Optimizacija homogenizacijskega žarjenja bram iz zlitine 8006.

Kresnik, Kristijan (author), Vončina, Maja (mentor)

Industrijska proizvodnja izdelkov, kot so folije in trakovi iz aluminijevih zlitin, se začne z izdelavo polizdelkov v obliki bram. Te proizvedemo s procesom kontinuirnega litja, ki je hiter in ne dopušča ravnotežnih pogojev strjevanja kovine. Nehomogenosti, mikroizceje, napetosti in ostale napake, ki nastanejo med neravnotežnim strjevanjem, odstranimo s pomočjo homogenizacijskega žarjenja. Tako se izognemo številnim tehnološkim težavam pri nadaljnjem preoblikovanju polizdelkov. Cilj diplomske naloge je bil optimizacija homogenizacijskega žarjenja bram iz zlitine EN AW 8006. Iz lite čelne ploskev brame smo izrezali vzorce v obliki kock ter jih laboratorijsko žarili. Vzorce smo žarili 4, 6, 8, 10, 12 ur na temperaturah 580 °C ter 600 °C z namenom določitve stopnje homogenizacije. S programsko opremo Thermo-Calc smo naredili termodinamično simulacijo ravnotežnega ter neravnotežnega strjevanja in izrisali ravnotežni fazni diagram. Na izbranih vzorcih v litem stanju in po različnih režimih homogenizacijskega žarjenja smo izvedli diferenčno vrstično kalorimetrijo (DSC). Z optičnim mikroskopom in vrstičnim elektronskim mikroskopom (SEM) smo pregledali mikrostrukturo vzorcev, ter z uporabo energijsko disperzijskega spektrometra (EDS) analizirali mikrostrukturne sestavine. S pomočjo termodinamične simulacije smo ugotovili katere faze se lahko pojavljajo v mikrostrukturi ter vpliv različnih temperatur homogenizacijskega žarjenja na le-te. Iz rezultatov DSC analize smo ugotovili, da se reakcijska entalpija pri taljenju oz. strjevanju zmanjšuje z daljšim časom homogenizacije, medtem ko temperatura taljenja raznih mikrostrukturnih sestavin narašča. Slike iz optičnega mikroskopa so razkrile kako se spreminja morfologija mikrostrukture žarjenih vzorcev v primerjavi z vzorcem v litem stanju. Na podlagi rezultatov SEM in EDS smo spremljali spreminjanje kemijske sestave intermetalnih faz pri različnih pogojih homogenizacije. Na podlagi vseh rezultatov smo zaključili, da je homogenizacijsko žarjenje zadostno že po 8 urah žarjenja na 580 °C.

• Language: Slovenian
• Keywords: Aluminijeve zlitine, homogenizacijsko žarjenje, termodinamično ravnotežje, mikrostruktura, intermetalne faze
• Work type: Bachelor thesis/paper
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Year: 2018
• PID: 20.500.12556/RUL-103877
• COBISS.SI-ID: 1769567
• Publication date in RUL: 28.09.2018

Secondary language

• Language: English
• Title: Optimization of homogenization annealing of slab from 8006

Abstract

Industrial production of products, such as strips and foils from aluminium alloys starts with semi-finished product in a form of slabs. Slabs are made with direct chilled continuous casting process, which is very fast and does not allow solidification at equilibrium conditions. Inhomogeneities, micro-segregations, residual stresses and other defects that occur in the material during un-equilibrium solidification are eliminated with homogenization annealing. In this way technological problems during deformation can be avoided. The main aim of the diploma work was optimization of homogenization annealing of slabs from EN AW 8006 alloy. From the front side of the slab the samples in the form of cubes were cut and laboratory annealed. With the purpose of determining the level of homogenization, samples were annealed for 4, 6, 8, 10, 12 h at temperature 580 °C and 600 °C. Using Thermo-Calc computer program thermodynamic simulation of equilibrium and unequilibrium solidification was made, whereas equilibrium phase diagram was calculated. On selected samples in as-cast state and after certain homogenization regimes differential scanning calorimetry (DSC) was made. Optical microscopy, scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS) were used in order to analyze microstructure and microstructural components. Using thermodynamic simulations the phases that can appear in the microstructure and the influence of different homogenization annealing temperatures on these phases were analyzed. Results of DSC analysis show that reaction enthalpy during melting and solidification decrease, with longer times of annealing, while melting temperatures of various microstructural components rise. Figures from optical microscope reveal the changes of morphology in annealed samples in compare to as-cast sample. Based on SEM and EDS results, differences in chemical composition of the intermetallic phases in as-cast samples and in samples after various homogenization regimes , were observed. Based on all results, it can be concluded that the homogenization is successful already after 8 hours of annealing on 580 °C.

• Keywords: Aluminium alloy, homogenization annealing, thermodynamic equilibrium, microstructure, intermetallic phases