Vpliv ohlajevalne hitrosti na preoblikovalnost zlitine EN AW-7075 v hladnem : magistrsko delo

Reberčnik, Domen (avtor), Fajfar, Peter (mentor), Cvahte, Peter (komentor)

V sklopu naloge je predstavljen in analiziran vpliv hitrosti ohlajanja in temperatur žarjenj na preoblikovalnost zlitine EN AW-7075 v hladnem. Analize so potekala na protismerno iztiskanih palicah premera 11 mm, ki se v dotičnem podjetju namensko uporabljajo za izdelavo visoko trdnostnih izdelkov, karabinov. Zaradi visokih mehanskih lastnosti, ki se jih doseže s preoblikovanjem in hitrim procesom naravnega staranja zlitine, je nadaljnje preoblikovanje v hladnem omejeno. Palice so se, za izogib temu, po procesu iztiskavanja mehko žarile in kontrolirano ohlajale v laboratorijski peči z vnaprej določenimi parametri. S tem se doseže znižanje mehanskih lastnosti, ki so potrebne za zagotovitev sposobnosti preoblikovanja materiala. Zagotovitev ozkih tolerančnih območij in geometrijsko zadovoljivih prerezov se doseže z deformacijskim vlečenjem preko votlic. Za namene raziskave sta bili izbrani 2 % in 6 % stopnja deformacije. Primerjava meritev mehanskih lastnosti skozi vse stopnje obdelave palic, tako termičnih kot mehanskih, poda podroben vpogled o dogajanju materiala skozi procesno verigo. Končni preizkus, preizkus upogibanja, se je izvedel v industrijskem procesu, po katerem se definira čas in temperatura žarjenja, hitrosti ohlajanja in stopnja deformacije. Po vseh stopnjah verige procesov in toplotnih obdelav so bili vzorci na vrstičnem elektronskem mikroskopu (SEM) pregledani z EBSD analizo. Opravljene so bile različne analize, s katerimi so bile opredeljene nastale razlike in spremembe mehanskih lastnosti. Podrobna analiza teksturnih komponent (Brass, Copper , Cube, Goss, P in S) z vrednotenjem posnetkov ODF in Polovih figur je omogočila razlago spreminjanja mehanskih lastnosti materiala. Opredelitve sposobnosti materiala k nadaljnjemu preoblikovanju so pokazale vrednosti rezultatov Schmidovega faktorja. Pregled stopnje rekristaliziranosti zrn pa je bila izvedena z GAM analizo. Z vrednotenjem rezultatov lahko podamo mnenje, da so za tovrstno hladno preoblikovanje v predobliko za izdelavo karabinov primerne vse v magistrski nalogi analizirane toplotne in deformacijske obdelave.

• Jezik: Slovenski jezik
• Ključne besede: aluminijeva zlitina EN AW-7075, protismerno iztiskavanje, parametri žarjenja, mehanske lastnosti, EBSD analiza
• Vrsta gradiva: Magistrsko delo/naloga
• Tipologija: 2.09 - Magistrsko delo
• Organizacija: NTF - Naravoslovnotehniška fakulteta
• Kraj izida: Ljubljana
• Založnik: [D. Reberčnik]
• Leto izida: 2022
• Št. strani: XVI, 74 f.
• PID: 20.500.12556/RUL-143451
• UDK: 669
• COBISS.SI-ID: 135943683
• Datum objave v RUL: 21.12.2022

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: Cooling rate effect on cold workability of alloy EN AW-7075 : master's thesis

Izvleček

As part of the assignment, the influence of cooling rates and annealing temperatures on the cold workability of EN AW-7075 alloy is presented and analyzed. The analyses were carried out on indirect extruded rods with a diameter of 11 mm, which are specifically used in the respective company for the production of high-strength products, carabiners. Due to the high mechanical properties achieved by the transformation and fast natural aging process of the alloy, further cold transformation is limited. To avoid this, the rods were soft annealed after the extrusion process and cooled in a controlled manner in a laboratory furnace with predefined parameters. This amplifies the reduction of mechanical properties, which are necessary to ensure the transformation ability of the material. Tight tolerance zones and geometrically satisfactory cross-sections are achieved by deformation drawing through the hollow tool. For the purposes of the study, deformation rates of 2 % and 6 % were chosen. A comparison of measured mechanical properties, both thermal and mechanical, provides a detailed insight into the material’s evolution through the process chain. The final test, i.e. the bending test, was carried out in an industrial process, after which the annealing time and temperature, the cooling rates and the rate of deformation are defined. After completing all stages of the processes chain and heat treatments, the samples were examined on a Scanning Electron Microscope (SEM) with EBSD analysis. Various analyzes have been carried out to identify the resulting differences and changes in mechanical properties. A detailed analysis of the textural components (Brass, Copper, Cube, Goss, P and S) by evaluation the ODF and Pole figure images allowed to explain the variations of mechanical properties of the material. The definition of the material’s ability to be further transformed was given by the Schmid factor values. The degree of recrystallisation of the grains was checked by GAM analysis. By evaluating the results, we can give the opinion that all the thermal and deformation treatments analyzed in the master's thesis are suitable for this kind of cold transformation into a preform for the production of carabiners.

• Ključne besede: aluminum alloy EN AW-7075, indirect extrusion, annealing parameters, mechanical properties, EBSD analysis