Preparation of semisolid AlSi7Mg alloy slurry through weak traveling-wave electromagnetic stirring

The semisolid AlSi7Mg alloy slurry with large capacity was prepared by low superheat pouring and week traveling-wave electromagnetic stirring. The effects of electromagnetic stirring power and frequency on the shape and distribution of primary α-A1 grains in the AlSi7Mg alloy slurry were discussed. The experimental results show that the AlSi7Mg alloy slurry with fine and spherical primary α-A1 grains distributed homogeneously can be obtained. Under the condition of low superheat pouring and week traveling-wave electromagnetic stirring, when the pouring temperature is 630℃, raising the stirring power or frequency appropriately can gain a better shape of primary α-Al grains; but if the stirring power or frequency is increased to a certain value （1.72 kW or10 Hz）, the shape of primary α-A1 grains cannot be obviously improved and spherical primary α-Al grains distributed homogeneously can be still obtained.

Multi-physical fields distribution in billet during helical electromagnetic stirring:A numerical simulation research

Electromagnetic stirring is one of the widely applied techniques to modify the quality of casting billets.Different from conventional rotate stirring,the helical stirring is more professional in assisting multi-dimensional flow of molten metal and eliminating solidification defects.In this study,the single-winding helical stirring(SWHS)was introduced,offering advantages such as smaller volume and lower electromagnetic shielding compared to traditional helical stirring methods.Following a comprehensive numerical simulation,the stirring parameters of SWHS were adjusted to yoke inclination angle of 43°and frequency of 12 Hz.The higher electromagnetic force and flow velocity in drawing direction,as well as the lower temperature gradient induced by the SWHS,are positive factors for homogeneous solidification of billet.The experimental results on Al-8%Si alloy and 0.4%C-1.1%Mn steel demonstrate that compared to rotate stirring,the SWHS process can induce better billet quality and is more effective in accelerating the equiaxed expansion and reducing element segregation.The SWHS process can enhance the equiaxed ratio of the billet by 58.3%and reduce segregation degree of carbon element by 10.97%.Consequently,SWHS holds great promise as a potential approach for improving the quality of continuous casting billets.

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.

Effect of electromagnetic stirrer centered outside the mold on steel flow field of bloom continuous casting

Mold electromagnetic stirring technology for optimizing the flow of molten steel is now widely used in the continuous casting production process of high-quality steels.However,studies on the case that the center of the electromagnetic stirrer is located outside the mold have not been reported.Herein,the effect of the electromagnetic stirrer centered outside the mold on the steel flow field was studied in detail by means of numerical simulations.A Gauss meter was used to measure the magnetic induction intensity at different positions,currents,and frequencies.The test results were compared with the simulation results of electromagnetic stirring to calibrate and verify the accuracy of the electromagnetic model.Then,electromagnetic force was introduced into the flow field model as a source term to study its effect on the flow field under anomalous conditions.The results show that when the center of the electromagnetic stirrer is located outside the mold,the magnetic field strength is about twice as strong as that located inside the mold.This also leads to an increase in the flow velocity near the electromagnetic stirrer.As a result,the optimal electromagnetic stirring parameters(200 A,2.5 Hz)were specified when the center of the electromagnetic stirrer is located outside the mold.

Effect of Ti on microstructure and properties of electromagnetic stirred Al-18wt.%Mg_(2)Si alloy

By adding different amounts of Ti into the electromagnetic stirred Al-18wt.%Mg_(2)Si alloy,the effect of Ti element on the microstructure and mechanical properties of the alloy was studied.The experimental results show that the microstructure is refined after modification with Ti,which is related to the heterogeneous nucleation of TiAl_(3) particles on theα-Al matrix.With the increase of Ti content and holding time after stirring,the primary Mg_(2)Si phase is refined firstly and then coarsened,and correspondingly,the mechanical properties of the alloy show a trend of increasing at first and then decreasing.When the addition of Ti is 0.5wt.%and the holding time is about 20 min,the refinement effect of primary Mg_(2)Si phase is the most significant and the mechanical properties of the alloy are optimal.

Preparation for Semi-Solid Aluminum Alloy Slurry under Weak Electromagnetic Stirring Conditions

The effects of pouring temperature, short electromagnetic stirring with low strength and then soaking treatment on the microstructure of AISi7Mg alloy were investigated. The results show that if AlSi7Mg alloy is poured at 630 or 650℃ and meanwhile stirred by an electromagnetic field at a low power for a short time, the pouring process can be easily controlled and most solidified primary α-Al grains become spherical and only a few of them are rosette-like. Weak electromagnetic stirring makes the temperature field more homogeneous and makes the primary α-Al grains disperse in a larger region, which leads to the spherical microstructures of primary α-Al grains. When the AISi7Mg alloy is soaked or reheated at the semisolid state, the primary α-Al grains ripen further and they become more spherical, which is favorable to the semi-solid forming of AlSi7Mg alloy.

Grain Size Control of Semisolid A356 Alloy Manufactured by Electromagnetic Stirring

To investigate the possibility of substituting the mechanical stirring system with electromagnetic stirring (EMS) system for aluminum rheo die-casting, the EMS under the different stirring cooling conditions was carried out. It was found that in the early period of solidification, the dendrite breakages led to a fine primary phase. When dendrites grew coarsely, the effect of ripening on grain size overwhelmed that of dendrite breakage. It was also found that the high cooling rate favored large nucleation rate, and led to a fine primary phase. But high cooling rate also made the growth rate of the dendrite arm, which prevented the dendrite arm from being sheared off. Therefore there were a suitable stirring time and suitable cooling rate to obtain the best rheo die-casting structure. Qualified semisolid A356 aluminum alloy was successfully manufactured with short time EMS.

Research on semi-solid slurry of a hypoeutectic Al-Si alloy prepared by low superheat pouring and weak electromagnetic stirring

The semi-solid slurry of a hypoeutectic Al-Si alloy was manufactured by low superheat pouring and weak electromagnetic stirring. The effects of pouting temperature and stirring power on the semi-solid slurry were investigated. The results indicated that the semi-solid slurry to satisfy rheocasting can be manufactured by low superheat pouring and weak electromagnetic stirring. The pouring temperature （or superheat） and the stirring power remarkably affected the morphology of primary α-Al and the size of primary α-Al, and there is no obvious effect of stirring time on primary α-Al. Compared with the samples made by low superheat pouring with no stirring, the nucleation rate, particle morphology and grain size of primary α-Al in A356 were markedly improved by low superheat pouring and weak electromagnetic stirring. On the condition of weak electromagnetic stirring, the pouring temperature with low superheat can be suitably raised to reach the effectiveness obtained from the lower pouring temperature without stirring.

Manufacture technique of semi-solid slurry of hypoeutectic Al-Si alloy by low superheat pouring and weak electromagnetic stirring

The semi-solid slurry of hypoeutectic Al-Si alloy was manufactured by low superheat pouring and weak electromagnetic stirring. The effects of pouring temperature and stirring power on the semi-solid slurry making process were investigated. The results indicate that the semi-solid slurry to satisfy rheocasting requirement can be made by a combination of low superheat pouring and weak electromagnetic stirring. The pouring temperature (or superheat) and the stirring power significantly affect the morphology and the size of primary α-Al, while there is no obvious effect of the stirring time on primary α-Al. Compared with the samples made by low superheat pouring without stirring, the nucleation rate, particle morphology and grain size of primary α-Al in A356 Al alloy are markedly improved by a process of applying both low superheat pouring and weak electromagnetic stirring. Under the condition of weak electromagnetic stirring applied, the pouring temperature with low superheat can be equivalently to reach the effectiveness obtained from the even lower pouring temperature without stirring.

Annular electromagnetic stirring——a new method for the production of semi-solid A357 aluminum alloy slurry

A new method for producing semisolid slurry, annular electromagnetic stirring （AEMS）, to refine and spheroidize grains was exploited. Experimental work was undertaken to investigate the effects of cooling rate, stirring power and stirring time on the solidification behavior of A357 alloy using A-EMS. It was found that increasing the cooling rate and stirring power gave rise to substantial grain refinement, which could be attributed to the increase of effective nucleation rate caused by the extremely uniform temperature and composition fields in the bulk liquid during the initial stage of solidification. Results showed that a fully grain refined spherical structure could be obtained using proper processing conditions within 10 s.

EFFECT OF GRAIN REFINING ON PRIMARYαPHASE IN SEMI-SOLID A356 ALLOY PREPARED BY LOW SUPERHEAT POURING AND SLIGHT ELECTROMAGNETIC STIRRING

The semi-solid slurry of A356 alloy, which is grain-refined by Al-Ti-B master alloy, is prepared by low superheat pouring and slight electromagnetic stirring. The effects of grain refining on the morphology and the grain size of the primary α phase in the slurry manufactured are researched. The results indicate that the slurry with particle-like and rosette-like primary α phases can be prepared by low superheat pouring and slight electromagnetic stirring from liquid A356 alloy grain-refined, in which the pouring temperature can be suitably raised. Compared with the A356 samples without grain refining, the grain size and particle morphology of primary α phase as well as the distribution of the grain with particle-like or rosette-like along radial in the ingot in A356 are markedly improved by grain refining.

Experimental studies and phase field modeling of microstructure evolution during solidification with electromagnetic stirring

Thixocasting requires manufacturing of billets with non-dendritic microstructure.Aluminum alloy A356 billets were produced by rheocasting in a mould placed inside a linear electromagnetic stirrer.Subsequent heat treatment was used to produce a transition from rosette to globular microstructure.The current and the duration of stirring were explored as control parameters.Simultaneous induction heating of the billet during stirring was quantified using experimentally determined thermal profiles.The effect of processing parameters on the dendrite fragmentation was discussed.Corresponding computational modeling of the process was performed using phase-field modeling of alloy solidification in order to gain insight into the process of morphological changes of a solid during this process.A non-isothermal alloy solidification model was used for simulations.The morphological evolution under such imposed thermal cycles was simulated and compared with experimentally determined one.Suitable scaling using the thermosolutal diffusion distances was used to overcome computational difficulties in quantitative comparison at system scale.The results were interpreted in the light of existing theories of microstructure refinement and globularisation.

Analysis of cracking phenomena in continuous casting of 1Cr13 stainless steel billets with final electromagnetic stirring

Solidification cracking that occurs during continuous casting of 1Cr13 stainless steel was investigated with and without final elec- tromagnetic stirring （F-EMS）. The results show that cracks initiates and propagates along the grain boundaries where the elements of carbon and sulfur are enriched. The final stirrer should be appropriately placed at a location that is 7.5 m away from the meniscus, and the appropri- ate thickness of the liquid core in the stirring zone is 50 ram. As a stirring current of 250 A is imposed, it can promote colurnnar-equiaxed transition, decrease the secondary dendrite arm spacing, and reduce the segregation of both carbon and sulfur. F-EMS can effectively de- crease the amount of cracks in 1Cr13 stainless steel.

Effect of electromagnetic stirring in mold on the macroscopic quality of high carbon steel billet

An industrial plant trial for optimizing the process parameters in a round billet continuous casting mold with electromagnetic stirring （M-EMS） was performed, in which the influences of stirring parameters with M-EMS on the solidification macrostructure of high carbon steel were investigated. The results show that the billet quality is not well controlled under the condition of working current and frequency with EMS, in which the subsurface crack of grade 1.0-2.0 ups to 38.09%, the central pipe of grade 1.0-1.5 reaches to 14.28%, and the central porosity of grade 1.5 is 14.29%. The parameters of current 260 A and frequency 8 Hz as the final optimum scheme has a remarkable effect for improving the macroscopic quality of billet, in which the subsurface crack, central pipe and skin blowhole are all disappeared, and the central porosity and carbon segregation are also well improved.

Numerical Simulation of Linear Electromagnetic Stirring in Secondary Cooling Region of Slab Caster

According to the theory of alternating magnetohydrodynamics and magnetic boundary renewal method,mathematical models were proposed for electromagnetic stirring in secondary cooling region( SEMS) of slab caster. The magnetic fields and flow fields of melt were simulated with SEMS. It's shown that the electromagnetic forces with inward and sidelong components produced by travel magnetic field at the wide faces of slab make the melt whirling in horizontal section,and the convection of the melt is strengthened obviously there. In addition,magnetic flux density attenuates from the edge to the center of slab,and the profile of the melt velocity along slab thickness in the center of the horizontal section takes a two-opposite-peak configuration. Ultimately,the stirring intensity and features are determined by the electromagnetic parameters,coil arrangement and stirring types.

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.

Effects of annular electromagnetic stirring processing parameters on semi-solid slurry production

A computational model coupling an electromagnetic model with a macroscopic heat and fluid flow model in semi-solid aluminum alloy slurry preparation by annular electromagnetic stirring(A-EMS) was developed.Effects of A-EMS processing parameters,such as stirring current,stirring frequency and stirring gap width,on macroscopic transport phenomena during the solidification were analyzed by commercial software ANSYS 10.0 with corresponding experimental verification.The results show that the magnetic flux density and the melt velocity increase and the temperature difference decreases as stirring gap width and stirring frequency decrease or the stirring current increases.The slurry with the fine and uniform globular grain structure can be gained by adjusting gap width,electromagnetic frequency and current,such as under the conditions of 10 mm of gap width,10 Hz of electromagnetic frequency and 50 A of current.The calculated results are in reasonably good agreement with the measured ones.

Preparation of CuCr alloys by thermit-reduction electromagnetic stirring

The influences of the additive CaF2, different molds, mold pre-heating temperature, electromagnetic stirring, and alloying elements on CuCr have been investigated respectively during the preparation of CuCr alloys by thermit-reduction electromagnetic stirring. The results indicate that the reasonable reactant mass ratio of CuO： Cr2O3：Al is 100：140：160; CaF2 can reduce the solidification point of slags to improve the metal separating efficiency from slags; the crystal particles become thinner because of the high cooling velocity in the metal mold; while casting in the graphite mold, the casting properties of CuCr improve with the increase of pre-heating temperature; the compact alloys are prepared at 500℃; electromagnetic stirring can prevent the growth of dendrite crystal into refine crystal particles, as well as homogenize Cu and Cr to improve the CuCr properties; the optimal stirring time is 7 min; when the alloying elements Ni and Co are added to the reactants, elements Cu and Cr can distribute evenly but the crystal particles become thick.

STUDY ON STRUCTURES OF Al-CuAl_2 EUTECTIC SOLIDIFIED UNDER ELECTROMAGNETIC STIRRING

An investigation on electromagnetically-stirred solidification of Al-CuAl2 eutectic system is presented in this paper. With electromagnetic stirring in solidification, structural transition from lamellar to rod-like eutectic has been found in the as-cast structures, and provided strong stirring is applied, proeutectic growth of α-Al phase is enhanced. Moreover, the interphase spacing of eutectic is clearly increased with melt flow intensified. Numerical computation of flow field is also presented, and the effect of stirring on structural formation is discussed.

STUDY OF ELECTROMAGNETIC STIRRING REFINING MICRO-STRUCTURES OF PIPE-LINE STEEL SAW DEPOSITS

The effects of electromagnetic stirring on the microstructures of pipe-linesteel SAW deposited metal were investigated. The results showed that electromagnetic stirringincreased the number density of inclusions with 0.2-0.6 mum in diameter and promoted the formationand refining of acicular ferrite within austenite grains. The low temperature toughness of depositedmetal was improved.