Modification of Al-Si alloys with particles of ultrafine tungsten powder

Purpose: A widespread method, exerting the influence on the homogeneous formation of the microstructure and enhancement of strength properties of Al-Si alloys, is a modification by super- and nanodispersed particles of different chemical compositions. Despite the significant advances in the studies of the influence of various modifying compositions on the structure and mechanical properties of casted silumins, there are no data about the influence of nanodispersed tungsten powder on the formation of the structural-phase state and mechanical properties of the Al-Si alloy in the literature. Materials and methods: The paper investigates the influence of the tungsten nanopowder in the amount of 0.01…0.5 mass.% on the structural-phase state and mechanical properties of the Al-12%Si alloy with different soaking time of the modified melt. Metal smelting is conducted in the muffle furnace. Modification of the melt by the ultrafine powder is carried out before pouring. Before introducing the powder into the melt, its chemical, phase and granulometric composition is studied. For the obtained samples, metallographic examinations are made and the chemical composition, as well as impact toughness are determined. Results and discussion: The results of the conducted experiments showed that a part of the powder is not assimilated by the melt, but precipitated on the walls and the bottom of the crucible. The amount of the powder, not assimilated by the melt, depends on the soaking time. The assimilated powder influences significantly the cast structure; silicon plates are significantly refined; the sizes of the first-order axes and the distances between the axes of the second order decrease for the matrix crystals of casts. These changes in the structure influence largely the properties. Modification of the Al-12%Si alloy by the tungsten powder and soaking it in the furnace during 10 minutes allow increasing impact toughness by ~15%. By the results of the experiments, it has been established that addition of 0.1 mass.% of tungsten into the melt and soaking it in the heated condition before pouring is an optimal mode. Such mode leads to a uniform distribution of eutectic (α-Al + Si), a 1.5-time reduction of eutectic silicon plates, a change of the form of coarse plates into a fine fibrous form and enhancement of mechanical properties by 15…20 %.

silumin, Al-Si alloy, modifying, ultradisperse powder, tungsten