National University of Science and Technology “MISiS”, Moscow, Russia:

S. V. Makhov, Senior Researcher
G. A. Kozlovskiy, Post-Graduate Student (Chair of Non-ferrous Metals and Gold)
V. I. Moskvitin, Professor, e-mail: vmoskvitin@mail.ru

Grain refinement is very important in aluminum alloy production. It is carried out by alloy modification: formation of intermetallic compounds (aluminum and modifying element) in melt. Titanium is one of the most efficient modifiers of aluminum and its alloys. Aluminothermic reduction of titanium dioxide in molten fluoride and chloride salts is a perspective method of Al – Ti master alloy production because of availability of raw materials, little losses of main components and relatively low power consumption. Solubility of titanium dioxide in molten fluoride and chloride salts equals 5% for cryolite at the temperature of 1050 oC and mole ratio (NaF/AlF₃), equal to 3.0. Solubility of TiO₂ in the system (40% Na₃AlF₆ + 60% KCl) is 2% under the same experimental conditions. Fusion diagrams of Na₃AlF₆ – TiO₂ and (40% Na₃AlF₆ + 60% KCl) – TiO2 systems were built by thermogravimetric method. As a result, the eutectic character of crystallization was shown and the temperature of formation of eutectic composition was determined. The thermodynamic probability of reactions between the main components was calculated, which shows that alkali metal hexafluorotitanates are formed in the system, and aluminothermic reduction of titanium occurs from these salts, followed by its reaction with aluminum in the melt to form intermetallic Al₃Ti. Theoretically possible extraction of titanium into the master alloy was calculated for different temperatures and equals 92–95%. Extraction of titanium was studied as a function of various factors of production under the laboratory conditions. It is confirmed that titanium extraction into the master alloy decreases with increasing temperature, and the best result (93%) was reached at the temperature of 850 ^oC and the mixing time of 15 minutes.

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