%以内,验证了模型的可行性。

电磁搅拌作用对铝合金显微组织的影响

研究了电磁搅拌对ＺＬ１０１Ａ 铝合金显微组织的影响， 阐明了不同搅拌工艺条件下ＺＬ１０１Ａ铝合金的显微组织的变化规律。结果表明： 在磁场强度大于０ ．０６５ Ｔ 的ＥＭＳ作用下，ＺＬ１０１Ａ 合金能够得到非树枝晶组织； 未经细化处理， 晶粒尺寸在１００ ～３００ μｍ 范围内； 随着ＥＭＳ 作用的增强， 晶粒向完全椭球形发展； 本实验条件下ＥＭＳ 没有细化共晶Ｓｉ 的作用， 也没有改变共晶Ｓｉ 的析出形态；

电磁搅拌作用下非树枝晶铝合金组织演变过程的数学描述

研究了电磁搅拌法制备半固态铝合金原材料工艺中 ,主要工艺参数 (磁场强度和冷却速度 )与非树枝晶组织之间的关系 ,半定量地描述了非树枝晶组织的演变过程 ,给出了非树枝晶组织参数随着磁场强度和冷却速度变化的数学关系 ,为合理选择工艺参数提供了理论指导。