Grain refining is a common practice at foundry casting plants when casting both wrought and casting aluminium alloys. The purpose of the grain refinement is to reduce crystal grains either by adding master alloys into the melt or by any other procedure such as ultrasonic melt processing, mechanical vibration and electromagnetic melt stirring. When adding master alloys to the melt, additives at foundry casting plants are for the most part constant. The aim of the master thesis was to study the possibility of adding a suitable quantity of grain refiner subject to the status of the EN AW-6110A alloy melt. We focused on undercooling and recalescence which we determined using cooling curves. The curve was plotted based on a simple thermal analysis. We then employed thermodynamic calculations, differential scanning calorimetry and images as well as scanning electron microscope EDS analyses to determine the characteristic temperatures and what is precipitated at these temperatures. Experiments were broken down into two parts. Within the scope of the first part, we studied the effects of undercooling and recalescence on the size of α-Al crystal grains. We determined the size of α-Al crystal grains under an optical microscope in accordance with the ASTM E112-96 standard. It has been found that the data on undercooling was sufficient for an indicative forecast of the size of α-Al crystal grains as we used a regression analysis to construct an empirical equation that shows the dependence of the size of α-Al crystal grains either on undercooling alone or on undercooling and recalescence. We have also found that the α-Al crystal grain size forecasting model is more reliable in grain refined samples than in non-grain refined samples. Within the scope of the second part of experiments, we verified whether a smaller addition of grain refiner can lead to the formation of grains of the same or smaller size than in the case of adding a larger quantity of grain refiner. The data on undercooling and recalescence were the main indicators in this case as well. It has been found that a larger addition of grain refiner is not necessarily the reason for the formation of smaller α-Al crystal grains. It is namely necessary to take into account undercooling and recalescence which are a good indicator of the quantity of active nuclei in the melt. In the end, we plotted the curve showing the dependence of α-Al crystal grain size on the Q growth restriction parameter. It has been found that a bigger role than crystal grain growth restriction is played by the formation of crystallization spots and also that excessive addition of titanium causes agglomeration of TiB2 particles, which results in the formation of larger α-Al crystal grains.
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