Influence of modifcation on the refinement of primary silicon crystals in hypereutectic silumin AlSi21CuNi

On the paper the influence of modifying micro additives on the refinement of primary silicon crystals in the hypereutectic AlSi21CuNi piston silumin have been examined. As the modifiers there were used micro additives of Phosphorus in the form of AlCu19P1.4 and CuP12 pre-alloys, sulfur in the form of CuS and iron in the powdered form. The modifying micro additives were used separately and together. Micro additions of iron were used together with phosphorus. Sulfur micro addition provided the fragmentation of the primary silicon crystals, but not as effective as the phosphorus micro additive. The best effect of fragmentation of the primary silicon crystals was ensured by the combined addition of phosphorus in the form of AlCu19P1,4 pre alloy with a micro additive of powdered iron which reduced the average size of the primary silicon crystals from 114 μm to 20 μm.