Study Of Al-Sc Alloy Prepared By Thermoelectric Reduction

The Al-Sc alloy is significant material with light weight, high strength, good plasticity, great thermostability, corrosion resistance and weldability, and is widely used in high-tech fields, such as aerospace, military project, sports equipment and so on. At present, the main methods for preparation of Al-Sc alloy are blending, metallothermic reduction and molten salt electrolysis. The blending method has big metal loss and high cost. The metallothermic reduction is complicated and current efficiency of molten salt electrolysis is general low. In this paper, the synthesis of Al-Sc alloy was examined by the combination of themo reduction and electrochemical reduction in the molten salt electrolyte system of nNaF-AlFs-NaCl-KCl.Sc2O3.was used as material and the method was named as thermoelectric reduction in this paper.The physical and chemical properties including initial crystallization temperature, density and conductivity of nNaF-AlF3(60wt%)-NaCl(20wt%)-KCl(20wt%) system were discussed. And the solubility of Sc2O3and SrO was examined, too. The result presented that when0～3wt%Sc2O3was added into the system, the temperature of initial crystallization decreased from735℃to705℃, the conductivity decreased from2.54S·cm-1to2.48S·cm-1and the density was around1.84g·cm-3with the temperature of900℃。When0～4wt%SrO was added into the system, the temperature of initial crystallization decreased from735℃to682℃, the density was around1.82g·cm-3with the temperature of900℃and the conductivity decreased from2.54S·cm-1to2.35S·cm-1. The solubility of SC2O3and SrO was inversely proportional to the molecular ratio of cryolite and was proportional to temperature.Thermodynamics of possible reactions in the process of thermoelectric reduction was analyzed. When the temperature was900℃, Sc2O3can be reducted by strontium in the melt of aluminum. When graphite was used as active anode, the theory decomposition voltage of Sc2O3is higher than SrO’s.In the system of molten aluminum, the reaction of Sc2O3being reduced by Sr was proved by metallothermic reduction and electrolysis.Under the normal electrolysis, the dissolved SrO was firstly reduced, then Sc2O3was reduced by Sr. At the same time, there existed the reaction of Sc2O3getting electron to form Sc. The cyclic voltammetry experiment showed that when molten aluminum was used as reference electrode, Sr was easier to separate than Sc.The synthesis of Al-Sc alloy by thermoelectric reduction showed that the content of Sc in Al-Sc alloy was inversely proportional to the molecular ratio of cryolite and was proportional to electrolytic temperature and time. And the optimal parameters of thermoelectric reduction were2.5V of cell voltage,2.2of molecular ratio of cryolite,900℃of electrolytic temperature and60min of electrolytic time.