Uticaj elektromagnetnog polja tokom livenja na karakteristike odlivaka aluminijumskih legura

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.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

The use of electromagnetic field in designing the high quality Al alloys for hot forging process

This work presents a way to obtain the better quality of EN AW 7075 aluminum high-strength alloy by application of electromagnetic field (EMF) during the casting process. In this way, the uniform fine-grained microstructure, and hence the better mechanical properties of the alloy can be achieved. The microstructure and mechanical characterization for samples obtained with and without EMF were performed. The application of numerical simulation for hot forging process, using appropriate software, is efficient and highly useful tool for problem prediction in industrial production, reducing the time and costs in the process of development of new products. The input data of high strength Al-alloy EN AW-7075 is used for simulation because it enables the development of parts with complex dimensions and shape.  http://dx.doi.org/10.5937/metmateng1404247

On the properties of hot forged Ti-6Al-4V alloy aimed for surgical implants

The investigation here is aimed to examine the structural and mechanical changes that might have occurred during the hot forging process, a process to obtain a surgical hip implant, and the subsequent heat treatment. Microstructural characterization, morphological and semi-quantitative chemical analyses have been accomplished using an optical and scanning electron microscope. Chemical analyses of all surfaces obtained by the dotted method in all analyzed samples have shown the approximate equal content of aluminum, titanium, vanadium, iron, and silicon. Tensile testing and measurements were following obtained microstructure, showing the uniformity of microstructure and properties along the forging part, as well as over its cross section. All tests proved that hot forging could be a suitable procedure for surgical implants processing

The use of electromagnetic field in designing the high quality Al alloys for hot forging process

This work presents a way to obtain the better quality of EN AW 7075 aluminum high-strength alloy by application of electromagnetic field (EMF) during the casting process. In this way, the uniform fine-grained microstructure, and hence the better mechanical properties of the alloy can be achieved. The microstructure and mechanical characterization for samples obtained with and without EMF were performed. The application of numerical simulation for hot forging process, using appropriate software, is efficient and highly useful tool for problem prediction in industrial production, reducing the time and costs in the process of development of new products. The input data of high strength Al-alloy EN AW-7075 is used for simulation because it enables the development of parts with complex dimensions and shape. http://dx.doi.org/10.5937/metmateng1404247

Predviđanje termičkih i mehaničkih svojstava kompozita na bazi akrilata korišćenjem modela veštačke neuronske mreže

Poly(methyl methacrylate) (PMMA) has a broad spectrum of uses, especially in medical applications. The role of fine-grained alumina particles of PMMA composites was investigated in this study. The composites were based on PMMA modified with dimethyl itaconate (DMI) as a matrix and alumina particles (Al2O3) and alumina doped with iron (Al2O3-Fe) modified with 3-aminopropyl-trimethoxysilane (AM) and flax oil fatty acid methyl esters (biodiesel) as reinforcements. Three particle sizes were measured (~0.4, ~0.6 and ~1.2 μm). The highest thermal conductivity values were measured for the composite 5 wt.% Al2O3-Fe-AM. With the addition of 3 wt.% Al2O3-AM to the PMMA/DMI matrix, mechanical properties were improved (tensile strength, strain, and modulus of elasticity). An artificial neural network model based on the Broyden-Fletcher-Goldfarb-Shanno iterative algorithm was investigated for prediction of thermal conductivity and mechanical properties of the composites showing satisfactory results. This is relevant for applications for optimization of dental materials to produce dentures, which were exposed to variations in temperature during the application.Poli (metil metakrilata) (PMMA) ima široku upotrebu, posebno u stomatologiji i medicini. Kompoziti su napravljeni od PMMA modifikovanog dimetil itakonatom (DMI) kao matrice. Kao pojačanje korišćene su čestice glinice (Al2O3) i glinice dopirane oksidom gvožđa (Al2O3-Fe) modifikovanim sa 3-aminopropiltrimetoksilanom (AM) i metil estrima masnih kiselina lanenog ulja (biodizel – BD). Prema merenjima toplotne provodljivosti, najveće vrednosti toplotne provodljivosti imao je kompozit sa česticama glinice 5 wt.% Al2O3-Fe-AM. Dodatkom modifikovanih čestica glinice u PMMA/DMI matricu, poboljšane su mehaničke osobine (zatezna čvrstoća, deformacija i modul elastičnosti). Razvijen je model veštačke neuronske mreže zasnovan na iterativnom algoritmu predloženom u literaturi (Broiden-Fletcher-Goldfarb-Shanno), za predviđanje toplotne provodljivosti i mehaničkih svojstava kompozita na bazi akrilata u kombinaciji sa česticama na bazi glinice, u zavisnosti od masenog udela čestica, i dodatka oksida gvožđa i modifikatora. Pokazano je da ovi matematički modeli mogu predvideti mehanička i termička svojstva kompozitnih materijala. Ovo je posebno relevantno za predviđanje toplotne provodljivosti materijala koji se koriste u stomatologiji za izradu proteza i koji su izloženi temperaturnim promenama tokom primene

Microstructure development during heat treatment of high chromium white cast iron

Even though it has been in use for a very long time, the high chromium white cast iron (HCWCI) still triggers scientists due to its outstanding wear resistance. Besides its well-known as-cast usage, it can be used as a coating material, as well. HCWCI owes this feature due to the presence of carbides in microstructure, which depends on the composition and heat treatment regime. This investigation was conducted on two HCWCI alloys, where in addition to chromium, the second important alloying element is molybdenum (Mo). Apart from other alloying elements, HCWCI_1 is alloyed with 24.48% Cr and 1.32% Mo, while HCWCI_2 contains 14.11% Cr and 2.47% Mo. The comprehensive microstructural characterization was carried out on as-cast samples and samples obtained after quenching (at -196oC) and/or quenching followed by tempering (at 250oC). Important microstructure indicators are: the stability of austenite, the ratio of microconstituents (especially different types of carbides), as well as their arrangement and morphology, so they are revealed and discussed in relation to the influencing mechanical properties

Microstructure assessment of Co alloy intended for dentistry

Cobalt–chromium–molybdenum (CoCrMo) alloys are known for medical use due to their biocompatibility, corrosion and wear resistance. The chemical and phase composition, as well as microstructure of the alloy directly affect the mechanical properties. In this investigation, CoCrMo alloy samples were obtained by vacuum precise casting. The procedure of melting and casting process as well as their parameters are given. Molds fabricated of copper, gray iron, steel, ceramics and graphite were used during the casting process. In this way, the cooling rate influence on the obtained microstructure was examined. Besides, different casting temperatures (1400°C, 1450°C and 1500°C) were applied for each kind of mold. After metallographic preparation, the microstructure was examined on the cross section of samples by optical microscopy. The obtained results show that by increasing the cooling rate, the microstructure of samples become finer and more homogeneous

Application Of Mechanochemically Activated Sodium Carbonate As A Co2 Absorbent In Environmental Protection

Problem zagađenja životne sredine odnosi se na vazduh, vodu i zemljište. Emisija CO2 u atmosferu smatra se glavnim uzrokom efekta staklene bašte i globalnog zagrevanja. Ovaj pronalazak se odnsoi na primenu mehanohemijski aktiviranog natrijum karbonata na zaštitu životne sredine, a zahvaljujući značajnom povećanjem apsopcionih i hemisorpcionih svojstava natrijum karbonata do kojih dolazi usled aktivacije uzorka. Mehanohemijskom aktivacijom natrijum karbonata i njegovom primenom pokazano je da se masa polaznog uzorka poveća i do 30% u atmosferi vazduha pri sobnim uslovima u toku vremena. Ovako aktiviran natrijum karbonat kome su značajno povećana apsorpciona svojstva je moguće primeniti i na postojećim aparaturama koje inače koriste natrijum karbonat u cilju apsorpcije CO2, radi zaštite životne sredine, čime bi se i njihova efektivnost značajno povećala.Environmental pollution is a serious problem that affects air, water and soil. Emission of CO2 into the atmosphere is considered to be a major cause of the greenhouse effect and global warming. The present invention relates to the application of mechanochemically activated sodium carbonate to the environment, owing to the significant increase in the absorption and chemisorption properties of sodium carbonate due to activation. Using activated sodium carbonate, it was shown that the mass of the starting sample increase up to 30% at room conditions and temperature over time. Sodium carbonate activated in mechanochemical activator, has significantly increased absorption properties, and also can be applied to existing appliances that otherwise use sodium carbonate for the purpose of CO2 absorption, for environmental protection, which would also increase their effectiveness

Predicting the modulus of elasticity of biocompatible titanium alloys using machine learning

Titanium alloys are widely employed in various fields, particularly in biomedical engineering, due to their mechanical and corrosion resistance properties combined with good biocompatibility. The modulus of elasticity is a distinguishing feature of this group of materials compared to others used for similar purposes. A database of approximately 238 titanium alloys free of toxic elements was compiled for this study. The influence of different factors (such as alloy element proportions, density, and specific heat) on the modulus of elasticity was predicted using four methods: support vector machine, XGBoost, Neural Network, and Random Forest. The Random Forest mean absolute error (MAE) of 7.33 GPa, falls within the range of experimentally obtained absolute errors in the literature (up to about 11 GPa). A strong correlation (R2 = 0.72) was observed between experimental and predicted data. Lastly, specific alloying element regions were identified for the modulus of elasticity, which can be used to design new biocompatible titanium alloys in the future

Bi2O3 influence on electronic ceramics sintering process and final properties

The influence of Bi2O3 as a functional additive on the process of obtaining cordierite, 2MgO-2Al2O3-5SiO2 (MAS) was studied by sintering the MgO / Bi2O3 system (sintered at 820 °C and 1100 °C), Al2O3 / Bi2O3 and SiO2 / Bi2O3 (sintered at 1100 °C ), the composition being 80% oxide and 20% Bi2O3. The effects of sintering, composition, and morphology were followed by X-ray diffraction, scanning electron microscopy and EDS analysis. It has been found that, in addition to the liquid phase, Bi2O3 produces intermediate metastable compounds with MgO and Al2O3. The sintering of MAS ceramics with 10% Bi2O3 at 1000 °C, 1100 °C and 1200 °C was also performed. Binary systems MgO / Bi2O3 at 820 ºC and 1100 ºC, Al2O3 / Bi2O3 and SiO2 / Bi2O3 were sintered at 1100 ºC, as well as MgO, Al2O3, SiO2 / Bi2O3 at 1000 ºC, 1100 ºC and 1200 ºC to examine the reaction of the cordierite synthesis. The results show the formation of a liquid phase at 820 °C (melting temperature Bi2O3), as well as the formation of metastable compounds forming MgO and Al2O3 with Bi2O3 at 1100 °C and which diffuse through the liquid phase, thus enabling the mechanism of reaction in the multi-component system to be accelerated from two aspects. By the sintering of a three-component MAS system in the presence of Bi2O3, the existence of cordierite was established. The lowest temperature at which the tracer cordierite was observed (in hexagonal form - indialite) is 1100 °C, while in the sintered system at 1200 ºC the most frequent phase is indialite. This study found that the presence of Bi2O3 in basic cordierite mixture allows the sintering temperature to decrease by ~ 170 ºC relative to the temperature of the formation of cordierite ceramics from the mixture without the presence of functional additives