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.