Cathodic reduction process of Al-Cu-Y alloy in fluoride-oxide eutectic system via molten salt electrolysis

Al-Cu-Y alloys were prepared by molten salt electrolysis in fluoride-oxide system composed of electrolyte (Na3AlF6-AlF3-LiF-MgF2) and oxide (Al2O3-CuO-Y2O3). Cathodic reduction process of Al2O3, CuO and Y2O3 were analyzed by cyclic voltammetry and chronoamperometry. Components and phase composition of alloy samples prepared by potentiostatic electrolysis were characterized by scanning electron microscopy and energy dispersive spectroscopy. The results show that the Al-Cu-Y alloy can be prepared in the AlF3-NaF-5 wt%LiF-5 wt%MgF2 (NaF/AlF3 = 2.2, molecular ratio) eutectic system with mixed oxide (Al2O3-CuO-Y2O3) through 2 h at the conditions of a temperature of 1208 K, cell voltage 3.0 V, cathode current density 0.7 A/cm2. Al (III) and Cu (II) ions can be reduced to zero valence Al (0) and Cu (0) directly on carbonaceous electrode surface by instantaneous nucleation, respectively, the reduction process is controlled by diffusion. The reduction potential of Y(III) ions is close to the active ions of fluoride melts, but strengthened phase Al3Y can be formed through electrochemical reduction and alloyed process with active Al (III) and Cu (II) ions, meanwhile, the Al2Cu and Al3Y phases are distributed at the grain boundary of Al matrix.