20.500.12556/RUL-171922 Tvorba plavajočih kristalov v bramah zlitine EN AW-8011A magistrsko delo Formation of floating crystals in slabs of EN AW-8011A alloy master's thesis Plavajoči kristali so neudrobnjena kristalna zrna, ki se pojavljajo v osrednjem delu bram iz aluminijeve zlitine EN AW-8011A. Ker jih ni mogoče odstraniti s homogenizacijskim žarjenjem, jih je potrebno preprečiti že med litjem. Namen magistrske naloge je bil raziskati nastanek plavajočih kristalov, opredeliti pogoje, pod katerimi nastajajo, ter poiskati učinkovit način za njihovo odpravo. S simulacijo polkontinuirnega litja smo ugotovili, da podaljšanje "combo-baga" (filtrirne mrežice iz steklenih vlaken) zmanjša velikost mrtve cone v kokili, kar lahko zmanjša verjetnost nastanka plavajočih kristalov. Polkontinuirno litje bram dimenzij 1450×510 mm je bilo izvedeno z osnovnim (450×120×100 mm) in novim (525×120×100 mm) "combo-bagom". Vzorčenje taline med livno mizo in zadrževalno pečjo je pokazalo, da plavajoči kristali ne nastajajo v livnem žlebu. Analize plošč odrezanih na dolžini 300 mm od pričetka in 100 mm od konca litja so potrdile, da se plavajoči kristali tvorijo med strjevanjem v tekočem korenu. Kemijske analize so pokazale, da je osrednji del brame obogaten z aluminijem in titanom, območje D/4 pa s silicijem in železom. Novi "combo-bag" je omogočil bolj homogeno porazdelitev zlitinskih elementov. Mikrostrukturna analiza je potrdila prisotnost plavajočih kristalov le v osrednjem delu brame, ulite z osnovnim "combo-bagom". Točkovna analiza z vrstičnim elektronskim mikroskopom je pokazala, da so plavajoči kristali bogati z aluminijem in titanom. Termodinamični izračuni in diferenčna vrstična kalorimetrija so potrdili potek nastanka mikrostrukture ter razlike v talilnih in strjevalnih entalpijah pri vzorcih s plavajočimi kristali in brez njih. Rezultati potrjujejo, da zmanjšanje mrtve cone s spremembo geometrije "combo-baga" omogoča učinkovito preprečevanje nastanka plavajočih kristalov pri litju bram iz zlitine EN AW-8011A. Floating crystals are unfragmented crystalline grains that form in the central region of EN AW-8011A aluminum alloy slabs. As they cannot be removed through homogenization annealing, their formation must be prevented during the casting process. The aim of this master's thesis was to investigate the formation of floating crystals, determine the conditions under which they develop, and propose an effective method for their elimination. Simulations of semi-continuous casting revealed that extending the combobag—a filtering mash made of fibre glass—reduces the size of the dead zone in the mold, which may lower the likelihood of floating crystal formation. Semi-continuous casting of 1450×510 mm slabs was performed using both the basic (450×120×100 mm) and newly designed (525×120×100 mm) combobags. Melt sampling between the casting table and the holding furnace confirmed that floating crystals do not form in the casting trough. Analysis of samples taken at 300 mm from the start and 100 mm from the end of the casting showed that floating crystals form during solidificaton in the liquid sump. Chemical analysis revealed that the slab center was enriched with aluminum and titanium, while the D/4 region contained higher concentrations of silicon and iron. The newly dimensioned combobag enabled a more homogeneous distribution of alloying elements. Microstructural examination confirmed the presence of floating crystals only in the center part of slabs casted with the original combobag. Spot analysis on the scanning electron microscope revealed that the crystals were rich in aluminum and titanium. Thermodynamic modeling and differential scanning calorimetry confirmed the formation of the microstructure and differences in melting and solidification enthalpies between samples with and without floating crystals. The results demonstrate that reducing the dead zone by optimizing combobag geometry effectively prevents the formation of floating crystals during the casting of EN AW-8011A alloy slabs. zlitina EN AW-8011A polkontinuirno litje bram plavajoči kristali makroizcejanje temodinamika mikrostruktura EN AW-8011A alloy semi-continuous casting of slabs floating crystals macrosegregation thermodynamics microstructure true false false T. Bohak Slovenski jezik Angleški jezik Magistrsko delo/naloga 2025-09-04 09:00:05 2025-09-04 09:00:11 2025-11-06 08:55:00 0000-00-00 00:00:00 2025 0 Ljubljana 0 Ljubljana XVII, 61 f. 0000-00-00 NiDoloceno NiDoloceno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 669 106984 256080899 26474.pdf 26474.pdf 1 D09C3F9C02EAF33D6B2958895136C614 b37f5f86fc1e24ea45602f40551091b2b512288a846d6d67e8e37fcfd5c696ce aa30033d-895c-11f0-9328-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=215492 Naravoslovnotehniška fakulteta 0 0 0