Method for preparing titanium alloys based on aluminothermic self-propagating gradient reduction and slag-washing refining

A method for preparing titanium alloys based on aluminothermic self-propagating gradient reduction and slag-washing refining, comprising the following steps:

• Step 1:
• material pre-treatment
• pre-treating aluminothermic reduction reaction materials separately to obtain pre-treated aluminothermic reduction reaction materials, wherein the aluminothermic reduction reaction materials include titanium-containing material, aluminum powder, V2O5 powder, CaO and KClO3, the titanium-containing material is at least one selected from the group consisting of rutile, titanium slags and titanium dioxide;
• weighing the pre-treated aluminothermic reduction reaction materials with a proportional ratio, wherein the proportional ratio is a mass ratio of titanium-containing material:aluminum powder:V2O5 powder:CaO:KClO3 being 1.0:(0.60-0.24):(0.042-0.048):(0.12-0.26):(0.22-0.30), respectively;
• wherein a particle size of the pre-treated aluminothermic reduction reaction materials is as follow:
• rutile and titanium slags no larger than 3 mm, titanium dioxide no larger than 0.02 mm, and aluminum powder, V2O5 powder, CaO and KClO3 no larger than 2 mm, 0.2 mm, 0.2 mm and 2 mm, respectively;
• Step 2:
• aluminothermic self-propagating reaction performing gradient aluminothermic reduction with one of the two following feeding manners:
• feeding manner I:
• mixing the weighed aluminothermic self-propagating reaction materials other than aluminum powder uniformly to obtain a material mixture, and dividing the material mixture into several parts;
• then assigning aluminum powder to each part of the material mixture according to a sequence of each part of the material mixture being fed into a reaction furnace, and gradually reducing the amount of aluminium powder assigned from 1.15-1.35 times the stoichiometric ratio to 0.85-0.65 times the stoichiometric ratio;
• wherein the mass of a part of the material mixture that is fed into the reaction furnace as a first batch accounts for 10-30% of the mass of the total material mixture, the first batch of the material mixture requires an addition of magnesium powder as an ignition substance to ignite the material mixture to induce a self-propagating reaction, so that a first-batch high-temperature melt, that is sufficient to initiate subsequent reactions, is obtained;
• feeding other parts of the material mixture into the reaction furnace according to a sequence with reduced stoichiometric ratio of the amount of aluminium powder assigned until all materials are fully reacted to obtain a high-temperature melt;
• or
• feeding manner II:
• mixing the aluminothermic self-propagating reaction materials other than aluminum powder uniformly to obtain a material mixture, and then feeding the material mixture into a continuous material mixer at a constant flow rate;
• at the same time, adding aluminum powder into the continuous material mixer at a flow rate with reduced gradient, so that the amount of aluminium powder assigned to the continuously fed material mixture is gradually reduced from 1.15-1.35 times the stoichiometric ratio to 0.85-0.65 times the stoichiometric ratio, wherein the times of gradient changes of the amount of aluminium powder assigned conforms the following formula:
• m=(b−c)÷a (1);
• wherein, m is the times of gradient changes of the amount of aluminum powder assigned, b is the maximum amount of aluminum powder assigned, c is the minimum amount of aluminum powder assigned, a represents a coefficient for gradient changes of the amount of aluminum powder assigned, and 0<a≤0.04;
• mixing the aluminothermic self-propagating reaction materials uniformly in the continuous material mixer, and continuously feeding the material mixture into the reaction furnace for aluminothermic reduction until all material are fully reacted to obtain a high-temperature melt;
• Step 3:
• melt separation under electromagnetic field
• heating the high-temperature melt through electromagnetic induction to perform heat insulation and melt separation, and realize slag-metal separation to obtain a layered melt with an upper layer being aluminum oxide based melt slags and a lower layer being alloy melt, wherein the temperature is controlled within the range of 1700-1800° C. and the heat insulation time is 5-25 minutes in the melt separation process;
• Step 4:
• slag washing refining
• (1) removing 85-95% of the total volume of the aluminum oxide based melt slags at the upper layer, stirring the remaining aluminum oxide based melt slags and the alloy melt at the lower layer by an eccentrically mechanical stirring at a stirring speed of 50-150 rpm under a temperature range of 1700−1800° C.;
• (2) after the melt being uniformly mixed, continuously stirring, meanwhile, spraying and blowing CaF2—CaO—TiO2—V2O5 based refining slags into the uniformly-mixed melt with inert gas as carrier gas, wherein the mass ratio of the aluminothermic self-propagating reaction materials in the weighing step to the CaF2—CaO—TiO2—V2O5 based refining slags is 1.0:(0.02-0.08);
• the CaF2—CaO—TiO2—V2O5 based refining slags comprise the following chemical ingredients and mass percentages:
• 5%-10% of CaF2, 40%-60% of CaO, 0-2% of Na2O, 30%-40% of TiO2, 5%-15% of V2O5 and the balance being inevitable impurities, wherein each component of CaO, CaF2, Na2O, TiO2 and V2O5 powder contained in CaF2—CaO—TiO2—V2O5 based refining slags has a particle size no larger than 0.2 mm;
• and
• (3) after spraying and blowing the CaF2—CaO—TiO2—V2O5 based refining slags, performing heat insulation at 1700-1800° C. and continuously stirring with the eccentrically mechanical stirring for 10-30 minutes, so as to obtain a titanium alloy melt;
• and
• Step 5:
• cooling
• cooling the titanium alloy melt to room temperature, and then removing the melting slags on a top to obtain titanium alloys.