The Research On Al-Li Alloy Preparation By Molten Salt Electrolysis

Aluminium-lithium alloys is widely used in aerospace and national defence areas due to its advantages of light specific gravity, high elasticity and intensity, corrosion resistance, and a good nature at high or ultra low temperatures. Nowadays, ingot metallurgy is mainly used to produce aluminium-lithium alloys. The process is complex with expensive equipments and the need for high purity metals. As an alternate process, the molten salts electrolysis process is attractive for high energy efficiency, simple process, little metal combustion loss, et al. In this paper, investigation was carried out to prepare Al-Cu-Mn-Zr-Li alloy by molten salt electrolysis with Li2O as feeding material. We developed a new method for controlling lithium content in alloy based on the principle of electrochemistry. A new process for low cost production of Li2O was also developed in this paper.The effect of the crucible materials on the products of vacuum pyrolysis reaction was studied, as well as the mechanism of the vacuum pyrolysis reaction for lithium oxide preparation in different crucibles. The optimal process conditions for synthesis of lithium oxide were also investigated. The results suggested that crucible material has a significant influence on the products of the vacuum pyrolytic process of lithium hydroxide monohydrate. High-purity lithium oxide was obtained in lithium modified corundum crucible. Lithium carbonate and lithium hydroxide were obtained firstly in the graphite crucible and the nickel crucible, respectively, and low-purity lithium oxide were obtained when holding time at 950? was prolonged. Lithium oxide could not be obtained in the iron crucible. In the lithium modified corundum crucible, higher pyrolytic temperature and longer holding time at pyrolytic temperature will benefit the purity of the lithium oxide. Lithium oxide with a purity of 98.7% higher can be obtained in the lithium modified corundum crucible by this new vacuum pyrolytic process.In order to identify the reduction potential of Li+ and its product in the LiCl-Li2O molten salts system,cyclic voltammetry, chronopotentiometry were used to investigate elcctrodeposition mechanism of Li+ ion on the liquid aluminium-copper electrode. The result showed that Li+ deposited on the Al-Cu electrode at potential of -2.48V (vs.Ag/AgCl) and formed Al-Cu-Li alloys at the temperature of 700?As one of the most common Al-Li alloys, Al-Cu-Mn-Zr-Li multi-element alloy were prepared using liquid Al-Cu-Mn-Zr alloy as the cathode, graphite as anode in LiCl-Li2O molten salts system at 700?. The relationship between cathode potential (vs.Ag/AgCl) and lithium content in Al-Cu-Mn-Zr-Li alloys was studied. The results showed that the potential of the cathodic liquid alloy moved linearly to more negative direction with increasing of lithium content in alloy. The lithium content in cathode alloy could be monitored and controlled effectively through detecting potential of cathode alloy during electrolysis. The research on current efficiency indicated that current efficiency increased with increasing of anode-cathode distance. The current efficiency could reach up to 60% at about 1A/cm2. SEM observation showed that lithium distributes uniformly in the Al-Cu-Mn-Zr-Li alloy prepared by molten salt electrolysis. XRD analysis confirmed that lithium is presented as Al2CuLi, Al5.1CuLi in the obtained alloy.