Low Frequency Electromagnetic Casting Research Articles

Microstructure and tensile properties of 5A90 Al–Mg–Li alloy containing minor Sc cast by low-frequency electromagnetic casting

The effects of low-frequency electromagnetic casting (LFEC) on the microstructure and tensile properties of 5A90 Al–Mg–Li alloy with and without minor Sc were investigated. In addition to minor Sc, the refined microstructures of the conventional direct chill cast (DCC) alloy and the microstructures of the as-cast alloy were refined further and more equiaxed grains formed in LFEC ingots with Sc. Higher density, smaller size, and more uniform distribution Al3(Sc, Zr) in the aged alloy with Sc induced by LFEC, which pins on grain boundaries, can effectively inhibit recrystallization. As a result, it had been a significant improvement in strength which was mainly due to the Orowan effect of Al3(Sc, Zr) dispersoids combined with grain refinement. The ultimate tensile strength of 565.4 MPa, yield strength of 475.3 MPa, and the corresponding elongation of 6.4% were obtained in the as-aged 5A90 alloy with 0.15 wt% Sc cast by LFEC at 10 Hz and 100 A.

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.

Low Frequency Electromagnetic Casting of 2195 Aluminum–Lithium Alloy and Its Effects on Microstructure and Mechanical Properties

In this study, the low frequency electromagnetic casting (LFEC) technology was adopted to fabricate 2195 Al–Li alloy. The microstructure and solid solubility of as-cast 2195 alloys, as well as the second phase precipitation and tensile properties after aging, were investiagated and compared with the counterpart direct chill casting 2195 alloy. Our results indicate that LFEC can significantly improve the microstructure and metallurgical quality of as-cast alloy, and increase the number density of θ′ (Al2Cu) and T1 (Al2CuLi) phases during aging treatment due to the enhanced solubilities of alloying elements. The tensile properties of 2195 aged alloy cast by LFEC were hence improved evidently.

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%.

Micro-Structure and Mechanical Properties of 2A97 Al-Li Alloy Cast by Low-Frequency Electromagnetic Casting

In this paper, the micro-structure and solid solubility of 2A97 aluminum-lithium alloy ingots prepared by conventional direct chill (DC) casting and low frequency electromagnetic casting (LFEC) as well as the density of precipitates and tensile properties of 2A97 alloy after T6 treatment were investigated. The results show that the low-frequency electromagnetic field during casting had a remarkable effect on the refinement of micro-structure and solid solubility of alloying elements within the grains, which is very helpful to obtain a large number of fine, uniformly-distributed T1 phases. The mechanical properties of 2A97 alloy prepared by low frequency electromagnetic casting after T6 treatment were improved by obtaining a larger number T1 phases.

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.

Heat transfer behavior of AZ80–1%Y alloy during low-frequency electromagnetic casting

Heat transfer behaviors of AZ80–1%Y alloy during low frequency electromagnetic casting (LFEC) and direct chilling casting were studied by in-situ temperature measurement. The results demonstrated that the low frequency electromagnetic field (EM) caused forced convection in the melt during LFEC. The forced convection led to uniform solidification velocity and temperature field. EM frequency, excitation current intensity and casting temperature could control the heat transfer behavior. The forced convection could improve the microstructure and degrade the difference in microstructure between the edge and center of billet. Appropriate parameters of low frequency EM for casting Mg alloy are 20 Hz of frequency and 60 A of electric current intensity.

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.

DC Casting of Large Sized Ingot of a High Strength 7xxx Alloy under the Influence of Electromagnetic Field

Hot tearing and cold cracks are major defects during direct chill (DC) casting of large sized ingots of high strength aluminium alloys. In order to solve these problems, based on a low frequency electromagnetic casting (LFEC) process, a new technology, electromagnetic casting with the application of an air blade (EMA) was developed. In the present work, this new technology was used to prepare large sized AA7055 aluminium alloy ingots and the effects of the low frequency electromagnetic field and the air blade on macro-physical fields, microstructure and cracking are studied by numerical and experimental methods. The results show that applying an electromagnetic field can modify the flow direction, increase the velocity of melt flow and homogenize the distribution of temperature in the sump. Applying an air blade can homogenize the distribution of temperature and decrease the stress and strain in the solidified ingot. Furthermore, the microstructure of the ingot is refined remarkably and cracking is eliminated by simultaneously applying the electromagnetic field and the air blade during DC casting.

Microstructure and RRA treatment of LFEC 7075 aluminum alloy extruded bars

The microstructures after casting and extruding, the mechanical properties and electrical conductivity after RRA treatment of conventional DC casting and low frequency electromagnetic casting (LFEC) 7075 aluminum alloy were investigated. The results showed that finer grains which distributed more homogeneously was obtained in LFEC ingots compared with those conventional DC ingots. The extruded bars of LFEC alloy kept its fine grain features of original as-cast structure. In the RRA treatment, with the extension of second aging time, the tensile strength and hardness of alloy decreased, but the electrical conductivity increased. Meanwhile, as the second aging temperature raised, the phase change rate in precipitation also increased. Under the same conditions, extruded bars of LFEC alloy had better performance than that of conventional DC cast alloy. The optimum RRA heat treatment process was 120 °C/24 h+180 °C/30 min+120 °C/24 h. The LFEC extruded bars acquired tensile strength 676.64 MPa, hardness 198.18, and electrical conductivity 35.7% IACS respectively, which were higher than that in the T6 temper, indicating that a notable RRA response takes place in LFEC extruded bars, whose second-step retrogression time was 30 min, and it was suitable for mass production.

Effect of DC Casting Processes on Microstructure of AlCu4.5Mn0.8 Alloy

The semi-solid billets of AlCu4.5Mn0.8 alloy were cast respectively by low frequency electromagnetic, low-superheated, and conventional direct chill casting. The effect of casting processes on microstructures was investigated. The results show that due to the effect of the low frequency electromagnetic field, the coarse dentritic microstructure is gradually broken up and turned into the homogeneous, fine rosette-shaped non-dentritic microstructures with the increase of electromagnetic frequency from 10 Hz to 30 Hz. When electromagnetic frequency is 30 Hz, the homogeneous, fine non-dentritic microstructure what is suitable for semi-solid reheating and thixo-forming could be obtained successfully.

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.

Examination of the Microstructure and Properties of Low-Frequency Electromagnetic Casting 6060 Aluminum Alloy Billets and Bars

Abstract This study investigated the advantages of using low-frequency electromagnetic casting (LFEC) process compared to conventional direct chill DC casting of aluminum alloy and considered possible energy savings. The obtained results have indicated that casting in low-frequency electromagnetic field offers a series of advantages regarding the quality of aluminum billet, such as smooth billet surface, uniform grain size on the cross section, finer macrostructure and balanced distribution of intermetallic phases in the alloy. This guarantees their good properties in further processing, i.e. pressing, drawing, anodizing, plasticization etc. If the material is properly prepared for melting and for the technological process of casting and if primary aluminum is used as the basic raw material, the 6xxx-series billets can be extruded with no or minor prior thermal homogenization. This is a significant argument for using low-frequency electromagnetic casting (LFEC) process, which allows for significant savings in energy and labor and simplifies the manufacturing process as well.

Microstructure and mechanical properties of low frequency electromagnetic casting 7075 aluminum alloy

This work explores the microstructure of low frequency electromagnetic casting (LFEC) 7075 aluminum alloys and investigates the effect of heat treatment process on its mechanical properties via the mechanical properties test, X-ray diffraction and transmission electron microscopy. It was found that the grains of LFEC ingot were finer and more evenly distributed than that of the conventional direct chill cast (DC) ingots. The microstructure of LFEC ingot extruded kept their original as-cast structure with small and fine grains. With the same extrusion ratio, the average grain diameters of LFEC and conventional DC extruded were about 10 and 20 μm, respectively. LFEC extruded also had a better aging property, since the regime of T6 treatment peak value aging was at 120 ◦C for 24 h, the tensile strength and hardness (HV) of the LFEC extruded were 673.50 MPa and 194.62, respectively, which were all higher than those of the conventional DC extruded, indicating that the process regime can be applied in the industrial production.

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.