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J. Laub:
"Experimental support for yield strength calculation in aluminium cast material A226";
Supervisor: A. Falahati, E. Kozeschnik; E308, 2013.

As the recent development of MatCalc computer software has it made possible to successfully model physical and thermo-physical properties, it is a natural step to go further in order to predict mechanical properties like yield strength of aluminium cast alloys. The Aluminium cast structure can be considered as a soft continuous matrix (aluminium solid solution), containing hard precipitates of silicon of different morphology. This structure is in much respect, like a metal matrix composite (MMC) for which numerous micromechanical models for tensile response have been proposed. The total yield strength of the cast can be considered as being given by the effect of the strength contribution of the pre-eutectic matrix and the eutectic matrix in which the effect of silicon is being considered. In the present study we investigated the A226 cast alloy in order to do a correct simulation of its yield strength via MatCalc. Scheil simulation of the A226 cast alloy was carried out to find the composition of the pre-eutectic and eutectic part of the matrix and the chemical composition of the eutectic part had a nearby chemical composition like AA2014. The eutectic matrix material AA2014 represents the eutectic strength contribution (excluding the effect of silicon) and experimental investigations were carried out in order to calibrate the precipitation kinetics for the eutectic part of the matrix (AA2014) satisfactory. Hardness and tensile tests on AA2014 have shown, that the higher the cooling rate after the solution heat treatment the higher the hardness and yield strength of the material. An experimental comparison of A226 squeeze- and gravity cast material has shown, that the values of maximum hardness and yield strength in A226 squeeze cast material in as-cast and artificial aged condition is higher in comparison to the gravity cast samples. Further, quenching the A226 squeeze and gravity cast material with a higher cooling rate after the solution heat treatment leads to improved mechanical properties and finally higher maximum hardness values were obtained in comparison to those, which were subjected to lower cooling rates after the solution heat treatment. By running a SEM analysis on the A226 gravity and squeeze cast material, in both the same phases θ-Al2Cu, AlSi, Q-Al5Mg8Cu2Si6, α-AlSiFeMnCu and β-AlFeSiMn were recognized, which differed in shape. Further, tensile tests on the gravity cast material (in heat treated and non-heat treated condition) have been carried out and the results can be used to validate the simulation of the cast.