Naslov (srp)

Uticaj elektromagnetnog polja tokom livenja na karakteristike odlivaka aluminijumskih legura

Autor

Patarić, Aleksandra. 1971-

Doprinosi

Jordović, Branka. 1946-
Maričić, Aleksa. 1947-
Mitrović1962-, Nebojša. 1962-
Gulišija, Zvonko. 1952-
Stefanović, Milentije, 1951-

Opis (srp)

Elektromagnetni postupak livenja zasniva se na teoriji metalurških procesa i magnetohidrodinamici. Prilikom livenja u prisustvu elektromagnetnog polja naizmenična struja generiše vremenski promenljivo mognetno polje u istopljenoj masi što povećava indukovanu struju u rastopu. Rastop metala je pod uticajem elektromagnetne sile koja je prouzrokovana interakcijom indukovane struje i magnetnog polja. Elektromagnetna sila izaziva veći protok fluida, prinudnu konvekciju, ravnomernije temperaturno polje i slabiji uticaj gravitacije. Na ovaj način se menjaju uslovi očvršćavanja. Dobijeni odlivci su kvalitetniji, struktura je finija i uniformnija po preseku. Zbog smanjenog kontaktnog pritiska, (što je takođe posledica delovanja elektromagnetnog polja) između kalupa i metala, kvalitet površine je poboljšan tako da nije potrebna veća dodatna mašinska obrada. U svetu postoje određena istraživanja u oblasti elektromagnetnog postupka livenja, ali je malo pažnje posvećeno karakterizaciji mikrostrukture i mehaničkih svojstava tako dobijenih odlivaka. Ovaj rad treba da doprinese boljem poznavanju uticaja elektromagnetnog polja na dobijenu mikrostrukturu (morfologiju, veličinu zrna, raspodelu i udeo dobijenih faza) i ostale karakteristike dobijenih odlivaka. Izabrana legura EN AW 7075 ima široku primenu u industriji, termički je obradiva i namenjena je za plastičnu preradu odnosno kovanje. Proizvodnja ove legure je dugotrajna i skupa, a prate je nedostaci tipa poroznosti, toplih pukotina i neujednačenosti u veličini zrna. Ove metalurške greške utiču na pogoršanje mehaničkih svojstava i kvaliteta dobijenih odlivaka. U cilju smanjenja ovih grešaka još u livenom stanju neophodno je primeniti odgovarajući postupak livenja sa optimalnim radnim parametrima. Da bi se ispitao uticaj elektromagnetnog polja prilikom livenja upoređeni su uzorci odliveni bez dejstva polja i pod dejstvom polja različite frekvencije 10, 15, 20 i 30 Hz. Rezultati ispitivanja mikrostrukture i mehaničkih svojstava pokazuju da je primenom elektromagnetnog polja moguće dobiti finiju i homogeniju mikrostrukturu, a samim tim i bolja mehanička svojstva. Dobijeni rezultati SEM/EDX, DTA analize kao i rezultati merenja elektroprovodljivosti i određivanja hemijske segregacije su prikazani i upoređeni. Primena matematičkih modela u obradi rezultata i numerička simulacija procesa toplog kovanja su urađeni prateći svetske trendove, a njihova praktična primena ima za cilj uštedu energije, smanjenje škarta i potrošnju sirovina Dobijeni rezultati se mogu koristiti za proširenje baza podataka primenjenih modela. Ova doktorska disertacija je rezultat istraživanja u okviru projekta „Razvoj tehnoloških postupaka livenja pod uticajem elektromagnetnog polja i tehnologija plastične prerade u toplom stanju eetvorokomponentnih legura Al-Zn za specijalne namene“, TR 34002, čiji je rukovodilac prof. dr Zvonko Gulišija, naučni savetnik, a koji finansira Ministarstvo prosvete, nauke i tehnološkog razvoja Republike Srbije u okviru programa tehnološkog razvoja u periodu od 01. 01.2011. – 30. 06. 2016. godine.

Opis (eng)

Electromagnetic casting (EMC) is the technology developed as by combining the magnetic hydrodynamics and casting technique. Electromagnetic forces, arising from the interaction of Eddy currents induced in the metal by inductor magnetic field, cause an increased flow of the fluid, forced convection, more uniform temperature field and weak gravitation influence thus changing the conditions of solidification. The advantage of EMC reflects in obtaining a better quality of ingots compared to convent ional continuous casting process. Namely, the structure obtained is finer and more uniform through the cross section, with reduced segregation of alloy element and porosity. Apart from that, due to the reduced contact pressure (result of electromagnetic field effect) between the mould and the metal, the quality of ingot surface is improved, having no need for additional machine processing. The investigations conducted in the world were aimed to investigate the effect of electromagnetic, magnetic and hydrodynamic phenomena on Al ingots, but very little attention was given to the characterization of microstructure and mechanical properties. This work, should contribute to better knowledge of the effect of electromagnetic field on the obtained microstructure (morphology, size, volume fraction and distribution of phases) and properties of Al alloys. The chosen alloy was EN AW 7075 heat treatable, intended for forge with wide industry use. It is characterized by a number of defects that occur during the solidific ation process: porosity, hot cracks, non -uniformal grain size and crystal segregation. Since the quality of final product is directly affected by these defects it is necessary to prevent or reduce their appearance by the choice of the appropriate process and optimal parameters of casting. To compare the results of electromagnetic casting, (with different operating parameters), the process of vertical continual casting without the presence of low frequency electromagnetic field was selected. The results were obtained from microstructure and mechanical examination of Al alloy 7075 ingots casted with and without low-frequency electromagnetic field. The microstructure characterization shows that it is possible to obtain finer and more homogeneous microstructure through the entire cross section of ingots casted with electromagnetic field, compared to ingots casted without electromagnetic field. As the consequence of microstructure-mechanical properties correlation, the use of electromagnetic field improved the mechanical properties, as well. The results obtained from SEM/EDX, DTA,electrical conductivity measurement were also shoved and compared. The chemometric approach for mechanical properties prediction and numerical simulation of the forging process of EN AW 7075 alloy were carried out following the latest world trends and the obtained results can be used as a basis for further training by expanding of database of derived models. This doctoral dissertation is the investigation result of the project: “The development of casting technologies under the influence of electromagnetic field and technologies of hot plastic forming of 7000 series aluminium alloys for special purposes” TR34002, leaded by professor Zvonko Gulišija, in the frame of Technological Development Program, funded by The Ministry of Education, Science and Technological Development of the Republic of Serbia, in the period from 2011 to June 2016.

Jezik

srpski

Datum

2016

Licenca

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