diplomsko delo
Tilen Bohak (Author), Peter Fajfar (Mentor), Peter Cvahte (Co-mentor)

Abstract

Zaradi zelo dobrih lastnosti, so aluminij in njegove zlitine zelo uporabne. Zlitine serije 7XXX so gnetne zlitine. Zaradi sposobnosti deformacijskega in izločevalnega utrjevanja, zlitina EN AW-7075 dosega najvišje vrednosti natezne trdnosti izmed vseh aluminijevih zlitin. Dodatek cinka, magnezija in bakra zviša natezno trdnost in poveča trdoto, zniža pa raztezek, žilavost in duktilnost. Zlitina je primerna za kovanje, zaradi majhne teže in visokih mehanskih lastnosti pa se uporablja v letalski industriji. Mikrostruktura materiala se opazuje pri večjih povečavah, kjer je mogoče opazovati kristalna zrna. Makrostruktura pa se opazuje pri manjših povečavah, kjer je mogoče analizirati večje napake v materialu. Da postane struktura vidna, je potrebno površino vzorca pred analizo pripraviti. Za opazovanje mikrostrukture se uporabljajo mikroskopi, za opazovanje makrostrukture pa makroskopi. V skupino mehanskih lastnosti sodijo modul elastičnosti, napetost tečenja, natezna trdnost, žilavost, duktilnost, trdota itd. To so vrednosti, ki povezujejo deformacijo z obremenitvijo. Odvisne so od kemijske sestave, predelave in stanja materiala. Vrednosti mehanskih lastnosti se pridobijo z mehanskimi preizkusi. Zlitina EN AW-7075 je bila polkontinuirno ulita v drogove, ki so bili nato homogenizacijsko žarjeni. Z vrstičnim elektronskim mikroskopom smo opazovali lito in homogenizirano mikrostrukturo droga. Homogenizirani drog je bil razrezan na okroglice, ki so bile središčene, stružene in ultrazvočno pregledane. Okroglice smo stisnili v palice, iz katerih smo odvzeli vzorce. Vzorce smo toplotno obdelali na več načinov. Z makroskopom smo izvedli primerjavo makrostrukture, z nateznim preizkusom in merjenjem trdote pa smo pridobili mehanske lastnosti vzorcev v različnih stanjih. Vrednosti mehanskih lastnosti smo primerjali med sabo in tako izvedeli učinkovitost posamezne toplotne obdelave.

Keywords

aluminijeva zlitina EN AW-7075;mehanske lastnosti;toplotna obdelava;mikrostruktura;makrostruktura;

Data

Language: Slovenian
Year of publishing:
Typology: 2.11 - Undergraduate Thesis
Organization: UL NTF - Faculty of Natural Sciences and Engineering
Publisher: [T. Bohak]
UDC: 669
COBISS: 167887107 Link will open in a new window
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Other data

Secondary language: English
Secondary title: effect of heat treatment on mechanical properties and microstructure of EN AW-7075 alloy
Secondary abstract: Because of very good properties, aluminium and its alloys are very useful. 7XXX series alloys are wrought alloys. Because of its ability of deformation and precipitation hardening, the alloy EN AW-7075 reaches the highest strengths among all aluminium alloys. The addition of zinc, magnesium and copper increases tensile strength and hardness, but decreases fracture strain, toughness and ductility. The alloy is adequate for forging, because of its low weight and high mechanical properties it is also used in the aircraft industry. The microstructure is observed at higher magnifications, where crystal grains can be observed. Macrostructure is observed at lower magnifications, where larger defects in the material can be analysed. The surface of the sample must be prepared before the analysis, for the structure to be visible. Microstructure is observed with microscopes, and macrostructure with macroscopes. Mechanical properties include modulus of elasticity, yield strength, tensile strength, toughness, ductility, hardness etc. These are values, that relate deformation to an applied load or force. They are dependent on the chemical composition, the processing and the state of the material. The values of mechanical properties are acquired with mechanical tests. The EN AW-7075 alloy was casted with the direct chill casting method into ingots, that were then homogenized. The casted and homogenized microstructure of the ingot was observed on the scanning electron microscope. The homogenized ingot was cut into billets, that were centred, planed and ultrasound examined. The billets were extruded into rods, from which samples were taken. The samples were differently heat treated. The comparison of the macrostructure was done with a macroscope, and the mechanical properties of samples in different states were obtained with the tensile test and hardness measurements. The effectiveness of the individual heat treatment was obtained with the comparison of the values of mechanical properties.
Secondary keywords: aluminium EN AW-7075 alloy;mechanical properties;heat treatment;microstructure;macrostructure;
Type (COBISS): Bachelor thesis/paper
Study programme: 0
Embargo end date (OpenAIRE): 1970-01-01
Thesis comment: Univ. v Ljubljani, Naravoslovnotehniška fak., Oddelek za materiale in metalurgijo
Pages: XI, 37 f.
ID: 19900750