Vpliv različnih temperatur staranja na razvoj mikrostrukture EN-AW 7175 zlitine z dodatkom lantana : magistrsko delo

Kavčič, Enej (avtor), Balaško, Tilen (mentor)

Aluminijeve zlitine serije 7xxx, še posebej zlitina EN AW-7175, so ključnega pomena v industrijah, kjer sta visoka trdnost in nizka gostota odločilni lastnosti, kot so vesoljska, letalska in avtomobilska. Glavni legirni elementi so cink, magnezij in baker, katerih vsebnost omogoča dosego visoke trdnosti. Za dosego optimalnih mehanskih lastnosti se uporablja širok spekter toplotnih obdelav med katero se tvorijo izločki, ki ovirajo premikanje dislokacij, kar povečuje trdnost. Namen magistrske naloge je bil raziskati vpliv različnih koncentracij lantana in temperature staranja na mikrostrukturo in lastnosti aluminijeve zlitine EN-AW-7175. Za preiskavo smo uporabili programsko orodje Thermo-Calc, diferenčno vrstično kalorimetrijo (DSC) ter vrstični elektronski mikroskop (FEG SEM) in energijsko disperzijsko rentgensko spektroskopijo (EDS). Prav tako smo izvedli toplotno obdelavo, ki je vključevala raztopno žarjenje, gašenje in staranje, ter analizirali vpliv teh omenjenih toplotnih obdelav na mikrostrukturo in lastnosti zlitin. Rezultati so pokazali, da temperatura staranja vpliva na izločanje faz, pri čemer se pri 90 °C pojavijo drobni izloči Al2Cu, ki pri višjih temperaturah preidejo v ?-fazo. DSC meritve so potrdile, da so se evtektične faze po raztopnem žarjenju raztopile, kar dokazuje pravilno izbrano temperaturo in čas žarjenja. Dodatek lantana ni spremenil vrstnega reda izločanja faz, vendar je močno vplival na njihovo morfologijo. Lantan spodbuja nastanek faze AlLaSi na račun faze Mg2Si, katere delež se zmanjšuje z naraščanjem vsebnosti lantana. Poleg tega je lantan modificiral fazo Al45Cr7 in tvoril velike, ostrorobe faze Al20Cr2La. Hitrejše ohlajanje bi zmanjšalo velikost te faze in zaviralo rast kristalnih zrn. Na podlagi teh ugotovitev smo potrdili, da lantan vpliva na faze v preiskovanih zlitinah in rast kristalov ter da temperatura staranja vpliva na izločanje faz.

• Jezik: Slovenski jezik
• Ključne besede: EN AW-7175, vpliv lantana, raztopno žarjenje, staranje
• Vrsta gradiva: Magistrsko delo/naloga
• Tipologija: 2.09 - Magistrsko delo
• Organizacija: NTF - Naravoslovnotehniška fakulteta
• Kraj izida: Ljubljana
• Založnik: E. Kavčič
• Leto izida: 2025
• Št. strani: XVI, 59 str.
• PID: 20.500.12556/RUL-168561
• UDK: 669
• COBISS.SI-ID: 233080835
• Datum objave v RUL: 17.04.2025

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: Influence of ageing temperature on development of microstructure in alloy EN-AW 7175 with lanthanum : master's thesis

Izvleček

Aluminium alloys of the 7xxx series, particularly the EN AW-7175 alloy, are of crucial importance in industries where high strength and low density are important properties, such as the aerospace and automotive industries. The most important alloying elements are zinc, magnesium and copper, with which high strength is achieved. A wide range of heat treatments, such as solution annealing and ageing, lead to the formation of precipitation particles that hinder dislocation movement and thereby increase strength. The aim of this master's thesis was to investigate the influence of different concentrations of lanthanum and ageing temperature on the microstructure and properties of the aluminium alloy EN AW-7175. For the investigation, we used the Thermo-Calc software, differential scanning calorimetry (DSC), a field emission gun scanning electron microscope (FEG-SEM), and energy-dispersive X-ray spectroscopy (EDS). We also performed heat treatments, including solution annealing, quenching and ageing, and analysed the effects of these processes on the microstructure and properties of the alloys. The results showed that the ageing temperature influences the phase precipitation, with fine Al2Cu precipitates forming at 90 °C and transitioning to the η-phase at higher temperatures. DSC measurements confirmed that the eutectic phases dissolved after solution annealing, indicating the correct temperature and time for annealing. The addition of lanthanum did not change the order of phase precipitation, but significantly influenced their morphology. Lanthanum promotes the formation of LaAlSi at the expense of Mg2Si, which disappears with increasing La content. La also modifies Al45Cr7 and forms larger, sharp-edged Al20Cr2La. Faster cooling would reduce the size of these new phases and could refine the grain size due to their precipitation along the grain boundaries. Based on these results, we have confirmed that lanthanum influences the phases in the investigated alloys and the crystal growth and that the ageing temperature influences the precipitation of phases.

• Ključne besede: EN AW-7175, the influence of lanthanum, solution annealing, aging