Vpliv ohljevalne hitrosti in nukleacijskega potenciala na mehanske lastnosti zlitine AlSI9Cu

Žbontar, Matic (author), Mrvar, Primož (mentor), Petrič, Mitja (comentor)

Namen magistrske naloge je opredelitev mehanskih lastnosti v tlačno litih delih iz zlitine AlSi9Cu3 v odvisnosti od kemijske sestave, nukleacijskega potenciala in lokalne ohlajevalne hitrosti. V ta namen smo določene ulitke iz industrijske tehnološke prakse sistematično izbrali in iz njih reprezentativno vzorčili epruvete s katerimi smo opredelili mehanske lastnosti. Za opredelitev mehanskih lastnosti smo načrtovali posebne nestandardne valjčke na katerih so bili izvedeni tlačni preizkusi. Posebnost naloge je v tem, da je premer valjčka prilagojen dejanski debelini stene ulitka. To je pomembno, saj se tekoča litina v livni votlini strjuje kompleksno, na površini so ohlajevalne hitrosti največje, v notranjosti pa manjše. Vzporedno s sekvenco litja na tlačnem stroju smo izvedli gravitacijsko litje iste zlitine v posebne merilne celice z instrumentiranim termočlenom (izvedena je bila enostavna termična analiza). Med samim procesom v fazi eksperimentiranja smo sistematično zasledovali kemijsko sestavo. Vzorčili smo tudi za metalografsko analizo, tako iz ulitka za posamezno debelino stene, kot tudi iz vzorcev iz enostavne termične analize in ploščic za opredeljevanje kemijske sestave. Ugotovili smo, da se s povečevanjem hitrosti ohlajanja povečujejo mehanske lastnosti zlitine AlSi9Cu3, v območju hitrosti ohlajanja od 4 K/s do 125 K/s. Nadalje je ugotovljeno, da nukleacijski potencial nima izrazitega vpliva na kristalizacijo pri zelo velikih hitrostih ohlajanja, ki so značilne za postopek HPDC (ang. High Pressure Die Casting). Ključen vpliv na velikost mikrostrukturnih sestavin in na mehanske lastnosti ima hitrost ohlajanja, kot tudi mikro in makro napake, ki izvirajo iz samega procesa HPDC in livarske tehnologije. To so plinska in krčilna poroznost ter nekovinski vključki.

• Language: Slovenian
• Keywords: hitrost ohlajanja, strjevanje, aluminij, tlačno litje
• Work type: Master's thesis/paper
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Year: 2019
• PID: 20.500.12556/RUL-110294
• COBISS.SI-ID: 1834335
• Publication date in RUL: 13.09.2019

ŽBONTAR, Matic, 2019, Vpliv ohljevalne hitrosti in nukleacijskega potenciala na mehanske lastnosti zlitine AlSI9Cu [online]. Master’s thesis. [Accessed 15 March 2025]. Retrieved from: https://repozitorij.uni-lj.si/IzpisGradiva.php?lang=eng&id=110294

Secondary language

• Language: English
• Title: Influence of cooling rate and nucleation potential on mechanical properties of AlSi9Cu3

Abstract

The purpose of master’s thesis is characterization of mechanical properties of high pressure die cast parts from alloy AlSi9Cu3 with dependence on chemical composition, nucleation potential and local cooling rate. For that purpose, the castings from industrial technological praxis were systematically picked and from that castings probes were extracted for characterization of mechanical properties. For characterization of mechanical properties, we have planned special non-standard cylinders on which compressive tests were carried out. The uniqueness of this research is that the diameters of designed cylinders was adjusted to the actual wall thickness of the casting. This is important because the solidification of metal in die cavity is complex, on the surface cooling rates are the highest and, in the centre, the lowest. During the process in the experimentational phase chemical composition was systematically monitored. Parallel to sequence of casting on high pressure casting machine gravitational casting of the same alloy was carried out in special measuring cells with instrumented thermocouple (Simple thermal analysis was conducted). Samples for metallographic analysis from the casting for different wall thicknesses as well as from STA samples and samples for chemical composition were extracted. We have discovered that with increasing cooling rates mechanical properties of alloy AlSi9Cu3 are increasing in the area of cooling rates from 4 K/s to 125 K/s. Further it was found that nucleation potential has no clear effect on crystallization at very high cooling rates which are typical for HPDC. The key influence on size of microstructural components and on mechanical properties has cooling rate as well as micro and macro defects which originate from HPDC process itself. Those are gas and shrinkage porosities and non-metallic inclusions.

• Keywords: cooling rate, solidification, aluminium, HPDC