No abstract

Light alloys like aluminum and its alloys have excellent physical and mechanical properties for a number of applications. The use of aluminum alloys can significantly decrease the mass of automobiles without decreasing structural strength. Therefore, the reason of this work was to determine the optimal cooling rate values, to achieve good mechanical properties for protection of this aluminum cast alloy from losing their work stability, and to make it more resistant to action in hard working conditions. The carried out investigations have allow to found that changes in the cooling rate do not cause changes in the phase composition, revealing the Al 2 Cu and Al 5 FeSi phase especially, but only changes the morphology of a ? b eutectic as well as the particle size and secondary dendrite arm spacing. As a result, the number of fine crystals in per unit volume increases, leading to a fine grain structure, which influences the recalescence temperature. The purpose of this research work is to investigate the thermoderivative interdependencies occurred in analyzed aluminum cast alloys using Universal Metallurgical Simulator and Analyzer. For the investigation, the cast AlSi9Cu aluminum alloy was used. As a result of this research, the cooling rate influence on the structure and mechanical properties changes was investigated. The cooling rate was set in a variable range of 0.16-1.25°C s -1 , where the cooling rate of 0.16°C s -1 corresponds to freely cooling, without any forced air flow.

In this study, the change of the cooling rate in the range of about 0.1-1°C s -1 and the addition of Sr on the crystallization kinetics of the cast zinc alloys of the ZnAlCu type, as well as its relation to the microstructure were also investigated. Therefore, the aim of the rapid crystallisation is the achievement of materials with better properties, which can be obtained by refinement of the dendritic or eutectic microstructure, elimination of segregation, or creation of metastable phases and their morphology changes. In the investigated alloys, the change of cooling rate of 1°C s -1 has caused microstructure's refinement as well as increase in hardness. Increase in the cooling rate causes also morphology changes of the g ? a eutectic, and makes generally a global overcooling of the alloy as well as change in the temperatures at the beginning of crystallization T DN and of the alloy crystallization T S . The presented investigations concerning the electron microscopy methods, including transmission electron microscopy, allow revealing the crystallographic structure, based on the d-spacing changes, as well as the diffraction method used for phase determination, which is a helpful tool for the explanation of the important points in the thermo-derivative analysis curve, where the relation between the amount of phase and the occurrence of new phases can be determined.

The microstructure that is attributable from the distinct casting method dictates new engineering and physical attributes of the material. To understand how to manage the microstructure of the casts, it is necessary to comprehend the differences in microstructure through crystallisation. The effects of cooling rate (0.5, 0.9 and 2.1°C s-1) on the characteristic parameters of the evaluation of aluminium dendrites in Al-Mg alloy during solidification at different cooling rates were investigated by thermal derivative analysis. Because of the facts that castability is influenced significantly by the dendrite coherency point, which represents the time, temperature, and solid fraction at which interlocking solid network forms through solidification, an increment in the solid fraction at coherency can improve the casting attributes of the material and diminish casting defects. Castability of aluminium is defined with a new approach based on one thermocouple thermal analysis technique of fraction solid at a dendrite coherency point. Changes of sample linear dimensions and the coefficient of linear thermal expansion and diagrams of this coefficient as a temperature function during heating and cooling cycle of investigated materials were registered and presented. The analysis shows that the thermal interpretation is carried out on Universal Metallurgical Simulator and Analyzer device which is a useful instrument for the accumulation and calculation of thermal parameters. The manuscript provides to the better understanding non-equilibrium metallurgical characterisation of aluminium alloys.

Although Zn alloys are a very widely used material, there is a need for investigations concerning the influence of thermal conditions on its microstructure and its properties, which makes it useful for the specific tasks it has to fulfil for mass-produced items manufactured by the metalworking industry, in the automotive industry, as well as in countless electronic components. One of the possibilities is to create finer microstructures and enhance their properties, to change their chemical composition by adding alloying additives, and inoculation using modifiers. So in this paper, investigation results are presented concerning the influence of chosen alloying additives, such as Sr, Ce and Ti-B on the measured and calculated thermal characteristics and microstructure of zinc alloys with the addition of aluminium and copper. Based on the results on the phase and chemical composition of the cast Zn-Al-Cu alloys, inoculated with Sr and Ti-B, no differences were detected in the phase composition of the investigated alloys, owing to changes in cooling rates, which were chosen for the sample cooling process. A small amount of added cerium caused the occurrence of new phases present in the microstructure. Modification of the Zn-Al-Cu alloy precipitates changes in the thermomorphology of the phase and the 'tweed' type changes in the microstructure. Moreover, the addition of cerium causes a decrease in the temperature at the beginning (T L ) and the end of the solidification, as well as the occurrence of a multicomponent eutectic, which can be detected on the derivative curve.