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The purpose of the present study was to examine the oxidation of Mg-Al alloys in the atmosphere of oxygen at various temperatures. The basic examination methods used were differential scanning calorimetry (DSC) and thermogravimetry (TG). The results show that the oxide layer can either protect the material against progressive oxidation or it can cause complete disintegration of material. The nature of the oxide layer formed depends on the external conditions, i.e. on the atmosphere, temperature, and type of alloy. A model of the Mg-Al alloy oxidation was calculated from the TG curves.

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The casting of different forms and dimensions of aluminium alloy EN WA-5083 test samples and the usage of different types of mould materials resulted in achieving different cooling rates of samples. The methods used were simple thermal analysis, using casting into a measuring cell made by the Croning process and using casting into a cone-shaped measuring cell, as well as simultaneous thermal analysis using the method of differential scanning calorimetry. Significant temperature phase transitions and times of solidification were determined, and the dependence model of the solidification time on the sample cooling rate was obtained. Determining the mean number of grains per unit area on samples after having performed the simple thermal analysis and differential scanning calorimetry makes it possible to develop a dependence model of the mean number of grains per unit area on the cooling rate. These models are the basis for carrying out numerical simulations of solidification and microstructure development in the cone-shaped measuring cell, and the comparison of the distribution of the mean number of grains per unit area obtained by simulation with the one obtained experimentally. The obtained results represent a part of the preliminary tests of the microstructure development of industrially cast ingots of EN AW-5083 alloy depending on the local ingot cooling rate.Keywords: EN AW-5083 aluminium alloy / numerical simulation / thermal analysis methods / mean number of grains per unit area / Beim Gießen verschiedener Versuchsmuster mit unterschiedlichen Formen und Größen der Aluminiumlegierung EN WA-5083 und Verwenden verschiedener Formstofftypen, wurden unterschiedliche Abkühlgeschwindigkeiten festgestellt. Dabei wurde die Methode der einfachen Thermalanalyse angewendet, die beim Gießen in eine Messzelle einmal mit dem Croning-Verfahren hergestellt wurde und einmal in eine kegelförmige Messzelle gegossen wurde, samt gleichzeitiger Thermalanalyse mit der Methode der differenzierten Wärmemessung. Dabei wurden die Temperaturphasenübergänge und Zeiten bis zur Erstarrung ermittelt sowie das Zeit-Modell in Abhängigkeit der Abkühlgeschwindigkeit bis zur Erstarrung der Versuchsprobe ermittelt. Durch die Bestimmung des Mittelwertes der Anzahl der Körner pro Fläche auf der Versuchsprobe nach der durchgeführten einfachen Thermalanalyse und der Methode der differenzierten Wärmemessung, kann ein Abhängigkeitsmodell des Mittelwertes der Anzahl der Körner pro Fläche über die Abkühlgeschwindigkeit erstellt werden. Diese Modelle sind die Basis, um die numerische Simulation des Festwerdens und die Mikrostruktur-Entwicklung in der kegelförmigen messenden Zelle, samt der Simulation des Vergleichs der Verbreitung des Mittelwertes der Anzahl von Körnern pro Fläche zu erlangen. Die erhaltenen Ergebnisse repräsentieren einen Teil der Forschung der Mikrostruktur-Entwicklung beim industriellen Gießen von Blöcken der Legierung EN AW-5083 in Abhängigkeit der lokalen Abkühlgeschwindigkeit der Blöcke.Schlüsselwörter: EN AW-5083 Aluminiumlegierung /...

Abstract. Metallographic analysis is applied to the study of the chunky graphite morphology in heavy-section castings of spheroidal graphite cast irons. Three castings with different Si and Ni contents were prepared. Three positions in casting from the edge to the centre, with different cooling rates, were chosen for microstructure observation. The effect of the Si and Ni content on the graphite morphology and mechanical properties of heavy-section spheroidal graphite cast iron parts was investigated. Cerium containing commercial inoculant was used for in-stream inoculation. Chunky graphite area was estimated in micro-and macrostructure. Mechanical properties were determined on tensile test bars taken from the centre of the casting. Macro-and microstructure examination showed that the castings with high Si-content and Ni addition had chunky graphite present, while the castings produced by use of low Si and Ni containing charge had no chunky graphite. High Si-content is strong chunky graphite promoter, especially in castings with slow cooling rate. Ni addition also promotes chunky graphite formation, but only in thermal centre of the casting (where the cooling rate is the lowest). The elongation is severely lowered when chunky graphite appears in the microstructure.