Aluminium is the third most common element and the most common metal in the Earth's crust. It is a soft, light, silvery-white metal with very good metallurgical properties, such as corrosion resistance, low density, electrical conductivity, toughness and non-magnetism. Aluminium alloys have significantly better mechanical properties than primary aluminium. Therefore, they often replace materials such as plastic, wood, steel, copper, etc., and are very popular in the automotive industry, construction, electrical engineering, households and so on. Aluminium scrap that consumers throw away is collected and sent to landfills, where it is later processed or recycled.
Aluminium recycling is a process by which aluminium scrap can be reused to make new products. Aluminium can be recycled many times without losing its properties, so the cost of processing secondary raw materials is much lower, because we use only about 5% of the energy required to extract primary aluminium from bauxite. Processing of aluminium scrap includes preparation of the raw material, sorting, melting, alloying, melt treatment, cleaning of the melt and casting.
The aim of the thesis was to determine the influence of the specific surface area of secondary aluminium on the melt properties of the alloy EN AW 5182. The considered alloy belongs to the 5XXX series aluminium alloys, the main alloying element is magnesium. It exhibits good corrosion resistance and good mechanical properties. The following were used to study the alloys produced: simple thermal analysis (ETA), X-ray fluorescence analysis (XRF), differential scanning calorimetry (DSC), thermodynamic modeling of the alloy (Thermo-Calc) and a scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS).
Using thermodynamic calculations, we predicted which phases may occur in the microstructure and how they are affected by the size of the specific surface area of the added secondary material. Using a simple thermal analysis, we plotted the cooling curves of all five alloys and determined their characteristic points. From the results, we conclude that the addition of secondary material decreases the enthalpy of reaction, so that less energy is expended for melting. For a material with a large specific surface area, more impurities are introduced into the melt than for a material with a small specific surface area. However, the impurities in the melt lower the temperatures of the characteristic points, so less energy is required for melting.
Using images of the microstructures taken with a scanning electron microscope, we identified the phases determined with an energy dispersive spectrometer and compared them with those obtained from thermodynamic calculations.
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