Opredelitev poteka strjevanja zlitine AlSi10Mg z merjenjem dimenzijskih sprememb in električne upornosti : diplomsko delo

Savič, Dragana (author), Petrič, Mitja (mentor)

Strjevanje kovinskih materialov najpogosteje spremljamo z enostavno termično analizo, s katero opredelimo karakteristične temperature ter razvoj posameznih faz med strjevanjem. S pomočjo metalografske analize preverjamo ujemanja z ohlajevalnimi krivuljami ter določimo velikost mikrostrukturnih sestavin, ki sestavljajo zlitino. Za boljšo opredelitev poteka strjevanja, lahko uporabimo tudi druge preiskovalne analize, kot so merjenje specifične električne upornosti, ter dilatometrijska analiza. V diplomski nalogi so razložene in opisane enostavna termična analiza, meritve temperature, meritve specifične električne upornosti in meritev dilatometrijskih sprememb ulitka med strjevanjem. Osnoven vzorec je predstavljala zlitina AlSi10Mg, ki smo ji dodali udrobnilna, ter modificirna sredstva v obliki AlTi5B1 in pred zlitine AlSr10. Ugotovili smo, da dodatek Sr vpliva tako na krčenje vzorca, kot tudi na specifično električno upornost. Krčenje se manjša z večjim deležem kristalizirane evtektske faze ßSi , ker pa Sr vpliva na nagnjenost taline k naplinjenosti, se plinska poroznost v ulitku poveča, kar vpliva na količino plinske poroznosti, v mikrostrukturi. S tem pa se skupno krčenje ulitka zmanjša. Z merjenjem specifične električne prevodnosti smo potrdili potek strjevanja, določen na podlagi ohlajevalnih krivulj. Določili smo sovpadanje solidus in likvidus temperature, ter definirali spreminjanje električne upornosti na prehodu iz tekočega v trdno. Pokazali smo, da je specifična električna upornost večja, če so delci evtektskega ßSi večji. Ugotovili pa smo, da z dano metodo, ne moremo natančno opredeliti vpliv udrobnjevanja, na spremembo specifične električne upornosti. Ključne besede: termična analiza, karakteristične temperature, metalografska analiza, specifična električna upornost, dilatometrijska analiza.

• Language: Slovenian
• Keywords: termična analiza, karakteristične temperature, metalografska analiza, specifična električna upornost, dilatometrijska analiza
• Work type: Bachelor thesis/paper
• Typology: 2.11 - Undergraduate Thesis
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Place of publishing: Ljubljana
• Publisher: [D. Savič]
• Year: 2022
• Number of pages: XII, 35 f.
• PID: 20.500.12556/RUL-142772
• UDC: 669
• COBISS.SI-ID: 131426819
• Publication date in RUL: 24.11.2022

Secondary language

• Language: English
• Title: Determination of the solidification process of an AlSi10Mg alloy by measurement dimensional changes and electrical resistance : diploma work

Abstract

The solidification of metallic materials is most often monitored by a simple thermal analysis, which lets us define characteristic temperatures, as well as the development of individual phases during solidification. With the help of metallographic analysis, we verify the correct matching with the cooling curves and determine the size of the microstructural components that compose the alloy. To better define the course of solidification, we can also use other scientific analyses, such as the measurement of specific electrical resistivity or dilatometric analysis. In this thesis we explain and describe concepts, such as simple thermal analysis, temperature measurements, measurements of specific electrical resistivity and measurement of dilatometric changes of the casting during solidification. The basic sample we present was the AlSi10Mg alloy, to which we added gran refining and modifying agents in the form of AlSr10 and AlSr10 alloys. We found that the addition of Sr affects both the shrinkage of the sample as well as the specific electrical resistivity. Shrinkage decreases with a greater proportion of the crystallized eutectic βSi phase, but since Sr affects the tendency of the melt to affinity to gassin, the gas porosity in the casting increases, which affects the amount of gas porosity in the microstructure. This, in turn, reduces the total shrinkage of the casting. By measuring the specific electrical resistivity, we confirmed the solidification process determined on the basis of the cooling curves. Determined the alignment of solidus and liquidus temperatures, and defined the change in electrical resistance during the transition from liquid to solid. We displayed that the specific electrical resistivity increases, if the eutectic βSi particles are larger. However, we found that with the given method, we cannot accurately define the impact of grain refinement on the change in specific electrical resistivity. Key words: thermal analysis, characteristic temperatures, metallographic analysis, specific electrical resistivity, dilatometric analysis.

• Keywords: thermal analysis, characteristic temperatures, metallographic analysis, specific electrical resistivity, dilatometric analysis