From the viewpoint of the protection of the earth environment, a crucial technical subject in recycling of scraps is how to develop an elimination method of tramp elements, which are harmful to the mechanical properties of its products and the elimination of which is difficult. The solution has been strongly desired these days. On aluminum scraps notorious tramp elements are iron, magnesium and zinc. Especially, in the molten aluminum alloys dissolving iron, an intermetallic compound of Al₅FeSi easily precipitates during solidification in a needle-like morphology, in which the length of the precipitate sometime extends up to several millimeters, and provides inferior mechanical properties.
In this paper, we propose a useful method for eliminating the tramp elements using EMF (electromagnetic force) which is induced by imposing a direct electric current and a steady magnetic field in a molten metal. The principle of this method is that as the EMF induced in the metal scarcely acts on non-metallic inclusions due to a low electric conductivity of them, the non-metallic inclusions are moved to the direction opposite to that of the EMF as the reaction of the force and are eliminated out of the bulk metal. The usefulness of the method was demonstrated in experimental works, in which at first the component of iron dissolved in aluminum alloys was precipitated as intermetallic compounds and then the compounds were eliminated by use of the EMF. The continuous operation of the method was studied through the visualization of the movement of polystyrene particles in a NaCl aqueous solution.