Kotliar S. Control of the phase-structural composition and level of mechanical properties of hypoeutectic silumin with a high content of impurities

The thesis is devoted to the establishment of regularities of doping of hypoeutectic silumin, their vibration treatment and flux and ligature processing in order to determine the optimal composition, the number of ligature and fluxes additives introduced to obtain the metal structure with the best consumer characteristics. Based on the results of a comprehensive study of the effect of alloying elements on the properties of alloys, the "composition-properties" models were constructed, the structures of the alloys after vibration treatment, as well as after flux and ligature treatments were investigated in combination with a critical analysis of literature data on this problem. The work solved the scientific and practical problem of establishing the optimal ratio of the main alloying elements of hypoeutectic silumins used in the cast state and providing an increased level of mechanical properties that is stably reproduced. The complex effect of the refining-modifying flux and grain-grinding ligature AlTi5B1 was investigated. The morphology of eutectic silicon is changed due to assimilation of sodium and the Al solid solution is crushed due to introduction of TiB2 particles. It is proved that reducing ща the temperature range of the vibratory treatment of the melt in the area of crystallization of the iron-containing phases reduces its efficiency insignificantly slightly with a significant reduction of cost of electricity compared to the vibration treatment in the entire crystallization range. This provides a change in the morphology of the iron-containing phases from the lamellar form to the branched skeletal one. Based on the results obtained, a universal scheme has been developed for purposeful control of the phase-structural composition and, accordingly, of the level of service properties, which makes it possible to obtain alloys with enhanced and consistently reproducible mechanical properties.