Preparation Of Al-Zr Master Alloy By Molten Salt Electrolysis

Al-Zr alloy has many excellent properties,such as high strength and toughness,good corrosion and recrystallization resistance.So it is widely applied in aerospace,nuclear energy,transmission lines and high-speed train fields.At present,the most economic and effective way to add Zr is in the form of Al-Zr master alloy.However,the preparation of Al-Zr master is of high cost and the alloy has unstable alloy composition,which limit the application of Al-Zr alloy.So in the paper,we got Al-Zr master alloy in Al-ZrO2 and Al-Zr(CO3)2 reduction system,studied the dissolution behavior of ZrO2 and Zr(CO3)2 in cryolite and analyzed the difference between the two reduction system.Meanwhile we designed a device for continuous preparation of Al-Zr master alloy.The dissolution behavior of ZrO2 and Zr(CO3)2 in cryolite-based molten salt(2.2NaF·AlF3-5wt%CaF2)was studied using a transparent cell and the solubility was measured by isothermal saturation method.The results indicate that Zr content in cryolite can reach the saturated value 3wt%after 1 hour's dissolving by adding Zr(CO3)2 to the cryolite,while by adding ZrO2 to the cryolite,Zr content can just reach 1.3wt%after about 2 hours' dissolving.So considered from the solubility and dissolution rate,Zr(CO3)2 has both advantages compared to ZrO2.Two reaction mechanisms exist in molten salt electrolysis to prepare Al-Zr alloy:thermal and electrochemical reduction.When preparing Al-Zr master alloy,whether electric power in or not has little effect on Zr content in Al-Zr alloy,but Zr can be better-distributed when electric power in.The factors,molten salt elements and reaction time,are investigated in aluminum-molten salt reduction.The results indicate that when the ratio of cryolite increases,the solubility and dissolution rate of ZrO2 improved,so as to enhance the Zr content in Al-Zr alloy.Al-Zr(CO3)2 has advantages in reaction speed and Zr content in Al-Zr master alloy,and Zr content in the lower part of the alloy can reach 13.0wt%with the form of granular Al3Zr,while the upper Zr content is about 2 wt%with long-strip Al3Zr.So it is feasible to prepare Al-Zr mater alloy by Zr(CO3)2 instead of ZrO2 in cryolite reduction system.A device,the molten salt electrolytic cell,was designed,which could continuously prepare Al-Zr master alloy.With the device a small batch of Al-Zr master alloy was prepared in the lab,and the Zr cotent in the alloy is 0.646-1.15wt%.