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Aluminij je najbolj uporabna neželezna kovina. Mehanske, fizikalne in kemijske lastnosti aluminijevih zlitin so odvisne od sestave in mikrostrukture. Dodatek izbranih legirnih elementov čistemu aluminiju močno poveča njegove lastnosti in uporabnost. Kovine z nizkim tališčem, kot so bizmut, svinec, kositer in kadmij, se dodajo aluminiju za izboljšanje obdelovalnosti. Ti elementi imajo omejeno topnost v trdnem aluminiju in tvorijo mehko fazo z nizkim tališčem, ki spodbuja lomljenje odrezkov in pomaga pri mazanju rezalnega orodja. V diplomskem delu smo termodinamično karakterizirali zlitine sistemov Al-In in Al-Bi-In. V eksperimentalnem delu smo najprej izdelali predzlitino Bi-In s 35 mas. % In. Izdelali smo tudi dve zlitini tako, da smo indij in predzlitino legirali tehnično čistemu aluminiju za dosego ustreznih intermentalnih faz z nizkim tališčem. Za analizo kemijske sestave vzorcev bizmuta, indija in obeh zlitin smo uporabili rentgensko fluorescenčno analizo. Za vse vzorce smo izvedli diferenčno vrstično kalorimetrijo, pri kateri smo dobili karakteristične temperature in entalpije prisotnih faz. Med litjem in procesom strjevanja predzlitine in Zlitine 1 (Al-In) ter Zlitine 2 (Al-Bi-In) smo izvajali enostavno termično analizo, s katero smo določili likvidus temperaturo, temperature strjevanja evtektikov in solidus temperaturo. Vzorce zlitin smo opazovali pod vrstičnem elektronskem mikroskopom. Iz mikrostruktur vzorcev smo definirali faze v zlitinah. Izvedeli smo tudi termodinamični izračun za izris izopletnih faznih diagramov in Scheilovih diagramov. Rezultati so pokazali, da se je v Zlitini 1 del indija strdil v obliki evtektika (?-Al + Al13Fe4 + (Al,In)), v Zlitini 2 pa se je del bizmuta in tudi indija strdil v obliki evtektika (?-Al + Al13Fe4 + HCP_A3). 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). |
