Tsir T. Formation of the structure of cast of pre-eutectic alloys of Al-Si system at rheocasting

The work is devoted to the experimental study of the patterns of formation of crystals with non-dendritic morphology, the development of an effective technological process of the rheocasting of pre-eutectic Al-Si alloys and its testing in industrial production. Using model and metal systems, the possibility of realizing non-dendritic growth of crystals from fragments obtained by partial melting of the original dendritic structure was studied. The formation of 4 characteristic types of fragments is established. However, regardless of their type, further growth leads to the formation of crystals with dendritic morphology if their total bulk density is less than the critical (1,6…2,7) x103 fragments/cm3. The obtained data show that the main mechanism of formation of non-dendritic morphology in the processes of rheocasting is the origin and growth of crystals without the stage of dendritic growth. Studies of the influence of external and internal thermal factors have shown that the most effective means of intensifying the processes of rheocasting is the creation of controlled heat removal from the walls of the mold and the introduction of a local cooler in the melt, which allows increasing the physical and mechanical properties of castings. The industrial testing of the technological process of rheocasting of AK7 and AK9M1 alloys in the conditions of the Prat "Vyshnivsʹkyy Lyvarno - Kovalʹsʹkyy Zavod" (Vyshneve town) was carried out using a high pressure diecasting machine (mod. 711I09). The aluminum alloy of the AK7 brand received a casting "Bracket" weighing 1.2 kg. Also, a second industrial testing was of “TALKO” Foundry Company (Melitopol), AK9M1 alloy on a using a high pressure diecasting machine (mod. 711A08), received castings of "Pneumatic cylinder body" weighing 0.3 kg. In both cases, the castings obtained by the technological process developed in the work are characterized by a homogeneous nondendritic structure, with an average size of primary crystals of a solid solution of aluminum of globular form 60…95 microns, with increased mechanical properties: temporal tensile strength σв increase up 9,8 %, elongation increased by 6 times. The service life of the steel molds for Al-Si alloy castings was increased by 13…14 %, power consumption decreased by 12,5 %.