Study On The Process Mechanism Of Al-Li Master Alloy Produced By Li-Aluminate Composite Oxide By Melting Salt Electrolysis

Aluminum-lithium alloy has good specific strength and specific modulus characteristics,excellent low temperature performance,corrosion resistance and superplastic forming performance.Because of this series of advantages,it is widely used in aerospace,military and other fields.Compared with the traditional process,the preparation of aluminum-lithium alloy by molten salt electrolysis has the advantages of low cost,low energy consumption and simple process.In this paper,aluminum-lithium composite oxide is prepared by vacuum-calcining lithium carbonate as the aggregate as the electrolysis raw material,graphite as the anode,and aluminum as the cathode.The sinking liquid cathode alloying method is adopted,and the cathode is reduced by molten salt electrolysis.Lithium metal is produced and combined with aluminum alloy to form an aluminum-lithium master alloy.In order to improve the characteristics of materials that are difficult to obtain oxides after melting and decomposition,this paper studies the vacuum calcination of alumina as the aggregate to promote the thermal decomposition of lithium carbonate,and prepares the oxide raw materials suitable for the production of aluminum-lithium alloy by molten salt electrolysis.The influencing factors of the decomposition rate and the kinetic behavior of the thermal decomposition reaction have been studied in depth.Through orthogonal experiments,the influence of each process parameter on the decomposition rate of lithium carbonate was investigated.The results show that the best experimental conditions obtained by orthogonal experiments are the mass ratio of clinker and lithium carbonate of 3:1,the pressure of agglomeration is 45MPa,the particle size of the material is 150μm,the calcination time is 5h,and the calcination temperature is 850℃.Under these conditions,lithium carbonate is decomposed.The highest rate can reach 74.71%.The product is lithium metaaluminate analyzed by XRD.The kinetic analysis of the thermal decomposition reaction of lithium carbonate shows that the average apparent activation energy of the decomposition reaction of lithium carbonate under vacuum is 146.23k J/mol.The reaction order is 1.The mechanism model of Li₂CO₃decomposition to CO₂is a chemical reaction,a deceleration curve,and the function is g（α）=（1-α）^-2.At 680℃,using Li Cl-Li F in a pure lithium salt system（with a mass ratio of 3:2）as the basic electrolyte,using the clinker lithium metaaluminate obtained by thermal decomposition as the raw material to prepare aluminum-lithium alloy by molten salt electrolysis,and study the electrolysis process The influence of various process parameters on the back EMF and current efficiency.The results show that the back-EMF before and after the feeding will increase with the increase of the current,and the back-EMF after feeding is reduced by 0.33V on average,and the feeding cycle of lithium metaaluminate（Li Al O₂）is 6.3min.As the current density increases,the current efficiency will first increase and then decrease.When the current density is0.353A/cm²,the current efficiency will reach a maximum of 72.85%.The polarization overvoltage increases as the current density increases.The electrode reaction control process is controlled by electrochemical polarization and concentration polarization.The three-electrode system used in the electrochemical test is used to study its electrochemical discharge behavior by linear voltammetry,chronopotentiometry,and chronoamperometry.The linear voltammetry study shows that the discharge of metal lithium in the tungsten electrode is a reduction process of electrons obtained in one step,and its reduction potential is-2.5V（vs Pt）.After adding lithium metaaluminate（Li Al O₂）,the co-deposition potential is reduced to-1.5V（vs Pt）,which is consistent with the theoretically calculated decomposition voltage.Chronoamperometry shows that the reduction process of lithium ions on the tungsten rod is controlled by diffusion and mass transfer,and the diffusion coefficient after the step is 4.7824×10^-8cm²/s.According to the theory of metal crystal nucleation and growth,the nucleation process on the tungsten electrode is instant nucleation.The study by chronopotentiometry showed that the diffusion coefficient of Li Al O₂was increased by 52%in the Li F-Li Cl system.Using aluminum-lithium composite oxide instead of lithium carbonate as the electrolysis raw material can avoid the carbonization reaction caused by the carbon increase in the molten salt,reduce the viscosity of the molten salt,and improve the current efficiency.This research can not only reduce the cell voltage,but also the anode product CO₂can replace the original chlorine,which can greatly improve the environmental protection,working environment and corrosion of experimental equipment,and realize the green metallurgy concept of energy saving,consumption reduction,low energy and high efficiency.