Spremljanje entalpijske bilance zlitine EN AW 5182 na celotni procesni poti

Kresnik, Kristijan (author), Vončina, Maja (mentor), Volšak, Darja (comentor)

Industrijska proizvodnja izdelkov, kot so trakovi, pločevine in plošče iz aluminijevih zlitin, se začne z izdelavo polizdelkov v obliki bram. Te proizvedemo s procesom polkontinuirnega litja, kateremu sledi proces homogenizacijskega žarjenja, ki odpravi negativne vplive neravnotežnega strjevanja ter hitrega ohlajanja. Homogenizirano bramo nato toplo zvaljamo v toplo valjan trak debeline pribl. 10 mm. Sledi hladno valjanje do želene končne debeline z vmesnim medfaznim žarjenjem, s katerim zmehčamo hladno valjan trak in tako omogočimo lažjo preoblikovanje. Proces zaključimo tako, da material dosega zahtevane mehanske lastnosti, kar dosežemo s pravilno kombinacijo deformacijskega utrjevanja ter končnega žarjenja. Cilj magistrske naloge je bil spremljati spremembo reakcijske entalpije vzorcev zlitine EN AW 5182 (AlMg5Mn) na celotni procesni poti izdelave pločevine z EDT površino. Vzorce smo pridobili po vsakem koraku procesa izdelave. S programsko opremo Thermo-Calc smo naredili termodinamično simulacijo neravnotežnega strjevanja in izrisali ravnotežni fazni diagram ter izračunali ravnotežni delež faz pri določenih temperaturah. Na vseh vzorcih smo izvedli diferenčno vrstično kalorimetrijo (DSC) in iz rezultatov odčitali premenske temperature taljenja in strjevanja ter taline in strjevalne entalpije. 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 predvideli, katere faze se lahko pojavljajo v mikrostrukturi ter kako nanje vplivajo temperature, katerim je material izpostavljen med celotnim procesom izdelave pločevine. Iz rezultatov DSC analize smo ugotovili, da se talilna entalpija in temperature taljenja raznih mikrostrukturnih sestavin po vsakem od opravljenih procesov spreminjajo. Slike iz optičnega mikroskopa so razkrile, kako opravljeni procesi spremenijo obliko intermetalnih faz. Iz posnetkov in analize mikrozrnatosti smo lahko opisali, kako posamezen proces vpliva na število, velikost ter obliko kristalnih zrn. Na podlagi rezultatov SEM in EDS analize smo spremljali spreminjanje kemijske sestave intermetalnih faz ter kristalnih zrn ?Al po vsakem procesu. Na podlagi vseh rezultatov smo zaključili, da vsak korak procesa, ki zajema različne temperature predelave in deformacij, izrazito vpliva na reakcijsko entalpijo in je ni možno enoznačno opisati.

• Language: Slovenian
• Keywords: Aluminijeva zlitina EN AW 5182, termodinamično ravnotežje, homogenizacija, deformacija, entalpija, mikrostruktura, DSC.
• Work type: Master's thesis/paper
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Year: 2021
• PID: 20.500.12556/RUL-125959
• COBISS.SI-ID: 62073603
• Publication date in RUL: 10.04.2021

Secondary language

• Language: English
• Title: Enthalpy balance analysis of aluminium alloy EN AW 5182 during entire process path

Abstract

Industrial production of products, such as strips, plates, and sheet 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. Negative effects of DC casting are eliminated with the process of homogenization annealing. Homogenized slabs are then hot rolled into strips with thickness of about 10 mm. Strips are then cold rolled to final thickness with possible intermediate annealing, which softens the strips and enables easier formation of the final product. The main aim of the master thesis was enthalpy balance analysis of the aluminium alloys EN AW 5182 during entire process path of sheet production with EDT (electron discharge texturing) surface. Samples were obtained after every step of sheet production process path. Using Thermo-Calc computer program thermodynamic simulation of equilibrium and nonequilibrium solidification was made, whereas equilibrium phase diagram and the equilibrium phase fraction at certain temperatures was calculated. Differential scanning calorimetry (DSC) was made on every sample, whereas the melting and solidification characteristic temperatures and the melting and solidification enthalpies from the results were obtained. Optical microscopy and 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 temperature during the different process on these phases were analyzed. Results of DSC analysis show that reaction enthalpy and melting temperatures of microstructural elements changes with every process in the process path. Figures from optical microscope reveal how each process affects the shape and size of the intermetallic phases. Figures and analysis of grain structure reveal how each process affects the size, texture, shape and number of αAl grains. Based on SEM and EDS results, differences in chemical composition of the intermetallic phases and in αAl grains, after each process, were observed. Based on all the results, we concluded that each step of the process, which includes different processing temperatures and deformation, has a significant effect on the reaction enthalpy and cannot be unambiguously described.

• Keywords: Aluminium alloy EN AW 5182, heat treatment, rolling, thermodynamic equilibrium, microstructure, intermetallic phases, DSC