Removal Of Iron Impurity And Inclusions From Aluminum By Electroslag Refining

The increasing demand for high integrity components in other industries requires super clean metal, and the recycled Al becomes more and more ubiquitous under the exhaustion of raw resources in all over the world. Thus, the restrictions of impurity elements and inclusions in aluminum have become increasingly strict. Various methods have being used to remove impurity elements and inclusions from aluminum, all of which have their own disadvantage. Hence, the increased attention is being given to find new or improved methods to efficiently refine and clean aluminum alloys.In the present work, electroslag refining(ESR) was applied to aluminum for removal of iron impurity and inclusions, which has already been well established for producing high quality steels. The effects of electroslag refining on removal of iron impurity and inclusions were investigated systemically. Furthermore, the mechanisms of electroslag refining on removal of iron impurity and inclusions were discussed thermodynamically and dynamically.In our research, according to the characteristic of electroslag refining of aluminum, the slags of electroslag refining of aluminum were selected on the basis of common refining fluxes in aluminum industry. The analysis of physical properties and electroslag refining effect indicated that47%KCl-30%NaCl-23%Na3AlF6,46%KF-54%AlF3and40%KCl-10%MgF2-50%MgCl2slags all can satisfy the request of electroslag refining of aluminum. In contrast to40%KCl-10%MgF2-50%MgCl2and46%KF-54%AlF3slags, the effect of electroslag refining by47%KCl-30%NaCl-23%Na3AlF6is optimal. The ternary phase diagrams of Al-Fe-B2O3and Al-Fe-P were calculated using CALPHAD method. The phase formation in the Al-Fe-B2O3and Al-Fe-P ternary phase diagrams was clarified. In the light of the calculated phase diagrams of Al-Fe-B2O3and Al-Fe-P, Na2B4O7and AlP were added to47%KCl-30%NaCl-23%Na3AlF6slag for the removal of iron, and the physical properties of47%KCl-30%NaCl-23%Na3AlF6slag ontaining Na2B4O7or AlP were measured.The effect of electroslag refining on removal of iron from commercial aluminum containing0.42wt%Fe by47%KCl-30%NaCl-23%Na3AlF6slag containing10wt.%Na2B4O7was studied. The iron content can decrease to about0.20%and the rate of iron reduction is more than50%through electroslag refining. The analysis of the sludge after electroslag refining indicated that the reaction of the molten slag to capture Fe2B formed in the chemical reaction between the melt and the molten slag was the main reason for iron reduction. Meanwhile, the effect of electroslag refining on removal of iron from commercial aluminum containing0.48wt%Fe by47%KCl-30%NaCl-23%Na3AlF6slag containing10wt.%AlP was studied. The iron content can decrease to about0.30%and the rate of iron reduction is more than35%through electroslag refining. The analysis of the sludge after electroslag refining indicated that the reaction of the molten slag to capture Fe2P formed in the chemical reaction between the melt and the molten slag was the main reason for iron reduction. Furthermore, the effect of electroslag refining on removal of iron from commercial aluminum by47%KCl-30%NaCl-23%Na3AlF6slag containing Na2B4O7was investigated under different conditions. After electroslag refining, iron content in commercial aluminum decreases with the increment of Na2B4O7addition or the decrement of remelting speed. Under9～10wt.%Na2B4O7addition and80-120g-min remelting speed, the effect of electroslag refining on removal of iron from commercial aluminum is optimal. Thermodynamic calculation of the chemical reaction between the slag containing Na2B4O7and the Al melt theoretically accounts for the formation of Fe2B spontaneously in the electroslag refining process. Moreover, the kinetic model of the reaction between melt and molten salg is established based on the academic hypothesis in the electroslag refining, and the kinetic model isThe effect of electroslag refining on removal of inclusions from aluminum was conducted by47%KCl-30%NaCl-23%Na3AlF6slag. It was found that the removal efficiency of electroslag refining for inclusions increases with the decrement of the remelting speed. The removal efficiency can exceed97.6%under the remelting speed of108g-min-1. The analysis of the sludge after electroslag refining indicated that the reaction of the molten slag to capture inclusions in the electroslag refining process wasthe main reason for the removal of inclusions.The Gibbs energy calculation of theinclusion-melt-slag system accounts for the transfer of inclusions from the aluminummelt to the molten slag thermodynamically, and the reaction of the molten slag tocapture inclusions in the electroslag refining process is discussed dynamically usingsurface renewal model and electro capillary effect.