Effect of Mn additions on diffusion behavior of Fe in molten magnesium alloys by solid-liquid diffusion couples

The effect of Mn additions on diffusion behavior of iron in molten magnesium alloys was investigated by solid-liquid diffusion couples at 720-800 °C. The Fe concentration curves in molten Mg and Mg-2Mn alloys were measured. The diffusion coefficients of Fe in molten magnesium alloys were decreased with Mn added at the same temperature. The reason was that no transition layer was formed at the interfaces of Fe/Mg diffusion couples, but continuous transition layers were formed at the interfaces of Fe/(Mg-2Mn) diffusion couples. The activation energies of Fe diffuse in Mg-(0 and 2)Mn melts were determined from the diffusion coefficients in the temperature range of 720-800 °C to be 8.83 ± 0.23 kJ/mol and 11.88 ± 0.14 kJ/mol, respectively. This study demonstrates that the transition layer at the interface of Fe/(Mg-2Mn) diffusion couple is an effective barrier to Fe atoms diffuse into the Mg-2Mn melt. The mechanism of iron removal in Mg-Mn alloy melt was revealed.