Aluminum is the most useful non-ferrous metal. The mechanical, physical and chemical properties of aluminum alloys depend on the composition and microstructure. The addition of selected alloying elements to pure aluminum greatly increases its properties and usability. Low melting point metals, such as bismuth, lead, tin and cadmium are added to aluminum to improve machinability. These elements have limited solubility in solid aluminum and form a soft phase with a low melting point that promotes chip breaking and aids in cutting tool lubrication.
In this thesis, we thermodynamically characterized alloys of the Al-In and Al-Bi-In systems. In the experimental work, we first produced a Bi-In pre-alloy with 35 wt. % In. We also made two alloys by alloying indium and the pre-alloy to technically pure aluminum to achieve appropriate intermetal phases with a low melting point. X-ray fluorescence analysis was used to determine the chemical composition of samples of bismuth, indium and both alloys. Differential scanning calorimetry was performed for all samples, during which the characteristic temperatures and enthalpies of the phases present were obtained. During the casting and solidification process of the pre-alloy and Alloy 1 (Al-In) and Alloy 2 (Al-Bi-In), a simple thermal analysis was performed to determine the liquidus temperature, the eutectic solidification temperature, and the solidus temperature. The alloy samples were observed under a scanning electron microscope. The phases in the alloys were defined from the microstructures of the samples. We also performed a thermodynamic calculation for plotting isopleth phase diagrams and Scheil diagrams.
The results showed that in Alloy 1 part of the indium solidified in the form of eutectic (α-Al + Al13Fe4 + (Al,In)), and in Alloy 2 part of the bismuth and also indium solidified in the form of eutectic (α-Al + Al13Fe4 + HCP_A3).
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