This master’s thesis investigates the aluminium alloy AlMg6, whose unfavourable as-cast microstructure causes difficulties during hot rolling. The aim was to identify the phases present in the as-cast state, to evaluate the effect of homogenisation time on their dissolution and to define a single-stage homogenisation regime that could replace the existing multi-stage industrial treatment. Phase equilibria for the actual alloy composition containing 6.16 wt.% Mg were calculated with the Thermo-Calc software. Three types of calculations were performed: an isopleth section, equilibrium phase fractions as a function of temperature and a Scheil calculation of non-equilibrium solidification. Samples taken from five positions across the cross-section of an industrially cast slab were annealed at 540 °C for 4 to 14 h, quenched in water and examined by differential scanning calorimetry, as well as by light and scanning electron microscopy with energy-dispersive X-ray spectroscopy. The Scheil calculation predicted the formation of the β phase (Al3Mg2) at the end of solidification at the non-equilibrium solidus temperature of 449.6 °C, which was consistent with an endothermic effect at 448–451 °C on the heating curves of the as-cast samples. After homogenisation, this effect was no longer detected, except in one edge sample after 6 h. Following homogenisation, the onset of the main melting peak increased from 553–555 °C to 562–570 °C, and the area fraction of intermetallic phases decreased to 0.6 % after longer annealing times. In agreement with the calculations, the Al13Fe4 and Mg2Si phases remained present even after 14 h. Single-stage homogenisation at 540 °C for 8 h is proposed as the most suitable regime; 6 h would theoretically be sufficient, but the longer time ensures more reliable dissolution of the β phase across the entire slab cross-section.
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