Razvoj nove livarske aluminijeve zlitine z dodatkom litija : doktorska disertacija

Zeka, Bastri (author), Petrič, Mitja (mentor), Markoli, Boštjan (comentor)

Aluminum-lithium (Al-Li) alloys represent a significant advancement in materials science, particularly valued in aerospace for their exceptional properties. Lithium incorporation reduces density and enhances mechanical characteristics, though it presents challenges due to high reactivity with oxygen and other elements, necessitating stringent control over processing conditions. Since the 1940s, Al-Li alloys have evolved through three generations. The first generation focused on weight reduction and stiffness enhancement via ?' (Al3Li) precipitation. Subsequent generations improved mechanical properties. The current generation optimizes these alloys for specific aerospace applications, focusing on manufacturability, environmental stability, and performance under extreme conditions. Evaluations of second-generation Al-Li alloys revealed gas porosity issues in shape casting, mitigated by graphite wash. Successful castings were achieved using metal and graphite molds or no-bake organic binder-based sand systems. Al-Li-Mg and Al-Li-Cu-Mg alloys with 2.5 wt. % lithium exhibited favourable castability, fluidity, and strength. The mechanical properties of Al-Li alloys are influenced by the type, size, volume fraction, and distribution of precipitates within grains and at grain boundaries. The primary strengthening phase is ?' (Al3Li), with additional strengthening from ?' (Al2Cu), T1 (Al2CuLi), and S (Al2CuMg) precipitates. Zirconium prevents recrystallization through ß' (Al3Zr) precipitates. Third-generation alloys improved corrosion resistance and anisotropy issues, leading to applications in aerospace and defence. This scientific PhD research develops a new cast AlSi7MgLi alloy featuring superior mechanical properties and the innovative AlLiSi phase. A comprehensive thermodynamic model for the AlSi7MgLi alloy elucidates its solidification process and microstructural characteristics, focusing on optimizing casting methodologies and understanding microstructural evolution. Advanced techniques, including light microscopy, SEM, EDS, XRD, and TEM, provided in-depth insights into the alloy phase composition and detailed the structure of the phases. Mechanical properties were evaluated using the Gleeble machine, and nanomechanical properties were meticulously assessed through nanoindentation.

• Language: English
• Keywords: Al-Li alloy, melting, solidification, phases, reactions, microstructure, structure.
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Place of publishing: Ljubljana
• Publisher: B. Zeka
• Year: 2024
• Number of pages: XXVIII, 131 f.
• PID: 20.500.12556/RUL-165953
• UDC: 669
• COBISS.SI-ID: 220029443
• Publication date in RUL: 14.12.2024

Secondary language

• Language: Slovenian
• Title: Development of new cast aluminium alloy with lithium addition : Ph. D. Thesis

Abstract

Zlitine aluminija in litija (Al-Li) predstavljajo pomemben napredek v znanosti o materialih, in so posebej primerne za uporabo ali aplikacije v vesolju zaradi svojih izjemnih lastnosti. Dodatek litija zmanjša gostoto Al-zlitine in izboljša mehanske lastnosti, čeprav predstavlja izziv zaradi visoke reaktivnosti s kisikom in drugimi elementi, kar zahteva strog nadzor nad pogoji izdelave in obdelave. Od leta 1940 so se zlitine Al-Li razvile skozi tri generacije. Prva generacija se je osredotočala na zmanjšanje teže in povečanje trdnosti s pomočjo izločkov δ' (Al₃Li). Pir naslednji generaciji so izboljšali mehanske lastnosti. Zadnja generacija te zlitine ima optimirane Lastnosti za posebne aplikacije v vesolju, pri čemer se osredotoča na proizvodnost, okoljsko stabilnost in zmogljivost v ekstremnih pogojih. Preiskave zlitin Al-Li druge generacije so pokazale težave s plinsko poroznostjo pri ulivanju kompleksnih oblik, kar so uspešno omilili z grafitnimi premazi. Strukturno dobri ulitki so bili izdelani z uporabo kovinskih in grafitnih form ali peščenih sistemov na osnovi organskega veziva brez termične obdelave. Zlitine Al-Li-Mg in Al-Li-Cu-Mg z 2,5 mas. % Li imajo ugodno livnost in trdnost. Na mehanske lastnosti zlitin Al-Li vplivajo vrsta, velikost, prostorninski delež in porazdelitev izločkov znotraj zrn in na mejah zrn. Primarna faza utrjevanja je δ' (Al₃Li), z dodatnim utrjevanjem z izločki θ' (Al2Cu), T1 (Al2CuLi) in S (Al2CuMg). Cirkonij preprečuje rekristalizacijo matrice preko izločanja delcev faze β' (Al3Zr). Pri zlitinah tretje generacije so izboljšali korozijsko odpornost in težave z anizotropnostjo, kar je privedlo do uporabe v vesolju in vojaški industriji. V okviru doktorskega dela bo razvita nova livna zlitina AlSi7MgLi z odličnimi mehanskimi lastnostmi in novo ternarno fazo AlLiSi. Obsežen termodinamični model za zlitino AlSi7MgLi pojasnjuje njen proces strjevanja in mikrostrukturne značilnosti, pri čemer se osredotoča na optimizacijo postopka litja in razumevanje mikrostrukturnega razvoja. Napredne preiskovalne tehnike, vključno s svetlobno mikroskopijo, vrstično elektronsko mikroskopijo (SEM), energijsko disperzijsko rentgensko spektroskopijo (EDS), rentgensko difrakcijo (XRD) in presevno elektronsko mikroskopijo (TEM), so omogočile poglobljen vpogled v fazno sestavo zlitine in podroben opis strukture faz. Mehanske lastnosti so bile ovrednotene z uporabo vii naprave za simulacijo termomehanskih stanj, Gleeble, lastnosti na nanonivoju pa so bile natančno ovrednotene z nanoindentacijo.

• Keywords: Al-Li zlitina, taljenje, strjevanje, faze, reakcije, mikrostruktura, kristalna struktura