The relationships between electromagnetic frequency, microstructure and mechanical properties of continuous casting aluminum alloys were studied in this paper. EN AW 2024 and EN AW 2007 aluminum alloys ingots were produced by electromagnetic continuous casting process. The microstructure and mechanical properties of as cast ingots were examined. The results showed that electromagnetic field, especially low frequency electromagnetic field, greatly influenced the microstructure and mechanical properties of as cast ingots. The significant energy savings and product quality can be achieved by the application of a proper frequency.U radu je prikazan utjecaj frekvencije na mikrostrukturu i mehanička svojstva Al legura dobijenih kontinuiranim elektromagnetnim postupkom ljevanja. Ispitivanja su obavljena sa dvije legure EN AW 2024 i EN AW 2007. Mikrostrukturna i mehanička karakterizacija urađena je na uzorcima u ljevanom stanju. Rezultati istraživanja pokazuju da elektromagnetno polje, posebno polje niže frekvencije, utječe na mikrostrukturu i mehanička svojstva ljevanih ingota. Na osnovu dobijenih rezultata može se zaključiti da se primjenom elektromagnetnog polja odgovarajuće frekvencije može postići značajna ušteda energije kao i poboljšanje kvaliteta dobijenih ingota

A. Patarić

M. Mihailović

Z. Gulišija

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Z. GULI[IJA, A. PATARI], M. MIHAILOVI]THE POSSIBILITY OF INCREASING PRODUCTION EFFICIENCYOF AL ALLOYS APPLYING ELECTROMAGNETIC FIELDReceived – Prispjelo: 2009-08-11Accepted – Prihva}eno: 2010-10-20Preliminary note – Prethodno priop}enjeINTRODUCTIONAluminum alloys of high strength have diverse andwide application in almost all fields of industry. Due totheir specific properties, mainly the strength to mass ra-tio, even though their production price is higher com-pared to iron alloys, these alloys took up a significantposition at the world market. Alloys applied in this in-vestigation are EN AW 2007 (AlCu4PbMg) and ENAW 2024 (AlCu4Mg1Mn). They are heat treatable al-loys and are intending for plastic processing.They belong to high strength group of alloys withwide application in almost all fields of industry. Theyhave long production and processing time, because theyinvolve a series of technological operations (modifica-tion, casting, homo-genization, pressing forming andthermal treatment). The homogenization is a long-last-ing and expensive process, because of high consump-tion of electrical energy. The main idea is shorteningthis process for increasing production process. It is wellknow that conventional horizontal or vertical continu-ous casting process due to unbalanced strengtheningconditions, leads to appearance of many defects 1-3.These are inhomogeneous microstructures, porosity, hotcracks, non-uniform grain size and crystal segregationin the ingot. All this leads to deterioration of mechanicalproperties of strength and toughness first of all. Theelectromagnetic casting of aluminum alloys is of greatinterest in metallurgical industry and intensive study hasbeen made in recent years, because it presents the abilityof improving product quality which could never beenachieved by conventional casting process. In this newprocess, the induction coil surrounds the ingot mold, analternating current is applied, thus the coil generates atime varying magnetic field and the melt can be induc-tively stirred 4, 5. In that way, the more balanced tem-perature field is established. The experiment shows thatthis process is an efficient dynamic method of grain re-finement, surface quality can be improved and the thick-ness of the segregation layer can be also reduced be-cause of the contact line between the metal and the moldcan be adjusted. Moreover, this method can be put intoindustrial practice relatively easily.EXPERIMENTALThe chemical composition of used alloys EN AW2007 (AlCu4PbMg) and EN AW 2024 (AlCu4Mg1Mn)is shown in Table 1.For melting alloys, induction furnace of medium fre-quency with capacity of 100 kg was used. The both in-gots, of alloy 2007, with diameter  50 mm and of alloyMETALURGIJA 50 (2011) 4, 253-256 253The relationships between electromagnetic frequency, microstructure and mechanical properties of continuo-us casting aluminum alloys were studied in this paper. EN AW 2024 and EN AW 2007 aluminum alloys ingotswere produced by electromagnetic continuous casting process. The microstructure and mechanical propertiesof as cast ingots were examined. The results showed that electromagnetic field, especially low frequency elec-tromagnetic field, greatly influenced the microstructure and mechanical properties of as cast ingots. The signi-ficant energy savings and product quality can be achieved by the application of a proper frequency.Key words: Al alloy, electromagnetic field, castingMogu}nost pove}anja efikasnosti proizvodnje Al legura primjenom elektromagnetnog polja. Uradu je prikazan utjecaj frekvencije na mikrostrukturu i mehani~ka svojstva Al legura dobijenih kontinuiranimelektromagnetnim postupkom ljevanja. Ispitivanja su obavljena sa dvije legure EN AW 2024 i EN AW 2007.Mikrostrukturna i mehani~ka karakterizacija ura|ena je na uzorcima u ljevanom stanju. Rezultati istra`ivanjapokazuju da elektromagnetno polje, posebno polje ni`e frekvencije, utje~e na mikrostrukturu i mehani~ka svoj-stva ljevanih ingota. Na osnovu dobijenih rezultata mo`e se zaklju~iti da se primjenom elektromagnetnog poljaodgovaraju}e frekvencije mo`e posti}i zna~ajna u{teda energije kao i pobolj{anje kvaliteta dobijenih ingota.Klju~ne rije~i: Al legura, elektromagnetno polje, ljevanjeISSN 0543-5846METABK 50(4) 253-256 (2011)UDC – UDK 621.74.04:669.715:538.69=111Z. Guli{ija, A. Patari}, M. Mihailovi}, Institute for Technology of Nu-clear and Other Raw Materials, Belgrade, Serbia2024, with diameter  60 mm were obtained by hori-zontal continual casting with pulse draw-out. At the bot-tom of the furnace there is a drainpipe with graphitecrystallizer that is intensively cooled with water. Theelectromagnetic field is present around the crystallizeritself, Figure 1.The temperature of casting was 710 – 720 °C and av-erage casting speed was 1,5 mm/s. The operating param-eters, during the casting of ingots, were strictly con-trolled and defined by various values of current (A), fre-quency (Hz) and strength of electromagnetic field (At).The number of turns in the coil was N=40. Table 2shows some of operating parameters of casting.Table 2 Operating parameters upon casting of samplesSamplemarkAlloyFrequency/HzNumber ofturns /N1 2007 0 402 2024 50 403 2024 30 404 2007 1 100 405 2007 1 830 40Frequencies were selected in broad diapason rangingfrom 1 830 to 30 Hz. There are literature data only forlow frequencies ( 100 Hz). Since we had the opportu-nity to test the influence of high frequencies as well,such tests were also performed on the alloy 2007, simi-lar with the alloy which is the main subject of our inter-est, i.e. 2024. The sample 1 was casted without the pres-ence of electromagnetic field to enable the observationof field effect on mechanical properties and micro-structure with other samples.Before the mechanical characterization was done thecomplete microstructure assessment was carried out.The microstructure parameters describe the structuredispersivity and directly affect the mechanical proper-ties of the alloy. The microstructure was examined on across section of a sample after the usual metallographicpreparation and etching in Keller’s reagent (revealingmorphology of Al segregation-solid solution andinter-metallic phase) and anode oxidation with Barker’sreagent (revealing size and shape of the grain in pres-ence of dendrite segregation). For the quantitativemicrostructure analysis the image analysis device LeicaQ500MC was used. Dendrite arm spacing (DAS),interdendritic space width (LIMF), where inter-metallicphases and eutecticum were separated, as well as theirvolume fraction, were acquired using linear method,through the measuring of total length of the line seg-ments belonging to each phase and calculating theamount of intersects with phase boundaries. These pa-rameters are the consequence of the solidification condi-tions.RESULTS AND DISCUSSIONThe microstructure obviously has shown that Al seg-regation from the solid solution resulted in celluar/den-dritic morphology, 6,7. Upon that, the structures ofsample 1, without the electromagnetic field effect, andsamples 4 and 5, with electromagnetic field of high fre-quency, are more dendritic compared to the samples 2and 3, which are casted with the presence of low-fre-quency electromagnetic field. It is obvious that the ap-plication of high frequency has no effect on the im-provement of microstructure. Quite oppositely, at 1 830Hz the structure was rougher compared to one obtainedwithout the influence of electromagnetic field. On theother hand, the regions of extracted inter-metallic phase,in the form of eutecticum or individually, become finerby the introduction of electromagnetic field and by de-creasing of frequency, (from 50 Hz in sample 2 to 30 Hzin sample 3). The decrease of microstructural parame-ters DAS and LIMF, observed in samples 2 to 3, was con-firmed by the analysis of cumulative distribution curves.However, the effect of electromagnetical field on pa-rameter DAS is greater compared to LIMF. By detailedanalysis of samples, the presence of interdentritic typewas established, as can be seen in Figure 2.It is determined that the porosity of interdendritictype is reduced from sample 2 (50 Hz) towards the sam-ple 3 (30 Hz), i.e. with the decrease of electromagneticfield frequency. It is also found that the grain size is sig-nificantly reduced from the sample 2 to the sample 3.This is important because the less amount of porosity254 METALURGIJA 50 (2011) 4, 253-256Z. GULI[IJA et al: THE POSSIBILITY OF INCREASING PRODUCTION EFFICIENCY OF AL ALLOYS APPLYING...Table 1 The chemical composition of used alloys / wt. %Wt./%AlloySi Fe Cu Mn Mg Pb2 007 0,3 0,3 3,9 0,8 0,9 1,12 024 0,1 0,2 4,1 0,6 1,2 -Figure 1 Schematic illustration of the electromagneticprocessand the smaller grain contributes the better quality of in-gots and thus to mechanical properties.Since it was concluded that there are no positive ef-fects of high frequency to the obtained microstructure, thefurther investigation included only the mechanical prop-erties of samples obtained by application the frequency of50 Hz and 30 Hz, and also of the one obtained without theinfluence of electromagnetic field from the same alloyEN AW 2024. For mechanical testing, the Zwick/Roell Z100 device was used. The samples for this tensile testingwere prepared according to JUS C.A4.002 and for thehardness according to JUS C.A4.103.The values of mechanical properties are given in Ta-ble 3.Table 3 Mechanical properties of alloy 2024 ingotsSamplemarkRp0.2/MpaRm/MpaA/%HB5/25/302 198,1 243,2 1,2 93,53 246,6 274,2 0,7 107,0The stress-strain curves can be seen in Figure 4.On the basis of previous microstructural analysis,such trend of change of alloy resistance properties, i.e.their increase, could have been expected. However, thedecrease of plasticity for specimen 3 can be interpretedby the appearance of rough continually extracted parti-cles of IMF, Figure 5, in relation to specimen 2. Thiscontinually grid of IMF particles has detrimental effecton mechanical properties, especially on plasticity. Fur-thermore, one should bear in the mind the fact that thevalues of mechanical properties for specimens of alloy2024 casted without the influence of electromagneticfield were: Rp0.2= 162,5 MPa, Rm=179,9 MPa andA=0,49 %. i.e. they were the lowest.This means that by the good combination of castingoperating parameters, a priori frequency, the increase ofresistance properties can be achieved, and also the plas-ticity increase by the use of microstructure control. Thisis significant because the good mechanical properties, inthe initial stage of production process, mean a great sav-ings in all the following production stages.CONCLUSIONThe investigations results of alloy EN AW 2024 andEN AW 2007 ingots obtained with different operatingconditions, with or without the presence of electromag-netic field, clearly show its effect on the microstructureand mechanical characteristics. It has been proved thatonly the application of low frequency electromagneticMETALURGIJA 50 (2011) 4, 253-256 255Z. GULI[IJA et al: THE POSSIBILITY OF INCREASING PRODUCTION EFFICIENCY OF AL ALLOYS APPLYING...(a) sample 2(a) sample-2 (b) sample-3Figure 2 The porosity of interdentritic type(a) sample-2 (b) sample-3Figure 3 The grain size(b) sample 3Figure 4 Stress-strain curvesFigure 5 Interdendrite extracted inter-metallic phasefield ( 50 Hz) has the positive effects, which obviouslychange strengthening conditions. Namely, when the fre-quency decreases (from 50 Hz in sample 2 to 30 Hz insample 3), the DAS and grain size decrease as well, thatis noticeable through the finer microstructure and itsuniformity throughout the cross-section. It is also deter-mined that the porosity of interdendritic type is reducedfrom sample 2 (50 Hz) towards the sample 3 (30 Hz). Allof this contributes the better mechanical properties andthus the quality of ingots. The better mechanical proper-ties in the initial stage of production process provide lessconsumption of electrical energy. Obtained results indi-cate that some steps in current technological process canbe avoided, namely better surface quality contributes thesurface machine processing elimination. Besides, thefiner microstructure contributes the shortening or elimi-nating of homogenization process, one of the longestand the most expensive processes during the aluminumalloys production. The literature data show that the in-tensity of electromagnetic field has also great effect onmicrostructural and mechanical properties, 8,9. So, thefurther work in this area should be focused towards theintensity of electromagnetic field and encompass theother aluminum alloys which are aimed for forging.AcknowledgementThe Authors wish to acknowledge the financial supportfrom the Ministry of Science and Technological Devel-opment of the Republic Serbia through the Project 34002.REFERENCES1 S. W. Kim and H. Hao, Mettal. Mater. Trans. A. 34A(2003), 1537 – 1543.2 C. Zhiqiang, J. Fei, Z. Xingguo, H. Hai, J. Junze, Mater. Sci.Eng. A 327 (2002), 133-137.3 Z. Zhao, J. Cui, J. Dong, Z. Eang, B. Zhang, J. Alloys andCompounds (2005), 587-593.4 B. Zhang, J. Cui, Mater. Let. 57(2003) 1701-1711.5 B. Zhang, J. Cui, Mater. Sci. Eng. A355 (25) (2003)325-330.6 A. Patari}, Z. Guli{ija, S. Markovi}, Practical Metallo-graphy, 44 (2007) 6, 290-298.7 A. Patari}, Z. Gulisija, B. Jordovi}, Metalurgija, 47 (2008)4, 343-346.8 J. Dong, Z. Cui, T. Lui, the Chinese Journal of NonferrousMetals 13 (2003) 6, 1494.9 J. C. Li, Y. L. Ma, B. F. Wang, Special Casting & Nonferro-us Alloy 25 (2005) 3,133.Note: The responsible for English language is the lecturer from Institute(ITNORM), Belgrade, Serbia.256 METALURGIJA 50 (2011) 4, 253-256Z. GULI[IJA et al: THE POSSIBILITY OF INCREASING PRODUCTION EFFICIENCY OF AL ALLOYS APPLYING...

Mogućnost povećanja efikasnosti proizvodnje Al legura primjenom elektromagnetnog polja

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