Thermodynamics of Formation of Al₃Fe Inter-Metallic Compound for Fe Removal from Molten Al–Mg Alloy

抄録

Recycling Al scraps is extremely important to achieve carbon neutrality. However, almost all impurity elements cannot be easily removed by oxidation and evaporation once dissolved in molten Al alloy. Therefore, it is necessary to develop an impurity removal process in molten Al. Iron is one of the impurity elements in Al, which easily forms intermetallic compounds with Al. On the contrary, Fe is immiscible with Mg in the liquid state. These facts suggest that the repulsive interaction between Fe and Mg in molten Al alloy enhances the precipitation of such intermetallic compounds as Al₃Fe. This study proposed the Fe removal method from molten Al alloy by the precipitation of the Al₃Fe inter-metallic compound by adding Mg. Molten Al–Mg alloy was equilibrated with Al₃Fe, and the Fe content of molten Al–Mg alloy was investigated. Fe content decreased with increasing Mg content, and this method was proved to be adequate for removing Fe from molten Al–Mg alloy. The standard Gibbs energy change for the precipitation of Al₃Fe at 873 K and the activity coefficient of Fe in molten Al–Mg alloy as a function of Mg content and temperature have been derived from the experimental results.

Using the derived values, the removal limit of Fe in molten Al–Mg alloy in the present method was discussed. Fe content can be decreased at higher Mg content and lower temperature, and the lowering limit of Fe is 0.0029 mass percent at the eutectic point of Al–Mg alloy.

Fig. 8 Contour lines of Fe content of molten Al–Mg alloy equilibrated with Al₃Fe.