Low Frequency Electromagnetic Casting Process Research Articles

Effect of Low-Frequency Electromagnetic Casting on Micro-Structure and Macro-Segregation of 5A90 Alloy Ingots.

The effect of low-frequency electromagnetic fields on the micro-structure and macro-segregation of 5A90 alloy ingots during the semi-continuous casting process were quantitatively investigated. The ingots of a 5A90 alloy with a diameter 170 mm were produced by the conventional direct chill casting (DCC) process and low-frequency electromagnetic casting (LFEC) with 10 Hz/100 A. The results showed that LFEC can substantially refine the micro-structure and shorten the width of the columnar grain area of an ingot. The refinement effect came with the relieving of grain boundary segregation and an improvement in the macro-segregation of the ingot. Compared with the traditional DCC process, the tensile properties of the aged alloy prepared by the LFEC process were improved due to the effects of the increase in solid solubility and the strengthening of the grain refinement, so that the stability of the tensile properties was also improved. Meanwhile, the rate of yield increased by 2.3% with a decrease in the peeling thickness of the ingot.

Study on micro-structure, solid solubility and tensile properties of 5A90 Al–Li alloy cast by low-frequency electromagnetic casting processing

In this paper, the low-frequency electromagnetic casting (LFEC) processing was introduced as an efficient pollution-free casting technique, and how it influenced the micro-structure and mechanical properties of 5A90 Al–Li alloy was investigated. The mechanical properties of the alloy had a close connection with the casting metallurgical quality and the precipitation phases. Compared to the conventional direct chill casting (DCC), the LFEC could promote the precipitate of the δ′ (Al3Li)/β′ (Al3Zr) and reduce the width of PFZ, which enhanced the effect of the precipitation strengthen and alleviated the strain localization. Meanwhile, the micro-structure of the ingot was refined significantly and the metallurgical quality was improved after LFEC treatment due to the modification of the flow and temperature field of the sump that caused by the application of low-frequency electromagnetic field. Maximum yield strength and ultimate tensile strength of as-aged alloy cast by LFEC with 150 A/15 Hz could reach 371.85 MPa and 495.5 MPa, while elongation remained at 9.82%.

Effects of electromagnetic field on physical behaviors during low-frequency electromagnetic casting of Mg alloy AZ31

A numerical model was established for the simulation of the multiple physics fields during the low-frequency electromagnetic casting (LFEC) process of AZ31 alloy by using ANSYS (FE commercial package) and FLUENT (finite volume package). The electromagnetic field was calculated in the former and the latter was aimed at analyzing the fluid flow driven by magnetic, heat transfer and solidification. Overall physical parameters, including magnetic flux density, Lorentz force, flowing velocity, temperature field and liquid cave feature were discussed. Results show that the electromagnetic field can significantly affect the flow field and temperature field of the melt during the LFEC process of AZ31 alloy by inducing the effect of Lorentz force. Different electromagnetic frequencies have different effects. In the experimental frequency range of 5 ∼ 35 Hz, a higher frequency can intensify the flowing of the melt near the cooled wall of the crystallizer, resulting in an increase in heat transfer intensity and further a decrease in liquid cavity depth.

Effect of Fe on microstructures and mechanical properties of an Al–Mg–Si–Cu–Cr–Zr alloy prepared by low frequency electromagnetic casting

The effects of different Fe contents (0.168, 0.356 and 0.601 wt%) on microstructures and mechanical properties of the Al–1.6Mg–1.2Si–1.1Cu–0.15Cr–0.15Zr (all in wt%) alloys prepared by low frequency electromagnetic casting process were investigated in the process of solidification, hot extrusion, solid solution and aging treatments. The results show that the increase of Fe content promotes the formation of feathery grains in the process of solidification and the precipitation of another important strengthening phase Q′ with small size. Additionally, it also results in no recrystallization even after solid solution at a high temperature of 550 °C, which is because of the increase number of elliptical shaped and fine DO22-Al3Zr dispersoids (∼70 nm long and ∼35 nm wide) and the spherical or elliptical shaped Fe-containing phases. When Fe content of the alloy increases to 0.356 wt%, both the ultimate tensile strength and yield strength of the alloy-T6 increase by more than 60 MPa and with little cost of ductility.

The effect of low frequency-electromagnetic field on temperature field and microstructure during magnesium slab casting process

The effect of low-frequency electromagnetic field (LFEF) on temperature pattern and microstructure on both symmetry planes was investigated during the semi-continuous direct chilling (DC) casting process of magnesium slab. The distribution characteristics of magnetic flux density (B) and time average electromagnetic volume force density (F) were calculated. The weak value of F was found near the slab corner, which was clearly distinguished from the distribution of B. According to the temperature measurement results, LFEF made the mushy region much flatter than that of conventional DC casting and it was much more obvious in the thickness direction. Compared with conventional DC casting, the low-frequency electromagnetic casting (LFEC) process could decrease the average temperature gradient between the centre and border in the mushy zone. The microstructures on both symmetry planes were also refined at different levels during the LFEC process.

Effect of electromagnetic field on microstructure and macrosegregation of flat ingot of 2524 aluminium alloy

Low frequency electromagnetic casting (LFEC) process with the application of an induction coil outside the conventional direct chill (DC) casting mould was used to prepare the flat ingot of 2524 alloy and the effect of electromagnetic field on the microstructure and macrosegregation of this alloy was systematically studied. The results show that the flat ingot prepared by the LFEC process has a finer and more uniform as-cast microstructure and the grain morphology is transformed from dendrite and rosette-like to equiaxed structure. The LFEC process also shows a significant effect on macrosegregation, and with the application of electromagnetic field during casting process, the segregation in the centre of the ingot is obviously reduced. The mechanism of these effects was also discussed.

Effect of Zr on microstructures and mechanical properties of an Al[sbnd]Mg[sbnd]Si[sbnd]Cu[sbnd]Cr alloy prepared by low frequency electromagnetic casting

The Al1.6Mg1.2Si1.1Cu0.15Cr (all in wt. %) alloys with and without Zr addition prepared by low frequency electromagnetic casting process were investigated by using the optical microscope, scanning electron microscope and transmission electron microscope equipped with energy dispersive analytical X-ray. The effects of Al3Zr phases on the microstructures and mechanical properties during solidification, homogenization, hot extrusion and solid solution were studied. The results show that Al3Zr phases reduce the grain size by ~29% and promote the formation of an equiaxed grain structure during solidification. Numerous spherical Al3Zr dispersoids with 35–60nm in diameters precipitate during homogenization, and these fine dispersoids change little during subsequent hot extrusion and solid solution. Adding 0.15wt. % Zr results in no recrystallization after hot extrusion and partial recrystallization after solid solution, while the recrystallized grain size is 400–550μm in extrusion direction in the Zr-free alloy. In addition, adding 0.15wt. % Zr can obviously promote Q′ phase precipitation, while the β″ phases are predominant in the alloy without Zr. Adding 0.15wt. % Zr, the ultimate tensile strength of the T6 treated alloy increases by 45MPa, while the elongation remains about 16.7%.

The Magnetic Field Interference in Dual-Ingot Low Frequency Electromagnetic Continuous Casting

The magnetic field interference was studied by numerical simulation and experimental examination during dual-ingot low-frequency electromagnetic casting process. By using ANSYS software package to mesh and compute, the magnetic field distribution of semi-continuous casting mold region was simulated. The calculated results were verified with the experimental ones and the effects of current direction, shield, silicon sheet and the coil distance on the distribution of magnetic field and ingot were observed. The result indicated that: regardless of current direction, the magnetic field interference among coils appears and the magnetic flux density weakens in the neighbor part of coils. When the current direction of adjacent coils is opposite, the magnetic intensity in ingots is stronger than that of in the same direction. As the distance between coils increases, the magnetic field reduction generated by interference decreases. The magnetic field interference can be alleviated by setting silicon steel sheets or shield.

Effect of Casting Temperature on the Microstructure of Al-Zn-Mg-Cu Aluminium Alloy Billets Prepared by LFEC Process

In order to understand the effect of casting temperature on the low frequency electromagnetic casting process, 200mm billets of an Al-Zn-Mg-Cu alloy were produced, the microstructure was analyzed and the temperature field was measured during the casting process. The experimental results showed that low frequency electromagnetic casting process has an evident grain refining effect on aluminum alloy and casting temperature is not a sensitive parameter for this process, which can tolerate a large range of casting temperature. In the range of 710 to 750 °C, casting temperature does not show significant effect on the microstructure.

Effects of Electromagnetic Field and Lubricate Condition on the Surface Quality of Aluminum Alloy Billet during LFEC Processing

The microstructures of the aluminum billets could be improved markedly by low-frequency electro-magnetic casting (LFEC) processing. In fact, the low-frequency electromagnetic field (LFEF) also has favorite effect on the surface quality of billet. However, few public reports on the surface quality of LFEC aluminum billets could be found. Therefore, a new crystallizer together with a kind of lubricant was designed aiming at lowing surface turning quantity, and the effects of casting velocity, electromagnetic condition and lubrication on the surface quality of aluminum billets were investigated. The results indicate that LFEF together with the lubricate condition would be responsible for the surface quality of the billets, and the high surface quality billets could be achieved by optimizing the casting conditions.

Mechanism of grain refinement of an Al–Zn–Mg–Cu alloy prepared by low-frequency electromagnetic casting

Low-frequency electromagnetic casting (LFEC) process had been developed and is being used for the past several years with the application of an induction coil placed outside the conventional direct chill (DC) casting mould. It has been demonstrated that the LFEC process has a significant grain refining effect on aluminium alloys. In the present study, temperature measurement and direct quenching from liquid and/or semi-solid were carried out to study the temperature field during casting process and to understand the mechanism of the grain-refining effect of the LFEC process. The experimental results showed that in contrast to the conventional DC casting process, the liquid melt from the launder, during the LFEC process, is cooled with very high cooling rate directly to 3–6 °C below the liquidus, and the temperature field of the entire melt in the mould, and the hot top is quite uniform, which results in the enhanced heterogeneous nucleation and improved survival rate of the nuclei. This is believed to be the main reason why the LFEC process can significantly refine the grain size of aluminium alloys.

Preparing Large Sized Billet of High Strength Aluminum Alloy with the Application of Low Frequency Electromagnetic Field

Grain refinement is quite important for producing 7050 alloy billet especially in large scale. Low frequency electromagnetic casting (LFEC) process was used to make 7050 aluminum alloy Φ500 mm billets and study the effect of electromagnetic field on the microstructure. The sound Φ500 mm billets of 7050 alloys without any grain refiner can be successfully prepared by the LFEC process. The results show that low frequency electromagnetic field has a significant grain refining effect on 7050 alloy and can effectively eliminate feather grain structure. The microstructures of LFEC ingot from the border to the center of the cross section are all equiaxed grains and are finer and more uniform than that of conventional direct chill (DC) cast billets. The LFEC process also shows a strong power to eliminate hot tearing during casting large sized billet of high strength aluminium alloy.

Grain Refinement of Direct Chill Cast 7050 Aluminium Alloy with Low Frequency Electromagnetic Field

Low frequency electromagnetic casting (LFEC) process was used to make 7050 aluminum alloy 162mm ingots and study its effect on the as-cast microstructure. Effects of electromagnetic field parameters such as frequency and current intensity on microstructures were systemically investigated. The results showed that LFEC has a significant grain refining effect on 7050 alloy. The microstructures of LFEC ingot from the border to the center of the cross section are all equiaxed or nearly equiaxed grains which are much finer and more uniform than those of DC cast ingot. It was also found that electromagnetic field frequency and current intensity play important roles on the microstructure refinement. The discussion was mainly focused on the mechanism of grain refinement by LFEC process.

Production of super-high strength aluminum alloy billets by low frequency electromagnetic casting

The effects of low frequency electromagnetic field on the macro-physical fields in the semi-continuous casting process of aluminum alloys and the microstructure and crack in the billets were studied and analyzed by the numerical and experimental methods. Comparison of the results for the macro-physical fields in the low frequency electromagnetic casting (LFEC) process with the conventional DC casting process indicates the following characters due to the application of electromagnetic field: an entirely changed direction and remarkably increased velocity of melt flow; a uniform distribution and a decreased gradient of temperature; elevated isothermal lines; a reduced sump depth; decreased stress and plastic deformation. Further, the microstructure of the billets is refined remarkably and the crack in the billets is eliminated in LFEC process because of modification of the macro-physical fields induced by the application of low frequency electromagnetic field.

Effects of the Low Frequency Electromagnetic Field on the Centerline Macrosegregation of 7075 Aluminum Ingots

The effects of the low frequency electromagnetic field on the macrosegregation of the 7075 aluminum ingots were investigated. The 7075 aluminum ingots with the diameter of 200 mm were prepared by the conventional direct chill casting and the low frequency electromagnetic field casting (LFEC) processes, respectively. The temperature during casting at steady state was measured, and the mushy region was observed from the temperature contour. The concentrations of the alloying elements were measured by the spectrograph. It was found that the transition region was broadened, but the mushy zone became narrower with presence of the low frequency electromagnetic field. The centerline macrosegregation of the ingots was alleviated by the low frequency electromagnetic casting process.

Effects of Electromagnetic Parameters on the Process of Low Frequency Electromagnetic Hot-Top Casting of Aluminium Alloy

During the low frequency electromagnetic casting process, the electromagnetic parameter plays an important role among the casting parameters. In this work, effects of electromagnetic parameters on the electromagnetic field and body force are analyzed by constructing a two-dimensional finite element model and using ANSYS software which is a kind of commercial FEM analysis software. The results show that the current frequency mainly influences the distribution of electromagnetic body force, the current intensity determines the intensity of electromagnetic body force, and the current frequency and intensity should be matched during the low frequency electromagnetic casting process.

Research on Heat Transfer during LFEC Processing by <i>In Situ</i> Temperature Measurement

Low-frequency electromagnetic casting (LFEC) processing could improve not only the metallurgical quality of magnesium billet including refining grain size, reducing regional microstructural difference and lightening segregation, but also its surface quality due to the effect of applied electromagnetic field according to the results by microstructure observation and the numerical simulation. In this research in-situ temperature measurement was carried out in LFEC processing in order to investigate heat transfer behavior of billet during solidification. The effects of the electromagnetic conditions (frequency and the intensity) together with the casting temperature on the sump and the mushy zone were investigated in detail. The results indicate that all the casting conditions affect the temperature field of magnesium billet markedly during solidification. Electromagnetic field could decrease not only the sump depth but also the difference of regional temperature field along the solidification direction leading to much more uniform cooling rate.

DC casting of light alloys under magnetic fields

The working principle of LFEC(Low frequency electromagnetic casting) process developed in Northeastern University, China was introduced and the metallurgical results of LFEC were discussed according to the casting practices. The low frequency field around the mold produces Lorenz force, which can be divided into two parts: one is the potential force which will be balanced by a pressure gradient of the liquid and results in the formation of a convex surface meniscus and improves the surface quality; the other is the rotary force which stirs the liquid in the mold to refine the microstructures and homogenize the distribution of alloying elements. LFEC can refine microstructures remarkably, improve surface quality of the ingots, depress macrosegregation and eliminate cracks. Some new technologies, such as horizontal direct chill casting under low-frequency electromagnetic field (HLEC), DC casting of hollow billets under electromagnetic fields (HBEC), electromagnetic modifying of hypereutectic Al-Si alloys(EMM), air film casting under static magnetic field (AFCM), and multi-ingots casting under low-frequency magnetic field (MLFEC) were developed based on LFEC.

Effects of electromagnetic field and lubricate condition on the surface quality of magnesium alloy billet during LFEC processing

The microstructures of the magnesium billets could be improved markedly by low-frequency electromagnetic casting (LFEC) processing. In fact, the low-frequency electromagnetic field (LFEF) also has favorite effect on the surface quality of billet. However, few public reports on the surface quality of LFEC magnesium billets could be found. Therefore, a new crystallizer with a metal internal sleeve together with a kind of lubricant was designed aiming at lowing surface turning quantity, and the effects of casting velocity, electromagnetic condition and lubrication on the surface quality of magnesium billets were investigated. The results indicate that LFEF together with the lubricate condition would be responsible for the surface quality of the billets, and the high surface quality billets could be achieved by optimizing the casting conditions.

Study on the sump and temperature field during low frequency electromagnetic casting a superhigh strength Al–Zn–Mg–Cu alloy

Abstract The effects of low frequency electromagnetic field on the sump depth and temperature field of a molten aluminum alloy (Al–Zn–Mg–Cu) were investigated by temperature measurement method. The results showed that during low frequency electromagnetic casting (LFEC) process the temperature field of the whole melt in the hot top is very uniform, and about 6 °C lower than liquidus temperature, which is very helpful to obtain uniform and fine microstructures. It was considered that LFEC process is like a kind of liquidus or near liquidus semi-continuous casting. It was also found that the sump depth during LFEC process is shallower than that of conventional direct chill (DC) casting process.