Preparation Of Al-Cu-Y Master Alloy By Molten Salt Electrolysis And Its Electrochemical Mechanism

Aluminum and copper alloys are important materials in the construction of national economy and national defense.The alloy properties,such as strength,hardness and electric conductivity,can be improved when joining heavy rare earth Y.The alloy of yttrium,aluminum and copper can be applied in many fields.This paper adopts molten salt electrolysis method to prepare the intermediate alloy of Al-Cu-Y in the electrolyte system of Na₃AlF₆-AlF₃-LiF-MgF₂-Al₂O₃-Y₂O₃-CuO.Firstly,the effects of temperature and raw materials content on the physical properties of electrolyte is studied.The results shows that in the molten salt system the viscosity decreases when temperature rising,but increases when, Al₂O₃,Y₂O₃,CuO content increasing.The density decreases with temperature or Al₂O₃ content increasing,but increases with the content of Y₂O₃,CuO increaseing in the molten salt system.The surface tension decreases with temperature or Al₂O₃,Y₂O₃ content increasing,but increases with CuO content increaseing.Conductivity increases with temperature or CuO content increasing,but decreases with content of Y₂O₃ increasing.When the Al₂O₃ content increasing,the conductivity decreases characterized by the linear ofy=3.12245-0.15912W_Al2O3.Using three electrode system with method of cyclic voltammetry,chronoamperometry and timing potential,the electrochemical reduction process and its control step of Al???,Cu???,Y???on the tungsten electrode is researched in the Na₃AlF₆-AlF₃-LiF-MgF₂ molten salt system under 1208 K temperature.Results show that the electrochemical process of Al???is a quasi reversible reaction,which transfer three electron in a step,deposition potential is near-1.0V,Al???deposition process is a instantaneous nucleation,electrochemical reaction process is controlled by diffusion,the diffusion coefficient D=1.58×10^-4cm²/s.The electrochemical process of Cu???is a quasi reversible reaction,which transfer three electron in a step,and deposition potential is near 0.36 V,the diffusion coefficient D=2.78×10^-5cm²/s.Oxidation peak and reduction peak of Y???can't be swept out.When adding the Al₂O₃,CuO,Y₂O₃,the electrochemical process of Al???,Cu???in molten salt systems is quasi reversible reaction,which transfer electron in a step,the deposition potential of Cu???and Al???are 0.19 V,1.12 V respectively.Oxidation peak and reduction peak of Y???also can't be swept out.The diffusion coefficient of Al???D=3.06×10^-5cm²/sand diffusion coefficient of Cu???D=2.43×10^-5cm²/s after calculating.The intermediate alloy of yttrium aluminum copper is prepared by change electrolytic temperature and current density under the condition of constant current.Research shows that:when the electrolytic temperature is 935?,the current density is 0.7A/cm²,the electrolytic time is 2h,in the intermediate alloy the content of Al,Y and the weight of the intermediate alloy reach maximum.Using polarization curve evaluation method to determine counter electromotive force of molten salt system,and the counter electromotive force E=1.75 V.SEM and energy spectrum diagram shows that the middle Al are mainly distributed in the matrix alloy,Cu are mainly distributed on the grain boundary,Cu format intermetallic compound with Al on the grain boundary.Yttrium is granularly distributed in the alloy,and part of it assemble on the grain boundary.The XRD test shows that intermetallic compounds in intermediate alloy mainly exists in the form of Al₂Cu phase and Cu₅Y phase.Characterization of the hardness and conductivity properties shows that Y is added into alloy which can significantly improve the properties such as hardness and electric conductivity of the alloy.