magistrsko delo
Jaka Dabanović (Author), Jože Medved (Mentor), Matej Steinacher (Co-mentor)

Abstract

Udrobnjevanje je stalna praksa v livarnah pri litju tako aluminijevih gnetnih kot aluminijevih livarskih zlitin. Namen postopka je zmanjševanje kristalnih zrn bodisi z dodajanjem predzlitin v talino ali kakršnimkoli drugim postopkom, kot so ultrazvočna obdelava taline, mehanske vibracije in elektromagnetno mešanje taline. Pri dodajanju predzlitin talinam so dodatki v livarnah večinoma konstantni. Cilj magistrskega dela je bil preučiti možnost dodajanja ustrezne količine udrobnjevalca ob upoštevanju stanja taline zlitine EN-AW-6110A. Osredotočili smo se na podhladitev in rekalescenco, ki smo ju določili s pomočjo ohlajevalnih krivulj. Te smo izrisali na podlagi enostavne termične analize. S termodinamičnim izračunom, diferenčno vrstično kalorimetrijo in posnetki ter EDS-analizami vrstičnega elektronskega mikroskopa smo nato določili karakteristične temperature ter kaj se pri teh temperaturah strjuje in izloča. Eksperimenti so bili razdeljeni na dva dela. V prvem delu smo preučevali vpliv podhladitve in rekalescence na velikost kristalnih zrn ?-Al. Velikosti kristalnih zrn ?-Al smo določevali v skladu s standardom ASTM E112-96 pod svetlobnim mikroskopom. Izkazalo se je, da je za okvirno napoved velikosti kristalnih zrn ?-Al dovolj že samo podatek o podhladitvi, saj smo s pomočjo regresijske analize določili empirične enačbe, ki prikazujejo odvisnost velikosti kristalnih zrn ?-Al posamezno od podhladitve in posamezno od podhladitve in rekalescence. Ugotovili smo tudi, da je model za napovedovanje velikosti kristalnih zrn ?-Al verodostojnejši pri udrobnjenih vzorcih kot pa pri neudrobnjenih. V drugem delu eksperimentov smo preučevali, ali se lahko pri manjšem dodatku udrobnjevalca tvorijo zrna enake ali manjše velikosti kot pri večjem dodatku udrobnjevalca. Tudi tukaj sta bila glavna podatka o podhladitvi in rekalescenci taline. Izkazalo se je, da večji dodatek udrobnjevalca ni nujno razlog tvorbe manjših kristalnih zrn ?-Al. Treba je upoštevati podhladitev in rekalescenco, ki sta dober kazalnik količine aktivnih kali v talini. Na koncu smo izrisali še krivuljo odvisnosti velikosti kristalnih zrn ?-Al od parametra omejitve rasti Q. Izkazalo se je, da ima pomembnejšo vlogo od omejitve rasti kristalnih zrn tvorba kristalizacijskih mest in da pri prevelikih dodatkih prihaja do aglomeracije delcev TiB2, kar se kaže v tvorbi večjih kristalnih zrn ?-Al.

Keywords

Ključne besede: zlitine EN-AW-6110A;enostavna termična analiza;ohlajevalna krivulja;podhladitev;rekalescenca;velikost kristalnih zrn alfa-Al;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL NTF - Faculty of Natural Sciences and Engineering
Publisher: [J. Dabanović]
UDC: 669
COBISS: 31864579 Link will open in a new window
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Other data

Secondary language: English
Secondary title: determining the proper additive of the grain refiner according to the state of alloy EN AW-6110A melt
Secondary abstract: Grain refining is a common practice at foundry casting plants when casting both wrought and casting aluminium alloys. The purpose of the grain refinement is to reduce crystal grains either by adding master alloys into the melt or by any other procedure such as ultrasonic melt processing, mechanical vibration and electromagnetic melt stirring. When adding master alloys to the melt, additives at foundry casting plants are for the most part constant. The aim of the master thesis was to study the possibility of adding a suitable quantity of grain refiner subject to the status of the EN AW-6110A alloy melt. We focused on undercooling and recalescence which we determined using cooling curves. The curve was plotted based on a simple thermal analysis. We then employed thermodynamic calculations, differential scanning calorimetry and images as well as scanning electron microscope EDS analyses to determine the characteristic temperatures and what is precipitated at these temperatures. Experiments were broken down into two parts. Within the scope of the first part, we studied the effects of undercooling and recalescence on the size of α-Al crystal grains. We determined the size of α-Al crystal grains under an optical microscope in accordance with the ASTM E112-96 standard. It has been found that the data on undercooling was sufficient for an indicative forecast of the size of α-Al crystal grains as we used a regression analysis to construct an empirical equation that shows the dependence of the size of α-Al crystal grains either on undercooling alone or on undercooling and recalescence. We have also found that the α-Al crystal grain size forecasting model is more reliable in grain refined samples than in non-grain refined samples. Within the scope of the second part of experiments, we verified whether a smaller addition of grain refiner can lead to the formation of grains of the same or smaller size than in the case of adding a larger quantity of grain refiner. The data on undercooling and recalescence were the main indicators in this case as well. It has been found that a larger addition of grain refiner is not necessarily the reason for the formation of smaller α-Al crystal grains. It is namely necessary to take into account undercooling and recalescence which are a good indicator of the quantity of active nuclei in the melt. In the end, we plotted the curve showing the dependence of α-Al crystal grain size on the Q growth restriction parameter. It has been found that a bigger role than crystal grain growth restriction is played by the formation of crystallization spots and also that excessive addition of titanium causes agglomeration of TiB2 particles, which results in the formation of larger α-Al crystal grains.
Secondary keywords: Keywords: EN AW-6110A alloys;simple thermal analysis;cooling curve;undercooling;recalescence;alpha-Al crystal grain size;
Type (COBISS): Master's thesis/paper
Study programme: 0
Embargo end date (OpenAIRE): 1970-01-01
Thesis comment: Univ. v Ljubljani, Naravoslovnotehniška fak., Odd. za materiale in metalurgijo
Pages: XIX, 129 f.
ID: 12046428