Analiza homogenosti kemijske sestave zlitine EN AW 2011 pred in po homogenizacijskem žarjenju - Avbelj, Luka (2020)
Aluminijeve zlitine imajo širok spekter uporabe in tako iz leta v leto postajajo bolj pogosto uporabljene, saj imajo zelo dobre mehanske lastnosti. Na grobo lahko delimo aluminijeve zlitine na livne in gnetene, ki jih nato delimo še na zlitine, ki jih je mogoče toplotno obdelati in na zlitine pri katerih ta postopek ni mogoč. Prav tako lahko zlitine delimo glede na legirane elemente, ki jih uporabljamo pri sami izdelavi zlitine. Aluminijeve zlitine iz skupine 2xxx vsebujejo kot glavni legirni element baker in sicer od 2 do 6 mas. %. Ta poveča trdnost in obdelovalnost zlitine vendar ob tem zmanjša odpornost proti koroziji in varljivost. Pri litju prihaja do neravnotežnega strjevanja, zato je potrebno ohlajeno zlitino toplotno obdelati, kar imenujemo homogenizacija. Ta nam omogoči, da odpravimo kristalne izceje in nizko taljive evtektike, povzroči pa tudi spremembo oblik intermetalnih faz. Zmožnost preoblikovanja zlitine se tako poveča. V diplomskem delu je bil predmet preiskav aluminijeva zlitina z oznako EN AW 2011 (AlCuBiPb), pri čemer smo naredili primerjalno analizo pred in po homogenizacijskem žarjenju. Homogenizacija je potekala 6 h pri 520 °C. Problema smo se lotili tako, da smo najprej iz dveh drogov pred in po homogenizaciji izrezali rezino, nato smo iz vsake rezine droga vzeli po tri vzorce in sicer na sredini, na D/4 in na robu rezine. Na vseh šestih vzorcih smo izvedli diferenčno vrstično kalorimetrijo (DSC), katere rezultate smo primerjali med seboj. Prav tako smo vzorce pripravili za optično mikroskopiranje in vrstično elektronsko mikroskopiranje (SEM), kjer smo analizirali fazno in kemično sestavo. S pomočjo programa Thermo-Calc smo izdelali ravnotežni fazni diagram, ohlajevalno krivuljo zlitine in preučili tvorjenje faz med strjevanjem. S pomočjo pridobljenih podatkov med eksperimentalnim delom smo ugotovili, da je bila homogenizacija izvedena uspešno, saj ima zlitina po njej dokaj homogeno kemijsko sestavo po celotnem prerezu. Aluminium alloys have a wide range of applications and they are becoming more commonly used, because they have very good mechanical properties. The aluminium alloys can be divided into casting and wrought alloys, which are further divided into alloys which can be heat treated and non-heat treated. Alloys can also be divided according to the alloying elements used in the alloy itself. Aluminium alloys in Group 2xxx contain as the main alloying element 2 to 6 wt. % of copper. This increases the strength and workability of the alloy, but also reduces corrosion resistance and weldability. At casting a non-equilibrium solidification occurs. Therefore, the cooled alloy needs to be heat treated, which is called homogenization. Homogenization allows to eliminate crystalline segregations and low-melting eutectics, but also causes changes in the forms of intermetallic phases. Deformation ability is in this way increased. In diploma work the subject of investigations was the aluminium alloy with designation EN AW 2011 (AlCuBiPb), whereas the comparative analysis before and after homogenization annealing was made. Homogenization was made at 520 °C for 6 h. First a slice from two rods before and after homogenization was cut out, then three samples from each slice of the rod, namely in the middle, on D/4 and at the edge of the slice was prepared. Differential scanning calorimetry (DSC) was performed on all six samples, whereas the results were compared with each other. Samples for optical microscopy and scanning electron microscopy (SEM) were also prepared, whereas phase and chemical composition was analysed. Using Thermo-Calc program, an equilibrium phase diagram, a cooling curve of the alloy and the phase formation during solidification was examined. From obtained results, it was found that the homogenization was carried out successfully, due to a fairly homogeneous chemical composition throughout the cross-section.